The disposition of chloroquine in healthy Nigerians after single intravenous and oral doses

Pulmonary Delivery of Aerosolized Chloroquine and Hydroxychloroquine to Treat COVID-19: In Vitro Experimentation to Human Dosing Predictions

In vitro screening for pharmacological activity of existing drugs showed chloroquine and hydroxychloroquine to be effective against severe acute respiratory syndrome coronavirus 2. Oral administration of these compounds to obtain desired pulmonary exposures resulted in dose-limiting systemic toxicity in humans. However, pulmonary drug delivery enables direct and rapid administration to obtain higher local tissue concentrations in target tissue. In this work, inhalable formulations for thermal aerosolization of chloroquine and hydroxychloroquine were developed, and their physicochemical properties were characterized. Thermal aerosolization of 40 mg/mL chloroquine and 100 mg/mL hydroxychloroquine formulations delivered respirable aerosol particle sizes with 0.15 and 0.33 mg per 55 mL puff, respectively. In vitro toxicity was evaluated by exposing primary human bronchial epithelial cells to aerosol generated from Vitrocell. An in vitro exposure to 7.24 μg of chloroquine or 7.99 μg hydroxychloroquine showed no significant changes in cilia beating, transepithelial electrical resistance, and cell viability. The pharmacokinetics of inhaled aerosols was predicted by developing a physiologically based pharmacokinetic model that included a detailed species-specific respiratory tract physiology and lysosomal trapping. Based on the model predictions, inhaling emitted doses comprising 1.5 mg of chloroquine or 3.3 mg hydroxychloroquine three times a day may yield therapeutically effective concentrations in the lung. Inhalation of higher doses further increased effective concentrations in the lung while maintaining lower systemic concentrations. Given the theoretically favorable risk/benefit ratio, the clinical significance for pulmonary delivery of aerosolized chloroquine and hydroxychloroquine to treat COVID-19 needs to be established in rigorous safety and efficacy studies.

Absence of gender influence on the pharmacokinetics of chloroquine combined with primaquine in malaria vivax patients

Chloroquine is the first-line therapy against the asexual stages of Plasmodium vivax . There is a high variation of chloroquine plasma levels after therapeutic doses, which can lead to inadequate exposure to the drug. The gender influence was low regarding the disposition of the drug, which is relevant as there are significant physiological variations between male and female patients. The objective of the study was to investigate whether gender modifies the pharmacokinetics parameters of chloroquine in patients with malaria vivax. A prospective study was performed in male and female adult patients using chloroquine (total dose of 25 mg/kg for three days) combined with primaquine. Serial blood samples were collected at admission and up to 672 h post-administration of the drugs. Chloroquine was measured in plasma samples by high-performance liquid chromatography with fluorescence detection. A non-compartmental analysis was used for modeling the data. A total of 26 male and 25 female patients were enrolled in the study. The pharmacokinetic parameters of chloroquine were similar between male and female patients: a half-life of 9.5 days and 10.2 days, maximum concentration (Cmax) of 1295 ng/ml and 1220 ng/ml, area-under-the-curve (AUC 0–28) of 241 µg/mL h and 237 µg/mL h, observed clearance (CL/f) of 5.8 and 5.5 L/h and the volume of distribution (V/f) of 1869 L and 1936 L. The study results suggest that a similar dose regimen of chloroquine combined with primaquine provides a comparable pattern of exposure in male and female patients.

Repurposing Drugs for COVID-19: Pharmacokinetics and Pharmacogenomics of Chloroquine and Hydroxychloroquine

Background

A new coronavirus SARS-CoV-2 has been identified as the etiological agent of the severe acute respiratory syndrome, COVID-19, the source and cause of the 2019–20 coronavirus pandemic. Hydroxychloroquine and chloroquine have gathered extraordinary attention as therapeutic candidates against SARS-CoV-2 infections. While there is growing scientific data on the therapeutic effect, there is also concern for toxicity of the medications. The therapy of COVID-19 by hydroxychloroquine and chloroquine is off-label. Studies to analyze the personalized effect and safety are lacking.

Methods

A review of the literature was performed using Medline/PubMed/Embase database. A variety of keywords were employed in keyword/title/abstract searches. The electronic search was followed by extensive hand searching using reference lists from the identified articles.

Results

A total of 126 results were obtained after screening all sources. Mechanisms underlying variability in drug concentrations and therapeutic response with chloroquine and hydroxychloroquine in mediating beneficial and adverse effects of chloroquine and hydroxychloroquine were reviewed and analyzed. Pharmacogenomic studies from various disease states were evaluated to elucidate the role of genetic variation in drug response and toxicity.

Conclusion

Knowledge of the pharmacokinetics and pharmacogenomics of chloroquine and hydroxychloroquine is necessary for effective and safe dosing and to avoid treatment failure and severe complications.

COVID-19 prevention and treatment: A critical analysis of chloroquine and hydroxychloroquine clinical pharmacology

Nicholas White and coauthors discuss chloroquine and hydroxychloroquine pharmacology in the context of possible treatment of SARS-CoV-2 infection.

Dose selection of chloroquine phosphate for treatment of COVID-19 based on a physiologically based pharmacokinetic model

Chloroquine (CQ) phosphate has been suggested to be clinically effective in the treatment of coronavirus disease 2019 (COVID-19). To develop a physiologically-based pharmacokinetic (PBPK) model for predicting tissue distribution of CQ and apply it to optimize dosage regimens, a PBPK model, with parameterization of drug distribution extrapolated from animal data, was developed to predict human tissue distribution of CQ. The physiological characteristics of time-dependent accumulation was mimicked through an active transport mechanism. Several dosing regimens were proposed based on PBPK simulation combined with known clinical exposure–response relationships. The model was also validated by clinical data from Chinese patients with COVID-19. The novel PBPK model allows in-depth description of the pharmacokinetics of CQ in several key organs (lung, heart, liver, and kidney), and was applied to design dosing strategies in patients with acute COVID-19 (Day 1: 750 mg BID, Days 2–5: 500 mg BID, CQ phosphate), patients with moderate COVID-19 (Day 1: 750 mg and 500 mg, Days 2–3: 500 mg BID, Days 4–5: 250 mg BID, CQ phosphate), and other vulnerable populations (e.g., renal and hepatic impairment and elderly patients, Days 1–5: 250 mg BID, CQ phosphate). A PBPK model of CQ was successfully developed to optimize dosage regimens for patients with COVID-19.

Chloroquine for SARS-CoV-2: Implications of Its Unique Pharmacokinetic and Safety Properties

Since in vitro studies and a preliminary clinical report suggested the efficacy of chloroquine for COVID-19-associated pneumonia, there is increasing interest in this old antimalarial drug. In this article, we discuss the pharmacokinetics and safety of chloroquine that should be considered in light of use in SARS-CoV-2 infections. Chloroquine is well absorbed and distributes extensively resulting in a large volume of distribution with an apparent and terminal half-life of 1.6 days and 2 weeks, respectively. Chloroquine is metabolized by cytochrome P450 and renal clearance is responsible for one third of total clearance. The lack of reliable information on target concentrations or doses for COVID-19 implies that for both adults and children, doses that proved effective and safe in malaria should be considered, such as ‘loading doses’ in adults (30 mg/kg over 48 h) and children (70 mg/kg over 5 days), which reported good tolerability. Here, plasma concentrations were < 2.5 μmol/L, which is associated with (minor) toxicity. While the influence of renal dysfunction, critical illness, or obesity seems small, in critically ill patients, reduced absorption may be anticipated. Clinical experience has shown that chloroquine has a narrow safety margin, as three times the adult therapeutic dosage for malaria can be lethal when given as a single dose. Although infrequent, poisoning in children is extremely dangerous where one to two tablets can potentially be fatal. In conclusion, the pharmacokinetic and safety properties of chloroquine suggest that chloroquine can be used safely for an acute virus infection, under corrected QT monitoring, but also that the safety margin is small, particularly in children.

Cardiac effects and toxicity of chloroquine: a short update

There is currently increased interest in the use of the antimalarial drugs chloroquine and hydroxychloroquine for the treatment of other diseases, including cancer and viral infections such as coronavirus disease 2019 (COVID-19). However, the risk of cardiotoxic effects tends to limit their use. In this review, the effects of these drugs on the electrical and mechanical activities of the heart as well as on remodelling of cardiac tissue are presented and the underlying molecular and cellular mechanisms are discussed. The drugs can have proarrhythmic as well as antiarrhythmic actions resulting from their inhibition of ion channels, including voltage-dependent Na⁺ and Ca²⁺ channels, background and voltage-dependent K⁺ channels, and pacemaker channels. The drugs also exert a vagolytic effect due at least in part to a muscarinic receptor antagonist action. They also interfere with normal autophagy flux, an effect that could aggravate ischaemia/reperfusion injury or post-infarct remodelling. Most of the toxic effects occur at high concentrations, following prolonged drug administration or in the context of drug associations.

[Chloroquine phosphate: therapeutic drug for COVID-19]

Since the outbreak of coronavirus disease 2019 (COVID-19) in the late 2019, a variety of antiviral drugs have been used in the first-line clinical trial. The Diagnostic and Treatment Protocol for COVID-19 (Trial Version 6) in China recommends chloroquine phosphate for the first time as an anti-coronavirus trial drug. As a classic drug for treatment of malaria and rheumatism, chloroquine phosphate has been used clinically for more than 80 years, and has also shown good results in the treatment of various viral infections. As the plasma drug concentration varies greatly among different races and individuals and due to its narrow treatment window, chloroquine in likely to accumulate in the body to cause toxicity. Among the treatment regimens recommended for COVID-19, reports concerning the safety of a short-term high-dose chloroquine regimen remain scarce. In this review, the authors summarize the current research findings of chloroquine phosphate in the treatment of COVID-19, and examine the pharmacokinetic characteristics, antiviral therapy, the therapeutic mechanism and safety of chloroquine.

Dose Optimization of Chloroquine by Pharmacokinetic Modeling During Pregnancy for the Treatment of Zika Virus Infection

The insidious nature of Zika virus (ZIKV) infections can have a devastating consequence for fetal development. Recent reports have highlighted that chloroquine (CQ) is capable of inhibiting ZIKV endocytosis in brain cells. We applied pharmacokinetic modeling to develop a predictive model for CQ exposure to identify an optimal maternal/fetal dosing regimen to prevent ZIKV endocytosis in brain cells. Model validation used 13 nonpregnancy and 3 pregnancy clinical studies, and a therapeutic CQ plasma window of 0.3-2 μM was derived. Dosing regimens used in rheumatoid arthritis, systemic lupus erythematosus, and malaria were assessed for their ability to target this window. Dosing regimen identified that weekly doses used in malaria were not sufficient to reach the lower therapeutic window; however, daily doses of 150 mg achieved this therapeutic window. The impact of gestational age was further assessed and culminated in a final proposed regimen of 600 mg on day 1, 300 mg on day 2 and 3, and 150 mg thereafter until the end of trimester 2, which resulted in maintaining 65% and 94% of subjects with a trough plasma concentration above the lower therapeutic window on day 6 and at term, respectively.

Prediction of inter-individual variability on the pharmacokinetics of CYP2C8 substrates in human

Inter-individual variability in pharmacokinetics can lead to unexpected side effects and treatment failure, and is therefore an important factor in drug development. CYP2C8 is a major drug-metabolizing enzyme known to be involved in the metabolism of over 100 drugs. In this study, we predicted the inter-individual variability in AUC/Dose of CYP2C8 substrates in healthy volunteers using the Monte Carlo simulation. Inter-individual variability in the hepatic intrinsic clearance of CYP2C8 substrates (CL_int,h,2C8) was estimated from the inter-individual variability in pharmacokinetics of pioglitazone, which is a major CYP2C8 substrate. The coefficient of variation (CV) of CL_int,h,2C8 was estimated to be 40%. Using this value, the CVs of AUC/Dose of other major CYP2C8 substrates, rosiglitazone and amodiaquine, were predicted to validate the estimated CV of CL_int,h,2C8. As a result, the reported CVs of both substrates were within the 2.5-97.5 percentile range of the predicted CVs. Furthermore, the CVs of AUC/Dose of the CYP2C8 substrates loperamide and chloroquine, which are affected by renal clearance, were also successfully predicted. Combining this value with previously reported CVs of other CYPs, we were able to successfully predict the inter-individual variability in pharmacokinetics of various drugs in clinical.

Pharmacokinetics of the Antimalarial Drug, AQ-13, in Rats and Cynomolgus Macaques

The purpose of this study was to evaluate the bioavailability and pharmacokinetics of a new antimalarial drug, AQ-13, a structural analog of chloroquine (CQ) that is active against CQ-resistant Plasmodium species, in rats and cynomolgus macaques. Sprague-Dawley rats ( n = 4 /sex) were administered a single dose of AQ-13 intravenously (i.v.) (10 mg/kg) or orally (20 or 102 mg/kg). Blood and plasma samples were collected at several timepoints. AQ-13 achieved Cmax after oral administration at approximately 3 to 4 h and could be detected in blood for 2 to 5 days after oral administration. The ratio of area under the curve (AUC) values at the high and low dose for AQ-13 deviated from an expected ratio of 5.0, indicating nonlinear kinetics. A metabolite peak was noted in the chromatograms that was identified as monodesethyl AQ-13. Oral bioavailability of AQ-13 was good, approximately 70%. The pharmacokinetics of AQ-13 was also determined in cynomolgus macaques after single (i.v., 10 mg/kg; oral, 20 or 100 mg/kg) and multiple doses (oral loading dose of 50, 100, or 200 mg/kg on first day followed by oral maintenance dose of 25, 50, or 100 mg/kg, respectively, for 6 days). The AUC and Cmax values following single oral dose administration were not dose proportional; the Cmax value for AQ-13 was 15-fold higher following an oral dose of 100 mg/kg compared to 20 mg/kg. MonodesethylAQ-13 was a significant metabolite formed by cynomolgus macaques and the corresponding Cmax values for this metabolite increased only 3.8-fold over the dose range, suggesting that the formation of monodesethyl AQ-13 is saturable in this species. The bioavailability of AQ-13 in cynomolgus macaques following oral administration was 23.8% for the 20-mg/kg group and 47.6% for the 100-mg/kg group. Following repeat dose administration, high concentrations of monodesethyl AQ-13 were observed in the blood by day 4, exceeding the AQ-13 blood concentrations through day 22. Saturation of metabolic pathways and reduced metabolite elimination after higher doses are suggested to play a key role in AQ-13 pharmacokinetics in macaques. In summary, the pharmacokinetic profile and metabolism ofAQ-13 are very similar to that reported in the literature for chloroquine, suggesting that this new agent is a promising candidate for further development for the treatment of chloroquine-resistant malaria.

Effect of Khat (Catha edulis) Use on the Bioavailability, Plasma Levels and Antimalarial Activity of Chloroquine

OBJECTIVES

This study aimed to evaluate the effect of khat (Catha edulis) on chloroquine (CQ) bioavailability in healthy Yemeni adults and its effect on CQ plasma levels and parasite clearance among malaria patients.

METHODS

This study took place between January and April 2007 in Bajil and Sana'a, Yemen. Two CQ doses (600 mg each) were given to 15 healthy males on separate occasions; the first dose was followed by a khat-chewing session (phase one) while controls abstained from khat-chewing for the second (phase two). Additionally, 103 patients with Plasmodium falciparum-induced malaria, including both regular khat chewers (n = 57) and non-khat chewers (n = 46), were treated with CQ (25 mg/kg) over three days. Pharmacokinetic parameters were analysed among both controls and malaria patients. Parasite clearance was also investigated for the latter group.

RESULTS

The mean area under the concentration-time curve (AUC) was 2,108.9 versus 2,797.4 ng/hour/mL, mean peak plasma concentration (Cmax) was 415.6 versus 508.7 ng/mL and mean time to reach Cmax was 3.8 versus 3.6 hours for controls in phase one versus phase two, respectively; both AUC and Cmax levels were significantly reduced by khat-chewing (P <0.050). For khat- versus non-khat-chewing malaria patients, mean plasma CQ concentrations were 266.4 ng/mL versus 427.5 ng/mL (P <0.001). Furthermore, CQ was effective in 71.7% and 75.4% of non-khat and khat-chewing malaria patients, respectively (P = 0.823).

CONCLUSION

Khat-chewing was found to significantly reduce plasma CQ levels among healthy volunteers and malaria patients. While receiving CQ treatment, patients should be advised not to chew khat.

Downregulation of Organic Anion Transporting Polypeptide (OATP) 1B1 Transport Function by Lysosomotropic Drug Chloroquine: Implication in OATP-Mediated Drug-Drug Interactions

Organic anion transporting polypeptide (OATP) 1B1 mediates the hepatic uptake of many drugs including lipid-lowering statins. Decreased OATP1B1 transport activity is often associated with increased systemic exposure of statins and statin-induced myopathy. Antimalarial drug chloroquine (CQ) is also used for long-term treatment of rheumatoid arthritis and systemic lupus erythematosus. CQ is lysosomotropic and inhibits protein degradation in lysosomes. The current studies were designed to determine the effects of CQ on OATP1B1 protein degradation, OATP1B1-mediated transport in OATP1B1-overexpressing cell line, and statin uptake in human sandwich-cultured hepatocytes (SCH). Treatment with lysosome inhibitor CQ increased OATP1B1 total protein levels in HEK293-OATP1B1 cells and in human SCH as determined by OATP1B1 immunoblot. In HEK293-FLAG-tagged OATP1B1 stable cell line, co-immunofluorescence staining indicated that intracellular FLAG-OATP1B1 is colocalized with lysosomal associated membrane glycoprotein (LAMP)-2, a marker protein of late endosome/lysosome. Enlarged LAMP-2-positive vacuoles with FLAG-OATP1B1 protein retained inside were readily detected in CQ-treated cells, consistent with blocking lysosomal degradation of OATP1B1 by CQ. In HEK293-OATP1B1 cells, without pre-incubation, CQ concentrations up to 100 μM did not affect OATP1B1-mediated [(3)H]E217G accumulation. However, pre-incubation with CQ at clinically relevant concentration(s) significantly decreased [(3)H]E217G and [(3)H]pitavastatin accumulation in HEK293-OATP1B1 cells and [(3)H]pitavastatin accumulation in human SCH. CQ pretreatment (25 μM, 2 h) resulted in ∼1.9-fold decrease in Vmax without affecting Km of OATP1B1-mediated [(3)H]E217G transport in HEK293-OATP1B1 cells. Pretreatment with monensin and bafilomycin A1, which also have lysosome inhibition activity, significantly decreased OATP1B1-mediated transport in HEK293-OATP1B1 cells. Pharmacoepidemiologic studies using data from the U.S. Food and Drug Administration Adverse Event Reporting System indicated that CQ plus pitavastatin, rosuvastatin, and pravastatin, which are minimally metabolized by the cytochrome P450 enzymes, led to higher myopathy risk than these statins alone. In summary, the present studies report novel findings that lysosome is involved in degradation of OATP1B1 protein and that pre-incubation with lysosomotropic drug CQ downregulates OATP1B1 transport activity. Our in vitro data in combination with pharmacoepidemiologic studies support that CQ has potential to cause OATP-mediated drug-drug interactions.

FIRST REPORTS OF CLINICAL PHARMACOKINETICS IN NIGERIA

The German Friedrich Hartmut Dost (1910-1985) introduced the word Pharmacokinetics. Clinical pharmacokinetics is the direct application of knowledge regarding a drug's pharmacokinetics to a therapeutic situation in an individual or a population. It is the basis of therapeutic drug monitoring with the ultimate goal of keeping drugs safe. This branch of pharmacology has become the most relevant to the sub-specialty of clinical pharmacology. First reports of Clinical Pharmacokinetics in Nigeria can be credited to two gifted Nigerians, Prof Ayodele O. Iyun and Prof Lateef A. Salako, both of whom were affiliated to the great institutions- University of Ibadan (UI) and the Teaching Hospital, University College Hospital (UCH). Prof A.O Iyun was Nigeria's first home-trained Clinical Pharmacologist, while Prof L.A. Salako played a most significant role in the creation of the Department of Clinical Pharmacology, UCH. This edition of the Chronicles highlights a few of the first reports of this exciting branch of pharmacology in Nigeria. This historical review is based on publications listed on the United States National Library of Medicine database (PUBMED).

Pharmacokinetics, pharmacodynamics, and allometric scaling of chloroquine in a murine malaria model

Chloroquine (CQ) is an important antimalarial drug for the treatment of special patient groups and as a comparator for preclinical testing of new drugs. Pharmacokinetic data for CQ in animal models are limited; thus, we conducted a three-part investigation, comprising (i) pharmacodynamic studies of CQ and CQ plus dihydroartemisinin (DHA) in Plasmodium berghei-infected mice, (ii) pharmacokinetic studies of CQ in healthy and malaria-infected mice, and (iii) interspecies allometric scaling for CQ from 6 animal and 12 human studies. The single-dose pharmacodynamic study (10 to 50 mg CQ/kg of body weight) showed dose-related reduction in parasitemia (5- to >500-fold) and a nadir 2 days after the dose. Multiple-dose regimens (total dose, 50 mg/kg CQ) demonstrated a lower nadir and longer survival time than did the same single dose. The CQ-DHA combination provided an additive effect compared to each drug alone. The elimination half-life (t(1/2)), clearance (CL), and volume of distribution (V) of CQ were 46.6 h, 9.9 liters/h/kg, and 667 liters/kg, respectively, in healthy mice and 99.3 h, 7.9 liters/h/kg, and 1,122 liters/kg, respectively, in malaria-infected mice. The allometric equations for CQ in healthy mammals (CL = 3.86 × W(0.56), V = 230 × W(0.94), and t(1/2) = 123 × W(0.2)) were similar to those for malaria-infected groups. CQ showed a delayed dose-response relationship in the murine malaria model and additive efficacy when combined with DHA. The biphasic pharmacokinetic profiles of CQ are similar across mammalian species, and scaling of specific parameters is plausible for preclinical investigations.

Molecular mechanism of renal tubular secretion of the antimalarial drug chloroquine

The antimalarial drug chloroquine is eliminated to a significant extent by renal tubular secretion. The molecular mechanism of renal chloroquine secretion remains unknown. We hypothesized that organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1), localized in the basolateral and luminal membranes of proximal tubule cells, respectively, are involved in chloroquine transport. The interaction of chloroquine with both transporters was investigated using single-transfected human embryonic kidney 293 (HEK293)-MATE1 cells in uptake experiments and single-transfected Madin-Darby canine kidney II (MDCK)-OCT2 and MDCK-MATE1 cells as well as double-transfected MDCK-OCT2-MATE1 cells grown as polarized monolayers on transwell filters. In HEK293-MATE1 cells, chloroquine competitively inhibited MATE1-mediated metformin uptake (K(i) = 2.8 μM). Cellular accumulation of chloroquine was significantly lower (P < 0.001) and transcellular chloroquine transport was significantly increased (P < 0.001) in MDCK-MATE1 and MDCK-OCT2-MATE1 cells compared to vector control cells after basal addition of chloroquine (0.1 to 10 μM). In contrast, no difference in cellular accumulation or transcellular transport of chloroquine was observed between MDCK-OCT2 and vector control cells. In line with an oppositely directed proton gradient acting as a driving force for MATE1, basal-to-apical transport of chloroquine by MDCK-OCT2-MATE1 cells increased with decreasing apical pH from 7.8 to 6.0. Transcellular transport of chloroquine by MDCK-OCT2-MATE1 cells was inhibited by cimetidine, trimethoprim, and amitriptyline. Our data demonstrate that chloroquine is a substrate and potent competitive inhibitor of MATE1, whereas OCT2 seems to play no role in chloroquine uptake. Concomitantly administered MATE1 inhibitors are likely to modify the renal secretion of chloroquine.

Pharmacokinetics of chloroquine and monodesethylchloroquine in pregnancy

In order to determine the pharmacokinetic disposition of chloroquine (CQ) and its active metabolite, desethylchloroquine (DECQ), when administered as intermittent presumptive treatment in pregnancy (IPTp) for malaria, 30 Papua New Guinean women in the second or third trimester of pregnancy and 30 age-matched nonpregnant women were administered three daily doses of 450 mg CQ (8.5 mg/kg of body weight/day) in addition to a single dose of sulfadoxine-pyrimethamine. For all women, blood was taken at baseline; at 1, 2, 4, 6, 12, 18, 24, 30, 48, and 72 h posttreatment; and at 7, 10, 14, 28, and 42 days posttreatment. Plasma was subsequently assayed for CQ and DECQ by high-performance liquid chromatography, and population pharmacokinetic modeling was performed. Pregnant subjects had significantly lower area under the plasma concentration-time curve for both CQ (35,750 versus 47,892 microg.h/liter, P < 0.001) and DECQ (23,073 versus 41,584 microg.h/liter, P < 0.001), reflecting significant differences in elimination half-lives and in volumes of distribution and clearances relative to bioavailability. Reduced plasma concentrations of both CQ and DECQ could compromise both curative efficacy and posttreatment prophylactic properties in pregnant patients. Higher IPTp CQ doses may be desirable but could increase the risk of adverse hemodynamic effects.

What is the Objective of the Mass Balance Study? A Retrospective Analysis of Data in Animal and Human Excretion Studies Employing Radiolabeled Drugs

Mass balance excretion studies in laboratory animals and humans using radiolabeled compounds represent a standard part of the development process for new drugs. From these studies, the total fate of drug-related material is obtained: mass balance, routes of excretion, and, with additional analyses, metabolic pathways. However, rarely does the mass balance in radiolabeled excretion studies truly achieve 100% recovery. Many definitions of cutoff criteria for mass balance that identify acceptable versus unacceptable recovery have been presented as ad hoc statements without a strong rationale. To address this, a retrospective analysis was undertaken to explore the overall performance of mass balance studies in both laboratory animal species and humans using data for 27 proprietary compounds within Pfizer and extensive review of published studies. The review has examined variation in recovery and the question of whether low recovery was a cause for concern in terms of drug safety. Overall, mean recovery was greater in rats and dogs than in humans. When the circulating half-life of total radioactivity is greater than 50 h, the recovery tends to be lower. Excretion data from the literature were queried as to whether drugs linked with toxicities associated with sequestration in tissues or covalent binding exhibit low mass balance. This was not the case, unless the sequestration led to a long elimination half-life of drug-related material. In the vast majority of cases, sequestration or concentration of drug-related material in an organ or tissue was without deleterious effect and, in some cases, was related to the pharmacological mechanism of action. Overall, from these data, recovery of radiolabel would normally be equal to or greater than 90%, 85%, and 80% in rat, dog, and human, respectively. Since several technical limitations can underlie a lack of mass balance and since mass balance data are not sensitive indicators of the potential for toxicity arising via tissue sequestration, absolute recovery in humans should not be used as a major decision criteria as to whether a radiolabeled study has met its objectives. Instead, the study should be seen as an integral part of drug development answering four principal questions: 1) Is the proposed clearance mechanism sufficiently supported by the identities of the drug-related materials in excreta, so as to provide a complete understanding of clearance and potential contributors to interpatient variability and drug-drug interactions? 2) What are the drug-related entities present in circulation that are the active principals contributing to primary and secondary pharmacology? 3) Are there findings (low extraction recovery of radiolabel from plasma, metabolite structures indicative of chemically reactive intermediates) that suggest potential safety issues requiring further risk assessment? 4) Do questions 2 and 3 have appropriate preclinical support in terms of pharmacology, safety pharmacology, and toxicology? Only if one or more of these four questions remain unanswered should additional mass balance studies be considered.

Pharmacokinetics and efficacy of piperaquine and chloroquine in Melanesian children with uncomplicated malaria

The disposition of chloroquine (CQ) and the related 4-aminoquinoline, piperaquine (PQ), were compared in Papua New Guinean children with uncomplicated malaria. Twenty-two children were randomized to 3 days of PQ phosphate at 20 mg/kg/day (12 mg of PQ base/kg/day) coformulated with dihydroartemisinin (DHA-PQ), and twenty children were randomized to 3 days of CQ at 10 mg base/kg/day with a single dose of sulfadoxine-pyrimethamine (CQ-SP). After a 42-day intensive sampling protocol, PQ, CQ, and its active metabolite monodesethyl-chloroquine (DECQ) were assayed in plasma by using high-performance liquid chromatography. A two-compartment model with first-order absorption was fitted to the PQ and CQ data. There were no significant differences in age, gender, body weight, or admission parasitemia between the two groups. The PCR-corrected 42-day adequate clinical and parasitological responses were 100% for DHA-PQ and 94% for CQ-SP, but P. falciparum reinfections during follow-up were common (33 and 18%, respectively). For PQ, the median volume of distribution at steady state, allowing for bioavailability (Vss/F), was 431 liters/kg (interquartile range [IQR], 283 to 588 liters/kg), the median clearance (CL/F) was 0.85 liters/h/kg (IQR, 0.67 to 1.06 liters/h/kg), the median distribution half-life (t 1/2 alpha) was 0.12 h (IQR, 0.05 to 0.66 h), and the median elimination half-life (t 1/2 beta) was 413 h (IQR, 318 to 516 h). For CQ, the median Vss/F was 154 liters/kg (IQR, 101 to 210 liters/kg), the median CL/F was 0.80 liters/h/kg (IQR, 0.52 to 0.96 liters/h/kg), the median t 1/2 alpha was 0.43 h (IQR, 0.05 to 1.82 h), and the median t 1/2 beta was 233 h (IQR, 206 to 298 h). The noncompartmentally derived median DECQ t 1/2 beta was 290 h (IQR, 236 to 368 h). Combined molar concentrations of DECQ and CQ were higher than those of PQ during the elimination phase. Although PQ has a longer t 1/2 beta than CQ, its prompt distribution and lack of active metabolite may limit its posttreatment malaria-suppressive properties.

The potential inhibitory effect of antiparasitic drugs and natural products on P-glycoprotein mediated efflux

The potential inhibitory effect on P-glycoprotein (Pgp) by antiparasitic drugs and natural compounds was investigated. Compounds were screened for Pgp interaction based on inhibition of Pgp mediated [3H]-taxol transport in Caco-2 cells. Bidirectional transport of selected inhibitors was further evaluated to identify potential Pgp substrates using the Caco-2 cells. Of 21 antiparasitics tested, 14 were found to inhibit Pgp mediated [3H]-taxol with K(iapp) values in the range 4-2000 microM. The antimalarial quinine was the most potent inhibitor with a K(iapp) of 4 microM. Of the 12 natural compounds tested, 3 inhibited [3H]-taxol transport with K(iapp) values in the range 50-400 microM. Quinine, amodiaquine, chloroquine, flavone, genistein, praziquantel, quercetin and thiabendazole were further investigated in bidirectional transport assays to determine whether they were substrates for Pgp. Transport of quinine in the secretory direction exceeded that in the absorptive direction and was saturable, suggesting quinine being a Pgp substrate. The rest of the compounds inhibiting Pgp showed no evidence of being Pgp substrates. In conclusion, we have demonstrated that a substantial number of antiparasitic and natural compounds, in a range of concentrations, are capable of inhibiting Pgp mediated [3H]-taxol efflux in Caco-2 cells, without being substrates and this may have implications for drug interactions with Pgp.

Predictors of the failure of treatment with chloroquine in children with acute, uncomplicated, Plasmodium falciparum malaria, in an area with high and increasing incidences of chloroquine resistance

Resistance to chloroquine (CQ) in Plasmodium falciparum has reached unacceptably high levels in many endemic countries. The pre-treatment factors that identify the children who are at risk of treatment failure after being given CQ were evaluated in 385 children with acute, uncomplicated, Plasmodium falciparum malaria. These children each took part in one of six antimalarial drug trials conducted, between July 1996 and July 2004, in a hyper-endemic area of south-western Nigeria. Following treatment with CQ, 149 (39%) of the children failed treatment by day 7 or 14. In a multivariate analysis, an age of < or =7 years [giving an adjusted odds ratio (AOR) of 2.17, with a 95% confidence interval (CI) of 1.19-3.85; P = 0.01], an asexual parasitaemia of > or =100,000/microl (AOR = 2.17; CI = 1.08-4.35; P = 0.03), the presence of gametocytaemia (AOR = 2.08; CI = 1.14-3.85; P = 0.02) and enrolment >4 years after commencement of the study (i.e. after 2000; AOR = 2.13; CI = 1.3-4.0; P = 0.003) were found to be independent predictors at presentation of the subsequent failure of treatment with CQ. Compared with the other children, those who failed to clear their parasitaemias within 3 days and those who still had fever 1-2 days after commencing treatment were more likely to be treatment failures. Together, these findings may have implications for malaria-control efforts in all areas of sub-Saharan Africa where treatment of malaria depends almost entirely on antimalarial monotherapy.

Predictors of the failure of treatment with chloroquine plus chlorpheniramine, in children with acute, uncomplicated, Plasmodium falciparum malaria

Resistance to chloroquine in Plasmodium falciparum can be reversed, both in vitro and in vivo, by chlorpheniramine, a histamine H(1) receptor antagonist. This reversal raises the possibility of using chlorpheniramine to prolong the clinical usefulness of chloroquine in resource-poor communities. The factors that identify children at risk of treatment failure after being given chloroquine plus chlorpheniramine have now been evaluated in 281 children with uncomplicated, P. falciparum malaria. The children, who had taken part in six trials of antimalarial drugs between February 1996 and September 1999, in a hyper-endemic area of south-western Nigeria, were enrolled prospectively for the present study. Following treatment with chloroquine plus chlorpheniramine, 13 (5%) of the children failed treatment by day 7 or 14. In a multivariate analysis, an age of < or =3 years (adjusted odds ratio = 11.1; 95% confidence interval = 2.2-55.3; P = 0.003) and a parasitaemia that took >3 days to clear (adjusted odds ratio=7.9; 95% confidence interval = 1.3-49.4; P = 0.027) were found to be independent predictors of treatment failure. In addition, compared with the children who had a lower axillary temperature then, the children who had an axillary temperature of > or =38 degrees C 2 days after commencing treatment were significantly more likely to be treatment failures. In resource-poor communities using chloroquine plus chlorpheniramine, the easily identifiable predictors of treatment failure might be used to identify children requiring alternative antimalarial drugs.

Identification of human cytochrome P(450)s that metabolise anti-parasitic drugs and predictions of in vivo drug hepatic clearance from in vitro data

OBJECTIVE

Knowledge about the metabolism of anti-parasitic drugs (APDs) will be helpful in ongoing efforts to optimise dosage recommendations in clinical practise. This study was performed to further identify the cytochrome P(450) (CYP) enzymes that metabolise major APDs and evaluate the possibility of predicting in vivo drug clearances from in vitro data.

METHODS

In vitro systems, rat and human liver microsomes (RLM, HLM) and recombinant cytochrome P(450) (rCYP), were used to determine the intrinsic clearance (CL(int)) and identify responsible CYPs and their relative contribution in the metabolism of 15 commonly used APDs.

RESULTS AND DISCUSSION

CL(int) determined in RLM and HLM showed low (r(2)=0.50) but significant ( P<0.01) correlation. The CL(int) values were scaled to predict in vivo hepatic clearance (CL(H)) using the 'venous equilibrium model'. The number of compounds with in vivo human CL data after intravenous administration was low ( n=8), and the range of CL values covered by these compounds was not appropriate for a reasonable quantitative in vitro-in vivo correlation analysis. Using the CL(H) predicted from the in vitro data, the compounds could be classified into three different categories: high-clearance drugs (>70% liver blood flow; amodiaquine, praziquantel, albendazole, thiabendazole), low-clearance drugs (<30% liver blood flow; chloroquine, dapsone, diethylcarbamazine, pentamidine, primaquine, pyrantel, pyrimethamine, tinidazole) and intermediate clearance drugs (artemisinin, artesunate, quinine). With the exception of artemisinin, which is a high clearance drug in vivo, all other compounds were classified using in vitro data in agreement with in vivo observations. We identified hepatic CYP enzymes responsible for metabolism of some compounds (praziquantel-1A2, 2C19, 3A4; primaquine-1A2, 3A4; chloroquine-2C8, 2D6, 3A4; artesunate-2A6; pyrantel-2D6). For the other compounds, we confirmed the role of previously reported CYPs for their metabolism and identified other CYPs involved which had not been reported before.

CONCLUSION

Our results show that it is possible to make in vitro-in vivo predictions of high, intermediate and low CL(int) drug categories. The identified CYPs for some of the drugs provide a basis for how these drugs are expected to behave pharmacokinetically and help in predicting drug-drug interactions in vivo.

A review and assessment of potential sources of ethnic differences in drug responsiveness

The International Conference on Harmonization (ICH) E5 guidelines were developed to provide a general framework for evaluating the potential impact of ethnic factors on the acceptability of foreign clinical data, with the underlying objective to facilitate global drug development and registration. It is well recognized that all drugs exhibit significant inter-subject variability in pharmacokinetics and pharmacologic response and that such differences vary considerably among individual drugs and depend on a variety of factors. One such potential factor involves ethnicity. The objective of the present work was to perform an extensive review of the world literature on ethnic differences in drug disposition and responsiveness to determine their general significance in relation to drug development and registration. A few examples of suspected ethnic differences in pharmacokinetics or pharmacodynamics were identified. The available literature, however, was found to be heterologous, including a variety of study designs and research methodologies, and most of the publications were on drugs that were approved a long time ago.

Management of HIV-infected pregnant patients in malaria-endemic areas: therapeutic and safety considerations in concomitant use of antiretroviral and antimalarial agents

Chemotherapy in pregnancy is an intricate process requiring prudent use of pharmacologic agents. Malarial infection during pregnancy is often fatal, and prophylaxis against the causative parasite necessitates rational therapeutic intervention. Various agents have been used for prophylaxis against malaria during pregnancy, including chloroquine, mefloquine, proguanil, pyrimethamine, and pyrimethamine-sulfadoxine. Use of these agents has been based on a risk-benefit criterion, without appropriate toxicologic or teratologic evaluation. Some of the aforementioned prophylactic agents have been shown to alter glutathione levels and may exacerbate the oxidation-reduction imbalance attendant on HIV infection. HIV-infected patients traveling to or residing in malaria-endemic areas require protection from malarial infection to avoid placing themselves in double jeopardy. Zidovudine (AZT) is recommended for the prevention of vertical transmission of HIV-1 from mother to child. Other agents, such as lamivudine alone or in combination with AZT, nevirapine, or the HIV-1 protease inhibitors, are either being considered or are currently undergoing trials for use in preventing vertical transmission of HIV-1 or managing HIV infection in infants and children. Although the potential for antimalarial agents to cause congenital malformations is low when they are used alone, their ability to cause problems when combined with antiretroviral drugs needs to be evaluated. In developing countries that have high birth rates, a high endemicity of malaria, and alarming rates of new cases of HIV, prophylaxis against both diseases with combination agents during pregnancy is a challenge.

Pharmacokinetics of quinine, chloroquine and amodiaquine. Clinical implications

Malaria is associated with a reduction in the systemic clearance and apparent volume of distribution of the cinchona alkaloids; this reduction is proportional to the disease severity. There is increased plasma protein binding, predominantly to alpha 1-acid glycoprotein, and elimination half-lives (in healthy adults quinine t1/2z = 11 hours, quinidine t1/2z = 8 hours) are prolonged by 50%. Systemic clearance is predominantly by hepatic biotransformation to more polar metabolites (quinine 80%, quinidine 65%) and the remaining drug is eliminated unchanged by the kidney. Quinine is well absorbed by mouth or following intramuscular injection even in severe cases of malaria (estimated bioavailability more than 85%). Quinine and chloroquine may cause potentially lethal hypotension if given by intravenous injection. Chloroquine is extensively distributed with an enormous total apparent volume of distribution (Vd) more than 100 L/kg, and a terminal elimination half-life of 1 to 2 months. As a consequence, distribution rather than elimination processes determine the blood concentration profile of chloroquine in patients with acute malaria. Parenteral chloroquine should be given either by continuous intravenous infusion, or by frequent intramuscular or subcutaneous injections of relatively small doses. Oral bioavailability exceeds 75%. Amodiaquine is a pro-drug for the active antimalarial metabolite desethylamodiaquine. Its pharmacokinetic properties are similar to these of chloroquine although the Vd is smaller (17 to 34 L/kg) and the terminal elimination half-life is 1 to 3 weeks.

Ethnic differences in nifedipine kinetics: comparisons between Nigerians, Caucasians and South Asians

Nifedipine was administered to 12 healthy Nigerian volunteers as a single oral dose of 20 mg capsule under fasting conditions. The pharmacokinetic results were compared with published data using the same protocol and analytical method for 27 Caucasians and 30 South Asians. The area under the plasma concentration-time curve (AUC) of nifedipine in Nigerians (808 +/- 250 ng ml-1 h) was significantly higher (P < 0.001) than that in Caucasians (323 +/- 116 ng ml-1 h) and the difference remained significant (P < 0.001) when corrected for body weight. The elimination half-life was also significantly higher (P < 0.01) in Nigerians (5.03 +/- 1.96 h) than in Caucasians (2.78 +/- 1.11 h). No significant differences were observed between Nigerians and South Asians in either AUC or half-life of nifedipine. The AUC of the nitropyridine metabolite was higher (P < 0.01) in Nigerians (220 +/- 51 ng ml-1 h) compared with that in Caucasians (154 +/- 56 ng ml-1 h) but the difference was not maintained when corrected for body weight. The AUC corrected for body weight and the elimination half-life of the metabolite were significantly higher in South Asians compared with those of Nigerians and Caucasians. The pharmacokinetics of oral nifedipine in Nigerians were similar to those in South Asians and therefore may also arise from a lower systemic clearance compared with Caucasians as has been reported previously for South Asians.

Antimalarial 4-aminoquinolines: mode of action and pharmacokinetics

In the last ten years, the widespread increase in Plasmodium falciparum resistance to chloroquine has prompted research into antimalarial 4-aminoquinolines, empirically used up to now. The mechanism of action of 4-aminoquinolines is characterized by the concentration of the drug in the digestive vacuole of the intraerythrocytic parasite. Various hypotheses have been advanced to explain the specificity of action on the parasite; the most recent one is the inhibition of the haem polymerase of the parasite, leading to the accumulation of soluble haem toxic for the parasite. Chloroquine-resistant parasites accumulate the drug to a lesser extent than do sensitive parasites. Recent findings have shown that chloroquine resistance can be reversed by various tricyclic drugs, which are able to restore the effective concentrations of chloroquine in the infected erythrocyte, but intrinsic mechanisms of action of these reversing agents are unknown. Four-aminoquinolines are extensively distributed in tissues and characterized by a long elimination half-life. Despite similarities in their chemical structures, these drugs show differences in their biotransformation and routes of elimination: chloroquine is partly metabolized into a monodesethylderivative and eliminated mainly by the kidney. In contrast, amodiaquine is a prodrug and amopyroquine is poorly metabolized; both drugs are excreted mainly in the bile. The understanding of the pharmacokinetics of 4-aminoquinolines has led to an improvement in empirically defined therapeutic regimens. Finally, the emergence of severe adverse-effects after prolonged prophylaxis with amodiaquine and the lack of cross resistance of Plasmodium falciparum between chloroquine and amopyroquine, have led to a proposal for the use of intramuscular amopyroquine as an alternative for the treatment of chloroquine-resistant malaria.

The effect of chloroquine on the pharmacokinetics and metabolism of praziquantel in rats and in humans

It is likely that a proportion of people treated with the anti-schistosomicidal drug praziquantel (PZQ) is also taking other drugs such as chloroquine (CHQ), a widely used anti-malarial. The effect of CHQ on the pharmacokinetics and metabolism of PZQ in rats and in humans was therefore studied. CHQ decreased the bioavailability of PZQ and reduced its maximum serum concentrations to a significant extent in rats and in humans. The clearance was increased to a statistically significant extent in rats but not in humans because of the wide interindividual variation. The effect of CHQ on PZQ pharmacokinetics was unexpected since drugs that inhibit hepatic drug metabolism usually increase the bioavailability of PZQ. We found that CHQ inhibits non-competitively the metabolism of PZQ to its major metabolite, 4-hydroxy-praziquantel, with a Ki of 1.65 mM in rat hepatic microsomes. Maximum concentrations attained by CHQ in serum, however, are low compared to the Ki value and significant inhibition is therefore unlikely in vivo. The explanation for CHQ's effect on the pharmacokinetics of PZQ may be due to other effects of CHQ rather than to a direct effect on drug-metabolizing enzymes.

Clinical pharmacokinetics of slow-acting antirheumatic drugs

The pharmacokinetics of the slow acting antirheumatic drugs (SAARDs), hydroxychloroquine, chloroquine, penicillamine, the gold complexes and sulphasalazine, in humans have been studied. For all these drugs, both in controlled clinical trials and in empirical observations from rheumatological practice, delays of several months are reported before full clinical effects are achieved. Variability in response is also characteristic of these agents. Pharmacokinetic factors may partially explain these clinical observations. Delays in the achievement of steady-state concentrations or of concentrations likely to have a therapeutic benefit may occur because of slow drug accumulation. Variable concentrations may arise after standard administered doses because of interindividual pharmacokinetic variability. These factors are likely to contribute to the delay in response and the variable response, respectively. Pharmacokinetics of the antimalarials, hydroxychloroquine and chloroquine, are characterised by extensive tissue sequestration with reported volumes of distribution in the thousands of litres. Both drugs have reported elimination half-lives of greater than 1 month. A 2- to 3-fold range occurs in the fraction of an oral dose absorbed from a tablet formulation. Variable interindividual clearance is also reported. Hydroxychloroquine and chloroquine are administered as racemates. Enantioselective disposition of both compounds occurs, again with notable interindividual variability. Sulphasalazine is split in the large intestine into sulphapyridine, proposed to be the active compound in rheumatoid arthritis, and mesalazine (5-aminosalicylic acid). Sulphapyridine is metabolised partly by acetylation, the rate of which is under genetic control. A wide range of sulphapyridine steady-state concentrations are reported after standard doses of sulphasalazine. The gold complexes are administered either intramuscularly or in an oral form (auranofin). Gold is widely distributed in the body. Very long terminal elimination half-lives and slow accumulation rates are reported. Penicillamine is administered orally. Its bioavailability is variable and may decrease by as much as 70% in the presence of food, antacids and iron salts. Penicillamine forms disulphide bonds with many proteins in the blood and tissues, creating potential slow release reservoirs of the drug. Like the other SAARDs, gold complexes and penicillamine are found in a wide range of blood concentrations after administration in standard doses to different individuals. More research must be conducted into the concentration-effect relationships of the SAARDs before the pharmacokinetic characteristics of these drugs can be used effectively to optimise patient therapy.

Simultaneous determination of chloroquine and quinine in human biological fluids by high-performance liquid chromatography

A high-performance liquid chromatographic method with fluorescence detection is described for the simultaneous measurement of quinine, chloroquine and mono- and bidesethylchloroquine in human plasma, erythrocytes and urine. After a liquid-solid extraction on a Bond Elut C8 cartridge, the compounds are separated on an Inertsil silica column by gradient elution; the mobile phase is a mixture of acetonitrile and methanol-25% ammonia solution (92.7:7.5, v/v). The eluent was monitored with a fluorescence detector (excitation wavelength 325 nm and emission wavelength 375 nm). The limit of detection was ca. 5 ng/ml for chloroquine and ca. 23 ng/ml for quinine. No chromatographic interferences could be detected from endogenous compounds or other antimalarial drugs. The method is accurate with inter- and intra-assay coefficients of variation lower than 7%. Hydroxychloroquine is used as an internal standard because of its structural similarity to chloroquine. The procedure requires 30 min and can be used for therapeutic drug monitoring.

Antimalarials in rheumatic diseases

The antimalarials hydroxychloroquine and chloroquine remain established and effective agents for the treatment of rheumatoid arthritis and systemic lupus erythematosus. Although the mechanisms of action remain uncertain, evidence is accumulating that the antirheumatic and immunological effects of the antimalarials are related to their massive distribution into the cellular acid-vesicle system. These drugs are attracting new interest because their relative safety recommends their use in early rheumatoid arthritis and as a component of second-line antirheumatic drug combinations. The absence of data examining the effect of antimalarials upon radiological progression of rheumatoid arthritis needs to be rectified. Recent understanding of the pharmacokinetics of these drugs reveals that steady-state concentrations are not achieved for at least 3-4 months. Preliminary information also suggests a relationship between blood concentrations and effect. Taken together, these data suggest that more effective dosage regimens will be possible when therapeutic concentration ranges are properly established.

Pharmacokinetics of intramuscular amopyroquin in healthy subjects and determination of a therapeutic regimen for Plasmodium falciparum malaria

The disposition of amopyroquin was investigated in 10 healthy volunteers after a single 2-mg/kg (body weight) intramuscular dose of amopyroquin base. The major form of the drug in plasma and in whole blood was nonmetabolized amopyroquin, and only very low levels of its primary amine derivative were detected. After a rapid absorption phase (15 min), levels in plasma declined, following a tri-exponential model with a terminal elimination half-life of 129.6 +/- 92.5 h. The apparent volume of distribution (V/F) and the systemic clearance (CL/F) were 238 +/- 75 liters/kg and 2,063 +/- 1,159 ml/min, respectively. The renal clearance, calculated by using urine excreted during the first 48 h, was 119 +/- 99 ml/min and represented about 6% of the systemic clearance. About 1.2 and 0.2% of the amopyroquin dose was excreted in the urine during the first 48 h as nonmetabolized amopyroquin and its primary amine metabolite, respectively. Twenty-two Plasmodium falciparum malaria patients were studied after treatment with one of the following regimens of intramuscularly injected amopyroquin base: 3 mg/kg (body weight), 6 mg/kg, or 6 mg/kg followed by 3 mg/kg 24 h later. Parasitemia was cleared at day 7 in one of six, four of seven, and seven of nine patients, respectively. On the basis of this study, a regimen of 12 mg/kg (body weight) administered in two or three injections is suggested.

A dose-ranging study of the pharmacokinetics of hydroxy-chloroquine following intravenous administration to healthy volunteers

1. The pharmacokinetics of hydroxychloroquine were studied in five healthy volunteers following an intravenous infusion of 155 mg (2.47 +/- 0.25 mg kg-1) racemic hydroxychloroquine. Four of these volunteers also received a further 310 mg (4.92 +/- 0.45 mg kg-1) infusion of hydroxychloroquine and evidence of nonlinearities in the pharmacokinetics of hydroxychloroquine were sought. 2. No nonlinear elimination or distribution processes appeared to be operating at the doses of hydroxychloroquine used in this study, supporting the hypothesis that in the therapeutic dosing range the pharmacokinetics of hydroxychloroquine are linear. 3. Half-life and mean residence time were long (around 40 days) and large volumes of distribution were calculated (5,522 l from blood, 44,257 l from plasma). Sequestration into the tissues is an important feature of the disposition of hydroxychloroquine. The persistence of hydroxychloroquine in the body is due primarily to this extensive tissue distribution, rather than to low clearance (667 ml min-1 based on plasma data, 96 ml min-1 based on blood data). 4. Plasma data were more variable than blood data. Blood to plasma concentration ratios were not constant (mean +/- s.d.: 7.2 +/- 4.2). The data indicate that it is preferable to measure whole blood concentrations of hydroxychloroquine, rather than plasma concentrations, in pharmacokinetic studies. 5. The pharmacokinetics of hydroxychloroquine are similar to those of chloroquine.

Single dose disposition of chloroquine in kwashiorkor and normal children--evidence for decreased absorption in kwashiorkor

The single dose disposition of chloroquine was studied in five children with kwashiorkor and six normal control children after an oral dose of 10 mg kg-1 of chloroquine base. Plasma concentrations of chloroquine and its main metabolite were assayed by high performance liquid chromatography (h.p.l.c.). Chloroquine was detectable for up to 21 days in all the subjects. Chloroquine was detectable in all the subjects within 30 min after giving the drug except in one subject. Peak levels were reached between 0.5 and 8 h in all the subjects (with no significant difference in the tmax between the two groups of children). Peak plasma chloroquine concentrations in the children with kwashiorkor varied from 9 ng ml-1 to 95 ng ml-1 (mean 40 +/- 34 ng ml-1). Peak chloroquine concentrations in the controls varied between 69 ng ml-1 and 330 ng ml-1 (mean 134 +/- 99 ng ml-1). The mean AUC in the kwashiorkor children was significantly lower than the mean AUC in the control children (P less than 0.001). Peak plasma desethylchloroquine concentrations in the children with kwashiorkor varied between 3 and 13 ng ml-1 (mean 6 +/- 9 ng ml-1) while in the controls the concentrations varied between 14 and 170 ng ml-1 (mean 50 +/- 61 ng ml-1). There was no significant difference in the half-life of chloroquine between the kwashiorkor children and the normal control children. The possible influence of a different binding and distribution pattern of chloroquine in kwashiorkor could not be assessed in this study.(ABSTRACT TRUNCATED AT 250 WORDS)