Indinavir-induced retinoid-like effects: incidence, clinical features and management.

Since 1998, many cases of antiretroviral therapy-related paronychia of the toes or fingers and ingrown toenails have been reported. Most of them were related to indinavir. Other indinavir-induced mucocutaneous disorders resembling the adverse effects of systemic retinoid therapy have also been reported. Although there is some uncertainty in the literature regarding a cause-effect relationship, results of several epidemiological and in vitro studies, together with cumulated clinical experience leave no doubt that indinavir causes a retinoid-like effect and nail alterations. Indeed, indinavir is the only antiretroviral drug that produces these disorders, although ritonavir may enhance indinavir-induced retinoid-like effects through pharmacokinetic interactions leading to increased plasma indinavir concentrations. Approximately 30% of patients receiving indinavir show two or more retinoid-like manifestations and 4-9% develop paronychia. These adverse effects are not related to other epidemiological variables such as the patient's sex, age or other risk factors or immune status. They seem to be exposure dependent and, therefore, largely dose-dependent. Chronic paronychia is considered generally to be caused by contact irritants and candidal infection. Nevertheless, indinavir is currently the most frequent cause of chronic or recurrent paronychia in HIV-infected patients. In addition, retinoid-like manifestations such as cutaneous xerosis and cheilitis are frequent mucocutaneous adverse effects related to indinavir. The exact mechanism of indinavir-induced retinoid-like effects is unclear. Hypotheses for pathogenesis include interference with retinoid metabolism by enhancing the retinoic acid signalling pathway, or by increasing retinoic acid synthesis, or by reducing cytochrome p450-mediated retinoic acid oxidative metabolism. Replacement of therapy by an antiretroviral regimen not containing indinavir, while retaining other protease inhibitors and lamivudine, resolves retinoid-like manifestations without recurrences.