A selected ion monitoring assay for primaquine in plasma and urine

Plasmodium falciparum gametocytes: with a view to a kill

Drugs that kill or inhibit the sexual stages of Plasmodium in order to prevent transmission are important components of malaria control programmes. Reducing gametocyte carriage is central to the control of Plasmodium falciparum transmission as infection can result in extended periods of gametocytaemia. Unfortunately the number of drugs with activity against gametocytes is limited. Primaquine is currently the only licensed drug with activity against the sexual stages of malaria parasites and its use is hampered by safety concerns. This shortcoming is likely the result of the technical challenges associated with gametocyte studies together with the focus of previous drug discovery campaigns on asexual parasite stages. However recent emphasis on malaria eradication has resulted in an upsurge of interest in identifying compounds with activity against gametocytes. This review examines the gametocytocidal properties of currently available drugs as well as those in the development pipeline and examines the prospects for discovery of new anti-gametocyte compounds.

Simultaneous determination of primaquine and carboxyprimaquine in plasma using high-performance liquid chromatography with electrochemical detection

A selective and sensitive high-performance liquid chromatographic method with electrochemical detection is described for the simultaneous quantitation of primaquine and carboxyprimaquine, its primary metabolite, in plasma. After addition of internal standard, plasma was deproteinized by addition of acetonitrile. Nitrogen-dried supernatants, resuspended in mobile phase were analyzed on a C8 reversed-phase column. Limits of detection for primaquine and carboxyprimaquine were 2 and 5 ng/ml with quantitation limits of 5 and 20 ng/ml, respectively. None of 47 tested antimicrobial agents interfered. In contrast to previously reported methods, the assay sensitivity and specificity are sufficient to permit quantitation of primaquine in plasma for pharmacokinetics following low dose (30 mg, base) oral administration of primaquine, typically used in the treatment of malaria and Pneumocystis carinii pneumonia.

High-performance liquid chromatographic determination of pamaquine, primaquine and carboxy primaquine in calf plasma using electrochemical detection

A high-performance liquid chromatographic method with electrochemical detection is described for quantification of pamaquine, primaquine and carboxy primaquine in calf plasma. After the proteins had been precipitated with acetonitrile, the drugs were separated on a 5-microns C18-modified polymer gel column with an isocratic mobile phase. The detection limit was 0.01 microgram/ml in plasma for all three compounds. The applicability of the method in pharmacokinetic studies was demonstrated by determining the plasma concentrations of the three substances in calves administered a single dose of pamaquine or primaquine.

The use of microorganisms for the study of drug metabolism

The potential for the use of microorganisms as tools in the study of drug metabolism appears to be unlimited. The selected examples cited here are only the beginning of what could develop into a widely accepted alternative in vitro model system for studying drug metabolism in humans. As with any other in vitro model system, it is not expected that microbial systems could ever replace animals in biomedical research. The acquisition of data regarding absorption, distribution, and excretion will still require whole animal systems. However, it is clear from the examples cited that microbial systems offer a reliable, reproducible alternative to small animal models for preliminary drug metabolism studies. Due to significant species variation, small animal models may, in many cases, be less reliable than microorganisms as predictive models of human metabolism. It has been estimated that approximately 70 million animals are used each year in the U.S. for biomedical research. The development of any techniques which curtail the sacrifice of such large numbers of animals is welcomed both by animal welfare groups who wish to ensure the humane treatment of laboratory animals and by researchers who additionally appreciate the more practical and economical benefits of such alternatives.

Plasma kinetics and urinary excretion of primaquine in man

1 The kinetics of primaquine have been studied in twenty volunteers after single and multiple dose regimes. 2 The kinetic parameters were similar in glucose-6-phosphate dehydrogenase (G6PD) normal Thais, G6PD deficient Thais and in Caucasians. 3 The Caucasian subjects showed about 1% of the dose was excreted in the urine. 4 The kinetic parameters obtained from multiple dose studies in Thais were very similar to those obtained from single dose studies in Thais.

Urinary primaquine excretion and red cell methaemoglobin levels in man following a primaquine:chloroquine regimen

1 Red cell methaemoglobin levels were found to be significantly raised in healthy subjects given a 14-day course of primaquine with chloroquine on the first 3 days. 2 The methaemoglobin levels were not related to the quantity of primaquine excreted. 3 No primaquine could be detected in the plasma at 24 h following the last three daily doses.