Editorial comment on Analysis of variation in plasma concentrations of nelfinavir and its active metabolite M8 in HIV-positive patients

Pharmacokinetics of indinavir and nelfinavir in treatment-naive, human immunodeficiency virus-infected subjects

AIDS Clinical Trials Group protocol 388 was designed to compare a three-drug regimen (indinavir with dual nucleosides) to a four-drug regimen (indinavir plus nelfinavir or indinavir plus efavirenz with dual nucleosides). Blood samples from patients taking indinavir and nelfinavir were collected over 8 to 12 h following a specified dose and were analyzed with high-performance liquid chromatography. Pharmacokinetic data were derived by using noncompartmental analysis. Following administration of indinavir every 8 h in the absence of nelfinavir (n = 8), the median predose indinavir concentration (C(0)) was 369 ng/ml (range, <10 to 949 ng/ml; one subject had a concentration of <10 ng/ml), and the concentration 8 h after administration of the study dose was 159 ng/ml (range, 85 to 506 ng/ml). In the group receiving 1000 mg of indinavir every 12 h with nelfinavir (n = 10), the median indinavir C(0) was <10 ng/ml (range, <10 to 3740 ng/ml; six subjects had a value of <10 ng/ml), and the C(12 h) was 44 ng/ml (range, <10 to 4236 ng/ml; five subjects had a value of <10 ng/ml), while the subjects who received 1200 mg of indinavir every 12 h with nelfinavir (n = 7) had a C(0) of 146 ng/ml (range, 58 to 5215 ng/ml) and a C(12 h) of 95 ng/ml (range, 12 to 954 ng/ml). Indinavir clearance was significantly lower in the presence of nelfinavir (median [interquartile range], 34.1 liters/h [range, 22.6 to 45.8 liters/h] versus 47.9 liters/h [range, 42.7 to 70.3 liters/h]; P < 0.017). For subjects receiving 1,000 mg of indinavir every 12 h, the median C(0) value for nelfinavir (n = 9) was 1,779 ng/ml (range, <187.5 to 4579 ng/ml), and the C(12 h) was 1554 ng/ml (range, <187.5 to 5,540 ng/ml). Due to the unacceptable number of undetectable indinavir trough concentrations, 1200 mg of indinavir appears to be the preferred dose in a twice-daily regimen that includes nelfinavir.

Subtherapeutic antiretroviral plasma concentrations in routine clinical outpatient HIV care

The objective of this study was to evaluate plasma concentrations of nonnucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) within several dosing schemes in a cohort of HIV-infected patients in routine clinical practice and to find possible explanations for subtherapeutic plasma concentrations. Patients were included if a PI or NNRTI was part of their antiretroviral regimen, at least one plasma concentration was obtained, and a complete medication overview from community pharmacy records was available. The study period was from January 1998 to September 2001. Each plasma concentration was related to median plasma concentrations of a pharmacokinetic reference curve, yielding a concentration ratio (CR). A cutoff CR was defined for each antiretroviral drug per specific regimen, discriminating between >or=therapeutic and subtherapeutic concentrations. For the patients with subtherapeutic concentrations, it was sorted out whether drug interactions, adverse events and self-reported symptoms, or nonadherence could be the cause of the lower than expected plasma concentration. Ninety-seven HIV-infected patients fulfilled the criteria. During the defined period, 1145 plasma concentrations were available (median, 11; interquartile range, 8-14). Three hundred fourteen (27.4%) plasma concentrations were classified subtherapeutic. Drug interactions (2; 0.6%), adverse events and self-reported symptoms (67; 21.3%), and nonadherence (14; 4.5%) could only partly explain the subtherapeutic drug levels. Consequently, a large number of the subtherapeutic plasma concentrations (73.6%) remained inexplicable. A high number of subtherapeutic plasma concentrations were observed. No clear causes were found; thus, corrective measures will be difficult to employ. Therefore, therapeutic drug monitoring (TDM) must maintain its crucial place in routine clinical care to be able to identify patients who need extra attention so that therapeutic plasma concentrations are achieved.