Pharmacokinetics of primaquine in patients with P. vivax malaria

Bioequivalence of a new coated 15 mg primaquine formulation for malaria elimination

BACKGROUND

With only one 15 mg primaquine tablet registered by a stringent regulatory authority and marketed, more quality-assured primaquine is needed to meet the demands of malaria elimination.

METHODS

A classic, two sequence, crossover study, with a 10-day wash out period, of 15 mg of IPCA-produced test primaquine tablets and 15 mg of Sanofi reference primaquine tablets was conducted. Healthy volunteers, aged 18-45 years, without glucose-6-phosphate dehydrogenase deficiency, a baseline haemoglobin ≥ 11 g/dL, creatinine clearance ≥ 70 mL/min/1.73 ms, and body mass index of 18.5-30 kg/m2 were randomized to either test or reference primaquine, administered on an empty stomach with 240 mL of water. Plasma primaquine and carboxyprimaquine concentrations were measured at baseline, then 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.333, 2.667, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 8.0, 10.0, 12.0, 16.0, 24.0, 36.0, 48.0 and 72.0 h by liquid chromatography coupled to tandem mass spectrometry. Primaquine pharmacokinetic profiles were evaluated by non-compartmental analysis and bioequivalence concluded if the 90% confidence intervals (CI) of geometric mean (GM) ratios of test vs. reference formulation for the peak concentrations (Cmax) and area under the drug concentration-time (AUC0-t) were within 80.00 to 125.00%.

RESULTS

47 of 50 volunteers, median age 33 years, completed both dosing rounds and were included in the bioequivalence analysis. For primaquine, GM Cmax values for test and reference formulations were 62.12 vs. 59.63 ng/mL, resulting in a GM ratio (90% CI) of 104.17% (96.92-111.96%); the corresponding GM AUC0-t values were 596.56 vs. 564.09 ngxh/mL, for a GM ratio of 105.76% (99.76-112.08%). Intra-subject coefficient of variation was 20.99% for Cmax and 16.83% for AUC0-t. Median clearances and volumes of distribution were similar between the test and reference products: 24.6 vs. 25.2 L/h, 189.4 vs. 191.0 L, whilst the median half-lives were the same, 5.2 h.

CONCLUSION

IPCA primaquine was bioequivalent to the Sanofi primaquine. This opens the door to prequalification, registration in malaria endemic countries, and programmatic use for malaria elimination. Trial registration The trial registration reference is ISRCTN 54640699.

Delayed gametocyte clearance in Plasmodium vivax malaria is associated with polymorphisms in the cytochrome P450 reductase (CPR)

Primaquine (PQ) is the main drug used to eliminate dormant liver stages and prevent relapses in Plasmodium vivax malaria. It also has an effect on the gametocytes of Plasmodium falciparum; however, it is unclear to what extent PQ affects P. vivax gametocytes. PQ metabolism involves multiple enzymes, including the highly polymorphic CYP2D6 and the cytochrome P450 reductase (CPR). Since genetic variability can impact drug metabolism, we conducted an evaluation of the effect of CYP2D6 and CPR variants on PQ gametocytocidal activity in 100 subjects with P. vivax malaria. To determine gametocyte density, we measured the levels of pvs25 transcripts in samples taken before treatment (D0) and 72 hours after treatment (D3). Generalized estimating equations (GEEs) were used to examine the effects of enzyme variants on gametocyte densities, adjusting for potential confounding factors. Linear regression models were adjusted to explore the predictors of PQ blood levels measured on D3. Individuals with the CPR mutation showed a smaller decrease in gametocyte transcript levels on D3 compared to those without the mutation (P = 0.02, by GEE). Consistent with this, higher PQ blood levels on D3 were associated with a lower reduction in pvs25 transcripts. Based on our findings, the CPR variant plays a role in the persistence of gametocyte density in P. vivax malaria. Conceptually, our work points to pharmacogenetics as a non-negligible factor to define potential host reservoirs with the propensity to contribute to transmission in the first days of CQ-PQ treatment, particularly in settings and seasons of high Anopheles human-biting rates.

Primaquine, an antimalarial drug that controls the growth of cryptococcal cells

INTRODUCTION

The treatment of Cryptococcus neoformans with fluconazole and amphotericin B is, at times, characterised by clinical failure. Therefore, this study sought to re-purpose primaquine (PQ) as an anti-Cryptococcus compound.

METHOD

The susceptibility profile of some cryptococcal strains towards PQ was determined using EUCAST guidelines, and PQ's mode of action was examined. In the end, the ability of PQ to enhance in vitro macrophage phagocytosis was also assessed.

RESULTS

We show that PQ had a significant inhibitory effect on the metabolic activity of all tested cryptococcal strains, with 60 µM, defined as MIC₅₀ in this preliminary study, as it reduced the metabolic activity by more than 50%. Moreover, at this concentration, the drug was able to affect mitochondrial function adversely, as treated cells displayed significant (p < 0.05) loss of mitochondrial membrane potential, cytochrome c (cyt c) leakage and overproduction of reactive oxygen species (ROS) when compared to non-treated cells. It is our reasoned summation that the produced ROS targeted the cell walls and cell membranes, inducing observable ultrastructural changes and a significant (p < 0.05) increase in membrane permeability when compared to non-treated cells. Concerning the PQ effect on macrophages, it was noted that it significantly (p < 0.05) enhanced macrophage phagocytic efficiency compared to non-treated macrophages.

CONCLUSION

This preliminary study highlights the potential of PQ to inhibit the in vitro growth of cryptococcal cells. Moreover, PQ could control the proliferation of cryptococcal cells inside macrophages, which they often manipulate in a Trojan horse-like manner.

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.

Measurements of 5,6 orthoquinone, surrogate for presumed active primaquine metabolite 5-hydroxyprimaquine, in the urine of Cambodian adults

The active metabolites of primaquine, in particular 5-hydroxyprimaquine, likely responsible for clearance of dormant hypnozoites, are produced through the hepatic CYP450 2D6 (CYP2D6) enzymatic pathway. With the inherent instability of 5-hydroxyprimaquine, a stable surrogate, 5,6 orthoquinone, can now be detected and measured in the urine as part of primaquine pharmacokinetic studies. This study performed CYP450 2D6 genotyping and primaquine pharmacokinetic testing, to include urine 5,6 orthoquinone, in 27 healthy adult Cambodians, as a preliminary step to prepare for future clinical studies assessing primaquine efficacy for Plasmodium vivax infections. The CYP2D6 *10 reduced activity allele was found in 57% of volunteers, and the CYP2D6 genotypes were dominated by *1/*10 (33%) and *10/*10 (30%). Predicted phenotypes were evenly split between Normal Metabolizer (NM) and Intermediate Metabolizer (IM) except one volunteer with a gene duplication and unclear phenotype, classifying as either IM or NM. Median plasma PQ area under the curve (AUC) was lower in the NM group (460 hr*ng/mL) compared to the IM group (561 hr*ng/mL), although not statistically significant. Similar to what has been found in the US study, no 5,6 orthoquinone was detected in the plasma. The urine creatinine-corrected 5,6 orthoquinone AUC in the NM group was almost three times higher than in the IM group, with peak measurements (T max ) at 4 hours. Although there is variation among individuals, future studies examining the relationship between the levels of urine 5,6 orthoquinone and primaquine radical cure efficacy could result in a metabolism biomarker predictive of radical cure.

Population Pharmacokinetics of Primaquine in the Korean Population

While primaquine has long been used for malaria treatment, treatment failure is common. This study aims to develop a population pharmacokinetic model of primaquine and its metabolite, carboxyprimaquine, and examine factors influencing pharmacokinetic variability. The data was obtained from a clinical study in 24 Korean subjects randomly assigned to normal and obese groups. The participants received primaquine 15 mg daily for 4 days and blood samples were collected at day 4. Pharmacokinetic modeling was performed with NONMEM and using simulations; the influences of doses and covariates on drug exposure were examined. A minimal physiology-based pharmacokinetic model connected with a liver compartment comprehensively described the data, with CYP450 mediated clearance being positively correlated with the body weight and CYP2D6 activity score (p < 0.05). In the simulation, while the weight-normalized area under drug concentration for primaquine in the obese group decreased by 29% at the current recommended dose of 15 mg, it became similar to the normal weight group at a weight-normalized dose of 3.5 mg/kg. This study has demonstrated that the body weight and CYP2D6 activity score significantly influence the pharmacokinetics of primaquine. The developed model is expected to be used as a basis for optimal malaria treatment in Korean patients.

Doses of primaquine administered to children with Plasmodium vivax according to an age-based dose regimen

Primaquine is still the first-line drug to eliminate hypnozoites of Plasmodium vivax. The therapeutic efficacy is related to the total dose administered. In several endemic areas, the drug is administered for children in an age-based regimen, which can lead to inadequate exposure, increasing the rates of recurrence of the infection. The present study aims to describe the mg/kg total dose of primaquine administered to children for treatment for vivax malaria when an age-based regimen is used and to measure the plasma concentrations of primaquine and carboxyprimaquine. A total of 85 children were included in the study. The total dose of primaquine administered based on mg/kg had a median value of 3.22 mg/kg. The percentage of patients with a total dose below the required dose of 3.5 mg/kg was 55.75%. The median primaquine maximum concentration was 94 ng/ml. For carboxy-primaquine, the median maximum concentration was 375 ng/ml. The results suggest that age-based dosing regimens likely lead to substantial under-dosing of primaquine, which is evident in the youngest children and is reflected in decreased levels of primaquine and carboxy-primaquine in plasma samples 13.

Population pharmacokinetics of primaquine and the effect of hepatic and renal dysfunction: An exploratory approach

OBJECTIVES

We attempted to develop a population pharmacokinetic model for primaquine (PQ) and evaluate the effect of renal and hepatic dysfunction on PQ pharmacokinetics.

MATERIALS AND METHODS

The data were collected from a prospective, nonrandomized clinical study in healthy volunteers and patients with mild-moderate hepatic dysfunction and renal dysfunction. Model development was conducted using NONMEM^® software, and parameter estimation was conducted using first-order conditional estimation with interaction method.

RESULTS

Final data included a total of 53 study participants (13 healthy individuals, 12 with mild hepatic dysfunction, 6 with moderate hepatic dysfunction, and 22 with renal dysfunction) with 458 concentrations records. Absorption rate constant (Ka) was constrained to be higher than elimination rate constant to avoid flip-flop situation. Mild hepatic dysfunction was a significant covariate on volume of distribution, and it is approximately three folds higher compared to other subjects. Fixed effects parameter estimates of the final model - absorption rate constant (Ka), volume of distribution (V), and clearance (CL) - were 0.95/h, 498 L, and 39 L/h, respectively. Between-subject variability estimates (% CV) on Ka, V, and CL were 77, 66, and 65, respectively. Residual error was modeled as combination error model with the parameter estimates for proportion error 12% CV and additive error (standard deviation) 1.5 ng/ml.

CONCLUSION

Population pharmacokinetic modeling showed that the volume of distribution of PQ in subjects with moderate hepatic dysfunction increases approximately three folds resulting in a significantly lower plasma concentration.

Levels of primaquine and carboxyprimaquine in patients with malaria vivax from the Brazilian Amazon basin

In the last two years, a substantial increase in the number of malaria vivax cases has occurred in the Brazilian Amazon basin. The adequate exposure of hypnozoites to primaquine is a matter of interest as these dormant forms are responsible for the maintenance or even the increase of malaria burden in endemic areas. The aim of this study was to estimate the levels of primaquine and carboxyprimaquine in whole blood samples of patients with P. vivax treated with chloroquine and an abbreviated regimen of primaquine (0.5 mg/kg/d for 7 days), with adequate clinical and parasitological outcomes after 180 days of follow-up. A total of 40 male patients met the criteria for inclusion in the study. Primaquine and carboxyprimaquine were measured by high-performance liquid chromatography. The levels of primaquine in whole blood samples ranged from 40-238 ng/mL, 42-196 ng/mL and 42-150 ng/mL on days 1, 3 and 7. The levels of carboxyprimaquine in whole blood samples ranged from 87-234 ng/mL, 96-252 ng/mL and 74-448 ng/mL on days 1, 3 and 7. These data provide a reliable estimation of exposure of the infecting parasite to primaquine. Based on the regional pattern of relapse, the estimated blood levels of primaquine can be considered effective against hypnozoites of the local circulating strains of P. vivax.

Primaquine in Plasma and Methemoglobinemia in Patients with Malaria Due to Plasmodium vivax in the Brazilian Amazon Basin

AbstractPrimaquine is the only licensed drug available for the elimination of Plasmodium vivax hypnozoites. Methemoglobinemia is currently reported in the course of treatment. There is evidence that metabolites of primaquine formed by the cytochrome pathway are responsible for methemoglobin formation; a genetic polymorphism of cytochrome isoforms; and a potential influence of gender in the activities of these enzymes requiring the establishment of dose × response curves profiles in different population groups. Concentrations of primaquine in plasma and methemoglobin levels were investigated in 54 patients with malaria due to P. vivax during the course of the standard regimen of chloroquine with primaquine (0.25 mg/kg/day for 14 days). All study subjects lived in an endemic area of the Brazilian Amazon Basin. The blood samples were collected before initiation of treatment and 3 hours (range 2-4 hours) after the administration of antimalarial drugs on days 2, 7, and 14. Plasma primaquine concentrations were similar in both genders (males: range = 164-191 ng/mL, females: range = 193-212 ng/mL). Methemoglobin levels ranged from 3.3% to 5.9% in males and from 3.1% to 6.5% in females. There were no significant correlations between the plasma primaquine concentrations or total dose and methemoglobin levels, suggesting that unidentified metabolites rather than parent drug were likely responsible for changes in methemoglobin levels. There was no significant influence of gender on primaquine concentrations in plasma or methemoglobin levels.

Efficacy in the treatment of malaria by Plasmodium vivax in Oiapoque, Brazil, on the border with French Guiana: the importance of control over external factors

Background

Plasmodium vivax malaria is an important public health issue in the Amazon region, and it accounts for approximately 84 % of cases of the disease. Migration across the border between Brazil and French Guiana contributes to the maintenance of the disease. The aim of this study was to evaluate the therapeutic and parasitological responses of patients with P. vivax malaria treated with chloroquine and primaquine in the socio-environmental context of cross-border interactions between Brazil and French Guiana. The factors controlled were diagnostic agreement, adherence, adjustment of primaquine doses for patient weight, and quality of the drugs used.

Methods

A prospective study was conducted in 2011 with 103 individuals aged 10–60 years with a positive diagnosis of P. vivax treated with chloroquine (10 mg base/kg on the first day, followed by 7.5 mg/kg on the second and third days) and primaquine for 7 days, who were followed for 28 days. The primaquine doses were adjusted for the patients’ weight. A number of factors were determined: epidemiological characteristics, origin of patients, signs and symptoms, initial parasitaemia and parasitaemia clearance time, blood concentrations of chloroquine and primaquine, quality of anti-malarial drugs and diagnostic agreement.

Results

Ninety-five patients were followed for 28 days. There was a 100 % agreement in microscopic diagnosis between field laboratory and reference centre. The adhesion to the treatment was 100 %. Of these patients, 32.6 % received a weight-adjusted dose of primaquine. The chloroquine and primaquine tablets were consistent with the optimal quality limits for human consumption. The investigated patients achieved optimal blood exposure to anti-malarial drugs. The parasitological and therapeutic response was adequate in 99.0 % of cases.

Conclusions

In the municipality of Oiapoque, the therapeutic regime used for the treatment of P. vivax malaria using chloroquine combined with primaquine remains effective, when external factors are controlled, such as the quality of anti-malarial drugs, the adhesion to the treatment prescribed, the correct diagnostic and the adjustment of primaquine dose for patient body weight.

Mass campaigns with antimalarial drugs: a modelling comparison of artemether-lumefantrine and DHA-piperaquine with and without primaquine as tools for malaria control and elimination

Background

Antimalarial drugs are a powerful tool for malaria control and elimination. Artemisinin-based combination therapies (ACTs) can reduce transmission when widely distributed in a campaign setting. Modelling mass antimalarial campaigns can elucidate how to most effectively deploy drug-based interventions and quantitatively compare the effects of cure, prophylaxis, and transmission-blocking in suppressing parasite prevalence.

Methods

A previously established agent-based model that includes innate and adaptive immunity was used to simulate malaria infections and transmission. Pharmacokinetics of artemether, lumefantrine, dihydroartemisinin, piperaquine, and primaquine were modelled with a double-exponential distribution-elimination model including weight-dependent parameters and age-dependent dosing. Drug killing of asexual parasites and gametocytes was calibrated to clinical data. Mass distribution of ACTs and primaquine was simulated with seasonal mosquito dynamics at a range of transmission intensities.

Results

A single mass campaign with antimalarial drugs is insufficient to permanently reduce malaria prevalence when transmission is high. Current diagnostics are insufficiently sensitive to accurately identify asymptomatic infections, and mass-screen-and-treat campaigns are much less efficacious than mass drug administrations. Improving campaign coverage leads to decreased prevalence one month after the end of the campaign, while increasing compliance lengthens the duration of protection against reinfection. Use of a long-lasting prophylactic as part of a mass drug administration regimen confers the most benefit under conditions of high transmission and moderately high coverage. Addition of primaquine can reduce prevalence but exerts its largest effect when coupled with a long-lasting prophylactic.

Conclusions

Mass administration of antimalarial drugs can be a powerful tool to reduce prevalence for a few months post-campaign. A slow-decaying prophylactic administered with a parasite-clearing drug offers strong protection against reinfection, especially in highly endemic areas. Transmission-blocking drugs have only limited effects unless administered with a prophylactic under very high coverage.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-0887-y) contains supplementary material, which is available to authorized users.

Enantioselective pharmacokinetics of primaquine in healthy human volunteers

Primaquine (PQ), a racemic drug, is the only treatment available for radical cure of relapsing Plasmodium vivax malaria and blocking transmission of P. falciparum malaria. Recent studies have shown differential pharmacologic and toxicologic profiles of individual PQ enantiomers in rodent, dog, and primate animal models. This study was conducted in six healthy adult human volunteers to determine the plasma pharmacokinetic profile of enantiomers of PQ and carboxyprimaquine (cPQ), the major plasma metabolite. The individuals were orally administered PQ diphosphate, equivalent to 45-mg base, 30 minutes after a normal breakfast. Blood samples were collected at different time intervals, and plasma samples were analyzed for enantiomers of PQ and cPQ. Plasma PQ concentrations were low and variable for both parent enantiomers and peaked around 2-4 hours. Peak (-)-(R)-PQ concentrations ranged from 121 ng/ml to 221 ng/ml, and peak (+)-(S)-PQ concentrations ranged from 168 ng/ml to 299 ng/ml. The cPQ concentrations were much higher and were surprisingly consistent from subject to subject. Essentially all the cPQ detected in plasma was (-)-cPQ. The peak concentrations of (-)-cPQ were observed at 8 hours (range: 1104-1756 ng/ml); however, very high concentrations were sustained through 24 hours. (+)-cPQ was two orders of magnitude lower than (-)-cPQ, and in a few subjects it was detected but only under the limit of quantification. In vitro studies with primary human hepatocytes also suggested more rapid metabolism of (-)-PQ compared with (+)-PQ. The results suggest more rapid metabolism of (-)-PQ to (-) cPQ compared with (+)-PQ. Alternatively, (+)-PQ or (+)-cPQ could be rapidly converted to another metabolite(s) or distributed to tissues. This is the first clinical report on enantioselective pharmacokinetic profiles of PQ and cPQ and supports further clinical evaluation of individual PQ enantiomers.

Pharmacokinetics and pharmacodynamics of (+)-primaquine and (-)-primaquine enantiomers in rhesus macaques (Macaca mulatta)

Primaquine (PQ) remains the sole available drug to prevent relapse of Plasmodium vivax malaria more than 60 years after licensure. While this drug was administered as a racemic mixture, prior studies suggested a pharmacodynamic advantage based on differential antirelapse activity and/or toxicities of its enantiomers. Oral primaquine enantiomers prepared using a novel, easily scalable method were given for 7 days to healthy rhesus macaques in a dose-rising fashion to evaluate their effects on the blood, liver, and kidneys. The enantiomers were then administered to Plasmodium cynomolgi-infected rhesus macaques at doses of 1.3 and 0.6 mg/kg of body weight/day in combination with chloroquine. The (-)-PQ enantiomer had higher clearance and apparent volume of distribution than did (+)-PQ and was more extensively converted to the carboxy metabolite. There is evidence for differential oxidative stress with a concentration-dependent rise in methemoglobin (MetHgb) with increasing doses of (+)-PQ greater than that seen for (-)-PQ. There was a marked, reversible hepatotoxicity in 2 of 3 animals dosed with (-)-PQ at 4.5 mg/kg. (-)-PQ in combination with chloroquine was successful in preventing P. cynomolgi disease relapse at doses of 0.6 and 1.3 mg/kg/day, while 1 of 2 animals receiving (+)-PQ at 0.6 mg/kg/day relapsed. While (-)-PQ was also associated with hepatotoxicity at higher doses as seen previously, this has not been identified as a clinical concern in humans during >60 years of use. Limited evidence for increased MetHgb generation with the (+) form in the rhesus macaque model suggests that it may be possible to improve the therapeutic window for hematologic toxicity in the clinic by separating primaquine into its enantiomers.

Pharmacokinetic interactions between primaquine and chloroquine

Chloroquine combined with primaquine has been the standard radical curative regimen for Plasmodium vivax and Plasmodium ovale malaria for over half a century. In an open-label crossover pharmacokinetic study, 16 healthy volunteers (4 males and 12 females) aged 20 to 47 years were randomized into two groups of three sequential hospital admissions to receive a single oral dose of 30 mg (base) primaquine, 600 mg (base) chloroquine, and the two drugs together. The coadministration of the two drugs did not affect chloroquine or desethylchloroquine pharmacokinetics but increased plasma primaquine concentrations significantly (P ≤ 0.005); the geometric mean (90% confidence interval [CI]) increases were 63% (47 to 81%) in maximum concentration and 24% (13 to 35%) in total exposure. There were also corresponding increases in plasma carboxyprimaquine concentrations (P ≤ 0.020). There were no significant electrocardiographic changes following primaquine administration, but there was slight corrected QT (QTc) (Fridericia) interval lengthening following chloroquine administration (median [range] = 6.32 [−1.45 to 12.3] ms; P < 0.001), which was not affected by the addition of primaquine (5.58 [1.74 to 11.4] ms; P = 0.642). This pharmacokinetic interaction may explain previous observations of synergy in preventing P. vivax relapse. This trial was registered at ClinicalTrials.gov under reference number NCT01218932.

Pharmacokinetic properties of single-dose primaquine in Papua New Guinean children: feasibility of abbreviated high-dose regimens for radical cure of vivax malaria

Since conventional 14-day primaquine (PMQ) radical cure of vivax malaria is associated with poor compliance, and as total dose, not therapy duration, determines efficacy, a preliminary pharmacokinetic study of two doses (0.5 and 1.0 mg/kg of body weight) was conducted in 28 healthy glucose-6-phosphate dehydrogenase-normal Papua New Guinean children, aged 5 to 12 years, to facilitate development of abbreviated high-dose regimens. Dosing was with food and was directly observed, and venous blood samples were drawn during a 168-h postdose period. Detailed safety monitoring was performed for hepatorenal function and hemoglobin and methemoglobin concentrations. Plasma concentrations of PMQ and its metabolite carboxyprimaquine (CPMQ) were determined by liquid chromatography-mass spectrometry and analyzed using population pharmacokinetic methods. The derived models were used in simulations. Both single-dose regimens were well tolerated with no changes in safety parameters. The mean PMQ central volume of distribution and clearance relative to bioavailability (200 liters/70 kg and 24.6 liters/h/70 kg) were within published ranges for adults. The median predicted maximal concentrations (Cmax) for both PMQ and CPMQ after the last dose of a 1.0 mg/kg 7-day PMQ regimen were approximately double those at the end of 14 days of 0.5 mg/kg daily, while a regimen of 1.0 mg/kg twice daily resulted in a 2.38 and 3.33 times higher Cmax for PMQ and CPMQ, respectively. All predicted median Cmax concentrations were within ranges for adult high-dose studies that also showed acceptable safety and tolerability. The present pharmacokinetic data, the first for PMQ in children, show that further studies of abbreviated high-dose regimens are feasible in this age group.

Pharmacokinetics of single-dose primaquine in patients with chronic kidney dysfunction

AIM

The pharmacokinetics of primaquine has not been studied in special populations. Being a basic compound, preferential binding to alpha-1 acid glycoprotein and substrate for P-glycoprotein, may predispose the drug for an altered pharmacokinetics in states of renal dysfunction. This study attempts to evaluate the pharmacokinetics of a single oral dose (15 mg) of primaquine in severely impaired renal function and end stage renal dysfunction patients compared to healthy participants.

MATERIALS AND METHODS

Twelve patients each with chronic kidney disease classified as either Stage IV or V (not on dialysis) were recruited. Data from 12 healthy participants was used as concurrent controls. Serial blood collections were performed following a single dose 15 mg Primaquine orally. Primaquine concentrations were measured in the plasma using a validated HPLC method.

RESULTS

The Cmax [median (range) in ng/ml] was 29.3 (14.6-104.3), 40.3 (14.8 - 78.6), and 49.8 (15 - 169.6) and the tmax [median (range) in hours] was 3.0 (1.0- 6.0), 2.0 (1.5 - 8) and 2.0 (1.0 - 4.0) for healthy and stage IV, V (not on dialysis) CKD participants, respectively. No statistically significant difference was observed in any of the pharmacokinetic parameters between healthy, stage IV and V CKD participants.

CONCLUSION

Pharmacokinetics of single oral dose primaquine (15 mg) does not appear to be altered in patients with severely impaired renal function and end stage renal dysfunction. A change in dose or frequency of the drug administration perhaps may not be required in this population.

Simultaneous determination of primaquine and carboxyprimaquine in plasma using solid phase extraction and LC-MS assay

Sensitive bioanalytical methods are required for pharmacokinetic studies in children, due to the small volume and modest number of samples that can be obtained. We sought to develop a LC-MS assay for primaquine and its active metabolite, carboxyprimaquine, following simultaneous, solid phase extraction of both analytes from human plasma. The analysis was conducted on a single-quad LC-MS system (Shimadzu Model 2020) in ESI+ mode, with quantitation by selected ion monitoring. Primaquine, carboxyprimaquine and 8-aminoquinoline (internal standard) were separated using a mobile phase of 80:20 methanol:water with 0.1% (v/v) formic acid and a Luna C(18) HPLC column, at ambient temperature. Solid phase extraction of the analytes from plasma (0.5 mL) was achieved with Oasis(®) HLB cartridges. The retention times for primaquine, 8-aminoquinoline and carboxyprimaquine were 3.3, 5.7 and 8.5 min, respectively. The calibration curve range (2-1500 μg/L) was appropriate for the limits of quantification and detection for primaquine (2 μg/L and 1μ g/L, respectively) and carboxyprimaquine (2.5 μg/L and 1 μg/L) and the anticipated plasma concentrations of the analytes. Intra- and inter-day precision for both primaquine and carboxyprimaquine was <10% across the concentration range 5-1000 μg/L. Accuracy for both analytes was <15% (5-500 μg/L). This validated LC-MS method with solid phase extraction facilitates the simultaneous analysis of primaquine and carboxyprimaquine from small volumes of human plasma, with run time <10 min, recovery >85% and sensitivity of 1-2 μg/L.

Efficacy of a 14-day primaquine regimen in preventing relapses in patients with Plasmodium vivax malaria in Mumbai, India

We studied the antirelapse efficacy of a supervised 14-d 15 mg/d regimen of primaquine therapy (n = 131) compared with no antirelapse therapy (n = 142) in 273 patients with confirmed Plasmodium vivax malaria in Mumbai, India, between July 1998 and April 2000. There were 6/131 (4.6%) recurrences in patients given primaquine compared with 13/142 (9.2%) in those not given antirelapse therapy. In the 14-d primaquine group, polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) genotyping analysis of pre- and post-treatment blood samples was done for the 6 patients who had a recurrence of parasitaemia and the results gave a true relapse rate of 2.29% (3/131), 2 samples were classified as reinfections and 1 sample did not amplify. Our results indicate probable resistance to the 14-d regimen of primaquine for the first time in India and illustrate the need to (i) monitor patients given this regimen and (ii) carry out comparative studies between primaquine and new drugs such as tafenoquine and bulaquine for preventing relapses.

Pharmacokinetics of primaquine and carboxyprimaquine in korean patients with vivax malaria

Primaquine is used for relapses caused by vivax malaria hypnozoites. No studies on the pharmacokinetics of primaquine (PMQ) has been reported in Korean patients. In our study, thirty vivax malaria patients were given 15 mg primaquine daily for 14 days after 3 days of chloroquine treatment. Plasma samples were taken at intervals after each daily dose of PMQ for 3 days. Plasma concentrations of PMQ and carboxyprimaquine (CPMQ), the major metabolite of primaquine, were measured by HPLC. The PMQ concentrations reached a maximum of 0.28+/-0.18 microg/mL at 1.5 h after the first dose. The maximum concentration of CPMQ was 0.32+/-0.13 microg/mL at 4 h. Higher drug concentrations with repeated dosing were observed for CPMQ, but not for the parent drug, PMQ. The elimination half-life was 3.76+/-1.8 h and 15.7+/-12.2 h, for PMQ and CPMQ, respectively. Large variation in the plasma concentrations of both drugs was observed. Overall, PMQ is absorbed and metabolized rapidly after oral administration. It was noted that the mean peak plasma concentration of PMQ was significantly higher and that of CPMQ was lower in our patients compared to other studies. This suggests a potential difference of inter-ethnic groups, which warrants further investigations.

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.

Pharmacokinetics of primaquine in G6PD deficient and G6PD normal patients with vivax malaria

The pharmacokinetics of primaquine have been studied in 13 G6PD normal and 13 G6PD deficient Thai male patients with Plasmodium vivax malaria who were given daily doses of 15 mg of primaquine over 14 d, following a full course of chloroquine. After the first dose (15 mg), primaquine underwent rapid absorption. Mean values (SD in parentheses) of maximum plasma concentration of 57.7 (7.7) vs. 55.7 (7.4) ng/mL were reached at 2.2 (0.6) vs. 2.2 (0.6) h, for the G6PD deficient and G6PD normal groups, respectively. Thereafter, drug levels declined rapidly and monoexponentially with a t1/2 lambda of 6.4 (1.9) vs. 6.3 (2.7) h. The respective mean values (SD in parentheses) for MRT, AUC0-varies; is directly proportional to Cl/f, and Vz/f were 6.8 (0.4) vs. 6.8 (0.5) h, 0.547 (0.070) vs. 0.521 (0.090) micrograms/h/mL, 8.54 (0.37) vs. 8.97 (1.46) mL/min/kg and 4.8 (1.7) vs. 5.1 (1.2) L/kg. There was no difference in the plasma concentrations or pharmacokinetics of primaquine between patients with normal G6PD and G6PD deficiency. In the G6PD deficient group, no relationship between the severity of haemolysis (< 20% or > 20% haemolysis) and the concentrations/pharmacokinetics of primaquine was observed.

Interactions among primaquine, malaria infection and other antimalarials in Thai subjects

1. The pharmacokinetics of rac-primaquine (45 mg base) and its principal plasma metabolite, carboxyprimaquine have been investigated in healthy Thai adults prior to and following a single oral dose of mefloquine (10 mg kg-1). 2. Primaquine was rapidly absorbed, attaining peak plasma concentrations (median and range) of 167 (113-532) micrograms l-1 in 2 (1-4) h. Thereafter, concentrations declined rapidly with an apparent terminal half-life of 6.1 (1.7-16.1) h and an oral clearance (CLpo) of 33.1 (17.6-49.3) l h-1. Administration of mefloquine had no effect on the values of any of these parameters at the 5% level of significance [Cmax 229 (114-503) micrograms l-1; tmax 3 (2-4) h; t1/2,z 3.9 (1.7-13.5) h; CLpo 34.0 (21.7-49.0) l h-1]. 3. The carboxylic acid metabolite of primaquine achieved maximum concentrations (median and range) of 890 (553-3634) micrograms l-1 at 6 (3-16) h. Thereafter, plasma concentrations of carboxyprimaquine declined to 346 (99-918) micrograms l-1 at 24 h. AUC (0,24 h) was 12737 (6837-27388) micrograms l-1 h. Administration of mefloquine had no effect on the plasma concentrations of this metabolite [Cmax 1035 (174-3015) micrograms l-1; tmax 8 (2-24) h; AUC(0,24) 13471 (2132-17863) micrograms l-1 h]. 4. The effect of falciparum malaria and treatment with quinine (10 mg salt kg-1 p.o.) on the pharmacokinetics of primaquine (45 mg base p.o.) has been investigated in adult Thai patients during and after infection with falciparum malaria.(ABSTRACT TRUNCATED AT 250 WORDS)