The U.S. Food and Drug Administration (FDA) has rejected the marketing application for the self-injectable version of AstraZeneca PLC's (AZN.US) lupus treatment, although the British pharmaceutical company stated it continues to communicate with regulators to advance the approval process. AstraZeneca released a statement on Tuesday indicating it has submitted the required information in response to the FDA's complete response letter and is committed to "progressing the application as quickly as possible." Impacted by this news, AstraZeneca's shares fell by as much as 1.9% during early trading in London, nearly erasing its gains for the entire year. The drug, named Saphnelo, currently has an approved intravenous formulation, requiring patients to visit a hospital or clinic for an IV infusion every four weeks. The application submitted by AstraZeneca was for a subcutaneous formulation; if approved, it would allow patients to self-administer a weekly injection. Compiled data shows that analysts project the drug could achieve annual revenues exceeding $1.6 billion by 2031. Saphnelo is used to treat systemic lupus erythematosus, an autoimmune disease where the patient's immune system mistakenly attacks healthy body tissues. AstraZeneca disclosed that over 3.4 million people worldwide are affected by this disease. The European Union approved the subcutaneous formulation of Saphnelo in December of last year. A late-stage clinical trial for the self-injectable version of Saphnelo demonstrated that the drug effectively reduced disease severity compared to a placebo. The FDA is expected to make a decision on AstraZeneca's supplemental application in the first half of this year, during which time the intravenous formulation of the drug will remain available.