Serum interferon β-1a (Avonex) levels following intramuscular injection in relapsing-remitting MS patients

Abstract

Background: The pharmacokinetics of IFNβ-1a in MS patients are poorly understood. We have previously reported an ELISA sensitive and specific for measuring serum IFNβ-1b levels in patients with MS.Objective: We describe an ELISA to measure interferon β-1a (Avonex) in the serum of MS patients following IM administration.Methods: We have developed an ELISA for detecting serum IFNβ-1a in MS patients receiving 6 million units (MU) of IFNβ-1a, IM once weekly. The specificity of this ELISA was confirmed by the lack of cross-reactivity with other cytokines except for IFNβ-1b.Results: Serum IFNβ-1a levels were measured at 3 and 6 months after initiating treatment with IFNβ-1a in 10 MS patients. At 3 months, all 10 patients had detectable levels ranging from 68 to 86 IU/mL. At 6 months, IFNβ-1a could be detected in the serum of all but three patients, with levels ranging from 64 to 81 IU/mL. A kinetic study of IFNβ-1a serum levels in a separate group of six MS patients who had been receiving IFNβ-1a for several months was carried out. Blood was drawn before and 2, 4, 6, 8, and 24 hours after IFNβ-1a injection. Peak serum IFNβ-1a levels were observed at 8 hours and became undetectable at 24 hours after injection.Conclusion: The described ELISA may have useful clinical applications in examining the correlation between serum IFNβ-1a levels and clinical efficacy.