Abstract
BackgroundAntiretroviral concentrations in hair provide a longer window of drug detection and are useful for measuring longer-term drug exposure. Efavirenz is an important component of first-line treatment in resource-limited settings, but its concentrations in hair have not been well studied.MethodsThis study is a supplementary to a randomised controlled trial of an adherence intervention using an electronic adherence measuring device. Hair and plasma samples were collected from human immunodeficiency virus-positive patients in Cape Town, South Africa. Previously validated liquid chromatography tandem mass spectrometry methods were used to measure efavirenz concentrations in the collected hair and plasma samples. CYP2B6 genotyping of participants was also performed. Data analysis was performed using descriptive and comparative statistics as well as regression modelling.ResultsHair samples were collected from 59% of patients enrolled in the parent study. Results indicated that hair efavirenz concentrations were significantly influenced by participants’ CYP2B6 metaboliser status. Median efavirenz concentrations for extensive, intermediate and slow metaboliser genotypes were 3.54 ng/mg, 5.11 ng/mg and 10.66 ng/mg, respectively. A strong correlation was observed between the efavirenz concentrations measured in hair and plasma samples (Spearman’s correlation coefficients, 0.672–0.741, p < 0.0001). No relationship between hair efavirenz concentrations and virological failure or adherence measured using an electronic adherence was shown.ConclusionThe results from this study provide further insight into the potential of using hair as a matrix for measuring antiretroviral concentrations. However, challenges experienced in collecting hair samples suggest that this adherence measure may have limited utility in an African population.
Highlights
For antiretroviral therapy (ART) to be successful in preventing disease progression, high levels of adherence are required.[1,2] Methods for measuring adherence include patient self-report, pill counts, pharmacy refill records, electronic drug monitoring and therapeutic drug monitoring (TDM)
Two hair samples were collected from each of the individuals who participated in the sub-study
There was no relationship between hair EFV concentrations and adherence measured by electronic adherence monitoring device (EAMD), which we have previously shown was the best adherence measure for predicting virological failure and resistance development.[19]
Summary
For antiretroviral therapy (ART) to be successful in preventing disease progression, high levels of adherence are required.[1,2] Methods for measuring adherence include patient self-report, pill counts, pharmacy refill records, electronic drug monitoring and therapeutic drug monitoring (TDM). TDM involves the determination of drug or drug metabolite concentrations in plasma and, more recently, hair.[3] Each of these methods has both advantages and disadvantages which have been discussed in detail in the literature.[1,2,4,5,6] There remains no gold standard for determining adherence.[7]. TDM is a direct method of monitoring adherence by measuring drug exposure. Antiretroviral concentrations in hair provide a longer window of drug detection and are useful for measuring longer-term drug exposure. Efavirenz is an important component of first-line treatment in resource-limited settings, but its concentrations in hair have not been well studied
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