Summary of Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”).
Revenue Recognition	Revenue Recognition The Company’s revenues consist of product sales of EMPAVELI and SYFOVRE and revenue derived from its collaboration arrangement with Sobi. See Note 12, License and Collaboration Agreements for further discussion related to the Sobi Collaboration and License Agreement. The Company accounts for contracts with its customers in accordance with ASC Topic 606, Revenue from Contracts with Customers, (“ASC 606”). Pursuant to ASC 606, for arrangements or transactions between participants determined to be within the scope of the contracts with customers guidance, the Company performs the following five steps to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation.
Product Revenue	Product Revenue The Company’s revenue from net product sales was generated in the United States following the FDA’s approval for marketing of EMPAVELI for the treatment of PNH in May 2021 and SYFOVRE in February 2023. The Company sells EMPAVELI and SYFOVRE principally through arrangements with specialty pharmacies (“SPs”) and specialty distributors (“SDs”), who are the Company’s customers. The customers subsequently resell the product to patients and health care providers. The Company applies the ASC 606 five step process discussed above to the contracts with SPs and SDs. The Company provides limited right of return to the customers in cases of shipment errors or expiring or defective products. Product revenues are recognized when the customers take control of the product, which typically occurs upon delivery to the customers. The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from estimates, the Company may need to adjust its estimates, which would affect net revenue in the period of adjustment. The following are the Company’s significant categories of variable consideration: Distribution Fees: Distribution fees include distribution service fees paid to SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (WAC). The Company does not receive a distinct good or service in exchange for the payment. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized. Chargebacks: Chargebacks are discounts and fees related to contracts with various third-party payers including pharmacy benefit managers, private healthcare insurers and government healthcare programs that purchase from SDs at a discounted price. SDs charge back to the Company the difference between the price initially paid by SDs and the discounted price paid to SDs by these entities. The Company issues credit notes for the chargeback which are applied to future sales. Product Returns: Consistent with industry practice, the Company offers SPs and SDs limited product return rights for shipment errors or expiring or defective products; provided that the return is within a specified period around the product expiration date as set forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient. As the Company receives inventory reports from SPs and SDs and has visibility into the inventory distribution channel, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from SPs and SDs. In arriving at its estimate for product returns, the Company also considers historical product returns (to the extent available), the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry.
Licensing and Collaboration Revenue	Licensing and Collaboration Revenue The Company analyzes license and collaboration arrangements pursuant to ASC Topic 808, Collaborative Arrangement Guidance and Considerations, (“ASC 808”) to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities or are more akin to a vendor-customer relationship. In making this evaluation, the Company considers whether the activities of the collaboration are considered to be distinct and deemed to be within the scope of the collaborative arrangement guidance or if they are more reflective of a vendor-customer relationship and, therefore, within the scope of ASC 606. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For elements of collaboration arrangements that are not accounted for pursuant to guidance in ASC 606, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. Amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer are presented as collaboration revenue and in a separate line item from revenue recognized from contracts with customers, if any, in the consolidated statements of operations. Pursuant to ASC 606, for arrangements or transactions between arrangement participants determined to be within the scope of the contracts with customers guidance, the Company performs the five-step process discussed above to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations. We evaluate the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determine whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential transaction price and the likelihood that the transaction price will be received. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and, if so, these options are considered performance obligations. The Company has not currently identified any such material rights. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the overall transaction price is allocated to the performance obligations on the same methodology as at contract inception. See Note 12, License and Collaboration Agreements, for further discussion related to the Sobi collaboration agreement.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: development liability, accrued expenses, prepaid expenses, convertible debt, reserves for variable consideration, reserves for excess or obsolete inventories, and income taxes.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company is required to disclose information on the fair value of financial instruments and inputs that enable an assessment of the fair value. The three levels of the fair value hierarchy prioritize valuation inputs based upon the observable nature of those inputs as follows: Level 1 – Quoted prices in active markets for identical assets or liabilities; Level 2 – Inputs other than quoted prices included within level 1 that are observable for the asset or liability, either directly or indirectly; Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. The Company’s financial instruments, in addition to those presented in Note 8, Long-term Debt, and Note 11, Fair Value Measurements, include cash and cash equivalents, accounts payable and accrued liabilities. Management believes that the carrying amounts of cash and cash equivalents, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents are valued at cost, which approximates the fair value. See Note 11, Fair Value Measurements, for additional information.
Accounts Receivable	Accounts Receivable The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write offs of its accounts receivable as of December 31, 2023, and its payment terms are generally 30-65 days for EMPAVELI and 60-150 days for SYFOVRE. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of December 31, 2023 and 2022, the credit profiles for the Company’s customers were deemed to be in good standing and an allowance for credit losses was not considered necessary.
Inventory	Inventory Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of sales. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required which would be recorded as a cost of sales in the consolidated statements of operations and comprehensive loss. Prior to regulatory approval of its product candidates, the Company expensed costs associated with the manufacturing of its product candidates to research and development expense unless the Company was reasonably certain such costs have future commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of its product candidates is probable, and the Company also expects future economic benefit from the sales of the product candidates to be realized, the Company will then capitalize the costs of production as inventory. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign. Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were expensed in a prior period and are, therefore, excluded from the cost of goods sold and inventory. As of December 31, 2023, the remaining pre-FDA approved inventory was $19.4 million, which primarily consisted of raw materials. Shipping and handling costs for product shipments are recorded as incurred in cost of sales along with costs associated with manufacturing the product and any inventory write-downs.
Development Liability	Development Liability From December 15, 2021 and thereafter until the final annual payment due December 2027, the development liability will be accreted from its initial carrying amount to the total payment amount using the effective interest rate method under ASC 835 over the remaining life of the SFJ agreement as defined in Note 6. The difference between the carrying amount and the total payment amount is presented as discount to the development liability. The accretion is recorded as interest expense in the consolidated income statement.
Foreign Currency	Foreign Currency The functional currency of each of the Company’s subsidiaries is its local currency, except for the wholly owned subsidiaries in Switzerland and Netherlands where the functional currency is the U.S. dollar. Revenues and expenses of the subsidiaries have been translated into U.S. dollars at average exchange rates prevailing during the respective periods. Assets and liabilities have been translated at the rates of exchange on the balance sheet date. The resulting translation gain and loss adjustments are recorded directly as a separate component of stockholders’ equity.
Research and Development	Research and Development Costs incurred in connection with research and development activities are expensed as incurred. Research and development expenses include (i) employee-related expenses, including salaries, benefits, travel and share-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research and contract manufacturing organizations, investigational sites and consultants, including share-based compensation expense for consultants; (iii) the cost of acquiring, developing and manufacturing clinical study materials; and (iv) costs associated with preclinical and clinical activities and regulatory operations. The Company enters into consulting, research and other agreements with commercial entities, researchers, universities and others for the provision of goods and services. Such arrangements are generally cancellable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided by the Company’s clinical sites and vendors. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.
Income Taxes	Income Taxes The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2023 and 2022, the Company did not have any significant uncertain tax positions.
Share Based Compensation - Option	Share-Based Compensation - Options The Company measures stock-based compensation cost at the accounting measurement date based on the fair value of the option and recognizes the expense related to awards to employees on a straight-line basis over the requisite service period of the option, which is typically the vesting period. Forfeitures are recognized as they occur. The Company estimates the fair value of each option using the Black-Scholes option pricing model that considers the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the SEC's Staff Accounting Bulletin No. 107, Share-Based Payment, to determine the expected life of the option grants. The estimate of expected volatility is based on a review of the historical volatility of similar publicly held companies in the biotechnology field over a period commensurate with the option's expected term. The Company has never declared or paid any cash dividends on its common stock and does not expect to do so in the foreseeable future. Accordingly, it uses an expected dividend yield of zero. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant valuation for a period commensurate with the option's expected term. These assumptions are subjective and changes in them could significantly impact the value of the option and hence the related compensation expense.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk include cash, cash equivalents, and marketable securities. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and the issuers of its cash equivalents and marketable securities. The Company maintains its cash, cash equivalents and marketable securities with highly-rated, federally-insured financial institutions. At times, such amounts may exceed federally-insured limits. The Company has not experienced any losses on its deposits since inception, and management believes that minimal credit risk exists with respect to these financial institutions.
Net Loss per Share	Net Loss per Share Basic net loss per common share is calculated by dividing net loss by the weighted-average shares outstanding during the period. For purposes of the diluted net loss per share calculation, convertible notes and common stock options are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.
Comprehensive Loss	Comprehensive Loss The Company’s components of comprehensive loss other than its net loss, are foreign currency gains/losses recorded from the remeasurement of the long-term intra-entity loan transaction to the Company’s wholly owned subsidiaries, foreign currency gain/loss from the translation of the Company’s wholly owned subsidiaries into U.S. dollars, unrealized gains and losses on marketable securities, and actuarial gains (losses) and prior service costs in connection with the Company's defined benefit plan.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In December 2023, the Financial Accounting Standards Board ("FASB") issued an amendment to the accounting guidance on income taxes which requires entities to provide additional information in the rate reconciliation and additional disaggregated disclosures about income taxes paid. This guidance requires public entities to disclose in their rate reconciliation table additional categories of information about federal, state, and foreign income taxes and to provide more details about the reconciling items in some categories if the items meet a quantitative threshold. The guidance is effective for annual periods beginning after December 15, 2024. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements disclosures. In November 2023, the FASB issued an amendment to the accounting guidance on segment reporting. The amendments require disclosure of significant segment expenses and other segment items and requires entities to provide in interim periods all disclosures about a reportable segment's profit or loss and assets that are currently required annually. The amendment also requires disclosure of the title and position of the chief operating decision maker ("CODM") and an explanation of how the CODM uses the reported measure(s) of segment profit or loss in assessing segment performance and deciding how to allocate resources. The guidance is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Retrospective application is required, and early adoption is permitted. The Company is currently evaluating the impact the guidance will have on its consolidated financial statements.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”).

Revenue Recognition

The Company’s revenues consist of product sales of EMPAVELI and SYFOVRE and revenue derived from its collaboration arrangement with Sobi. See Note 12, License and Collaboration Agreements for further discussion related to the Sobi Collaboration and License Agreement.

The Company accounts for contracts with its customers in accordance with ASC Topic 606, Revenue from Contracts with Customers, (“ASC 606”). Pursuant to ASC 606, for arrangements or transactions between participants determined to be within the scope of the contracts with customers guidance, the Company performs the following five steps to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation.

Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation.

Product Revenue

The Company’s revenue from net product sales was generated in the United States following the FDA’s approval for marketing of EMPAVELI for the treatment of PNH in May 2021 and SYFOVRE in February 2023. The Company sells EMPAVELI and SYFOVRE principally through arrangements with specialty pharmacies (“SPs”) and specialty distributors (“SDs”), who are the Company’s customers. The customers subsequently resell the product to patients and health care providers. The Company applies the ASC 606 five step process discussed above to the contracts with SPs and SDs. The Company provides limited right of return to the customers in cases of shipment errors or expiring or defective products. Product revenues are recognized when the customers take control of the product, which typically occurs upon delivery to the customers.

The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from estimates, the Company may need to adjust its estimates, which would affect net revenue in the period of adjustment. The following are the Company’s significant categories of variable consideration:

Distribution Fees: Distribution fees include distribution service fees paid to SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (WAC). The Company does not receive a distinct good or service in exchange for the payment. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized.

Chargebacks: Chargebacks are discounts and fees related to contracts with various third-party payers including pharmacy benefit managers, private healthcare insurers and government healthcare programs that purchase from SDs at a discounted price. SDs charge back to the Company the difference between the price initially paid by SDs and the discounted price paid to SDs by these entities. The Company issues credit notes for the chargeback which are applied to future sales.

Product Returns: Consistent with industry practice, the Company offers SPs and SDs limited product return rights for shipment errors or expiring or defective products; provided that the return is within a specified period around the product expiration date as set

forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient. As the Company receives inventory reports from SPs and SDs and has visibility into the inventory distribution channel, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from SPs and SDs. In arriving at its estimate for product returns, the Company also considers historical product returns (to the extent available), the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry.

Licensing and Collaboration Revenue

The Company analyzes license and collaboration arrangements pursuant to ASC Topic 808, Collaborative Arrangement Guidance and Considerations, (“ASC 808”) to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities or are more akin to a vendor-customer relationship. In making this evaluation, the Company considers whether the activities of the collaboration are considered to be distinct and deemed to be within the scope of the collaborative arrangement guidance or if they are more reflective of a vendor-customer relationship and, therefore, within the scope of ASC 606. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement.

For elements of collaboration arrangements that are not accounted for pursuant to guidance in ASC 606, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. Amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer are presented as collaboration revenue and in a separate line item from revenue recognized from contracts with customers, if any, in the consolidated statements of operations.

Pursuant to ASC 606, for arrangements or transactions between arrangement participants determined to be within the scope of the contracts with customers guidance, the Company performs the five-step process discussed above to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations.

We evaluate the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determine whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential transaction price and the likelihood that the transaction price will be received. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and, if so, these options are considered performance obligations. The Company has not currently identified any such material rights.

After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the overall transaction price is allocated to the performance obligations on the same methodology as at contract inception.

See Note 12, License and Collaboration Agreements, for further discussion related to the Sobi collaboration agreement.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: development liability, accrued expenses, prepaid expenses, convertible debt, reserves for variable consideration, reserves for excess or obsolete inventories, and income taxes.

Fair Value of Financial Instruments

The Company is required to disclose information on the fair value of financial instruments and inputs that enable an assessment of the fair value. The three levels of the fair value hierarchy prioritize valuation inputs based upon the observable nature of those inputs as follows:

Level 1 – Quoted prices in active markets for identical assets or liabilities;

Level 2 – Inputs other than quoted prices included within level 1 that are observable for the asset or liability, either directly or indirectly;

Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability.

The Company’s financial instruments, in addition to those presented in Note 8, Long-term Debt, and Note 11, Fair Value Measurements, include cash and cash equivalents, accounts payable and accrued liabilities. Management believes that the carrying amounts of cash and cash equivalents, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments.

Cash and Cash Equivalents

Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents are valued at cost, which approximates the fair value. See Note 11, Fair Value Measurements, for additional information.

Accounts Receivable

The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write offs of its accounts receivable as of December 31, 2023, and its payment terms are generally 30-65 days for EMPAVELI and 60-150 days for SYFOVRE. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of December 31, 2023 and 2022, the credit profiles for the Company’s customers were deemed to be in good standing and an allowance for credit losses was not considered necessary.

Inventory

Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of sales. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required which would be recorded as a cost of sales in the consolidated statements of operations and comprehensive loss.

Prior to regulatory approval of its product candidates, the Company expensed costs associated with the manufacturing of its product candidates to research and development expense unless the Company was reasonably certain such costs have future

commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of its product candidates is probable, and the Company also expects future economic benefit from the sales of the product candidates to be realized, the Company will then capitalize the costs of production as inventory. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign.

Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were expensed in a prior period and are, therefore, excluded from the cost of goods sold and inventory. As of December 31, 2023, the remaining pre-FDA approved inventory was $19.4 million, which primarily consisted of raw materials.

Shipping and handling costs for product shipments are recorded as incurred in cost of sales along with costs associated with manufacturing the product and any inventory write-downs.

Development Liability

From December 15, 2021 and thereafter until the final annual payment due December 2027, the development liability will be accreted from its initial carrying amount to the total payment amount using the effective interest rate method under ASC 835 over the remaining life of the SFJ agreement as defined in Note 6. The difference between the carrying amount and the total payment amount is presented as discount to the development liability. The accretion is recorded as interest expense in the consolidated income statement.

Foreign Currency

The functional currency of each of the Company’s subsidiaries is its local currency, except for the wholly owned subsidiaries in Switzerland and Netherlands where the functional currency is the U.S. dollar. Revenues and expenses of the subsidiaries have been translated into U.S. dollars at average exchange rates prevailing during the respective periods. Assets and liabilities have been translated at the rates of exchange on the balance sheet date. The resulting translation gain and loss adjustments are recorded directly as a separate component of stockholders’ equity.

Research and Development

Costs incurred in connection with research and development activities are expensed as incurred. Research and development expenses include (i) employee-related expenses, including salaries, benefits, travel and share-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research and contract manufacturing organizations, investigational sites and consultants, including share-based compensation expense for consultants; (iii) the cost of acquiring, developing and manufacturing clinical study materials; and (iv) costs associated with preclinical and clinical activities and regulatory operations.

The Company enters into consulting, research and other agreements with commercial entities, researchers, universities and others for the provision of goods and services. Such arrangements are generally cancellable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided by the Company’s clinical sites and vendors. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company.

Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.

Income Taxes

The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The

determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2023 and 2022, the Company did not have any significant uncertain tax positions.

Share Based Compensation - Option

Share-Based Compensation - Options

The Company measures stock-based compensation cost at the accounting measurement date based on the fair value of the option and recognizes the expense related to awards to employees on a straight-line basis over the requisite service period of the option, which is typically the vesting period. Forfeitures are recognized as they occur.

The Company estimates the fair value of each option using the Black-Scholes option pricing model that considers the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the SEC's Staff Accounting Bulletin No. 107, Share-Based Payment, to determine the expected life of the option grants. The estimate of expected volatility is based on a review of the historical volatility of similar publicly held companies in the biotechnology field over a period commensurate with the option's expected term. The Company has never declared or paid any cash dividends on its common stock and does not expect to do so in the foreseeable future. Accordingly, it uses an expected dividend yield of zero. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant valuation for a period commensurate with the option's expected term. These assumptions are subjective and changes in them could significantly impact the value of the option and hence the related compensation expense.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk include cash, cash equivalents, and marketable securities. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and the issuers of its cash equivalents and marketable securities. The Company maintains its cash, cash equivalents and marketable securities with highly-rated, federally-insured financial institutions. At times, such amounts may exceed federally-insured limits. The Company has not experienced any losses on its deposits since inception, and management believes that minimal credit risk exists with respect to these financial institutions.

Net Loss per Share

Basic net loss per common share is calculated by dividing net loss by the weighted-average shares outstanding during the period. For purposes of the diluted net loss per share calculation, convertible notes and common stock options are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.

Comprehensive Loss

The Company’s components of comprehensive loss other than its net loss, are foreign currency gains/losses recorded from the remeasurement of the long-term intra-entity loan transaction to the Company’s wholly owned subsidiaries, foreign currency gain/loss from the translation of the Company’s wholly owned subsidiaries into U.S. dollars, unrealized gains and losses on marketable securities, and actuarial gains (losses) and prior service costs in connection with the Company's defined benefit plan.

Recent Accounting Pronouncements

In December 2023, the Financial Accounting Standards Board ("FASB") issued an amendment to the accounting guidance on income taxes which requires entities to provide additional information in the rate reconciliation and additional disaggregated disclosures about income taxes paid. This guidance requires public entities to disclose in their rate reconciliation table additional categories of information about federal, state, and foreign income taxes and to provide more details about the reconciling items in some categories if the items meet a quantitative threshold. The guidance is effective for annual periods beginning after December 15, 2024. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements disclosures.

In November 2023, the FASB issued an amendment to the accounting guidance on segment reporting. The amendments require disclosure of significant segment expenses and other segment items and requires entities to provide in interim periods all disclosures about a reportable segment's profit or loss and assets that are currently required annually. The amendment also requires disclosure of the title and position of the chief operating decision maker ("CODM") and an explanation of how the CODM uses the reported measure(s) of segment profit or loss in assessing segment performance and deciding how to allocate resources. The guidance is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15,

2024. Retrospective application is required, and early adoption is permitted. The Company is currently evaluating the impact the guidance will have on its consolidated financial statements.