Protease inhibitor monotherapy and the CNS: peace of mind?

Boosted protease inhibitor (bPI) monotherapy has demonstrated high efficacy for maintaining viral suppression in the blood. bPI monotherapy has the theoretical advantage of avoiding the long-term toxicity associated with the use of nucleoside reverse transcriptase inhibitors. Concern about the efficacy of bPI monotherapy in preventing HIV replication in the CNS is one reason that has precluded the widespread use of this therapeutic strategy. In several studies, a low CNS penetration-effectiveness (CPE) score has been associated with a higher risk of virological failure in the CNS and with neurocognitive impairment. Since the CPE score is substantially lower for bPI monotherapy than for triple-drug highly active antiretroviral therapy (HAART), it has been postulated that bPI monotherapy might have a higher risk for CNS virological failure and neurocognitive impairment. However, the available evidence, although limited, does no support this notion. Lopinavir and darunavir achieve CSF drug levels that are sufficient to fully suppress HIV replication. In clinical trials, when compared with triple-drug HAART, patients receiving bPI monotherapy with lopinavir and darunavir who maintain full virological suppression in plasma do not appear to be at a higher risk of discordant HIV replication in the CSF or of neuropsychiatric adverse events. It should be noted that several studies have suggested that nucleoside reverse transcriptase inhibitors might have neurotoxic effects and, consequently, bPI monotherapy might be able to avoid the CNS toxicity induced by nucleosides. It is clear that more studies including detailed neurocognitive testing are needed to completely establish the risk/benefit ratio of bPI monotherapy or triple-drug HAART for preserving neurocognitive function in HIV-infected patients.