Background: The effect of adherence on the risk of virologic failure and mutations selection was verified in a prospective study.
Method: At baseline, all patients had a viral load (VL) <50 copies/mL and completed a self-reported questionnaire. Patients were followed for the subsequent 4 months to document virologic rebound (VL > 50 copies/mL).
Results: 1,133 patients completed 2,240 questionnaires/follow-up (non-nucleoside reverse transcriptase inhibitor [NNRTI] = 1,479; single protease inhibitor [PI] = 200; boosted PI = 561). Only the type of treatment and the baseline adherence rate were significantly associated with the virologic endpoint. A viral rebound rate >10% was observed in patients treated with single PI (14.7%) or boosted PI (11.7%) up to an adherence rate of 95%, whereas a similar (17.6%) rebound rate was observed only in NNRTI-treated patients with very low adherence (<55%). After adjustment for other baseline predictors of adherence, patients on NNRTIs showed a higher adherence rate than those on PIs but not higher than those on boosted PIs. The same adherence rate did not have the same result, in terms of virologic rebound, in patients on the same HAART for shorter or longer periods of time. Overall, the risk of virologic rebound for patients with >95% adherence rate was 6.2% in the first 6 months of therapy, lowered to 5.0% in the following 6 months, and was 3.2% thereafter. The risk of selecting for resistance-inducing viral mutation for NNRTI-treated patients was higher (4.9%) at very low adherence rates (<75%); the opposite was true for single PI-treated patients (4.2% for adherence >95%). Boosted PI-treated patients showed an intermediate pattern, even if at a much lower level of risk.
Conclusion: Low adherence is a major determinant of virologic failure, however different therapies have different adherence cutoffs determining a significant increment of risk.