Evaluation of adherence to antiretroviral therapy using efarivenz as a marker

Abstract

Background: Patients on antiretroviral (ART) are expected to be at least 95% adherent to their treatment, as this will increase their chances of achieving treatment success (maximum and durable suppression of HIV-1 viral load); non-adherence may lead to the development of HIV drug resistance, which may lead to virologic failure and treatment failure. Therapeutic drug monitoring (TDM) has been reported to be the most efficient method to assess treatment adherence in HIV individuals, since it quantifies the concentration of ARTs in biological matrices. This is very effective when using a robust technique such as liquid chromatography tandem mass spectrometry (LCMS/MS), which has played a significant role in the evaluation and interpretation of bioavailability, bioequivalence and pharmacokinetic data. Even with patient adherence, various intra-individual factors have an influence on the expression and function of the genes responsible for the transport (MDR1) and metabolism (CYP2B6) of Efavirenz (EFV). This may lead to single nucleotide polymorphisms (SNPs) in these genes, and this may affect the way antiretrovirals (ARVs) are metabolized. The aim of this study was to evaluate the EFV concentration in plasma to assess patient adherence to treatment and correlate this with genomic occurrences in human and viral genes. Hypothesis: The concentration of ARVs in patient plasma can be used to estimate adherence to treatment; while ARVs’ transport and metabolism can affect bioavailability in a patient’s system. Research Question: Can EFV concentration in plasma be used to estimate patient adherence to treatment? Can transport and metabolism of EFV affect their bioavailability in the patient’s system? Objectives: To determine EFV concentration in plasma to assess patient adherence to treatment and correlate this with genomic occurrences in human genes and viral genes. Methodology: Twenty blood samples were collected from HIV positive individuals before treatment initiation (baseline) and between six to twelve months following treatment initiation (follow-up). The concentration of EFV in patient plasma was measured by LC-MS/MS technique. To infer other factors influencing patient pharmacokinetics output, drug resistance and human genetic characteristics were analyzed. A 1.65kb fragment of the HIV-1 Pol gene was amplified and sequenced to determine drug resistant mutations; while 363bp and 289bp of the MDR-1 and CYP2B6 human genes respectively, were also amplified and sequenced to determine polymorphisms in the transport and metabolism genes. Obtained sequences were manually edited and analyzed using Geneious Version 11.1.5 software. The Stanford HIV Drug Resistance database was used for drug resistant mutation (DRMs) analysis and MDR1 and CYP2B6 test sequences were compared with variant reference sequences to detect the presence of any SNPs. Results: The plasma EFV concentration at baseline and follow-up range was as follows: 0 – 1183ng/ml and below limits of quantification (BLQ) to 15,670ng/ml, respectively. At baseline, 0ng/ml is the expected plasma EFV concentration for patients about to commence treatment; however, two out of twenty patients had 769.9 and 1,183ng/ml drug levels in their system. Post treatment, plasma EFV levels in patients are expected to range from 1,000 – 4,000ng/ml, however, of the twenty patients, two had <1,000ng/ml, and three patients had >4,000ng/ml in their plasma. For Pol amplification, 35% (7/20) were positively amplified at baseline and 25% (5/20) were positively amplified from the follow-ups; 100% (20/20) samples were amplified for both CYP2B6 and MDR1 genes. Detection of drug resistance in the baseline Pol sequences revealed the absence of major mutations in both NRTI and NNRTI drug classes. The G516T polymorphism was present in 15% of the study participants while the homozygous GG and heterozygous GT genotype was present in 25% and 40% of the study participants, respectively. Allele determination was impossible in 20% of the samples, due to the poor nature of the sequence. The homozygous TT variant polymorphism at position 3435 was absent in the entire population, however, the CC and CT genotype was present in 15% and 85% of the study participants respectively. Analysis of EFV concentration in close proximity with the human genetic characteristics reveals that the presence of a Single Nucleotide Polymorphism affects the pharmacokinetic output observed. Discussion and Conclusion: Post treatment, 90% of the study participants indicate adherence to treatment, with only 10% of them having lower than expected EFV concentrations, implying they were non-adherent to their treatment. However, because plasma drug concentrations only reflect a patient’s adherence pattern for a few hours to at most two days, the adherence patterns of these individuals cannot be concluded with certainty. Using plasma EFV as a biomarker to evaluate adherence to treatment in HIV seropositive individuals is a feasible technique, however, its application in non-research settings is still a drawback due to the cost of the method. Characterizing patient inter-individual differences should be taken into consideration, especially since any polymorphism in their transporter and metabolizing genes may influence their overall treatment success.