Variability in non‐nucleoside reverse transcriptase and protease inhibitor concentrations among HIV‐infected adults in routine clinical practice

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Abstract
What is already known about this subject: The concentration of protease and non‐nucleoside reverse transcriptase inhibtors in plasma has been related to both efficacy and toxicity. Most antiretroviral concentration data come from selected populations of patients undergoing therapeutic drug monitoring programmes, which may overestimate interindividual variability. What this study adds: Our study has demonstrated the large interindividual variability in antiretroviral drug concentrations in an unselected population of patients during routine clinical practice. These results may provide interesting information to clinicians for the management of antiretroviral therapy in HIV‐infected patients. Aims: The objective of this study was to assess interindividual variability in trough concentrations of plasma of non‐nucleoside reverse transcriptase inhibitors (NNRTI) and protease inhibitors (PI) among HIV‐infected adults in a routine outpatient setting.Methods: One hundred and seventeen patients who attended our clinic for routine blood tests, and who were receiving antiretroviral therapy which included NNRTI or PI were studied. Patients were not informed that drug concentrations were going to be measured until blood sampling. The times of the last antiretroviral dose and of blood sampling were recorded. Drug concentrations were considered optimal if they were above the proposed minimum effective value. In addition, efavirenz, nevirapine and atazanavir concentrations were considered potentially toxic if they were > 4.0 mg l−1, > 6.0 mg l−1 and > 0.85 mg l−1, respectively.Results: Overall, interindividual variability of NNRTI and PI concentrations in plasma was approximately 50%, and only 68.4% of the patients had drug concentrations within the proposed therapeutic range. Poor adherence explained only 35% of subtherapeutic drug concentrations.Conclusion: Interindividual variability in trough concentrations of NNRTI and PI among HIV‐infected adults is large in routine clinical practice, with drug concentrations being outside the therapeutic window in a significant proportion of patients. These findings provide further evidence that therapeutic drug monitoring may be useful to guide antiretroviral therapy in clinical practice.

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