Protease inhibitor levels in hair strongly predict virologic response to treatment.

Objective: Antiretroviral (ARV) therapies fail when behavioral or biologic factors lead to inadequate medication exposure. The currently available methods to assess ARV exposure are limited. Levels of ARVs in hair reflect plasma concentrations over weeks to months, and may provide a novel method for predicting therapeutic responses. Design/methods: The Women's Interagency HIV Study, a prospective cohort of HIV-infected women, provided the basis for developing and assessing methods to measure commonly prescribed protease inhibitors (lopinavir/ritonavir and atazanavir) in small hair samples. We examined the association between hair protease inhibitor levels and initial virologic responses to therapy in multivariate logistic regression models. Results: ARV concentrations in hair were strongly and independently associated with treatment response for 224 women starting a new protease inhibitor-based regimen. For participants initiating lopinavir/ritonavir, the odds ratio (OR) for virologic suppression was 39.8 [95% confidence interval (Cl)=2.8-564] for those with lopinavir hair levels in the top tertile (>1.9 ng/mg) compared to the bottom ( 3.4 ng/mg) compared to the lowest (≤1.2 ng/mg). Conclusion: Protease inhibitor levels in small hair samples were the strongest independent predictor of virologic success in a diverse group of HIV-infected adults. This non-invasive method for determining ARV exposure may have particular relevance for the epidemic in resource-poor settings due to the ease of collecting and storing hair.