The Effect of Cimetidine and Ranitidine Administration With Zidovudine

Study Objective . To evaluate the possibility of a drug interaction with zidovudine and histamine₂-receptor antagonists in individuals infected with the human immunodeficiency virus. Design . Randomized crossover study. Setting . University-affiliated research center. Patients . Six HIV-infected individuals. Interventions . The subjects received 7-day regimens of zidovudine 600 mg/day alone, zidovudine with cimetidine 1200 mg/day, and zidovudine with ranitidine 300 mg/day. Measurements and Main Results . The renal clearance of zidovudine when given alone was 0.41 L/kg/hour, and was reduced to 0.18 L/kg/hour (p=0.002) when given with cimetidine. In the presence of cimetidine the urinary excretion of zidovudine decreased from 89.5 to 53.7 μM (p=0.01), the urinary ratio of metabolite to parent increased from 5.16 to 9.96 (p=0.0001), and the fraction of zidovudine converted to metabolite increased from 0.86 to 0.92 (p=0.0025). Conclusion . Cimetidine presumably inhibits the renal clearance of zidovudine by competing for tubular secretion. Based on the observation that neither cimetidine nor ranitidine had a significant effect on serum concentrations of zidovudine or zidovudine glucuronide, a change in the dosage of zidovudine is not warranted.