High-performance liquid chromatographic-ultraviolet determination of primaquine and its metabolites in human plasma and urine

Simultaneous and enantiospecific quantification of primaquine and carboxyprimaquine in human plasma using liquid chromatography-tandem mass spectrometry

Background

The enantiomers of the 8-aminoquinoline anti-malarial primaquine have different pharmacological properties. Development of an analytical method for simultaneous quantification of the enantiomers of primaquine and its metabolite, carboxyprimaquine, will support clinical pharmacometric assessments.

Methods

A simple and sensitive method consisting of liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) was developed for simultaneous and enantiospecific determination of primaquine and its metabolite, carboxyprimaquine, in human plasma. Stable isotopes were used as internal standards to compensate for potential interference and matrix effects. Plasma samples (100 µL) were precipitated with 1% formic acid in acetonitrile followed by phospholipid removal solid phase extraction. Primaquine and carboxyprimaquine enantiomers were separated on a Chiralcel OD-3R (150 mm × 4.6 mm; I.D. 3 μm) column using a LC gradient mode. For separation of racemic primaquine and carboxyprimaquine, the LC method was modified and validated using a reverse phase column (Hypersil Gold 100 mm × 4.6 mm; I.D. 3 µm) and a mobile phase composed of 10 mM ammonium acetate buffer, pH 3.5 and acetonitrile in the isocratic mode. Method validation was performed according to regulatory guidelines.

Results

The calibration range was set to 0.571–260 ng/mL and 2.44–2,500 ng/mL for primaquine and carboxyprimaquine enantiomers, respectively, resulting in a correlation coefficient (r²) ≥ 0.0998 for all calibration curves. The intra- and inter-day assay precisions were < 10% and the accuracy was between 94.7 to 103% for all enantiomers of primaquine and carboxyprimaquine. The enantiospecific method was also modified and validated to quantify racemic primaquine and carboxyprimaquine, reducing the total run time from 30 to 8 min. The inter-, intra-day assay precision of the racemic quantification method was < 15%. The absolute recoveries of primaquine and carboxyprimaquine were between 70 and 80%. Stability was demonstrated for up to 2 years in − 80 °C. Both the enantiomeric and racemic LC–MS/MS methods were successfully implemented in pharmacokinetic studies in healthy volunteers.

Conclusions

Simple, sensitive and accurate LC–MS/MS methods for the quantification of enantiomeric and racemic primaquine and carboxyprimaquine in human plasma were validated successfully and implemented in clinical routine drug analysis.

PHARMACOKINETICS OF PRIMAQUINE PHOSPHATE AFTER A SINGLE ORAL ADMINISTRATION TO AFRICAN PENGUINS (SPHENISCUS DEMERSUS)

Primaquine is an 8-aminoquinolone drug commonly used for the chemoprophylaxis and treatment of avian malarial infections in managed penguin populations worldwide. Little is known about its pharmacokinetic properties in avian species. The objective of this study was to describe the disposition of primaquine phosphate after a single oral dose in 15 healthy African penguins (Spheniscus demersus). A single tablet containing 26.3 mg of primaquine phosphate (equivalent to 15 mg primaquine base) was administered orally to each bird in a herring fish. Blood samples were collected prior to drug administration and at predetermined timepoints through 144 hr postadministration. Plasma was analyzed for drug concentration by high-performance liquid chromatography with ultraviolet detection. Mean maximum plasma concentration of primaquine phosphate was 277 ± 96 ng/ml at approximately 3.1 hr following oral administration. The mean disappearance half-life was 3.6 ± 1.6 hr. Plasma concentrations were below detectable limits in all but one penguin by 36 hr. A single oral administration of 26.3 mg of primaquine phosphate in African penguins resulted in a pharmacokinetic profile comparable to those attained in human studies. These results suggest that a dosing interval similar to human regimens may be of potential use in the prevention and treatment of avian malaria in penguins. Additional clinical studies are needed to determine the efficacy and safety of this regimen.

A pilot randomized controlled trial to compare the effectiveness of two 14-day primaquine regimens for the radical cure of vivax malaria in South India

BACKGROUND

Radical cure of Plasmodium vivax malaria requires treatment with a blood schizonticide and a hypnozoitocide (primaquine) to eradicate the dormant liver stages. There has been uncertainty about the operational effectiveness and optimum dosing of the currently recommended 14-day primaquine (PQ) course.

METHODS

A two centre, randomized, open-label, two arm study was conducted in South India. Patients were randomized to receive either high dose (0.5 mg base/kg body weight) or conventional dose (0.25 mg/kg) PQ for 14 days. Plasma concentrations of PQ and carboxyprimaquine (CPQ) on the 7th day of treatment were measured by reverse phase high performance liquid chromatography. Study subjects were followed up for 6 months. Recurrent infections were genotyped using capillary fragment length polymorphism of two PCR-amplified microsatellite markers (MS07 and MS 10).

RESULTS

Fifty patients were enrolled. Baseline characteristics and laboratory features did not differ significantly between the groups. Mean age of the study population was 42 ± 16.0 years. Recurrences 80-105 days later occurred in 4 (8%) patients, two in each the groups. All recurrences had the same microsatellite genotype as that causing the index infection suggesting all were relapses. One relapse was associated with low CPQ concentrations suggesting poor adherence.

CONCLUSIONS

This small pilot trial supports the effectiveness of the currently recommended lower dose (0.25 mg/kg/day) 14 day PQ regimen for the radical cure of vivax malaria in South India. Trial registration Clinical Trials Registry-India, CTRI/2017/03/007999. Registered 3 March 2017, http://ctri.nic.in/Clinicaltrials/regtrial.php?modid=1&compid=19&EncHid=82755.86366 .

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.

Analysis of primaquine and its metabolite carboxyprimaquine in biological samples: enantiomeric separation, method validation and quantification

The clinical formulation of primaquine (PQ) is a mixture of (-)-(R)- and (+)-(S)- primaquine enantiomers which may show different pharmacokinetic and pharmacodynamic properties. To assess the efficacy and toxicity of primaquine enantiomers, a method using LC-MSD-TOF has been developed. The enantiomers were well separated using a Chiralcel OD column (250 × 4.6 mm, 10 µm) with a linear gradient of mobile phase consisting of acetonitrile (0.1% formic acid) and aqueous ammonium formate (20 mm; 0.1% formic acid) adjusted to pH 5.9 at a flow rate of 0.7 mL/min. The method was validated for linearity, precision, accuracy and limits of detection and quantification. The calibration curves were linear with all correlation coefficients being >0.999. The average recoveries of (-)-(R)- and (+)-(S)-primaquine and (-)-(R)- and (+)-(S)-carboxyprimaquine were 88 and 92%, respectively, in spiked human plasma and 89 and 93% respectively in spiked mouse plasma samples. The RSD of (-)-(R)- and (+)-(S)-primaquine and (-)-(R)- and (+)-(S)-carboxyprimaquine were 2.15, 1.74, 1.73 and 2.31, respectively, in spiked human plasma and 2.21, 1.09, 1.95 and 1.17% in spiked mouse plasma, respectively. The intra-day and inter-day precisions expressed as RSD were lower than 10% in all analyzed quality control levels. The method as reported is suitable for study of the pharmacokinetic and pharmacodynamic properties of the enantiomers of primaquine. The method was successfully applied to study plasma pharmacokinetic profile of enantiomers of primaquine and carboxyprimaquine in mice administered with primaquine in racemic form. The analytical method was found to be linear, accurate, precise and specific.

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.

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.

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.

Effect of aliphatic side-chain substituents on the antimalarial activity and on the metabolism of primaquine studied using mitochondria and microsome preparations

The substitution of two deuterium atoms on the alpha-carbon of the primaquine side chain was found to produce a sevenfold decrease in the rate of conversion of primaquine to carboxyprimaquine by enzymatic oxidative deamination, but the deuterium substitution was found to have no significant effect on the in vitro antimalarial activity or on in vitro hepatocyte toxicity. Placing a single methyl group on the alpha-carbon was found to produce only a slight decrease in the rate of oxidative deamination. Although metabolic attack occurred adjacent to either the aniline nitrogen or the aliphatic amine, metabolic attack occurred primarily adjacent to the more basic nitrogen at the 1'-position, even when this position bore a methyl substituent. Primaquine, the alpha-dideutero analogue, and the alpha-methyl analogue were all found to have about the same in vitro antimalarial activity as determined in the liver hepatocyte assay.

Activity of clindamycin with primaquine against Pneumocystis carinii in vitro and in vivo

The combination of primaquine with clindamycin is effective in both in vitro and in vivo models of Pneumocystis infection. Primaquine alone at concentrations from 10 to 300 micrograms/ml reduced the numbers of organisms in cultures to less than 7% of control. Significant inhibition was observed down to 0.1 microgram/ml. Clindamycin at 5 micrograms/ml was ineffective alone. Combinations of clindamycin and primaquine in culture at various concentrations were effective, but there was no evidence of true synergy. In rats with established Pneumocystis pneumonia, clindamycin alone at 5 or 225 mg/kg was ineffective. Primaquine alone at 0.5 or 2 mg/kg did not significantly affect the numbers of organisms remaining. The combination of 0.5 mg of primaquine per kg and 225 mg of clindamycin per kg was effective for therapy, lowering the numbers of organisms in the lungs by about 90%. The combination of 2 mg of primaquine per kg and 225 mg of clindamycin per kg was more effective, lowering the numbers of organisms by almost 98%. In the in vivo prophylaxis model, primaquine at 0.1 or 0.2 mg/kg did not prevent the development of Pneumocystis pneumonia in immune-suppressed rats. Clindamycin at 50 mg/kg had a modest effect alone, but at 5 mg/kg all animals became heavily infected. At 0.5 mg/kg, primaquine alone reduced the severity of infection, but seven of eight rats were still infected. In contrast, the combination of 5 mg of clindamycin per kg and 0.5 mg of primaquine per kg prevented infection in 8 of 10 rats; 2 rats had minimal infection. These studies suggest that the combination of clindamycin and primaquine should be tested in therapy or prophylaxis of Pneumocystis infections in humans.

Biodegradable microspheres. VI: Lysosomal release of covalently bound antiparasitic drugs from starch microparticles

The possibilities of using polyacryl starch microparticles as a carrier for low molecular weight drugs have been investigated. Two drugs containing primary amino groups, primaquine and trimethoprim, have been covalently coupled to the starch microparticles via tri-, tetra-, and pentapeptide spacer arms. The drug-particle complexes were prepared by coupling different drug-peptide derivatives to the particles after activation of the starch with carbonyldiimidazole. The activation process with subsequent removal of activated groups did not change the degradability of the starch microparticles. The resulting drug-carrier complexes were stable in serum, while free drugs were released in a lysosome fraction. Thus, the microparticle-peptide-drug conjugates fulfill the basic requirements for a drug carrier used to target drugs to the lysosomes (e.g., for the treatment of lysosomal parasitic diseases).

Fungal metabolism of 4-methylprimaquine

4-Methylprimaquine (4-MPQ), an 8-aminoquinoline antimalarial drug, was subjected to microbial metabolism studies in an effort to isolate, identify, and predict the probable mammalian metabolite(s). Preliminary screening with a number of strains of Aspergillus indicated that several species were capable of metabolizing 4-MPQ to one major metabolite based on thin-layer chromatographic analysis. Preparative scale conversion of 4-MPQ using whole-cell suspensions of Aspergillus ochraceus afforded one major metabolite (4-MPQ-I). Based on spectroscopic and chemical evidence, the structure of the metabolite is proposed as 6-methoxy-8-(3-carboxyl-l-methylpropylamino)-lepidine.

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.