Metabolic interaction of recombinant interferon-beta and zidovudine in AIDS patients.

Zidovudine (AZT), the only currently approved drug for treatment of human immunodeficiency virus (HIV) in AIDS, is known to be metabolized by mammalian systems to a variety of metabolites including 3'-azido-3'-deoxy-5'-O-glucuronide (GAZT). Interferons (IFNs) are known to alter the microsomal enzyme system responsible for the metabolism of some compounds. The aim of the present study was to investigate the effect of combination therapy of recombinant (r) IFN-beta and AZT on the rates of metabolism of AZT in AIDS patients. AZT was given orally (200 mg every 4 h) for 8 weeks prior to initiation of rIFN-beta therapy (45 X 10(6) U/day, s.c.). Serum samples from 8 patients were obtained prior to and at days 3 and 15 following initiation of rIFN-beta therapy. Serum was analyzed by high-performance liquid chromatography (HPLC) for both AZT and GAZT. The serum data were analyzed by a computer-assisted pharmacokinetics program that calculates rates of AZT metabolism. The half life for AZT was increased approximately two-fold by day 15. The rate of metabolism of AZT was diminished from 1.43 h-1 prior to IFN-beta therapy, to 0.4 h-1 and 0.05 h-1 at days 3 and 15, respectively. The volume of distribution of AZT was 2 l/kg at day 0 and increased to 3.2 and 3.5 l/kg on days 3 and 15, respectively. In conclusion, the results indicate that rIFN-beta inhibits the rate of AZT metabolism in AIDS patients.