Lab Overview

Many drugs are incorporated from the systemic circulation into hair as it grows.1 In a manner analogous to glycosylated hemoglobin A1C (HbA1C) providing information on average glucose levels over long periods of time,2 the concentration of medications in hair reflects drug uptake from the systemic circulation over weeks to months. Our group has pioneered the use of small hair samples to monitor antiretroviral (ARV) adherence and exposure for patients on antiretroviral therapy.3-50 We have developed methods to extract and analyze prevalent-use ARVs from hair4,5,25,26 and demonstrated that hair concentrations of ARVs are the strongest independent predictor of virologic success in large prospective cohorts7-15,43,44 or trials16,44 of HIV-infected patients, providing pharmacodynamic relevance for the longitudinal exposure data provided by hair samples. Hair levels of ARVs are stronger predictors of treatment outcomes than self-reported adherence8-10,12,14,15,51 or single plasma ARV concentrations.7,8 Furthermore, we have shown increases in hair ARV levels pre-and-post adherence interventions in various settings.22,23

Single plasma levels of ARVs, like single glucose measurements, are limited in their ability to predict long-term treatment outcomes, because they reflect only a short duration of exposure,52-54 demonstrate significant day-to-day variation52 and are subject to “white-coat” effects, where adherence improves transiently prior to study or clinic visits.55,56 Average adherence to ARVs may be a better predictor of virologic suppression than duration or frequency of missed doses.57 Drug levels in peripheral blood mononuclear cells (PBMCs) relay information on exposure over longer periods (7-14 days), although processing, isolating and counting PBMCs are costly and technically challenging. Dried blood spots are easier to collect and process than PBMCs,58 and drug levels in red blood cells (RBCs) from dried blood spots represent longer-term exposure,59 but dried blood spot assays (which are useful only for drugs which are processed intracellularly (e.g. tenofovir or emtricitabine)) require phlebotomy, a cold chain, standardization against hemoglobin concentrations and adequate sample volume for interpretation.60

We have demonstrated a strong correlation between tenofovir (TFV) dose and concentrations of TFV in hair in HIV-negative individuals,26 and a strong correlation between hair levels of TFV and DBS concentrations of TFV-diphosphate, paving the way for the use of hair measures in the setting of pre-exposure prophylaxis (PrEP).27-40,50,61 We have additionally demonstrated that hair levels of TFV are associated with PrEP-related toxicities in open-label studies, specifically declines in renal function.29,32 We have also examined the relationship between hair concentrations of ARVs to other pharmacologic and traditional adherence measures in the context of PrEP.27,28,30,32,33,50 In terms of PMTCT, hair levels of ARVs in an infant can reflect exposure to maternal ARVs administered during pregnancy and breastfeeding.17,20 Moreover, we have shown hair levels of ARVs to be strong predictors of virologic suppression during the critical periods of pregnancy and breastfeeding.12 We are now able to analyze multiple ARVs in hair, including nevirapine, efavirenz, atazanavir,25 lopinavir, ritonavir, raltegravir, darunavir, dolutegravir, TFV and emtricitabine in hair (as well as isoniazid and other TB drugs)62-66 to assess adherence during latent and active TB infection treatment). Our assays are peer reviewed and approved by the NIH DAIDS-supported Clinical Pharmacology and Quality Assurance (CPQA) program.67

Unlike phlebotomy, hair collection is noninvasive and does not require specific skills, sterile equipment, or specialized storage conditions. The avoidance of phlebotomy in assessing drug adherence may be particularly desirable in pediatric populations.17,19,68 Hair sample collection merely requires a pair of scissors and storage is at room temperature. We have published data on high rates of acceptability and feasibility (>95%) of collecting hair samples for hair ARV monitoring in African and Asian settings8,11,12,14,18,27 and among U.S. adolescents33 and women.9,10,15 Moreover, self-collection of hair samples (which may enhance feasibility of collection) provides equivalent ARV concentration data to hair samples collected by field staff.31 Hair concentrations of TFV are similar in men and women under conditions of directly observed therapy so the same range of hair levels can be used to predict adherence to PrEP/ART in both men and women.40 Finally, segmental analysis of hair samples allows for the assessment of adherence at various time points over the past months, which can be useful in the context of PrEP failure.38,41

Hair can be stored for long periods prior to analysis, shipped without biohazardous precautions, and a high through-put hair analysis laboratory, such as the UCSF Hair Analytical Laboratory (HAL), can run measurements economically. Moreover, we have developed a low-cost assay for measuring nevirapine concentrations in hair21 and are working further to develop lower-cost measures for other drugs. We are also working on a point-of-care (POC) testing method to analyze PrEP or treatment adherence via a urine-based immunoassay.69-71 This POC assay can allow for real-time monitoring and feedback on adherence.

In sum, hair measures circumvent many barriers and limitations to commonly-used adherence monitoring tools in the resource-rich and resource-limited settings and have gained increasing interest in research settings as an objective biomarker of adherence/exposure. We therefore propose the inclusion of this measure in the attached proposal.

References:

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