Pharmacokinetic study of tenofovir disoproxil fumarate combined with rifampin in healthy volunteers.

Tenofovir disoproxil fumarate (tenofovir DF) was studied in combination with rifampin in 24 healthy subjects in a multiple-dose, open-label, single-group, two-period study. All subjects were given tenofovir DF at 300 mg once a day (QD) from days 1 to 10 (period 1). From days 11 to 20 the subjects received tenofovir DF at 300 mg combined with rifampin at 600 mg QD (period 2). The multiple-dose pharmacokinetics of tenofovir (day 10 and 20) and rifampin (day 20) were assessed. The drug-related adverse events (AEs) experienced during this study were mostly mild. Only one grade 3 AE possibly or probably related to the treatment (raised liver enzyme levels) occurred during period 2; the subject was withdrawn from the study. Pharmacokinetic data for 23 subjects were thus evaluable. Point estimates for the mean ratios of tenofovir with rifampin versus tenofovir alone for the area under the concentration-time curve from time zero to 24 h (AUC(0-24)), the maximum concentration of drug in plasma (C(max)), and the minimum concentration of drug in plasma (C(min)) were 0.88, 0.84, and 0.85, respectively. The 90% classical confidence intervals for AUC(0-24), C(max), and C(min) were 0.84 to 0.92, 0.78 to 0.90, and 0.80 to 0.91, respectively, thus suggesting pharmacokinetic equivalence. Similarly, coadministration of rifampin and tenofovir DF did not result in changes in the values of the tenofovir pharmacokinetic parameters. For rifampin, the values of the pharmacokinetic parameters found in this study were comparable to those found in the literature, indicating that tenofovir DF has no effect on the pharmacokinetics of rifampin. In conclusion, adaptation of either the rifampin or the tenofovir DF dose for the simultaneous treatment of tuberculosis and human immunodeficiency virus (HIV) infection in HIV-infected patients is probably not required.

Simultaneous determination of the HIV nucleoside analogue reverse transcriptase inhibitors lamivudine, didanosine, stavudine, zidovudine and abacavir in human plasma by reversed phase high performance liquid chromatography.

A reversed phase high performance liquid chromatography method was developed for the simultaneous quantitative determination of the nucleoside reverse transcriptase inhibitors (NRTIs) lamivudine, didanosine, stavudine, zidovudine and abacavir in plasma. The method involved solid-phase extraction with Oasis MAX cartridges from plasma, followed by high performance liquid chromatography with a SymmetryShield RP 18 column and ultraviolet detection set at a wavelength of 260 nm. The assay was validated over the concentration range of 0.015-5 mg/l for all five NRTIs. The average accuracies for the assay were 92-102%, inter- and intra-day coefficients of variation (CV) were <2.5% and extraction recoveries were higher than 97%. This method proved to be simple, accurate and precise, and is currently in use in our laboratory for the quantitative analysis of NRTIs in plasma.

Simultaneous determination of the HIV drugs indinavir, amprenavir, saquinavir, ritonavir, lopinavir, nelfinavir, the nelfinavir hydroxymetabolite M8, and nevirapine in human plasma by reversed-phase high-performance liquid chromatography.

A reversed-phase high-performance liquid chromatography method for the simultaneous quantitative determination of the currently available HIV protease inhibitors amprenavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir, the active nelfinavir metabolite M8, and the nonnucleoside reverse transcriptase inhibitor nevirapine in human plasma is described. The method involved liquid-liquid extraction from plasma, followed by high-performance liquid chromatography with an OmniSpher 5 C18 column and ultraviolet detection set at a wavelength of 215 nm for the protease inhibitors and 280 nm for nevirapine. The runtime was 25 minutes. The assay has been validated over the concentration range of 0.05 to 30 mg/L for indinavir, nelfinavir, ritonavir, and saquinavir, 0.07 to 30 mg/L for amprenavir and lopinavir, and 0.05 to 15 mg/L for M8 and nevirapine. This method proved to be simple, accurate, and precise and is useful for the therapeutic drug monitoring of protease inhibitors and the nonnucleoside reverse transcriptase inhibitor nevirapine on a routine basis.

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

OBJECTIVE: To characterize sources of variation in plasma concentrations of nelfinavir and its active metabolite M8 and to evaluate the use of therapeutic drug monitoring for nelfinavir treatment. METHODS: Plasma samples and patient's characteristics were obtained from outpatient clinic. Differences between groups of patients were studied by comparing the observed plasma concentrations with the corresponding concentration on a pharmacokinetic population curve based on median plasma levels. RESULTS: Plasma samples (618) were available from 355 patients taking 1250 mg nelfinavir twice daily. The median ratio between M8 and nelfinavir concentrations was 0.29. This ratio appeared to be independent of the time after ingestion. Statistically significantly lower M8 concentrations were found in Black and Asian patients, or when comedication with CYP3A4 inducers was used. Coadministration of CYP2C19 inhibitors, such as omeprazole, decreased the median M8/nelfinavir ratio. Nevertheless, nelfinavir concentrations and summed concentrations of nelfinavir and M8 were only marginally affected in these patients. Diarrhoea was identified as a cause for lower nelfinavir concentrations, without changing the M8/nelfinavir ratio. In a number of patients with suspected therapy failure or intoxication, abnormal nelfinavir plasma concentrations were found. Dose adjustments based on nelfinavir plasma levels were helpful in a number of patients. CONCLUSION: This study shows that the total concentration of nelfinavir and M8 together is not significantly influenced when variation in M8 levels occurs. Consequently, measuring M8 concentrations in addition to nelfinavir concentrations is not required for the purpose of therapeutic drug monitoring for this drug.

High-performance liquid chromatography of HIV protease inhibitors in human biological matrices.

Methods for HPLC analysis of protease inhibitors (PIs) in human biological matrices were reviewed. Assays have been developed for analysis of single PIs or for simultaneous measurement of multiple PIs in plasma-serum, saliva, cerebrospinal fluid and semen. Liquid-liquid extraction was most often applied for sample pretreatment, but solid-phase extraction and protein precipitation were used as well. Reversed-phase or ion-pair chromatography have been used to separate PIs. Detection of PIs should be sensitive enough for quantitation of plasma concentrations below trough levels of single PIs, or below proposed therapeutic thresholds for PIs. The large majority of assays employs UV detection. As the potential for interferences is large, the selectivity of every method should be evaluated properly. The available high-performance liquid chromatography (HPLC) methods have been applied in clinical pharmacokinetic studies and for therapeutic drug monitoring of PIs. Participation in an interlaboratory quality control program is recommended for every laboratory engaged in the bioanalysis of PIs.

Simultaneous determination of the HIV-protease inhibitors indinavir, nelfinavir, saquinavir and ritonavir in human plasma by reversed-phase high-performance liquid chromatography.

A sensitive high-performance liquid chromatographic method has been developed for the simultaneous determination of the four licensed HIV-protease inhibitors indinavir, nelfinavir, saquinavir and ritonavir. An aliquot of 500 microl plasma, spiked with internal standard, was extracted with 0.5 ml 0.1 M NH4OH and 5 ml methyl tert.-butyl ether. After evaporating, the residue was dissolved in eluent consisting of acetonitrile-50 mM phosphate buffer, pH 5.63 (40:60, v/v). Subsequently, the eluent was washed with hexane. Chromatography was performed using a C18 reversed-phase column and gradient elution with a linear increase of acetonitrile from 36 to 66%. Ultraviolet detection at 215 nm was used. Linearity of the method was obtained in the concentration range of 45-30 000 ng/ml for all four analytes. The method was validated extensively and stability tests under various conditions were performed. The assay is now in use to analyse plasma samples from patients treated with (combinations of) HIV-protease inhibitors.

Pharmacokinetics of nicomorphine and its metabolites in man after epidural administration.

In ten patients who received an epidural injection of 15 mg of nicomorphine, the compound was relatively slowly released from the epidural space and was found in plasma for approximately 1.5 h. Nicomorphine is relatively slowly metabolized into 6-nicotinoylmorphine and morphine. The rate of release is patient-dependent. The relative AUC values are 15.3% for nicomorphine, 23.9% for 6-nicotinoylmorphine and 60.8% for morphine. The mean clinical effect lasts for 18.2 +/- 10.1 h.