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Protease inhibitor monotherapy: darunavir/ritonavir less effective than three-drug therapy
Keith Alcorn, 2014-11-07 17:50:00

Darunavir/ritonavir monotherapy results in a lower rate of viral suppression after 48 weeks when compared to darunavir/ritonavir plus two nucleoside analogues, but may be just as effective as three-drug therapy in people with nadir CD4 cell counts above 200, according to a 48-week analysis of the PROTEA study presented on Thursday at the International Congress of Drug Therapy in HIV Infection in Glasgow

Monotherapy with a boosted protease inhibitor has been proposed as a form of maintenance therapy in people who have achieved viral load suppression, as a means of reducing toxicity and cost whilst preserving future treatment options in the event of virological rebound.

Monotherapy with a ritonavir-boosted protease inhibitor has been evaluated in numerous studies of lopinavir/ritonavir, atazanavir/ritonavir and darunavir/ritonavir. A meta-analysis and review of ten studies of protease inhibitor monotherapy found a lower rate of viral suppression (76% vs 82%) but no increased risk of drug resistance in the monotherapy arm in these studies (Arribas 2014).

The largest study of boosted protease inhibitor monotherapy, PIVOT, conducted in the United Kingdom by the Medical Research Council, randomised 587 patients to continue a three-drug regimen containing either a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor, or to switch to a boosted protease inhibitor chosen by patient and clinician. In that study 79% of the participants in the monotherapy arm took darunavir/ritonavir. After five years of follow up, 32% of participants in the monotherapy arm had to return to taking a three-drug regimen in order to re-suppress viral load, but despite the higher rate of viral rebound in the monotherapy arm, the study found no significant difference in the rate at which participants lost future treatment options as a consequence of developing drug resistant. Since loss of future drug options was the primary endpoint in the PIVOT study, the strategy of boosted PI monotherapy was found to be non-inferior. However, in the three-drug arm only 3.2% of participants experienced viral rebound (Paton 2014).

A health economic analysis of PIVOT presented to the Congress by Simon Walker of York University showed that protease inhibitor monotherapy was cost-effective compared to three-drug therapy and cost-saving (Oddershede 2014).