Optimized antiretroviral therapy: the role of therapeutic drug monitoring and pharmacogenomics

Therapeutic drug monitoring of protease inhibitors and efavirenz in HIV-infected individuals with active substance-related disorders

BACKGROUND

Achieving targeted antiretroviral (ARV) plasma concentrations during long-term treatment in human immunodeficiency virus (HIV)-infected patients with substance-related disorders (SRDs) may be challenging due to a number of factors, including medication adherence, coinfection with hepatitis B or C virus, medication intolerance, and drug interactions. One approach to investigate these factors is to conduct therapeutic drug monitoring to measure ARV exposure during treatment. The objective of this study was to utilize therapeutic drug monitoring to compare efavirenz (EFV) and protease inhibitor pharmacokinetics in patients with and without SRDs.

METHODS

This was a multicenter, cross-sectional open-label study in patients with HIV-1 infection receiving antiretroviral therapy (ART), with active (n=129) or without (n=146) SRD according to National Institute on Drug Abuse criteria. Two hundred seventy-five subjects who were receiving either protease inhibitor-based or EFV-based ART regimens for >6 months were enrolled at 4 HIV treatment centers with an equal distribution of SRD and non-SRD at each site. The patients were instructed during enrollment visits with regard to the importance of adherence before and after study visits. Demographics and routine clinical laboratory tests were recorded.

RESULTS

Among the 275 patients, 47% had SRD with at least 1 substance. There were no significant differences between SRD and non-SRD groups for race, gender, age, or CD4 count at entry. A significantly higher proportion of patients with SRD had an entry HIV RNA plasma concentration>75 copies per milliliter compared with patients without SRD (40% vs 28%, P=0.044). Logistic regression modeling revealed an association between HIV RNA plasma concentration and African American race (P=0.017). A significantly higher proportion of SRDs also had an EFV or protease inhibitor trough concentration below the desired range (23% vs 9%, P=0.048). Significantly lower trough concentrations were noted in patients with SRDs receiving atazanavir (0.290 vs 0.976 μg/mL) or lopinavir (3.75 vs 5.30 μg/mL).

CONCLUSIONS

The pharmacokinetic data indicate differences between HIV-infected patients with and without SRDs that may influence viral load suppression during long-term ART. These findings require additional investigation in a randomized design with more intensive pharmacokinetic assessment to identify individual factors that are contributing to suboptimal ARV exposure in patients with SRDs.

Pharmacogenomics of CYP3A: considerations for HIV treatment

The understanding of the cytochrome P450 3A SNP in antiretroviral therapy is important, because it is highly inducible, extremely polymorphic and metabolizes many of the drugs that are key components of highly active antiretroviral therapy regimens. This enzyme is prolific and promiscuous towards drug and xenobiotic substrate selection and it is also unpredictable among individuals, having a 5- to 20-fold variability in its ability to contribute to drug clearance. The importance of human CYP3A pharmacogenetics is also gaining attention in other established areas of pharmacotherapy as it may contribute to the goal of predicting efficacy and/or toxicity, specifically with the discovery of null allele CYP3A4*20. This review summarizes the current understanding, implications of genetic variation in the CYP3A enzymes, the central role of CYP3A in linking human genetics, the pharmacokinetics and resulting pharmacodynamic responses to certain antiretroviral drugs, and their eventual place in applied clinical pharmacotherapy.

HIV entry inhibitors: a new generation of antiretroviral drugs

AIDS is presently treatable, and patients can have a good prognosis due to the success of highly active antiretroviral therapy (HAART), but it is still not curable or preventable. High toxicity of HAART, and the emergence of drug resistance add to the imperative to continue research into new strategies and interventions. Considerable progress in the understanding of HIV attachment and entry into host cells has suggested new possibilities for rationally designing agents that interfere with this process. The approval and introduction of the fusion inhibitor enfuvirtide (Fuzeon) for clinical use signals a new era in AIDS therapeutics. Here we review the crucial steps the virus uses to achieve cell entry, which merit attention as potential targets, and the compounds at pre-clinical and clinical development stages, reported to effectively inhibit cell entry.

Quantification of antiretroviral drugs in dried blood spot samples by means of liquid chromatography/tandem mass spectrometry

For the first time approved antiretroviral drugs, i.e. protease inhibitors (PI) and non-nucleoside reverse transcriptase inhibitors (NNRTI), were quantified in dried blood spots (DBS) from HIV/AIDS patient whole blood samples as the basis for therapeutic drug monitoring (TDM) by a robust simultaneous liquid chromatography/tandem mass spectrometry (LC/MS/MS) method. This study included seven PI (amprenavir, nelfinavir, indinavir, lopinavir, saquinavir, ritonavir, atazanavir) and two NNRTI (nevirapine, efavirenz). LC/MS/MS coupling was realized using a Phenomenex Synergy Max RP LC column (150 x 2 mm, 4 micro) in combination with a tandem mass spectrometer (API 2000, Applied Biosystems/MDS Sciex Concord) operating in positive and negative multiple reaction monitoring (MRM) mode with reserpine as internal standard. DBS samples were punched out and extracted with 50:50 MeOH/0.2 M ZnSO4 (v/v) as extraction reagent. The method performance data for the drugs in DBS like limits of detection (LOD, 8-70 ng/mL), lower limits of quantification (LLOQ, 41-102 ng/mL), linearity (R2, 0.9981-0.9999), linear concentration ranges (41-10.000 ng/mL), accuracies (92-113%), recoveries (62-94%), and ion suppression were investigated and are comparable to data obtained from human plasma, which is the current standard matrix for TDM of PI and NNRTI. In this case, off-line plasma sample preparation was performed by means of simple protein precipitation with 80:20 methanol/0.2 M ZnSO4 (v/v) as precipitation reagent. Significant correlations between real patient plasma and DBS were obtained for samples containing lopinavir, atazanavir, ritonavir, saquinavir, and efavirenz. DBS preparation as sampling alternative is well suited and practicable for TDM minimizing the high infection risk of HIV/AIDS samples and may facilitate sample mailing.