High-performance liquid chromatographic--electrochemical assay method for primaquine in plasma and urine

Increased bioavailability of primaquine using poly(ethylene oxide) matrix extended-release tablets administered to beagle dogs

Primaquine (PQ) is used for the radical cure of Plasmodium vivax malaria and can cause serious side effects in some individuals. The development of an extended-release dosage with poly(ethylene oxide) as a hydrophilic polymer has been investigated to improve drug efficacy and tolerability. The aim of this study was to evaluate in vivo a new extended-release formulation of PQ (60 mg). The formulation was administered to beagle dogs and plasma PQ concentrations were compared to a conventional immediate-release formulation of PQ (60 mg). The evaluation was carried out using a validated high-performance liquid chromatography method using solid-phase extraction. Total PQ exposure in beagle dogs was 2.2 times higher (area under curve of 12 193 versus 5678 ng h/ml) and the elimination half-life of PQ was a 19-fold greater (12.95 hours versus 0.68 hours) with the extended-release tablets compared with the immediate-release tablets. These findings suggest that the extended-release formulation of PQ merits further evaluation for the treatment of P. vivax malaria and/or chemoprophylaxis.

HPLC and HPTLC assays for the antimalarial agents Chloroquine, Primaquine and Bulaquine

A combination Kit for antirelapse treatment of P. vivax malaria, consisting of Chloroquine phosphate tablets and Bulaquine capsules has been recently developed, and marketed under the trade name Aablaquine. Bulaquine is prepared from Primaquine. Several methods of analysis are reported for each drug separately as well two drugs in combination but no method for simultaneous estimation of these three drugs is known. Therefore, the present study was undertaken to develop a sensitive and reproducible high performance liquid chromatographic as well as high performance thin layer chromatographic assay method for the simultaneous estimation of Chloroquine, Primaquine and Bulaquine.

High-performance liquid chromatographic determination of primaquine and carboxyprimaquine concentrations in plasma and blood cells in Plasmodium vivax malaria cases following chronic dosage with primaquine

A reversed-phase HPLC method using acetonitrile-methanol-1 M perchloric acid-water (30:9:1:95, v/v) at a flow-rate of 1.5 ml/min on a mu-Bondapak C18 column with UV detection at 254 nm was developed for the separation of primaquine, its major metabolite carboxyprimaquine and other metabolites such as N-acetylprimaquine, 4-hydroxyprimaquine, 5-hydroxyprimaquine, 5-hydroxy-6-methoxyprimaquine, demethylprimaquine and 6-methoxyprimaquine, and also other antimalarials. The calibration graphs were linear in the range 0.025-100 micrograms/ml for primaquine and 4-1000 micrograms/ml for carboxyprimaquine. The within-day and day-to-day coefficients of variation averaged 3.65 and 6.95%, respectively, for primaquine and 3.0 and 7.52%, respectively for carboxyprimaquine in plasma. The extraction recoveries for primaquine and carboxyprimaquine were 89 and 83%, respectively. The mean carboxyprimaquine concentration was much higher in plasma and blood cells of Plasmodium vivax patients than that in plasma from healthy subjects. The carboxyprimaquine level was also higher in blood cells than plasma whereas the primaquine concentration was the same in both cases.

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 method for the determination of a candidate 8-aminoquinoline antimalarial drug (WR 242511) using oxidative electrochemical detection

WR 242511 (or I) is a new compound of the 8-aminoquinoline class designed to replace primaquine for the treatment of malaria. In order to perform preclinical and clinical testing, an assay was needed to determine drug levels in plasma samples. A simple and reliable reversed-phase high-performance liquid chromatographic (HPLC) method for the measurement of I in plasma using oxidative electrochemical detection is described. A 250-microliters plasma sample containing WR 256408 (or II) as internal standard was extracted with tert.-butyl methyl ether-2-propanol. A 25-microliters aliquot of the extractant was used for HPLC analysis. The mobile phase was 50:50 acetonitrile-sodium acetate (50 mM, pH 6) with 1 mM EDTA. Compounds I and II were separated within 10 min. The limit of detection for I was 10 ng/ml (plasma) with a recovery around 72%. The method was validated in a dog experiment where levels were followed for 48 h. The method is sensitive and robust and can be used for routine drug analysis during pharmacokinetic studies.

Simultaneous determination of a new antimalarial agent, CDRI compound 80/53, and its metabolite primaquine in serum by high-performance liquid chromatography

Compound 80/53 (I) is a new substance being developed as an antimalarial agent. It is unstable in acidic conditions where it is converted into primaquine. A high-performance liquid chromatographic assay for simultaneous determination in serum of I and primaquine has been developed. Conditions were optimized to minimize the conversion of I into primaquine. The method includes extraction of the unchanged compound and primaquine from serum samples with hexane-2-propanol (pH > 8). Separation was accomplished by reversed-phase chromatography on a C18 column with acetonitrile-tetrahydrofuran-phosphate buffer. The recoveries of I and primaquine were always greater than 70%. No interference was observed in extracts obtained from drug-free serum. The detector response was linear with concentrations of I and the metabolite in the ranges 25-400 and 10-180 ng/ml, respectively, and the within-day precision (coefficient of variation) remained less than 13.7% for I and 12.5% for primaquine. The method is suitable for the determination of concentration-time profiles of I and primaquine in human serum.

The pharmacokinetics of primaquine in calves after subcutaneous and intravenous administration

The pharmacokinetics of primaquine was studied in calves of 180-300 kg live weight. Primaquine was injected at 0.29 mg/kg (0.51 mg/kg as primaquine diphosphate) intravenously (IV) or subcutaneously (SC) and the plasma concentrations of primaquine and its metabolite carboxyprimaquine were determined by high-performance liquid chromatography. The extrapolated concentration of primaquine at zero time after IV administration was 0.50 +/- 0.48 microgram/ml (mean +/- SD) which decreased with an elimination half-life of 0.16 +/- 0.07 h. Primaquine was rapidly converted to carboxyprimaquine after either route of administration. The peak concentration of carboxyprimaquine was 0.50 +/- 0.08 microgram/ml at 1.67 +/- 0.15 h after IV administration. The corresponding value was 0.47 +/- 0.07 micrograms/ml at 5.05 +/- 1.20 h after SC administration. The elimination half-lives of carboxyprimaquine after IV and SC administration were 15.06 +/- 0.99 and 12.26 +/- 3.06 h, respectively. The areas under the concentration-time curve for carboxyprimaquine were similar following either IV or SC administration of primaquine; the values were 11.85 +/- 2.62 micrograms.h/ml after the former and 10.95 +/- 2.65 micrograms.h/ml after the latter. The mean area under the concentration-time curve for primaquine was less than 0.1 micrograms.h/ml after either route of administration.

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.

Effects of an NADPH-generating system on primaquine degradation by hamster liver fractions

1. Primaquine (PQ) often causes severe anaemia in individuals with glucose 6-phosphate dehydrogenase (G6PD) deficient erythrocytes, and metabolites have been implicated as the toxic substance. These studies present data identifying additional metabolites of PQ. 2. Two metabolites of primaquine (PQ) previously identified in human studies, namely, 6-methoxy-8-aminoquinoline (MAQ) and 8-(3-carboxy-1-methylpropylamino)-6-methoxyquinoline (PQC) were also formed on incubation of PQ with hamster liver fractions for up to 24 h without an NADPH-generating system. 3. The alcohol (PQAOH) and lactam (PQLT) derivatives of PQ were also formed on incubation with hamster liver fraction used in these studies. 4. The microsomal metabolism of PQ was decreased in presence of an NADPH-generating system, but not by SKF-525A or glutathione (GSH) indicating that the oxidative reactions were probably not due to the cytochrome P-450 system or free radical mechanisms.

Retention behaviour of acidic, neutral and basic drugs on a CN column using phosphate buffers in the mobile phase

The retention behaviour of a set of sixteen more or less drugs on a CN column with methanol-phosphate buffer as eluent was studied. The influence of the volume percentage of methanol, pH and the ionic strength on the capacity factors (k') of the drugs was determined using an experimental design consisting of three pH values (3, 5 and 7), four ionic strengths (0.025, 0.05, 0.075 and 0.1) and three volume percentages of methanol (10, 30 and 50%). The selected drugs were basic, acidic and neutral compounds with different polarity properties. The number of carbon atoms, considered here as reflecting the hydrophobic characteristics of the solutes, varied from 7 to 25. The influence on the retention of drugs on a CN column of the different parameters studied was evaluated. The volume percentage of organic modifier and the pH are the most important factors. A change in ionic strength is important only when large molecules are chromatographed. As the interaction between pH, ionic strength and volume percentage of methanol is small, optimization of the three parameters separately is possible.

Characterization of the urinary metabolites of primaquine in rats

Following the synthesis of reference standards of the primaquine metabolites, a high-performance liquid chromatographic (HPLC) analytical method for carboxyprimaquine, its glycine conjugate, and its glucuronide conjugate in urine samples was developed. After the administration of primaquine, only trace quantities of primaquine and carboxyprimaquine (each less than 1% of dose) and no significant quantity of the two conjugates of carboxyprimaquine were excreted in the urine. When carboxyprimaquine was administered, only 0.3% of the dose was excreted in the urine. When carboxyprimaquine glycinate was administered, the compound was found in the 700- to 1300-µg/ml concentration range in the urine within the first few hours. Using (14)C-labeled primaquine, six new metabolites were found in the urine and partially characterized. The purported metabolites of primaquine (8-amino-6-methoxyquinoline, 5-hydroxyprimaquine, and 6-desmethyl-5-hydroxyprimaquine) were not found in the urine. A field screening test for the quantitation of primaquine metabolites in urine was also investigated. The inexpensive, but sensitive assay was found to give results that closely paralleled the more complex HPLC method and it was moderately well correlated with the total radioactivity in the urine samples.

Drug level monitoring: chromatography of some minor groups of drugs

Some important facts about the chromatographic separation of a number of selected categories of drugs are summarized. The data refer to the chromatographic method of choice, stationary phase, mobile phase (carrier gas), detection procedure and (where available) method sensitivity. Also, fundamental instrumental parameters, namely injector, column and detector temperature, carrier gas and mobile phase flow-rate and gradient set-up are reported here. In all cases also the source material used for analysis is specified. The data are presented in table form, each table dealing with a particular category of drugs. The following categories of drugs are being dealt with: anthelmintics, antiarteriosclerotics, antibacterials, anticholinergics and cholinergics, anticoagulants, antidiabetics, antiemetics, antimycotics, antihistamines, antimalarials, antiparasitics, antiparkinsonics, antitussives, antiulcer drugs, antiviral compounds, appetite depressants and immunosuppressives.