Patrice Jaillon

Quantification of the HIV-integrase inhibitor raltegravir (MK-0518) in human plasma by high-performance liquid chromatography with fluorescence detection

A simple and sensitive HLPC method with fluorescence detection was developed for the accurate determination of the first licensed HIV integrase inhibitor raltegravir in human plasma. A 500-microL plasma sample was spiked with delavirdine as internal standard and subjected to liquid-liquid extraction based on a previously described assay i.e. using hexane/methylene chloride (1:1, v/v%) at pH 4.0. HPLC was performed using a Symmetry Shield RP18 column (150 mm x 4.6 mm), a gradient elution of acetonitrile -0.01% (v/v) triethylamine in water adjusted to pH 3.0 at a flow rate of 1 mL/min and a fluorimetric detector set at 299 and 396 nm as excitation and emission wavelengths, respectively. The retention time was 5.0 min for internal standard and 6.4 min for raltegravir. Calibration curves were linear in the range 5-1000 ng/mL and the accuracy of quality control samples in the range 10-750 ng/mL varied from 98.3 to 99.1% and 98.3 to 101.0% of the nominal concentrations for intra-day and day-to-day analysis, respectively with a precision of 6.3% or less. Among the other antiretroviral drugs which can be given in association to HIV-infected patients, none was found to interfere with internal standard or raltegravir. The described assay was developed for the purpose of therapeutic drug of this HIV integrase inhibitor.

Modelling the influence of MDR1 polymorphism on digoxin pharmacokinetic parameters

ObjectivesDigoxin is a well-known probe for the activity of P-glycoprotein. The objective of this work was to apply different methods for covariate selection in non-linear mixed-effect models to study the relationship between the pharmacokinetic parameters of digoxin and the genotype for two major exons located on the multi-drug-resistance 1 (MDR1) gene coding for P-glycoprotein.MethodsThirty-two healthy volunteers were recruited in three pharmacokinetic drug interaction studies. The data after a single oral administration of digoxin alone were pooled. All subjects were genotyped for the MDR1 C3435T and G2677T/A genotypes. The concentration-time profile of digoxin was established using 12–16 blood samples taken between 15xa0min and 72xa0h after administration. We modelled the pharmacokinetics of digoxin using non-linear mixed-effect models. Parameter estimation was performed using the stochastic approximation EM method (SAEM). We used three methods to select the covariate model: selection from a full model using Wald tests, forward inclusion using the log-likelihood ratio test and model selection using the Bayesian Information Criterion.ResultsThe three covariate inclusion methods led to the same final model. Carriers of two T alleles for the C3435T polymorphism in exon 26 of MDR1 had a lower apparent volume of distribution than carriers of a C allele. The only other covariate effect was a shorter absorption time-lag in women.ConclusionThe apparent volume of distribution of digoxin is lower in TT subjects, probably reflecting differences in bioavailability. Non-linear mixed-effect models can be useful for detecting the influence of covariates on pharmacokinetic parameters.

Mibefradil, a potent CYP3A inhibitor, does not alter pravastatin pharmacokinetics.

Abstract— Dramatic drug‐drug interactions have been observed between several HMG‐CoA reductase inhibitors and cytochrome P450 3A (CYP3A) inhibitors. The aim of the present study was to investigate the effects of mibefradil, a potent CYP3A inhibitor, on pravastatin pharmacokinetics. 12 healthy volunteers were included in this open‐label one‐period study. Pravastatin pharmacokinetics (following a single oral dose of 40 mg) was studied in the absence of mibefradil (day 1) and after repeated doses (100 mg/day) of mibefradil (day 8). Pravastatin pharmacokinetics after repeated doses of 40 mg/day was also studied in association with repeated doses (100 mg/day) of mibefradil (day 16). Pravastatin area under the plasma concentration vs. time curve (AUC0‐∞,) and Cmax in the absence of mibefradil on day 1 (170 [117 to 395] ng h/mL and 91 [72 to 200] ng/mL respectively, geometric mean [95% confidence intervals]) were not significantly altered in the presence of mibefradil on day 8 (224 [174 to 381] ng h/mL and 124 [72 to 200] ng/mL) and on day 16 (200 [137 to 555] ng h/mL and 91 [74 to 184] ng/mL). Tmax of pravastatin in the absence of mibefradil (0.9 ± 0.1 h, arithmetic mean ± SD) was slightly delayed in the presence of mibefradil on day 8 and 16 (1.1 ± 0.3 and 1.2 ± 0.3 h respectively, p < 0.01 for both comparisons). The results of the present study confirm the lack of pharmacokinetic interactions between mibefradil and pravastatin and indicate that pravastatin may be safely prescribed in the presence of potent CYP3A inhibitors.

Improved sensitivity of digoxin assay by modification of the EMIT 2000 method

A modified EMIT 2000 digoxin assay was developed on the Cobas Mira plus analyzer for the determination of very low plasma concentrations of the drug. The major modifications were a higher plasma volume withdrawn during the analysis step and calibration curves constructed in the range 0-2 ng/ml using calibrators made up with biological matrix. Assays were controlled with an internal, four-level quality control (targets: 0.15; 0.60; 1.70; 2.70 ng/mL). The within-day and day-to-day mean observed values +/- SD (n = 10) of these quality controls were 0.14 +/- 0.02 and 0.15 +/- 0.02 ng/mL; 0.57 +/- 0.01 and 0.64 +/- 0.03 ng/mL; 1.55 +/- 0.06 and 1.62 +/- 0.04 ng/mL, 2.82 +/- 0.09 and 2.82 +/- 0.12 ng/mL, respectively. The detection and the quantification limits were 0.02 and 0.08 ng/mL, respectively. No significant difference was observed between digoxin plasma concentrations measured by the original and the modified EMIT 2000 digoxin assay in 25 plasma specimens, ranging from 0.4 to 3.0 ng/mL, from patients receiving the drug. This modified digoxin EMIT 2000 assay was subsequently used to study digoxin pharmacokinetics after each of 18 healthy volunteers was administered a single 0.5 mg oral dose. The pharmacokinetic parameters found in this study were in accordance with the literature in healthy subjects, using radioimmunoassay (RIA) for digoxin plasma concentration determinations. In conclusion, the lower limit of quantification of this modified EMIT 2000 digoxin assay is similar to that of RIA and can serve as a valuable screen for digoxin pharmacokinetic interactions studies.

IMPROVED SENSITIVITY OF DIGOXIN ASSAY BY MODIFICATION OF THE EMIT 2000 METHOD - APPLICATION TO THE PHARMACOKINETIC INTERACTION BETWEEN DIGOXIN AND MACROGOL 4000, A LAXATIVE POLYMER, IN HEALTHY VOLUNTEERS.

A modified EMIT 2000 digoxin assay was developed on the Cobas Mira plus analyzer for the determination of very low plasma concentrations of the drug. The major modifications were a higher plasma volume withdrawn during the analysis step and calibration curves constructed in the range 0-2 ng/ml using calibrators made up with biological matrix. Assays were controlled with an internal, four-level quality control (targets: 0.15; 0.60; 1.70; 2.70 ng/mL). The within-day and day-to-day mean observed values +/- SD (n = 10) of these quality controls were 0.14 +/- 0.02 and 0.15 +/- 0.02 ng/mL; 0.57 +/- 0.01 and 0.64 +/- 0.03 ng/mL; 1.55 +/- 0.06 and 1.62 +/- 0.04 ng/mL, 2.82 +/- 0.09 and 2.82 +/- 0.12 ng/mL, respectively. The detection and the quantification limits were 0.02 and 0.08 ng/mL, respectively. No significant difference was observed between digoxin plasma concentrations measured by the original and the modified EMIT 2000 digoxin assay in 25 plasma specimens, ranging from 0.4 to 3.0 ng/mL, from patients receiving the drug. This modified digoxin EMIT 2000 assay was subsequently used to study digoxin pharmacokinetics after each of 18 healthy volunteers was administered a single 0.5 mg oral dose. The pharmacokinetic parameters found in this study were in accordance with the literature in healthy subjects, using radioimmunoassay (RIA) for digoxin plasma concentration determinations. In conclusion, the lower limit of quantification of this modified EMIT 2000 digoxin assay is similar to that of RIA and can serve as a valuable screen for digoxin pharmacokinetic interactions studies.