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 microM (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.