Indinavir nephrolithiasis more prevalent than initially thought

The prevalence of nephrolithiasis caused by the HIV protease inhibitor indinavir is much greater than originally reported, according to the results of a study by Canadian researchers published in the December issue of The Journal of Urology. Dr. E. Saltel and colleagues from the University of Ottawa in Ontario retrospectively assessed the prevalence of indinavir-induced nephrolithiasis in 155 HIV-infected patients for 5732 patient-weeks. All of the subjects were prescribed the standard daily dose of 800 mg of the drug. At 78 weeks, the authors found that 43.2% of the patients had nephrolithiasis. Increasing age was the only variable identified that significantly predicted indinavir stone formation, the researchers report. The mean duration of indinavir therapy was the same in patients with and without stone formation, “despite the observed mean time to stone formation of 23 weeks.”

“The overall prevalence of indinavir nephrolithiasis in our cohort was 7-fold higher than the 4% stated in the product insert,” the investigators point out. “This finding may be a result of the difference in a controlled clinical setting and the everyday uncontrolled clinical environment in which we practice,” they speculate. The high rate of stone formation, however, did not seem to contribute to discontinuation of the drug. The authors suggest that further studies are needed to understand the biological factors associated with age that lead to a higher risk of nephrolithiasis in patients on indinavir. “Clinical experience continues to support adequate hydration as the best strategy for preventing indinavir nephrolithiasis,” Dr. Saltel’s team concludes.