Population pharmacokinetics of lumefantrine in pregnant women treated with artemether-lumefantrine for uncomplicated Plasmodium falciparum malaria.

Artemether-lumefantrine has become one of the most widely used antimalarial drugs in the world. The objective of this study was to determine the population pharmacokinetic properties of lumefantrine in pregnant women with uncomplicated multidrug-resistant Plasmodium falciparum malaria on the northwestern border of Thailand. Burmese and Karen women (n = 103) with P. falciparum malaria and in the second and third trimesters of pregnancy were treated with artemether-lumefantrine (80/480 mg) twice daily for 3 days. All patients provided five capillary plasma samples for drug quantification, and the collection times were randomly distributed over 14 days. The concentration-time profiles of lumefantrine were assessed by nonlinear mixed-effects modeling. The treatment failure rate (PCR-confirmed recrudescent infections at delivery) was high; 16.5% (95% confidence interval, 9.9 to 25.1). The population pharmacokinetics of lumefantrine were described well by a two-compartment open model with first-order absorption and elimination. The final model included interindividual variability in all pharmacokinetic parameters and a linear covariate relationship between the estimated gestational age and the central volume of distribution. A high proportion of all women (40%, 41/103) had day 7 capillary plasma concentrations of <355 ng/ml (which corresponds to approximately <280 ng/ml in venous plasma), a threshold previously associated with an increased risk of therapeutic failure in nonpregnant patients in this area. Predictive modeling suggests that a twice-daily regimen given for 5 days would be preferable in later pregnancy. In conclusion, altered pharmacokinetic properties of lumefantrine contribute to the high rates of failure of artemether-lumefantrine treatment in later pregnancy. Dose optimization is urgently needed.

A high-performance liquid chromatographic method for determination of praziquantel in plasma.

A simple, sensitive, selective and reproducible method based on a reversed-phase chromatography was developed for the determination of praziquantel in human plasma. Praziquantel was separated from the internal standard (diazepam) on a Luna C18 column (250 mm x 4.6mm, 5 microm particle size), with retention times of 4.8 and 6.2 min, respectively. Ultraviolet detection was set at 21 7 nm. The mobile phase consisted of acetonitrile and distilled water (70:30, v/v), running through the column at a flow rate of 1.0 ml/min. The chromatographic analysis was operated at 25 degrees C. Sample preparation (1 ml plasma) was done by a single step liquid-liquid extraction with the mixture of methyl-tert-butylether and dichloromethane at the ratio of 2:1 (v/v). Calibration curves in plasma at the concentrations 0, 50, 100, 200, 400, 800 and 1600 ng/ml were all linear with correlation coefficients better than 0.999. The precision of the method based on within-day repeatability and reproducibility (day-to-day variation) was below 15% (relative standard deviation: R.S.D.). Good accuracy was observed for both the intra-day or inter-day assays, as indicated by the minimal deviation of mean values found with measured samples from that of the theoretical values (below +/-15%). Limit of quantification (LOQ) was accepted as 5 ng using 1 ml samples. The mean recovery for praziquantel and the internal standard were greater than 90% for both praziquantel and internal standard. The method was free from interference from the commonly used antibiotic and antiparasitic drugs. The method appears to be robust and has been applied to a pharmacokinetic study of praziquantel in three healthy Thai volunteers following a single oral dose of 40 mg/kg body weight praziquantel.

Quantification of the anti-influenza drug zanamivir in plasma using high-throughput HILIC-MS/MS.

BACKGROUND: parenteral zanamivir is a promising drug for the treatment of severe influenza. However, quantification of this polar drug in biological matrices has traditionally been difficult and the methods developed have been relatively insensitive. RESULTS: a high-throughput bioanalytical method for the analysis of zanamivir in human plasma using SPE in the 96-well plate format and LC coupled to positive MS/MS has been developed and validated according to US FDA guidelines. The method uses 50 microl of plasma and covers a large working range from 1-50, 000 ng/ml with a LOD of 0.50 ng/ml. CONCLUSION: this new LC-MS/MS assay is more sensitive than previous methods despite using a small plasma volume sample. It is particularly suitable for clinical studies on both parenteral and inhaled zanamivir.

Quantification of dihydroartemisinin, artesunate and artemisinin in human blood: overcoming the technical challenge of protecting the peroxide bridge.

BACKGROUND: Quantification of artemisinin (ARN) and its derivatives in whole blood has hitherto been thought impossible. RESULTS: A LC-MS/MS method for the analysis of artesunate (ARS), its metabolite dihydroartemisinin (DHA) and artemisinin in human whole blood has been developed and successfully validated. The method includes stabilization of the blood matrix at the time of collection and at the time of analysis. Addition of potassium dichromate to the blood samples deactivated the Fe(2+) core in hemoglobin, while deferoxamine chelated Fe(3+) and prevented back conversion into Fe(2+). A pilot study showed that the blood:plasma ratio for ARS and DHA is approximately 0.75, indicating a significantly lower uptake in red blood cells than had previously been estimated using radiolabeled drug methodology. CONCLUSIONS: The developed LC-MS/MS assay is the first method available for quantification of ARN and its derivatives in blood and opens up new possibilities of studying these drugs inside infected red blood cells.

A liquid chromatographic-tandem mass spectrometric method for determination of artemether and its metabolite dihydroartemisinin in human plasma.

BACKGROUND: Artemether-lumefantrine is the most widely recommended artemisinin-based combination treatment for falciparum malaria. Quantification of artemether and its metabolite dihydroartemisinin in biological matrices has traditionally been difficult, with sensitivity being an issue. RESULTS: A high-throughput bioanalytical method for the analysis of artemether and its metabolite dihydroartemisinin in human plasma using solid-phase extraction in the 96-well plate format and liquid chromatography coupled to positive ion mode tandem mass spectroscopy has been developed and validated according to US FDA guidelines. The method uses 50 µl plasma and covers the calibration range 1.43-500 ng/ml with a limit of detection at 0.36 ng/ml. CONCLUSIONS: The developed liquid chromatography-tandem mass spectrometry assay is more sensitive than all previous methods despite using a lower plasma volume (50 µl) and is highly suitable for clinical studies where plasma volumes are limited, such as pediatric trials.