Metabolism Of Amodiaquine Research Articles

Prevalence of CYP2C8*2 and *3 amongEritreans and its Potential Impact on Artesunate/Amodiaquine Treatment.

BackgroundIn Eritrea, artesunate–amodiaquine is the first-line treatment against uncomplicated malaria. Amodiaquine, which is mainly bio-transformed by CYP2C8, is known to be associated with adverse events of different severity. Extrapyramidal events are among the less common but have been reported with non-negligible frequency in Eritrea. This study was conducted to investigate the allele frequencies of CYP2C8*2 and *3, both associated with decreased amodiaquine metabolism, among the Eritrean population.MethodsDuring September–November 2018, dried blood samples from 380 participants and 17 patients who previously had experienced extrapyramidal symptoms following treatment of artesunate–amodiaquine were collected and PCR-RFLP genotyped for CYP2C8*2 and *3.ResultsThe allele frequencies of CYP2C8*2 and *3 were determined as 5.9% (95% CI: 4.4–7.8) and 4.6% (95% CI: 3.2–6.3), respectively. Four out of the 17 patients with extrapyramidal reactions showed to be carriers of the alleles.ConclusionCYP2C8*2 and *3 frequencies among Eritreans were found to be intermediate between the documented for Caucasian and African populations. These findings, along with the alleles not being decisive for the occurrence of extrapyramidal events, might be of importance regarding the amodiaquine-containing malaria treatment in Eritrea. Furthermore, it suggests a significant proportion of slow amodiaquine metabolizers in the Sahel region, information of potential interest in the context of amodiaquine-involving seasonal malaria chemoprevention.

Plasmodium falciparum genetic factors rather than host factors are likely to drive resistance to ACT in Ghana

BackgroundArtemisinin-based combination therapy (ACT) partner drugs, currently used in Ghana are lumefantrine, amodiaquine and piperaquine. Plasmodium falciparum isolates with reduced susceptibility to these partner drugs may affect treatment outcome. Mutations in pfmdr1 gene is linked to reduced parasite susceptibility to amodiaquine and lumefantrine. In addition, the potency of the partner drugs in vivo depends on the metabolism by the cytochrome P450 (CYP) enzyme in the host. Mutations in the CYP2C8 and CYP3A4 genes are linked to reduced metabolism of amodiaquine and lumefantrine in vitro, respectively. This study investigated the host and parasite genetic factors affecting the susceptibility of the malaria parasite to ACT partner drugs.MethodsArchived samples from 240 patients age ≤ 9 years participating in anti-malarial drug resistance survey in Ghana, and given artemether with lumefantrine (AL) or artesunate with amodiaquine (AA), were selected and analysed. Polymerase chain reaction (PCR) followed by Sanger sequencing was used to determine the polymorphisms in CYP2C8, CYP3A4 and pfmdr1 genes.ResultsFor CYP3A4, all had wild type alleles, suggesting that the hosts are good metabolizers of lumefantrine. For CYP2C8 60% had wild type alleles, 35% heterozygous and 5% homozygous recessive alleles suggesting efficient metabolism of amodiaquine by the hosts. For pfmdr1 gene, at codon 86, 95% were wild type (N86) and 5% mutant (Y86). For codon 184, 36% were wild type (Y184) and 64% mutant (F184) while for codons 1034, 1042 and 1246, 100% (all) were wild type. The high prevalence of N86-F184-D1246 haplotype (NFD) suggest presence of parasites with reduced susceptibility to lumefantrine and not amodiaquine. Delayed clearance was observed in individuals with mutations in the pfmdr1 gene and not cytochrome 450 gene. Both synonymous and non-synonymous mutations were observed in the pfmdr1 at low prevalence.ConclusionThe outcome of this study indicates that the parasite's genetic factors rather than the host’s are likely to drive resistance to ACT in Ghana.

Investigating selected host and parasite factors potentially impacting upon seasonal malaria chemoprevention in Bama, Burkina Faso

BackgroundSince 2014, seasonal malaria chemoprevention (SMC) with amodiaquine–sulfadoxine–pyrimethamine (AQ–SP) has been implemented on a large scale during the high malaria transmission season in Burkina Faso. This paper reports the prevalence of microscopic and submicroscopic malaria infection at the outset and after the first round of SMC in children under 5 years old in Bama, Burkina Faso, as well as host and parasite factors involved in mediating the efficacy and tolerability of SMC.MethodsTwo sequential cross-sectional surveys were conducted in late July and August 2017 during the first month of SMC in a rural area in southwest Burkina Faso. Blood smears and dried blood spots were collected from 106 to 93 children under five, respectively, at the start of SMC and again 3 weeks later. Malaria infection was detected by microscopy and by PCR from dried blood spots. For all children, day 7 plasma concentrations of desethylamodiaquine (DEAQ) were measured and CYP2C8 genetic variants influencing AQ metabolism were genotyped. Samples were additionally genotyped for pfcrt K76T and pfmdr1 N86Y, molecular markers associated with reduced amodiaquine susceptibility.Results2.8% (3/106) of children were positive for Plasmodium falciparum infection by microscopy and 13.2% (14/106) by nested PCR within 2 days of SMC administration. Three weeks after SMC administration, in the same households, 4.3% (4/93) of samples were positive by microscopy and 14.0% (13/93) by PCR (p = 0.0007). CYP2C8*2, associated with impaired amodiaquine metabolism, was common with an allelic frequency of 17.1% (95% CI 10.0–24.2). Day 7 concentration of DEAQ ranged from 0.48 to 362.80 ng/mL with a median concentration of 56.34 ng/mL. Pfmdr1 N86 predominated at both time points, whilst a non-significant trend towards a higher prevalence of pfcrt 76T was seen at week 3.ConclusionThis study showed a moderate prevalence of low-level malaria parasitaemia in children 3 weeks following SMC during the first month of administration. Day 7 concentrations of the active DEAQ metabolite varied widely, likely reflecting variability in adherence and possibly metabolism. These findings highlight factors that may contribute to the effectiveness of SMC in children in a high transmission setting.

Mechanistic mathematical representation of CD8+ T cell mediated drug-induced liver injury (DILI) Part 2: translation from experimental antigen, ovalbumin (OVA), to drug, amodiaquine (AQ) response

Abstract Idiosyncratic DILI (iDILI) is poorly understood and costly to patients and drug developers. Some iDILI events appear immune-mediated. This work builds on the DILIsym representation of T cell cytotoxicity against OVA-expressing hepatocytes1, to translate the OVA representation to AQ-induced hepatotoxicity. AQ-related changes include a physiologically-based pharmacokinetic (PBPK) model for mouse AQ exposure, AQ metabolism to reactive metabolites (RMs), RM-mediated ER stress leading to inflammation, fewer endogenous AQ responsive T cells of reduced affinity and avidity for AQ antigen. Simulations show no CD8+ T cell mediated ALT elevations in simulated wild-type mice treated with AQ, consistent with data2 and provide a mechanistic basis for the result. With low levels of AQ antigen, low T cell numbers and lower affinity and avidity interactions were insufficient for a cytotoxic T lymphocyte (CTL) response. With high levels of AQ antigen, T cell expansion and differentiation occurred but regulatory pathways, i.e., T cell exhaustion, inhibited an effective CTL response. In PD1−/− mice treated with anti-CTLA4, CD8+ T cell mediated AQ DILI was apparent (ALT >100 U/L)3,4. In DILIsym, blocking coinhibitory activity on proliferation and differentiation was permissive for AQ DILI (ALT >100 U/L) and could be further exacerbated by blocking differentiation to an exhausted phenotype (ALT >200 U/L). The results provide proof-of-concept for translation of OVA hepatotoxicity to AQ DILI and set the stage for exploration of human AQ DILI5.

Distribution of the cytochrome P450 CYP2C8*2 allele in Brazzaville, Republic of Congo

BackgroundCytochrome P450 (CYP) enzymes are essential in the metabolism of most drugs used today. Single nucleotide polymorphism(s) occurring in CYP genes can adversely affect drug pharmacokinetics, efficacy, and safety. Individuals carrying the CYP2C8*2 c.805A > T (CYP2C8*2; rs11572103) allele have impaired amodiaquine metabolism, increased risk of amodiaquine-related adverse events, and may promote the selection of drug-resistant parasite strains. This study investigated the distribution of the CYP2C8*2 allele in Brazzaville, Republic of Congo, where artesunate + amodiaquine is used as the second-line treatment for uncomplicated Plasmodium falciparum malaria. MethodsA total of 285 febrile children visiting the Marien Ngouabi paediatric hospital were genotyped for CYP2C8*2 using PCR-restriction fragment length polymorphism (PCR-RFLP). The allele frequencies and genotype distribution were determined. ResultsThe CYP2C8*2 allele was successfully genotyped in 75% (213/285) of the study participants. The CYP2C8*2A allele had a frequency of 63%, whereas the CYP2C8*2T allele had a frequency of 37%. Genotypes CYP2C8*2AA (rapid metabolizer), CYP2C8*2AT (intermediate metabolizer), and CYP2C8*2TT (poor metabolizer) were observed in 44%, 38%, and 18% of the investigated participants, respectively. ConclusionsThis study gives the first description of CYP2C8*2 allele distribution in the Republic of Congo and highlights the potential risk of amodiaquine-related adverse events. Information from this study will be beneficial during pharmacovigilance investigations.

Investigation of amodiaquine localization in liver lobules using matrix-assisted laser desorption/ionization imaging mass spectrometry.

High mass and high spatial resolution matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) opens new possibilities for the detailed study of the hepatic metabolism of drugs. The spatial and temporal distribution of drug metabolites within liver lobules, anatomical subunits of the liver, may aid in the understanding of the formation of reactive metabolites that bind to liver proteins and cause drug-induced liver injury. Frozen livers obtained from rats dosed orally with amodiaquine (100 mg/kg) were sectioned at 10 μm and coated with a MALDI matrix. The liver sections were then analyzed using a Fourier transform ion cyclotron resonance mass spectrometer. Images corresponding to amodiaquine and its metabolites were obtained at a spatial resolution of 25 μm. Molecular images of amodiaquine within liver lobules have higher intensities near the portal triad and lower intensities near the central vein. This study demonstrates that MALDI IMS can be used to investigate the metabolism of drugs within liver lobules. The results are consistent with existing knowledge of amodiaquine metabolism and reactive metabolite formation.

Induction of Amodiaquine Metabolism by Rifampicin Following Concurrent Administration in Healthy Volunteers

Malaria and tuberculosis remain endemic in tropical regions and most often coexist, increasing the burden of malaria mortality due to unintended interactions of the co-administered drugs employed in the management of the infections. Rifampicin (RIF) and amodiaquine (ADQ) are likely to be administered concurrently in the treatment of patients with tuberculosis and malaria. The metabolism of ADQ is mediated principally by CYP2C8, while RIF is a known inducer of this enzyme. This study, therefore, investigated the effect of RIF on the disposition of ADQ, a major partner drug in the first-line treatment against uncomplicated malaria in line with the World Health Organization recommendations.

Role of cytochrome P450 2C8*3 (CYP2C8*3) in paclitaxel metabolism and paclitaxel-induced neurotoxicity.

The CYP2C8*3 allele has been suggested as a risk factor for paclitaxel-induced neuropathy but the data hitherto published are conflicting. In total 435 patients were investigated with respect to maximum neuropathy grade and accumulated paclitaxel dose. The enzymatic properties of CYP2C8.3 variant were analyzed using heterologous mammalian HEK293 cell expression system. No significant association between CYP2C8*3 allele and neuropathy was found, although a trend was observed. The paclitaxel and amodiaquine metabolism by CYP2C8.3 were found similar to CYP2C8.1, whereas CYP2C8.3 was more efficient in the metabolism of rosiglitazone. These results indicate a difference in substrate specificity between CYP2C8.1 and CYP2C8.3; however, the CYP2C8*3 allele has no major impact on paclitaxel metabolism in vitro or of paclitaxel-induced neuropathy in vivo. Original submitted on 6 February 2015; revision submitted on 9 April 2015.

Effects of concurrent administration of efavirenz on the disposition kinetics of amodiaquine in healthy volunteers

Background/ObjectivesEfavirenz and amodiaquine are likely to be administered concurrently for the treatment of patients with HIV and malaria. The metabolism of amodiaquine is mediated principally by CYP2C8 while efavirenz is known to inhibit this enzyme. This study therefore investigated the effect of efavirenz on amodiaquine disposition. MethodsFourteen healthy volunteers were each given 600 mg single oral doses of amodiaquine alone or with the 9th dose of efavirenz (400 mg daily for 12 days) in a crossover fashion. Blood samples were collected at pre-determined time intervals and analyzed for amodiaquine and its major metabolite, desethylamodiaquine, using a validated HPLC method. ResultsCo-administration of amodiaquine and efavirenz resulted in significant increases (p < 0.05) in Cmax, Tmax, AUCT and elimination half-life (T1/2) of amodiaquine compared with values for amodiaquine alone. Also, efavirenz caused a pronounced decrease in the AUC (metabolite)/AUC (unchanged drug) ratio of amodiaquine along with a significant decrease (p < 0.05) in Cmax and AUC of the metabolite. ConclusionEfavirenz significantly alters the pharmacokinetics of amodiaquine, exposure to amodiaquine is increased leading to toxic effect, and reduction in the antimalarial activity since amodiaquine is a prodrug that relies on its active metabolite against malaria parasites.

In-vitro inhibitory effect of Tualang honey on cytochrome P450 2C8 activity

To investigate the effect of Tualang honey on cytochrome P450 2C8 (CYP2C8) activity in vitro using an amodiaquine N-desethylase assay. CYP2C8 and NADPH cytochrome P450 reductase was cotransformed, expressed and harvested. The incubation assay contained expressed proteins, MgCl(2), NADP, glucose 6-phosphate, glucose-6-phosphate dehydrogenase, potassium phosphate buffer, and amodiaquine. The rate of conversion of amodiaquine to desethylamodiaquine, the metabolite, was determined using a high performance liquid chromatography (HPLC) method. The inhibition parameters, IC50 (concentration of inhibitor causing 50% inhibition of original enzyme activity) and apparent inhibition constant (K(i) ) values were determined. The recombinant proteins were successfully expressed and used to investigate the effect of Tualang honey on CYP2C8 activity. The activity was measured by the rate of metabolism of amodiaquine to desethylamodiaquine determined using a successfully developed HPLC method. Kinetic parameters as determined by nonlinear least-squares regression and evaluated with Aikeike's goodness of fit criteria revealed that Tualang honey competitively inhibited CYP2C8 activity in a dose-dependent manner. Maximum inhibition of 80% occurred at 0.01% honey. The IC50 and K(i) values were (10.0 ± 3.0) × 10(-3) % and (5.1 ± 0.5) × 10(-3) % w/v, respectively. This study has provided evidence for the in vitro inhibition of CYP2C8-mediated amodiaquine N-desethylase activity by Tualang honey. It revealed that honey, through this inhibition, may have the potential to cause in-vivo drug-food interaction with drugs metabolized by CYP2C8.

Cytochrome 1A1 and 1B1 gene diversity in the Zanzibar islands

Amodiaquine (AQ) is a 4-aminoquinoline widely used in the treatment of malaria as part of the artemisinin combination therapy (ACT). AQ is metabolised towards its main metabolite desethylamodiaquine mainly by cytochrome P450 2C8 (CYP2C8). CYP1A1 and CYP1B1 play a minor role in the metabolism but they seem to be significantly involved in the formation of the short-lived quinine-imine. To complete the genetic variation picture of the main genes involved in AQ metabolism in the Zanzibar population, previously characterised for CYP2C8, we analysed in this study CYP1A1 and CYP1B1 main genetic polymorphisms. The results obtained show a low frequency of the CYP1A1*2B/C allele (2.4%) and a high frequency of CYP1B1*6 (approximately 42%) followed by CYP1B1*2 (approximately 27%) in Zanzibar islands. Genotype data for CYP1A1 and CYP1B1 show a low incidence of fast metabolisers, revealing a relatively safe genetic background in Zanzibar's population regarding the appearance of adverse effects.

Amodiaquine-associated adverse effects after inadvertent overdose and after a standard therapeutic dose

A case of an acute dystonic reaction in a child presumptively treated for malaria with amodiaquine, and a case of persistent asymptomatic bradycardia in another child with mild pulmonary stenosis treated with a standard dose of amodiaquine for parasitologically confirmed uncomplicated malaria, is reported. Both subjects were homozygous for the wild type allele of cytochrome P450 2C8, the main enzyme responsible for amodiaquine metabolism. In both subjects, plasma concentrations of N-desethylamodiaquine and N-bis-desethylamodiaquine, the main metabolites of amodiaquine, were normal. No other drugs were detectable in the plasma of these two subjects after further toxicological screening. These observations, which suggest altered metabolism in the subject with an acute dystonic reaction, support the assertion that amodiaquine-associated dystonia is an idiosyncratic reaction. However, the occurrence of bradycardia after a standard dose of amodiaquine, which coincided with the time of expected peak concentrations of the active metabolite of amodiaquine, suggests a direct drug effect. These less reported adverse effects are likely to increase in parallel with the increased use of amodiaquine as a partner drug for combination therapy of malaria in Ghana. Further studies aimed at elucidating the mechanisms underlying these effects are, therefore, required.

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.

Short communication: High prevalence of the cytochrome P450 2C8*2 mutation in Northern Ghana

Recently, Ghana has changed the first-line treatment of uncomplicated malaria from chloroquine to amodiaquine (AQ) plus artesunate. AQ may cause adverse events such as agranulocytosis and hepatoxicity. The pro-drug AQ is transformed by cytochrome P450 CYP2C8 to the active metabolite N-desethylaminodiaquine. Several polymorphic variants of CYP2C8 are known, some with reduced activity. In 200 randomly selected children from Northern Ghana, we determined the allele frequencies of the CYP2C8 variants CYP2C8*1 (wild type), CYP2C8*2, CYP2C8*3, and CYP2C8*4. We did not detect CYP2C8*3 and CYP2C8*4, but CYP2C8*2 showed an allele frequency of 0.1675. AQ metabolism in patients with CYP2C8*2 may be impaired, and with an increase of AQ based treatment the risk of severe adverse events may mount.

CYP2C8 polymorphism frequencies among malaria patients in Zanzibar

The determination of the prevalence of the CYP2C8 main alleles in a typical set of malaria patients in Zanzibar, as these patients represent a typical population exposed to amodiaquine, an antimalarial mainly metabolized by CYP2C8. Also, to determine for the first time the frequencies of CYP2C8 alleles in native African populations. Polymerase chain reaction-restriction fragment polymorphism for the identification of CYP2C8*1, CYP2C8*2, CYP2C8*3 and CYP2C8*4 on a random population of 165 unrelated malaria patients. The allele frequencies found were: CYP2C8*1 (wild type, 83.4%), CYP2C8*2 (13.9%), CYP2C8*3 (2.1%) and CYP2C8*4 (0.6%). In terms of genotypes, 70.4% of the patients showed the CYP2C8*1/ CYP2C8*1 genotypes, while heterozygous between the wild type and other minor alleles were seen in 26.0%. Finally, 3.6% of the patients were homozygous for slow metabolizer alleles. The frequencies observed are equivalent to those documented for African-Americans. CYP2C8 non-wild type alleles have a significant prevalence in the East African population studied. The consequent frequency of 3.6% of patients homozygous for slow metabolizer alleles represent a significant fraction of the population potentially in higher risk of adverse effects due to a less efficient metabolism of amodiaquine. As approximately 10(6) first-line treatments are currently performed in Zanzibar per year, this represents a non-negligible absolute number of amodiaquine exposures. This information constitutes a background for the pharmacovigilance programs presently being employed in Zanzibar.

Examination of 209 Drugs for Inhibition of Cytochrome P450 2C8

Cytochrome P450 2C8 is involved in the metabolism of drugs such as paclitaxel, repaglinide, rosiglitazone, and cerivastatin, among others. An in vitro assessment of 209 frequently prescribed drugs and related xenobiotics was carried out to examine their potential to inhibit CYP2C8. A validated sensitive, moderate-throughput high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) assay was used to detect N-desethylamodiaquine, the CYP2C8-derived major metabolite of amodiaquine metabolism, using heterologously expressed recombinant CYP2C8 (rhCYP2C8) and pooled human liver microsomes. The 209 drugs were first tested at 30 muM for their ability to inhibit rhCYP2C8. Forty-eight compounds exhibited greater than 50% inhibition and were further evaluated for measurement of IC50. The six most potent inhibitors (IC50 <1 microM) from this set were measured for IC50 in pooled human liver microsomes, and the most potent inhibitor identified was the leukotriene receptor antagonist, montelukast (IC50 = 19.6 nM). Inhibitors of CYP2C8 were identified from a wide variety of therapeutic classes, with no single class predominating. Other potent inhibitors included candesartan cilexetil (cyclohexylcarbonate ester prodrug of candesartan), zafirlukast, clotrimazole, felodipine, and mometasone furoate. Seventeen moderate inhibitors of rhCYP2C8 (1 < IC50 < 10 microM) included salmeterol, raloxifene, fenofibrate, ritonavir, levothyroxine, tamoxifen, loratadine, quercetin, oxybutynin, medroxyprogesterone, simvastatin, ketoconazole, ethinyl estradiol, spironolactone, lovastatin, nifedipine, and irbesartan. These in vitro data were used along with clinical pharmacokinetic information in predicting potential drug-drug interactions that could occur by inhibition of CYP2C8. Although almost all drugs tested are not expected to cause drug interactions via inhibition of CYP2C8, montelukast was identified as being of concern as a potential inhibitor of clinical relevance. These findings are discussed in context to potential drug interactions that could be observed between these agents and drugs for which CYP2C8 is involved in metabolism and warrant investigation of the possibility of clinical drug interactions mediated by inhibition of this enzyme.

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.

The bioactivation of amodiaquine by human polymorphonuclear leucocytes in vitro: Chemical mechanisms and the effects of fluorine substitution

Amodiaquine, a 4-aminoquinoline antimalarial, has been associated with hepatitis and agranulocytosis in humans. Drug hypersensitivity reactions, especially agranulocytosis, have been attributed to reactive intermediates generated by the oxidants discharged from stimulated polymorphonuclear leucocytes (PMN). The metabolism of amodiaquine to both stable and chemically reactive metabolites by human PMN has been investigated in vitro. Incubation of [ 14C]-amodiaquine with PMN resulted in irreversible binding of radiolabel to protein and depletion of intracellular reduced glutathione, which were enhanced by phorbol myristate acetate (PMA), a PMN activator. Two metabolites were identified: the C-5′ glutathione adduct of amodiaquine, derived from both endogenous and exogenous glutathione, and 4-amino-7-chloroquinoline, which was presumed to be formed by hydrolysis of amodiaquine quinoneimine. Desethylamodiaquine, the major plasma metabolite of amodiaquine in humans, also underwent bioactivation to a chemically reactive species in the presence of PMA-stimulated PMN. Substitution of the 4′-hydroxyl group in amodiaquine with fluorine significantly reduced irreversible binding to protein and abolished depletion of intracellular glutathione in the presence of PMA. These findings indicate that the bioactivation of amodiaquine by PMN is associated with the formation of a quinoneimine intermediate. Such a reactive metabolite, if produced in PMN or bone marrow in vivo, may be responsible for the drug's myelotoxicity.

The Disposition and Metabolism of Amodiaquine in Small Mammals

1. 7-Chloro-4-(3′-diethylamino-4′-hydroxyanilino)quinoline (amodiaquine) labelled with 14C has been synthesized and administered in single doses to rats including bile-duct-cannulated rats, to guinea-pigs and to mice, by oral or parenteral routes.2. Amodiaquine was extensively and rapidly absorbed from the rat intestinal tract. Excretion of total radioactivity from rats and guinea pigs was slow and prolonged and was <50% dose in 9 days. Excretion of 14C was predominantly in faeces of rats after oral and i.p. dosage, and guinea-pigs after i.p. dosage. Radioactivity in rat and guinea-pig urine was <11% dose.3. Biliary excretion of 14C following oral or i.v. dosage to rats was 21% dose in 24 h.4. Amodiaquine was extensively metabolized and conjugated with <10% dose excreted unchanged in urine or bile. Two major basic metabolites in rat urine were tentatively identified as the mono- and bis-desethyl amines.5. 7-Chloro-4-(4′-diethyl-1′-methylbutylamino)quinoline (chloroquine) was excreted largely unchanged in ...