Increased prevalence and analysis of risk factors for indinavir nephrolithiasis

PURPOSE: Indinavir is a protease inhibitor used for treating HIV-1. The drug is lithogenic and was thought to cause a 3% incidence of kidney stones. We evaluated a cohort of patients positive for HIV on indinavir to determine the incidence of indinavir nephrolithiasis and identify risk factors for indinavir stone formation. MATERIALS AND METHODS: Our cohort study of the prevalence of indinavir nephrolithiasis included 155 patients with HIV for 5,732 patient-weeks. The same cohort was then used for a retrospective chart review to assess patient age, weight, duration of drug use, time to stone formation, CD4 count, creatinine, alanine transaminase, and urinary pH and specific gravity as risk factors for stone formation. RESULTS: We estimated the cumulative incidence of indinavir stone formation by the Kaplan-Meier product limit estimator method. At 78 weeks 43.2% of patients had stones (95% confidence interval [CI] 0.292 to 0.543). Increasing age was the only variable that was a statistically significant predictor of indinavair urolithiasis (relative risk 0.955, 95% CI 0.918 to 0.993, p = 0.0159). The mean duration plus or minus standard deviation of indinavir use was statistically the same in each group (42.5 +/- 27. 2 and 40.3 +/- 27.1 weeks in those without and with stones, respectively) despite the observed mean time to stone formation of 23.0 +/- 19.8 weeks. CONCLUSIONS: The clinical prevalence of indinavir nephrolithiasis is much greater than initially reported. Nephrolithiasis during indinavir use does not appear to induce patients to withdraw from the drug.