Renal stone composed of ritonavir

Nephrolithiasis is a well-known side effect of many HIV protease inhibitors. However, there have not been reports of stones associated with ritonavir use. Here, we report the case of a 33-year-old woman with HIV on antiretroviral therapy who presented with sharp left flank pain and passed a stone that was later found to contain only ritonavir. Of note, the patient's treatment regimen had not included ritonavir for 2 years prior to this incidence. This case is notable both for the novel finding of a renal calculus composed entirely of ritonavir and the development of nephrolithiasis years after cessation of the aggravating drug. This finding suggests that patients on ritonavir should be more closely monitored and for longer periods of time for potential lithiasis formation.