Adjusting Antiretroviral Therapy Dosage Using Therapeutic Drug Monitoring

Overview

Background Low concentrations of protease inhibitors (PIs) or nonnucleoside reverse transcriptase inhibitors (NNRTIs) are associated with an increased risk of virological failure. Likewise, excessive antiretroviral drug concentrations increase the risk of toxicity. Therapeutic drug monitoring (TDM) may identify and correct excessively high or low PI and/or NNRTI concentrations, and thus minimize toxicity and risk of treatment failure. Treatment guidelines only recommend using TDM to help optimize ARV therapy in selected patients, and there are no clear recommendations to guide the clinician who decides to adjust drug doses. Prospective studies have demonstrated the relationship between EFV plasma concentration and neuropsychiatric symptoms. Moreover, EFV is metabolized mainly by cytochrome P450 2B6 and its concentration was reported to be associated with the CYP2B6 516GrT genetic polymorphism. For drugs such as EFV or LPV/r, lower doses than the ones validated for standard clinical use have demonstrated efficacy in dose-ranging studies. The investigators will use a standardised algorithm to reduce doses in patients with plasma EFV or LPV/r concentration above percentile 75. This algorithm is based on a Bayesian approach from the pharmacology unit in Lausanne. The investigators hypothesize that a dosage individualisation is feasible and safe. 2.2 Study Aims The investigators aim at testing a simplified algorithm for dose reduction in patients with documented virological efficacy, treated by a stable LPV/r or EFV based regimen with elevated plasma concentration of these drugs. Study Design Prospective open label study in which all eligible patients screened with a plasma drug concentration of either EFV or LPV/r above percentile 75 will be included. After confirmation of the results at baseline, patients will be offered to decrease drug dosage by a third or a half according to a standardised algorithm. All patients will undergo HIVRNA, biochemistry and validated questionnaires after 3 and 6 months to assess the safety and the benefit of this strategy.