Meta-analysis of the global distribution of clinically relevant CYP2C8 alleles and their inferred functional consequences.

BACKGROUND: CYP2C8 is responsible for the metabolism of 5% of clinically prescribed drugs, including antimalarials, anti-cancer and anti-inflammatory drugs. Genetic variability is an important factor that influences CYP2C8 activity and modulates the pharmacokinetics, efficacy and safety of its substrates. RESULTS: We profiled the genetic landscape of CYP2C8 variability using data from 96 original studies and data repositories that included a total of 33,185 unrelated participants across 44 countries and 43 ethnic groups. The reduced function allele CYP2C8*2 was most common in West and Central Africa with frequencies of 16-36.9%, whereas it was rare in Europe and Asia (< 2%). In contrast, CYP2C8*3 and CYP2C8*4 were common throughout Europe and the Americas (6.9-19.8% for *3 and 2.3-7.5% for *4), but rare in African and East Asian populations. Importantly, we observe pronounced differences (> 2.3-fold) between neighboring countries and even between geographically overlapping populations. Overall, we found that 20-60% of individuals in Africa and Europe carry at least one CYP2C8 allele associated with reduced metabolism and increased adverse event risk of the anti-malarial amodiaquine. Furthermore, up to 60% of individuals of West African ancestry harbored variants that reduced the clearance of pioglitazone, repaglinide, paclitaxel and ibuprofen. In contrast, reduced function alleles are only found in < 2% of East Asian and 8.3-12.8% of South and West Asian individuals. CONCLUSIONS: Combined, the presented analyses mapped the genetic and inferred functional variability of CYP2C8 with high ethnogeographic resolution. These results can serve as a valuable resource for CYP2C8 allele frequencies and distribution estimates of CYP2C8 phenotypes that could help identify populations at risk upon treatment with CYP2C8 substrates. The high variability between ethnic groups incentivizes high-resolution pharmacogenetic profiling to guide precision medicine and maximize its socioeconomic benefits, particularly for understudied populations with distinct genetic profiles.

Carboxymefloquine, the major metabolite of the antimalarial drug mefloquine, induces drug-metabolizing enzyme and transporter expression by activation of pregnane X receptor.

Malaria patients are frequently coinfected with HIV and mycobacteria causing tuberculosis, which increases the use of coadministered drugs and thereby enhances the risk of pharmacokinetic drug-drug interactions. Activation of the pregnane X receptor (PXR) by xenobiotics, which include many drugs, induces drug metabolism and transport, thereby resulting in possible attenuation or loss of the therapeutic responses to the drugs being coadministered. While several artemisinin-type antimalarial drugs have been shown to activate PXR, data on nonartemisinin-type antimalarials are still missing. Therefore, this study aimed to elucidate the potential of nonartemisinin antimalarial drugs and drug metabolites to activate PXR. We screened 16 clinically used antimalarial drugs and six major drug metabolites for binding to PXR using the two-hybrid PXR ligand binding domain assembly assay; this identified carboxymefloquine, the major and pharmacologically inactive metabolite of the antimalarial drug mefloquine, as a potential PXR ligand. Two-hybrid PXR-coactivator and -corepressor interaction assays and PXR-dependent promoter reporter gene assays confirmed carboxymefloquine to be a novel PXR agonist which specifically activated the human receptor. In the PXR-expressing intestinal LS174T cells and in primary human hepatocytes, carboxymefloquine induced the expression of drug-metabolizing enzymes and transporters on the mRNA and protein levels. The crucial role of PXR for the carboxymefloquine-dependent induction of gene expression was confirmed by small interfering RNA (siRNA)-mediated knockdown of the receptor. Thus, the clinical use of mefloquine may result in pharmacokinetic drug-drug interactions by means of its metabolite carboxymefloquine. Whether these in vitro findings are of in vivo relevance has to be addressed in future clinical drug-drug interaction studies.

Plasmodium falciparum drug resistance phenotype as assessed by patient antimalarial drug levels and its association with pfmdr1 polymorphisms.

BACKGROUND: Multidrug-resistant Plasmodium falciparum is a major threat to global malaria control. Parasites develop resistance by gradually acquiring genetic polymorphisms that decrease drug susceptibility. The aim of this study was to investigate the extent to which parasites with different genetic characteristics are able to withstand individual drug blood concentrations. METHODS: We analyzed 2 clinical trials that assessed the efficacy and effectiveness of artemether-lumefantrine. As a proof of concept, we used measured day 7 lumefantrine concentrations to estimate the concentrations at which reinfections multiplied. P. falciparum multidrug resistance gene 1 (pfmdr1) genotypes of these parasites were then correlated to drug susceptibility. RESULTS: Reinfecting parasites with the pfmdr1 N86/184F/D1246 haplotype were able to withstand lumefantrine blood concentrations 15-fold higher than those with the 86Y/Y184/1246Y haplotype. CONCLUSIONS: By estimating drug concentrations, we were able to quantify the contribution of pfmdr1 single-nucleotide polymorphisms to reduced lumefantrine susceptibility. The method can be applied to all long-half-life antimalarial drugs, enables early detection of P. falciparum with reduced drug susceptibility in vivo, and represents a novel way for unveiling molecular markers of antimalarial drug resistance.

Quinine treatment selects the pfnhe-1 ms4760-1 polymorphism in Malian patients with Falciparum malaria.

BACKGROUND: The mechanism of Plasmodium falciparum resistance to quinine is not known. In vitro quantitative trait loci mapping suggests involvement of a predicted P. falciparum sodium-hydrogen exchanger (pfnhe-1) on chromosome 13. METHODS: We conducted prospective quinine efficacy studies in 2 villages, Kollé and Faladié, Mali. Cases of clinical malaria requiring intravenous therapy were treated with standard doses of quinine and followed for 28 days. Treatment outcomes were classified using modified World Health Organization protocols. Molecular markers of parasite polymorphisms were used to distinguish recrudescent parasites from new infections. The prevalence of pfnhe-1 ms4760-1 among parasites before versus after quinine treatment was determined by direct sequencing. RESULTS: Overall, 163 patients were enrolled and successfully followed. Without molecular correction, the mean adequate clinical and parasitological response (ACPR) was 50.3% (n = 163). After polymerase chain reaction correction to account for new infections, the corrected ACPR was 100%. The prevalence of ms4760-1 increased significantly, from 26.2% (n = 107) before quinine treatment to 46.3% (n = 54) after therapy (P = .01). In a control sulfadoxine-pyrimethamine study, the prevalence of ms4760-1 was similar before and after treatment. CONCLUSIONS: This study supports a role for pfnhe-1 in decreased susceptibility of P. falciparum to quinine in the field.

Temporal trends of molecular markers associated with artemether-lumefantrine tolerance/resistance in Bagamoyo district, Tanzania.

BACKGROUND: Development and spread of Plasmodium falciparum resistance to artemisinin-based combination therapy (ACT) constitutes a major threat to recent global malaria control achievements. Surveillance of molecular markers could act as an early warning system of ACT-resistance before clinical treatment failures are apparent. The aim of this study was to analyse temporal trends of established genotypes associated with artemether-lumefantrine tolerance/resistance before and after its deployment as first-line treatment for uncomplicated malaria in Tanzania 2006. METHODS: Single nucleotide polymorphisms in the P. falciparum multidrug resistance gene 1 (pfmdr1) N86Y, Y184F, D1246Y and P. falciparum chloroquine transporter gene (pfcrt) K76T were analysed from dried blood spots collected during six consecutive studies from children with uncomplicated P. falciparum malaria in Fukayosi village, Bagamoyo District, Tanzania, between 2004-2011. RESULTS: There was a statistically significant yearly increase of pfmdr1 N86, 184F, D1246 and pfcrt K76 between 2006-2011 from 14% to 61% (yearly OR = 1.38 [95% CI 1.25-1.52] p < 0.0001), 14% to 35% (OR = 1.17 [95% CI 1.07-1.30] p = 0.001), 54% to 85% (OR = 1.21 [95% CI 1.03-1.42] p = 0.016) and 49% to 85% (OR = 1.33 [95% CI 1.17-1.51] p < 0.0001), respectively. Unlike for the pfmdr1 SNP, a significant increase of pfcrt K76 was observed already between 2004-2006, from 26% to 49% (OR = 1.68 [95% CI 1.17-2.40] p = 0.005). From 2006 to 2011 the pfmdr1 NFD haplotype increased from 10% to 37% (OR = 1.25 [95% CI 1.12-1.39] p < 0.0001), whereas the YYY haplotype decreased from 31% to 6% (OR = 0.73 [95% CI 0.56-0.98] p = 0.018). All 390 successfully analysed samples had one copy of the pfmdr1 gene. CONCLUSION: The temporal selection of molecular markers associated with artemether-lumefantrine tolerance/resistance may represent an early warning sign of impaired future drug efficacy. This calls for stringent surveillance of artemether-lumefantrine efficacy in Tanzania and emphasizes the importance of molecular surveillance as a complement to standard in vivo trials.

Rapid diagnostic tests for molecular surveillance of Plasmodium falciparum malaria -assessment of DNA extraction methods and field applicability.

BACKGROUND: The need for new malaria surveillance tools and strategies is critical, given improved global malaria control and regional elimination efforts. High quality Plasmodium falciparum DNA can reliably be extracted from malaria rapid diagnostic tests (RDTs). Together with highly sensitive molecular assays, wide scale collection of used RDTs may serve as a modern tool for improved malaria case detection and drug resistance surveillance. However, comparative studies of DNA extraction efficiency from RDTs and the field applicability are lacking. The aim of this study was to compare and evaluate different methods of DNA extraction from RDTs and to test the field applicability for the purpose of molecular epidemiological investigations. METHODS: DNA was extracted from two RDT devices (Paracheck-Pf® and SD Bioline Malaria Pf/Pan®), seeded in vitro with 10-fold dilutions of cultured 3D7 P. falciparum parasites diluted in malaria negative whole blood. The level of P. falciparum detection was determined for each extraction method and RDT device with multiple nested-PCR and real-time PCR assays. The field applicability was tested on 855 paired RDT (Paracheck-Pf) and filter paper (Whatman® 3MM) blood samples (734 RDT negative and 121 RDT positive samples) collected from febrile patients in Zanzibar 2010. RDT positive samples were genotyped at four key single nucleotide polymorphisms (SNPs) in pfmdr1 and pfcrt as well as for pfmdr1 copy number, all associated with anti-malarial drug resistance. RESULTS: The P. falciparum DNA detection limit varied with RDT device and extraction method. Chelex-100 extraction performed best for all extraction matrixes. There was no statistically significant difference in PCR detection rates in DNA extracted from RDTs and filter paper field samples. Similarly there were no significant differences in the PCR success rates and genotyping outcomes for the respective SNPs in the 121 RDT positive samples. CONCLUSIONS: The results support RDTs as a valuable source of parasite DNA and provide evidence for RDT-DNA extraction for improved malaria case detection, molecular drug resistance surveillance, and RDT quality control.

PXR variants and artemisinin use in Vietnamese subjects: frequency distribution and impact on the interindividual variability of CYP3A induction by artemisinin.

Artemisinins induce drug metabolism through the activation of the pregnane X receptor (PXR) in vitro. Here, we report the resequencing and genotyping of PXR variants in 75 Vietnamese individuals previously characterized for CYP3A enzyme activity after artemisinin exposure. We identified a total of 31 PXR variants, including 5 novel single nucleotide polymorphisms (SNPs), and we identified significantly different allele frequencies relative to other ethnic groups. A trend of significance was observed between the level of CYP3A4 induction by artemisinin and two PXR variants, the 8118C→T (Y328Y) and 10719A→G variants.

Decreased prevalence of Plasmodium falciparum resistance markers to amodiaquine despite its wide scale use as ACT partner drug in Zanzibar.

BACKGROUND: Zanzibar has recently undergone a rapid decline in Plasmodium falciparum transmission following combined malaria control interventions with artemisinin-based combination therapy (ACT) and integrated vector control. Artesunate-amodiaquine (ASAQ) was implemented as first-line treatment for uncomplicated P. falciparum malaria in Zanzibar in 2003. Resistance to amodiaquine has been associated with the single nucleotide polymorphism (SNP) alleles pfcrt 76T, pfmdr1 86Y, 184Y and 1246Y. An accumulation of these SNP alleles in the parasite population over time might threaten ASAQ efficacy.The aim of this study was to assess whether prolonged use of ASAQ as first-line anti-malarial treatment selects for P. falciparum SNPs associated with resistance to the ACT partner drug amodiaquine. METHODS: The individual as well as the combined SNP allele prevalence were compared in pre-treatment blood samples from patients with uncomplicated P. falciparum malaria enrolled in clinical trials conducted just prior to the introduction of ASAQ in 2002-2003 (n = 208) and seven years after wide scale use of ASAQ in 2010 (n = 122). RESULTS: There was a statistically significant decrease of pfcrt 76T (96-63%), pfmdr1 86Y (75-52%), 184Y (83-72%), 1246Y (28-16%) and the most common haplotypes pfcrt/pfmdr1 TYYD (46-26%) and TYYY (17-8%), while an increase of pfcrt/pfmdr1 KNFD (0.4-14%) and KNYD (1-12%). CONCLUSIONS: This is the first observation of a decreased prevalence of pfcrt 76T, pfmdr1 86Y, 184Y and 1246Y in an African setting after several years of extensive ASAQ use as first-line treatment for uncomplicated malaria. This may support sustained efficacy of ASAQ on Zanzibar, although it was unexpected considering that all these SNPs have previously been associated with amodiaquine resistance. The underlying factors of these results are unclear. Genetic dilution by imported P. falciparum parasites from mainland Tanzania, a de-selection by artesunate per se and/or an associated fitness cost might represent contributing factors. More detailed studies on temporal trends of molecular markers associated with amodiaquine resistance are required to improve the understanding of this observation.

Efficacy and effectiveness of artemether-lumefantrine after initial and repeated treatment in children <5 years of age with acute uncomplicated Plasmodium falciparum malaria in rural Tanzania: a randomized trial.

BACKGROUND: We assessed the efficacy, effectiveness and safety of artemether-lumefantrine, which is the most widely used artemisinin-based combination therapy in Africa, against Plasmodium falciparum malaria during an extended follow-up period after initial and repeated treatment. METHODS: We performed an open-label randomized trial of artemether-lumefantrine with supervised (n=180) and unsupervised intake (n=179) in children <5 years of age with uncomplicated falciparum malaria in rural Tanzania. Recurrent infections between day 14 and day 56 were retreated within the same study arm. Main end points were polymerase chain reaction (PCR)-corrected cure rates by day 56 and day 42 after initial and repeated treatment, respectively, as estimated by survival analysis. RESULTS: The PCR-corrected cure rate after initial treatment was 98.1% (95% confidence interval [CI], 94.2%-99.4%) after supervised and 95.1% (95% CI, 90.7%-98.1%) after unsupervised intake (P=.29). After retreatment of recurrent infections, the cure rates were 92.9% (95% CI, 81.8%-97.3%) and 97.6% (95% CI, 89.3%-98.8%), respectively (P=.58). Reinfections occurred in 46.9% (82 of 175) versus 50.9 % of the patients (relative risk [RR], 0.92 [95% CI, 0.74-1.14]; P=.46) after initial therapy and 32.4% (24 of 74) versus 39.0% (32 of 82) (RR, 0.83 [95% CI, 0.54-1.27]; P=.39) after retreatment. Median blood lumefantrine concentrations in supervised and unsupervised patients on day 7 were 304 versus 194 ng/mL (P<.001) after initial treatment and 253 versus 164 ng/mL (P=.001) after retreatment. Vomiting was the most commonly reported drug-related adverse event (in 1% of patients) after both initial and repeated treatment. CONCLUSIONS: Artemether-lumefantrine was highly efficacious even after unsupervised administration, despite significantly lower lumefantrine concentrations, compared with concentration achieved with supervised intake, and was well-tolerated and safe after initial and repeated treatment. CLINICAL TRIAL REGISTRATION: ISRCTN69189899.

Effectiveness of artemether-lumefantrine provided by community health workers in under-five children with uncomplicated malaria in rural Tanzania: an open label prospective study.

BACKGROUND: Home-management of malaria (HMM) strategy improves early access of anti-malarial medicines to high-risk groups in remote areas of sub-Saharan Africa. However, limited data are available on the effectiveness of using artemisinin-based combination therapy (ACT) within the HMM strategy. The aim of this study was to assess the effectiveness of artemether-lumefantrine (AL), presently the most favoured ACT in Africa, in under-five children with uncomplicated Plasmodium falciparum malaria in Tanzania, when provided by community health workers (CHWs) and administered unsupervised by parents or guardians at home. METHODS: An open label, single arm prospective study was conducted in two rural villages with high malaria transmission in Kibaha District, Tanzania. Children presenting to CHWs with uncomplicated fever and a positive rapid malaria diagnostic test (RDT) were provisionally enrolled and provided AL for unsupervised treatment at home. Patients with microscopy confirmed P. falciparum parasitaemia were definitely enrolled and reviewed weekly by the CHWs during 42 days. Primary outcome measure was PCR corrected parasitological cure rate by day 42, as estimated by Kaplan-Meier survival analysis. This trial is registered with ClinicalTrials.gov, number NCT00454961. RESULTS: A total of 244 febrile children were enrolled between March-August 2007. Two patients were lost to follow up on day 14, and one patient withdrew consent on day 21. Some 141/241 (58.5%) patients had recurrent infection during follow-up, of whom 14 had recrudescence. The PCR corrected cure rate by day 42 was 93.0% (95% CI 88.3%-95.9%). The median lumefantrine concentration was statistically significantly lower in patients with recrudescence (97 ng/mL [IQR 0-234]; n = 10) compared with reinfections (205 ng/mL [114-390]; n = 92), or no parasite reappearance (217 [121-374] ng/mL; n = 70; p ≤ 0.046). CONCLUSIONS: Provision of AL by CHWs for unsupervised malaria treatment at home was highly effective, which provides evidence base for scaling-up implementation of HMM with AL in Tanzania.

Different Plasmodium falciparum clearance times in two Malian villages following artesunate monotherapy.

BACKGROUND: Artemisinin resistance described as increased parasite clearance time (PCT) is rare in Africa. More sensitive methods such as qPCR might better characterize the clearance phenotype in sub-Saharan Africa. METHODS: PCT is explored in Mali using light microscopy and qPCR after artesunate for uncomplicated malaria. In two villages, patients were followed for 28 days. Blood smears and spots were collected respectively for microscopy and qPCR. Parasitemia slope half-life was calculated after microscopy. Patient residual parasitemia were measured by qPCR. RESULTS: Uncorrected adequate clinical and parasitological responses (ACPR) observed in Faladje and Bougoula-Hameau were 78% and 92%, respectively (p=0.01). This reached 100% for both after molecular correction. Proportions of 24H microscopy positive patients in Faladje and Bougoula-Hameau were 97.2% and 72%, respectively (p<0.0001). Slope half-life was 2.8h in Faladje vs 2H in Bougoula-Hameau (p<0.001) and Proportions of 72H patients with residual parasitemia were 68.5% and 40% in Faladje and Bougoula-Hameau, respectively (p=0.003). The mean residual parasitemia was 2.9 in Faladje vs. 0.008 in Bougoula-Hameau (p=0.002). Although artesunate is efficacious in Mali, the longer parasite clearance time with submicroscopic parasitemia observed may represent early signs of developing P. falciparum resistance to artemisinins.

Carriers, channels and chloroquine efficacy in Guinea-Bissau.

Recent studies suggest that chloroquine resistance is mediated by an energy-dependent saturable chloroquine efflux carrier. An alternative explanation is that resistance is mediated by a channel. In Guinea-Bissau high doses of chloroquine are effective, well-tolerated and commonly used. This suggests that chloroquine resistance can be overcome by higher doses. Research on the mechanism of chloroquine resistance is of utmost importance and should include the effect of higher doses.

Short report: polymorphisms in the pfcrt and pfmdr1 genes of Plasmodium falciparum and in vitro susceptibility to amodiaquine and desethylamodiaquine.

The potential role of polymorphisms in the pfcrt and pfmdr1 genes and in vitro susceptibility to amodiaquine and desethylamodiaquine were explored in 15 chloroquine-resistant Colombian Plasmodium falciparum isolates. Single nucleotide polymorphisms in the pfcrt gene, including a newly reported mutation (S334N), were seen in isolates with decreased susceptibility to amodiaquine and desethylamodiaquine. The lowest susceptibility found to amodiaquine was observed in an isolate carrying a pfcrt and pfmdr1 Dd2-like haplotype, whereas a pfcrt haplotype related to the 7G8 Brazilian strain was found in a Colombian isolate with the lowest susceptibility to desethylamodiaquine. This exploratory study suggests that polymorphisms in the pfcrt and pfmdr1 genes play a role in amodiaquine and desethylamodiaquine resistance and warrants further study.

Amodiaquine resistant Plasmodium falciparum malaria in vivo is associated with selection of pfcrt 76T and pfmdr1 86Y.

The choice of partner drug is critical for artemisinine-based combination therapy (ACT) to remain effective and amodiaquine (AQ) is one important candidate to evaluate. We treated 81 children <5 years with uncomplicated Plasmodium falciparum malaria with AQ alone and related the treatment outcome to the possible selection of pfcrt 76T, 152T, 163S, 326S, pfmdr1 86Y and pfmrp 191H, 437S in recurrent infections (recrudescenses and re-infections) and to the blood concentration of desethylamodiaquine (DEAQ). During 21 days follow-up 28 children had a recurrent infection (9 recrudescenses, 13 re-infections and 6 mixed). Neither genotyping of the polymorphisms before treatment nor DEAQ blood concentrations could predict treatment outcome. pfcrt 76T was however significantly selected for in recurrent infections (p=0.020). pfmdr1 86Y was also selected for, but only in recrudescent infections (p=0.048). The study showed high prevalence of AQ resistant parasites in vivo, which appeared to be associated to pfcrt 76T and pfmdr1 86Y.

In vitro recrudescence of Plasmodium falciparum parasites suppressed to dormant state by atovaquone alone and in combination with proguanil.

We studied the viability of Plasmodium falciparum parasites reappearing in long-term cultures after repetitive exposure to atovaquone and proguanil. Parasites (F32 and FCR3) exposed to 100-5000 nM atovaquone for 96 hours were reduced to <5% of initial parasitaemia but recrudesced after 9-15 days. Also, parasites exposed to 1000 nM atovaquone for 48, 72, 96 and 144 hours recrudesced after 9, 14, 21 and 23 days respectively. Immediately after removal of the drug, only 1-3 schizonts per 10000 red blood cells were found consistently, apparently unable to produce trophozoites and thus, possibly, adopting a "dormant state". Parasites (F32 and FCR3) exposed to 500 nM atovaquone for 72 hours reappeared after 14 days. These recrudescing parasites were then re-exposed and suppressed by atovaquone in three consecutive follow-up experiments. They reappeared after 12, 11 and 9 days respectively. No known point mutations in cytochrome b gene (cytb), associated with atovaquone resistance, were detected in any recrudescing parasites. Finally, parasites (F32) exposed to various concentrations of atovaquone and proguanil in combination for 72 hours reappeared after 9-17 days. The baseline susceptibilities of the parasites to individual drugs were similar before and after recrudescence in all experiments.

In vivo selection of Plasmodium falciparum parasites carrying the chloroquine-susceptible pfcrt K76 allele after treatment with artemether-lumefantrine in Africa.

BACKGROUND: Artemether-lumefantrine (AL) is a major and highly effective artemisinin-based combination therapy that is becoming increasingly important as a new first-line therapy against Plasmodium falciparum malaria. However, recrudescences occurring after AL treatment have been reported. Identification of drug-specific parasite determinants that contribute to treatment failures will provide important tools for the detection and surveillance of AL resistance. METHODS: The findings from a 42-day follow-up efficacy trial in Tanzania that compared AL with sulfadoxine-pyrimethamine (SP) were analyzed to identify candidate markers for lumefantrine tolerance/resistance in the chloroquine resistance transporter gene (pfcrt) and multidrug resistance gene 1 (pfmdr1). The findings were corroborated in vitro with genetically modified isogenic P. falciparum parasite lines. RESULTS: Treatment with AL selected for the chloroquine-susceptible pfcrt K76 allele (P < .0001) and, to a lesser extent, the pfmdr1 N86 (P = .048) allele among recurrent infections. These genotypes were not selected during SP treatment. No pfmdr1 gene amplifications were observed. Isogenic pfcrt-modified parasite lines demonstrated a 2-fold increase in susceptibility to lumefantrine, which was directly attributable to the K76T mutation. CONCLUSIONS: Our findings suggest that the pfcrt K76T mutation is a drug-specific contributor to enhanced P. falciparum susceptibility to lumefantrine in vivo and in vitro, and they highlight the benefit of using AL in areas affected by chloroquine-resistant P. falciparum malaria.

The role of pfmdr1 in Plasmodium falciparum tolerance to artemether-lumefantrine in Africa.

OBJECTIVE: Artemether-lumefantrine (AL), presently the most favoured combination therapy against uncomplicated Plasmodium falciparum malaria in Africa, has recently shown to select for the pfmdr1 86N allele. The objective of this study was to search for the selection of other mutations potentially involved in artemether-lumefantrine tolerance and/or resistance, i.e. pfmdr1 gene amplification, pfmdr1 Y184F, S1034C, N1042D, D1246Y, pfcrt S163R and PfATP6 S769N. METHODS: The above mentioned SNPs were analysed by PCR-restriction fragment length polymorphism and pfmdr1 gene amplification by real-time PCR based protocols in parasites from 200 children treated with AL for uncomplicated P. falciparum malaria in Zanzibar. RESULTS: A statistically significant selection of pfmdr1 184F mostly in combination with 86N was seen in reinfections after treatment. No pfmdr1 gene amplification was found. CONCLUSION: The results suggest that different pfmdr1 alleles are involved in the development of tolerance/resistance to lumefantrine.

In vivo selection of Plasmodium falciparum pfmdr1 86N coding alleles by artemether-lumefantrine (Coartem).

Artemisinin derivative-based combination therapy is expected to suppress the development of Plasmodium falciparum drug resistance in Africa. We have performed an artemether-lumefantrine (Coartem; Novartis) follow-up clinical trial in Zanzibar, in which pfcrt K76T and pfmdr1 N86Y frequencies were determined before drug administration and in all recurrent parasites during a follow-up period of 42 days. A significant increase in pfmdr1 86N was observed after exposure to the drug. This points to 86N as a potential marker of lumefantrine resistance in vivo, while suggesting that Coartem is not robust enough to avoid selection of resistance-associated mutations in some malarial settings.