Isolation, characterization and standardization of a major metabolite of amodiaquine by chromatographic and spectroscopic methods

An update on pharmacogenetic factors influencing the metabolism and toxicity of artemisinin-based combination therapy in the treatment of malaria

INTRODUCTION

Artemisinin-based combination therapies (ACTs) are recommended first-line antimalarials for uncomplicated Plasmodium falciparum malaria. Pharmacokinetic/pharmacodynamic variation associated with ACT drugs and their effect is documented. It is accepted to an extent that inter-individual variation is genetically driven, and should be explored for optimized antimalarial use.

AREAS COVERED

We provide an update on the pharmacogenetics of ACT antimalarial disposition. Beyond presently used antimalarials, we also refer to information available for the most notable next-generation drugs under development. The bibliographic approach was based on multiple Boolean searches on PubMed covering all recent publications since our previous review.

EXPERT OPINION

The last 10 years have witnessed an increase in our knowledge of ACT pharmacogenetics, including the first clear examples of its contribution as an exacerbating factor for drug-drug interactions. This knowledge gap is still large and is likely to widen as a new wave of antimalarial drug is looming, with few studies addressing their pharmacogenetics. Clinically useful pharmacogenetic markers are still not available, in particular, from an individual precision medicine perspective. A better understanding of the genetic makeup of target populations can be valuable for aiding decisions on mass drug administration implementation concerning region-specific antimalarial drug and dosage options.

Population Pharmacokinetics of the Antimalarial Amodiaquine: a Pooled Analysis To Optimize Dosing

Amodiaquine plus artesunate is the recommended antimalarial treatment in many countries where malaria is endemic. However, pediatric doses are largely based on a linear extrapolation from adult doses.

Amodiaquine plus artesunate is the recommended antimalarial treatment in many countries where malaria is endemic. However, pediatric doses are largely based on a linear extrapolation from adult doses. We pooled data from previously published studies on the pharmacokinetics of amodiaquine, to optimize the dose across all age groups. Adults and children with uncomplicated malaria received daily weight-based doses of amodiaquine or artesunate-amodiaquine over 3 days. Plasma concentration-time profiles for both the parent drug and the metabolite were characterized using nonlinear mixed-effects modeling. Amodiaquine pharmacokinetics were adequately described by a two-compartment disposition model, with first-order elimination leading to the formation of desethylamodiaquine, which was best described by a three-compartment disposition model. Body size and age were the main covariates affecting amodiaquine clearance. After adjusting for the effect of weight, clearance rates for amodiaquine and desethylamodiaquine reached 50% of adult maturation at 2.8 months (95% confidence interval [CI], 1.5 to 3.7 months) and 3.9 months (95% CI, 2.6 to 5.3 months) after birth, assuming that the baby was born at term. Bioavailability was 22.4% (95% CI, 15.6 to 31.9%) lower at the start of treatment than during convalescence, which suggests a malaria disease effect. Neither the drug formulation nor the hemoglobin concentration had an effect on any pharmacokinetic parameters. Results from simulations showed that current manufacturer dosing recommendations resulted in low desethylamodiaquine exposure in patients weighing 8 kg, 15 to 17 kg, 33 to 35 kg, and >62 kg compared to that in a typical 50-kg patient. We propose possible optimized dosing regimens to achieve similar drug exposures among all age groups, which require further validation.

TiO2 Photocatalysis-DESI-MS Rotating Array Platform for High-Throughput Investigation of Oxidation Reactions

We present a new high-throughput platform for studying titanium dioxide (TiO₂) photocatalytic oxidation reactions by performing reactions on a TiO₂-coated surface, followed by direct analysis of oxidation products from the surface by desorption electrospray ionization mass spectrometry (DESI-MS). For this purpose, we coated a round glass wafer with photocatalytically active anatase-phase TiO₂ using atomic layer deposition. Approximately 70 aqueous 1 μL samples can be injected onto the rim of the TiO₂-coated glass wafer, before the entire wafer is exposed to UV irradiation. After evaporation of water, the oxidation products can be directly analyzed from the sample spots by DESI-MS, using a commercial rotating sample platform. The method was shown to provide fast photocatalytic oxidation reactions and analysis with throughput of about four samples per minute. The feasibility of the method was examined for mimicking phase I metabolism reactions of amodiaquine, buspirone and verapamil. Their main photocatalytic reaction products were mostly similar to the products observed earlier in TiO₂ photocatalysis and in in vitro phase I metabolism assays performed using human liver microsomes.

The pharmacogenetics of antimalaria artemisinin combination therapy

INTRODUCTION

Plasmodium falciparum malaria is one of the world's most lethal infectious diseases, commanding millions of drug administrations per year. The pharmacogenetics of these drugs is poorly known, although its application can be pivotal for the optimized management of this disease.

AREAS COVERED

The main components of artemisinin combination therapy (ACT), the worldwide main antimalarial strategy, are metabolized by the polymorphic CYP3A4 (mefloquine, artemether, lumefantrine), CYP2C8 (amodiaquine), CYP2A6 (artesunate) and CYP1A1/2 (amodiaquine/desethylamodiaquine), with dihydroartemisinin being acted by Phase II UDP-glucuronosyltransferases. The worldwide adoption of ACT is leading to a large number of antimalarial treatments. Simultaneously, the feared development of parasite drug resistance might drive dosing increases. In these scenarios of increased drug exposure, pharmacogenetics can be a key tool supporting evidence-based medicine aiming for the longest possible useful lifespan of this important chemotherapy.

EXPERT OPINION

Translation in this moment is not operationally possible at an individual level, but large population studies are achievable for: i) the development of robust pharmacogenetics markers; and ii) the parallel development of a pharmacogenetic cartography of malaria settings. Advances in the understanding of antimalarial pharmacogenetics are urgent in order to protect the exposed populations, enhance the effectiveness of ACT and, consequently, contributing for the long aimed elimination of the disease.

Quantifying the metabolic activation of nevirapine in patients by integrated applications of NMR and mass spectrometries

Nevirapine (NVP), an antiretroviral drug, is associated with idiosyncratic hepatotoxicity and skin reactions. Metabolic pathways of haptenation and immunotoxicity mechanisms have been proposed. NVP is metabolized by liver microsomes to a reactive intermediate that binds irreversibly to protein and forms a GSH adduct. However, no reactive metabolite of NVP, trapped as stable thioether conjugates, has hitherto been identified in vivo. This study has defined the metabolism of NVP with respect to reactive intermediate formation in patients and a rat model of NVP-induced skin reactions. An integrated NMR and mass spectrometry approach has been developed to discover and quantify stable urinary metabolite biomarkers indicative of NVP bioactivation in patients. Two isomeric NVP mercapturates were identified in the urine of HIV-positive patients undergoing standard antiretroviral chemotherapy. The same conjugates were found in rat bile and urine. The mercapturates were isolated from rat bile and characterized definitively by NMR as thioethers substituted at the C-3 and exocyclic C-12 positions of the methylpyrido ring of NVP. It is proposed that NVP undergoes bioactivation to arene oxide and quinone methide intermediates. The purified major mercapturate was quantified by NMR and used to calibrate a mass spectrometric assay of the corresponding metabolite in patient urine. This is the first evidence for metabolic activation of NVP in humans, and only the second minimum estimate in patients of bioactivation of a widely prescribed drug associated with idiosyncratic toxicities. The method can be used as a template for comparative estimations of bioactivation of any drug in patients.

Effect of concomitant artesunate administration and cytochrome P4502C8 polymorphisms on the pharmacokinetics of amodiaquine in Ghanaian children with uncomplicated malaria

Artesunate (AS) is used in combination with amodiaquine (AQ) as first-line treatment for uncomplicated malaria in many countries. We investigated the effect of concomitant AS administration on the pharmacokinetics of AQ and compared concentrations of desethylamodiaquine (DEAQ), the main metabolite of AQ, in plasma between patients with different variants of the cytochrome P4502C8 (CYP2C8) gene. A two-compartment model was fitted to 169 plasma DEAQ concentrations from 103 Ghanaian children aged 1 to 14 years with uncomplicated malaria treated either with AQ alone (n = 15) or with AS plus AQ (n = 88). The population clearance of DEAQ appeared to increase nonlinearly with body weight, and the central volume of distribution of DEAQ was higher (P < 0.001) in the AS-plus-AQ group than in the AQ-only group. The maximum plasma DEAQ concentration was higher (P < 0.001), and the population distribution half-life was shorter (P < 0.01), in the AQ-only group than in the AS-plus-AQ group. The total areas under the plasma DEAQ concentration-time curves (P = 0.68) and elimination half-lives (P = 0.39) were similar for the two groups. There was a high frequency (0.179) of the non-wild-type allele of CYP2C8, but no differences between CYP2C8 genotypes with regard to AQ efficacy or safety were evident. The sample size, however, was limited, so monitoring of AQ toxicity in the study area is still indicated. The nonlinear clearance of DEAQ and the wide variability in kinetic parameters have safety implications for weight-based dosing of higher-body-weight children with AQ. The pharmacokinetics of artemisinin combination therapies should be studied in malaria patients, because the rapid parasite clearance caused by the artemisinin may affect the kinetics of the partner drug and the combination.

Study on the biochemical basis of mefloquine resistant Plasmodium falciparum

Increase in drug detoxification and alteration of drug uptake and efflux of Plasmodium falciparum were investigated for their possible association with mefloquine (MQ) resistance in five different clones of P. falciparum from Thailand (T994b(3), K1CB(2), PR70CB(1), PR71CB(2) and TM(4)CB8-2.2.3). Fifty percent inhibitory concentration (IC(50)) values from these five clones varied between 30- and 50-fold. Regarding the detoxification mechanism, the ability of P. falciparum clones to biotransform MQ was shown in vitro by parasite microsomal protein prepared from parasite infected red blood cells protein (30mug), NADPH (1nM) and phosphate buffer pH 7.4, carried out at 37 degrees C with agitation. Radiolabelled unmetabolized MQ and possible metabolite(s) generated from the reaction was extracted into ethylacetate and separated by radiometric-HPLC after 1 h. All clones were capable of converting MQ into carboxymefloquine (CMQ), which is the main metabolite in human plasma. In addition, another unidentified metabolite eluted at 4.2 min on the chromatograph could be detected from the incubation reaction. This metabolite has never been detected in human liver microsomes before. There was no significant difference in the percentages of CMQ formed in the resistant (T994(b3), PR(70)CB(1), PR(71)CB(2)) and sensitive (TM(4)CB8-2.2.3, K1CB(2)) clones. Another possible mechanism, i.e., alteration in the accumulation of MQ in the parasites was investigated in vitro using [(14)C]MQ as a tracer. The time courses of [(14)C]MQ uptake and efflux were generally characterized by two phases. A trend of increased efflux of [(14)C]MQ was observed in the resistant compared with sensitive clones.

Amodiaquine metabolism is impaired by common polymorphisms in CYP2C8: implications for malaria treatment in Africa

Metabolism of the antimalarial drug amodiaquine (AQ) into its primary metabolite, N-desethylamodiaquine, is mediated by CYP2C8. We studied the frequency of CYP2C8 variants in 275 malaria-infected patients in Burkina Faso, the metabolism of AQ by CYP2C8 variants, and the impact of other drugs on AQ metabolism. The allele frequencies of CYP2C8*2 and CYP2C8*3 were 0.155 and 0.003, respectively. No evidence was seen for influence of CYP2C8 genotype on AQ efficacy or toxicity, but sample size limited these assessments. The variant most common in Africans, CYP2C8(*)2, showed defective metabolism of AQ (threefold higher K(m) and sixfold lower intrinsic clearance), and CYP2C8(*)3 had markedly decreased activity. Considering drugs likely to be coadministered with AQ, the antiretroviral drugs efavirenz, saquinavir, lopinavir, and tipranavir were potent CYP2C8 inhibitors at clinically relevant concentrations. Variable CYP2C8 activity owing to genetic variation and drug interactions may have important clinical implications for the efficacy and toxicity of AQ.

Synergism between amodiaquine and its major metabolite, desethylamodiaquine, against Plasmodium falciparum in vitro

The in vitro activity of the prodrug amodiaquine and its metabolite monodesethyl-amodiaquine has been studied for three strains of Plasmodium falciparum: LS-2, LS-3, and LS-1. Both compounds showed significant activity against all three strains; the activity of amodiaquine was slightly higher than that of the metabolite. By use of a checkerboard design, interaction studies with both compounds yielded evidence of significant synergism; means of the sums of the fractional inhibitory concentrations were 0.0392 to 0.0746 for strain LS-2, 0.1567 to 0.3102 for strain LS-3, and 0.025 to 0.3369 for strain LS-1. In further investigations, the interaction of amodiaquine with monodesethyl-amodiaquine was tested at clinically relevant concentrations of both compounds. In these studies, involving amodiaquine at picomolar and femtomolar concentrations, the compound was found to exert high potentiating activity on monodesethyl-amodiaquine. This interaction produced mean ratios of observed to expected activity of 0.0505 to 0.0642 for strain LS-2, 0.0882 to 0.3820 for strain LS-3, and 0.0752 to 0.2924 for strain LS-1. The synergistic activity was most marked at monodesethyl-amodiaquine/amodiaquine ratios up to 100,000:1 but was still evident at higher ratios.

Amodiaquine clearance and its metabolism to N-desethylamodiaquine is mediated by CYP2C8: a new high affinity and turnover enzyme-specific probe substrate

Amodiaquine (AQ) metabolism to N-desethylamodiaquine (DEAQ) is the principal route of disposition in humans. Using human liver microsomes and two sets of recombinant human cytochrome P450 isoforms (from lymphoblastoids and yeast) we performed studies to identify the CYP isoform(s) involved in the metabolism of AQ. CYP2C8 was the main hepatic isoform that cleared AQ and catalyzed the formation of DEAQ. The extrahepatic P450s, 1A1 and 1B1, also cleared AQ and catalyzed the formation of an unknown metabolite M2. The K(m) and V(max) values for AQ N-desethylation were 1.2 microM and 2.6 pmol/min/pmol of CYP2C8 for recombinant CYP2C8, and 2.4 microM and 1462 pmol/min/mg of protein for human liver microsomes (HLMs), respectively. Relative contribution of CYP2C8 in the formation of DEAQ was estimated at 100% using the relative activity factor method. Correlation analyses between AQ metabolism and the activities of eight hepatic P450s were made on 10 different HLM samples. Both the formation of DEAQ and the clearance of AQ showed excellent correlations (r(2) = 0.98 and 0.95) with 6alpha-hydroxylation of paclitaxel, a marker substrate for CYP2C8. The inhibition of DEAQ formation by quercetin was competitive with K(i) values of 1.96 for CYP2C8 and 1.56 microM for HLMs. Docking of AQ into the active site homology models of the CYP2C isoforms showed favorable interactions with CYP2C8, which supported the likelihood of an N-desethylation reaction. These data show that CYP2C8 is the main hepatic isoform responsible for the metabolism of AQ. The specificity, high affinity, and high turnover make AQ desethylation an excellent marker reaction for CYP2C8 activity.

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 toxicity of amodiaquine and its principal metabolites towards mononuclear leucocytes and granulocyte/monocyte colony forming units

The cytotoxicity of amodiaquine (AQ), amodiaquine quinoneimine (AQQI) and desethylamodiaquine (AQm) has been assessed in comparison with that of chloroquine (CQ) using mononuclear leucocytes (MNL) and granulocyte/monocyte colony forming units (GM-CFU) from haematologically normal subjects. Toxicity toward MNL was assessed after 2 h and 16 h incubations with each compound. After 2 h, AQ, AQm and AQQI but not CQ (within the concentration range 1-100 mumols l-1) produced a significant decrease in cell viability. After 16 h, all four compounds significantly increased cell death. After both 2 h and 16 h incubations CQ was the least toxic and AQQI the most toxic of the four compounds towards MNL. Toxicity to GM-CFU was assessed by the inhibition of colony formation in vitro. After 10-14 days incubation, there was significant concentration-dependent inhibition of colony formation by AQ, AQm, AQQI and CQ (within the range 0.1-10.0 mumols l-1). There were no significant differences between the ability of the four compounds to inhibit colony formation but toxicity towards GM-CFU was observed at drug concentrations at least 10-fold lower than those that were toxic to MNL. These data show that the four compounds are equally toxic in vitro toward GM-CFU, although some differences in their toxicity toward MNL were seen. The possible mechanisms of AQ's toxicity are discussed.

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.

Detection and determination of antimalarial drugs and their metabolites in body fluids

This review of methods for determining antimalarial drugs in biological fluids has focused on the various analytical techniques for the assay of chloroquine, quinine, amodiaquine, mefloquine, proguanil, pyrimethamine, sulphadoxine, primaquine and some of their metabolites. The methods for determining antimalarials and their metabolites in biological samples have changed rapidly during the last eight to ten years with the increased use of chromatographic techniques. Chloroquine is still the most used antimalarial drug, and various methods of different complexity exist for the determination of chloroquine and its metabolites in biological fluids. The pharmacokinetics of chloroquine and other antimalarials have been updated using these new methods. The various analytical techniques have been discussed, from simple colorimetric methods of intermediate selectivity and sensitivity to highly sophisticated, selective and sensitive chromatographic methods applied in a modern analytical laboratory. Knowledge concerning the method for a particular study is determined by the type of application and the facilities, equipment and personnel available. Often is it useful to apply various methods when conducting a clinical study in malaria-endemic areas. Field-adapted methods for the analysis of urine samples can be applied at the study site for screening, and corresponding blood samples can be preserved for subsequent analysis in the laboratory. Selecting samples for laboratory analysis is based on clinical, parasitological and field-assay data. The wide array of methods available for chloroquine permit carefully tailored approaches to acquire the necessary analytical information in clinical field studies concerning the use of this drug. The development of additional field-adapted and field-interfaced methods for other commonly used antimalarials will provide similar flexibility in field studies of these drugs.

Tissue distribution and excretion of amodiaquine in the rat

14C-Labelled amodiaquine ([14C]AQ) has been administered to male Wistar rats by oral and intravenous routes (n = 6 for each route of administration). Excretion of total 14C-activity was predominantly in the faeces after both oral and intravenous administration. After oral administration 86 +/- 8.3% (mean +/- s.d.) of the 14C administered had been excreted (77 +/- 9% in the faeces, 7 +/- 1% in the urine and 2 +/- 2% in cage washings) over 72 h. Of the 14C administered, 4 +/- 1% was recovered from the tissues, and this was widely distributed, with the main organs of accumulation being kidney, liver, red bone marrow and spleen. After intravenous administration, 102.6 +/- 9.7% of the 14C had been excreted (90.9 +/- 9.6% in faeces, 10.9 +/- 0.8% in urine and 0.5 +/- 0.2% in cage washings) over 72 h. High-performance liquid chromatographic analysis of urine and faeces samples following oral administration of 14C-AQ (8.6 mg kg-1; base) revealed recoveries of 210 +/- 70 micrograms amodiaquine (AQ) and 123 +/- 32 micrograms desethylamodiaquine (AQm) in the faeces, and 2.4 +/- 0.5 micrograms AQ and 18.5 +/- 4.1 micrograms AQm in the urine. Female Wistar rats (n = 6) each received [14C]AQ orally and were killed at the following times: 0.5, 1, 3, 6, 24 and 48 h. Autoradiographs were prepared from each animal and these revealed significant amounts of radioactivity in the tissues at 48 h. This was accumulated maximally by liver and kidney. Radioactivity was detected in bone marrow at 48 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug-protein conjugates--XIV. Mechanisms of formation of protein-arylating intermediates from amodiaquine, a myelotoxin and hepatotoxin in man

The enzymic and non-enzymic formation of protein-arylating intermediates from amodiaquine (AQ,7-chloro-4-(3'-diethylamino-4'-hydroxyanilino) quinoline), an anti-malarial associated with agranulocytosis and liver damage in man, was studied in vitro. [14C]AQ in phosphate buffer, pH 7.4, under air was autoxidized to a reactive derivative(s) which possessed characteristics indicative of a semiquinone/quinone imine: reduction by NADPH and ascorbic acid, conjugation with thiols and irreversible binding to microsomal and soluble proteins. Cysteinyl SH groups were major sites of arylation. Radiolabelled material irreversibly bound to HSA after 24 hr and to human liver microsomes after 4 hr represented 26.5 +/- 1.8% and 31.4 +/- 0.6% (means +/- SD, N = 3) of incubated [14C]AQ (10 microM), respectively. The quinone imine of AQ(AQQI) was synthesized, and displayed the same oxidative and electrophilic reactions as the product(s) of AQ's autoxidation. A water-soluble product formed in buffered solutions of AQ and N-acetylcysteine was identified as an AQ mercapturate by comparison with an adduct prepared from synthetic AQQI. Irreversible binding of [14C]AQ was inhibited by a radical scavenger; this indicated that the semiquinone imine contributed to the binding. Although AQ was extensively de-ethylated by human liver microsomes, oxidation by cytochrome P-450 did not appear to be principally responsible for its activation and irreversible binding in microsomal incubations. AQ was oxidized to protein-arylating intermediates by horseradish peroxidase. It also formed reactive derivatives, possibly N-chloro compounds, in chlorine solutions. These findings indicated that AQ can give rise to chemically reactive species by at least three distinct mechanisms, viz. autoxidation in neutral solution under air, peroxidase-catalyzed oxidation and N-chlorination. Formation of such species in liver and myeloid cells might be responsible for the adverse reactions associated with AQ.

Disposition of monodesethylamodiaquine after a single oral dose of amodiaquine and three regimens for prophylaxis against Plasmodium falciparum malaria

The disposition of monodesethylamodiaquine was studied in four healthy subjects after a single oral dose of 10 mg/kg amodiaquine base. Amodiaquine was not found in any sample, but the major metabolite monodesethylamodiaquine was detected and was assumed to be the sole derivative that contributed significantly to antimalarial activity in the blood. The best fit for the decay of the metabolite was obtained with a three-compartment model. The half-lives of the first two phases were 3.2 to 11.4 h for t1/2 alpha 1 and 22.7 to 50.3 h for t1/2 alpha 2 in plasma. The half-life of the terminal phase (t1/2 beta) was between 9 and 18.2 days. The concentration in whole blood was 4- to 6-times higher than in plasma. Three schedules (alternate days, weekly, daily) of the conventional prophylactic dose of 10 mg/kg per week were compared in six other healthy subjects. There were significant differences in the plasma monodesethylamodiaquine levels between the three schedules.

Effect of dose size on amodiaquine pharmacokinetics after oral administration

Plasma and urine concentrations of amodiaquine (AQ) and desethylamodiaquine (AQm) have been measured after oral administration of AQ 200, 400 and 600 mg in randomised order to 6 healthy subjects. The relationships between AQ dose size and the areas under the plasma concentration vs time curves for AQ and AQm were linear. Likewise there were linear relationships between AQ dose size and the mass of both AQ and AQm excreted in the urine. These data indicate that after oral administration within this dose range AQ displays first-order pharmacokinetics.

The disposition of amodiaquine in man after oral administration

A method is described for the simultaneous determination of amodiaquine (AQ) and desethylamodiaquine (AQm) in plasma, urine, whole blood and packed red cells. After oral administration of AQ (600 mg) to seven healthy subjects, absorption of AQ was rapid, reaching peak concentrations in plasma, whole blood, and packed cells at 0.5 +/- 0.03, 0.5 +/- 0.1 and 0.5 +/- 0.1 h respectively (mean +/- s.e. mean). The apparent terminal half-life of AQ was 5.2 +/- 1.7 h. AQ was detectable for no longer than 8 h. AQ underwent rapid conversion to AQm, which reached peak concentrations in plasma, whole blood and packed cells at 3.4 +/- 0.8, 2.3 +/- 0.5 and 3.6 +/- 1.1 h respectively. AQm was still detectable at the end of the sampling period (96 h) when the plasma concentration was 29 +/- 8 ng ml-1. The area under the plasma concentration vs time curve (AUC(0, infinity] for AQ was 154 +/- 38 ng ml-1 h; the corresponding value for AQm was 8037 +/- 1383 ng ml-1 h. There were no significant differences in the values for AUC of AQ between plasma, whole blood, or packed cells. The whole blood to plasma concentration ratio for AQm was 3.1 +/- 0.2, and the AUC (0.24) for AQm in whole blood (6811 +/- 752 ng ml-1 h) was significantly greater than that in plasma (2304 +/- 371 ng ml-1 h), P less than 0.001. The recovery of AQm from urine collected 0-24 h was 6.8 +/- 0.8 mg (n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitive analysis of blood for amodiaquine and three metabolites by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method using oxidative electrochemical detection has been developed for selective and sensitive quantification of the antimalarial drug amodiaquine and three of its metabolites in the blood of dosed individuals. The method requires only one extraction step and has detection limits of 1 ng/ml for amodiaquine and its metabolites desethylamodiaquine and bisdesethylamodiaquine and 3 ng/ml for 2-hydroxydesethylamodiaquine. Minor modification of the mobile phase preserves the chromatographic separation and allows ultraviolet spectroscopic detection, which, although appreciably less sensitive, permits monitoring of levels of amodiaquine and the three metabolites in blood and urine samples if an electrochemical detector is unavailable. Levels of amodiaquine and the three metabolites were determined for two volunteers undergoing a nine-week chemoprophylactic regimen in connection with travel to a malarious area. Data are included to compare the in vitro antimalarial activities against three strains of Plasmodium falciparum of amodiaquine and the three metabolites considered.