Sunil Parikh

Artemether-lumefantrine treatment of uncomplicated Plasmodium falciparum malaria: a systematic review and meta-analysis of day 7 lumefantrine concentrations and therapeutic response using individual patient data

Achieving adequate antimalarial drug exposure is essential for curing malaria. Day 7 blood or plasma lumefantrine concentrations provide a simple measure of drug exposure that correlates well with artemether-lumefantrine efficacy. However, the ‘therapeutic’ day 7 lumefantrine concentration threshold needs to be defined better, particularly for important patient and parasite sub-populations. The WorldWide Antimalarial Resistance Network (WWARN) conducted a large pooled analysis of individual pharmacokinetic-pharmacodynamic data from patients treated with artemether-lumefantrine for uncomplicated Plasmodium falciparum malaria, to define therapeutic day 7 lumefantrine concentrations and identify patient factors that substantially alter these concentrations. A systematic review of PubMed, Embase, Google Scholar, ClinicalTrials.gov and conference proceedings identified all relevant studies. Risk of bias in individual studies was evaluated based on study design, methodology and missing data. Of 31 studies identified through a systematic review, 26 studies were shared with WWARN and 21 studies with 2,787 patients were included. Recrudescence was associated with low day 7 lumefantrine concentrations (HR 1.59 (95 % CI 1.36 to 1.85) per halving of day 7 concentrations) and high baseline parasitemia (HR 1.87 (95 % CI 1.22 to 2.87) per 10-fold increase). Adjusted for mg/kg dose, day 7 concentrations were lowest in very young children (<3 years), among whom underweight-for-age children had 23 % (95 % CI −1 to 41 %) lower concentrations than adequately nourished children of the same age and 53 % (95 % CI 37 to 65 %) lower concentrations than adults. Day 7 lumefantrine concentrations were 44 % (95 % CI 38 to 49 %) lower following unsupervised treatment. The highest risk of recrudescence was observed in areas of emerging artemisinin resistance and very low transmission intensity. For all other populations studied, day 7 concentrations ≥200 ng/ml were associated with >98 % cure rates (if parasitemia <135,000/μL). Current artemether-lumefantrine dosing recommendations achieve day 7 lumefantrine concentrations ≥200 ng/ml and high cure rates in most uncomplicated malaria patients. Three groups are at increased risk of treatment failure: very young children (particularly those underweight-for-age); patients with high parasitemias; and patients in very low transmission intensity areas with emerging parasite resistance. In these groups, adherence and treatment response should be monitored closely. Higher, more frequent, or prolonged dosage regimens should now be evaluated in very young children, particularly if malnourished, and in patients with hyperparasitemia.

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 Km 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.

Antimalarial Activity of Human Immunodeficiency Virus Type 1 Protease Inhibitors

ABSTRACT Aspartic proteases play key roles in the biology of malaria parasites and human immunodeficiency virus type 1 (HIV-1). We tested the activity of seven HIV-1 protease inhibitors against cultured Plasmodium falciparum. All compounds inhibited the development of parasites at pharmacologically relevant concentrations. The most potent compound, lopinavir, was active against parasites (50% inhibitory concentration [IC50], 0.9 to 2.1 μM) at concentrations well below those achieved by ritonavir-boosted lopinavir therapy. Lopinavir also inhibited the P. falciparum aspartic protease plasmepsin II at a similar concentration (IC50, 2.7 μM). These findings suggest that use of HIV-1 protease inhibitors may offer clinically relevant antimalarial activity.

Lopinavir/ritonavir affects pharmacokinetic exposure of artemether/lumefantrine in HIV-uninfected healthy volunteers.

Objectives:Antimalarial combination therapy is used in persons with HIV infection in the absence of data on drug interactions. The objective of this study was to investigate the pharmacokinetics (PK) of antimalarial combination artemether/lumefantrine (AL) when administered with the protease inhibitor combination lopinavir/ritonavir (LPV/r) in HIV-uninfected healthy volunteers to determine if important drug interactions exist between these agents. Design:Open-label study in healthy HIV-seronegative adults. Methods:Participants received standard 6-dose treatment courses of AL 80/480 mg twice daily on days 1-4 and 28-31. LPV/r 400/100 mg twice daily was administered on days 16-41 after a 2-week washout period. Plasma concentrations of AL, dihydroartemisinin (DHA, artemether metabolite), lopinavir, and ritonavir were measured. Results:PK of lumefantrine was influenced by LPV/r resulting in 2- to 3-fold increases in area under the curve (AUC) (AUC0-264: 413 versus 931 h·μg·mL−1; AUC0-inf: 456 versus 1073 h·μg·mL−1). For artemether, trends toward Cmax and AUC decreases (Cmax 14.3 versus 11.2 ng/mL and 42.7-62.0 versus 25.9-40.5 h·ng·mL−1 for AUC) were noted during coadministration. For DHA, decreases in Cmax (58.8 versus 37.3 ng/mL) and AUC (190-198 versus 104-109 h·ng·mL−1) were observed during coadministration without changes in DHA:artemether AUC ratios. AL did not affect LPV/r PK. Conclusions:Coadministration of artmether/lumefantrine and LPV/r can be carried out for patients coinfected with malaria and HIV. Formal safety analysis of concomitant therapy should be addressed by future studies among individuals living in malaria-endemic regions.

Population Pharmacokinetics and Pharmacodynamics of Piperaquine in Children With Uncomplicated Falciparum Malaria

Dihydroartemisinin–piperaquine is being increasingly used as a first–line artemisinin combination treatment for malaria. The aim of this study was to describe the pharmacokinetic and pharmacodynamic properties of piperaquine in 236 children with uncomplicated falciparum malaria in Burkina Faso. They received a standard body weight–based oral 3–day fixed–dose dihydroartemisinin–piperaquine regimen. Capillary plasma concentration–time profiles were characterized using nonlinear mixed–effects modeling. The population pharmacokinetics of piperaquine were described accurately by a two–transit–compartment absorption model and a three–compartment distribution model. Body weight was a significant covariate affecting clearance and volume parameters. The individually predicted day 7 capillary plasma concentration of piperaquine was an important predictor (P < 0.0001) of recurrent malaria infection after treatment. Young children (2–5 years of age) received a significantly higher body weight–normalized dose than older children (P = 0.025) but had significantly lower day 7 piperaquine concentrations (P = 0.024) and total piperaquine exposures (P = 0.021), suggesting that an increased dose regimen for young children should be evaluated.

Pharmacokinetics of Artemether-Lumefantrine and Artesunate-Amodiaquine in Children in Kampala, Uganda

ABSTRACT The World Health Organization recommends the use of artemisinin-based combination therapies (ACTs) for the treatment of uncomplicated malaria. The two most widely adopted ACT regimens are artemether (AR)-lumefantrine (LR) (the combination is abbreviated AL) and amodiaquine (AQ)-artesunate (AS). Pharmacokinetic (PK) data informing the optimum dosing of these drug regimens is limited, especially in children. We evaluated PK parameters in Ugandan children aged 5 to 13 years with uncomplicated malaria treated with AL (n = 20) or AQ-AS (n = 21), with intensive venous sampling occurring at 0, 2, 4, 8, 24, and 120 h following administration of the last dose of 3-day regimens of AL (twice daily) or AQ-AS (once daily). AS achieved an estimated maximum concentration in plasma (Cmax) of 51 ng/ml and an area under the concentration-time curve from time zero to infinity (AUC0-∞) of 113 ng·h/ml; and its active metabolite, dihydroartemisinin (DHA), achieved a geometric mean Cmax of 473 ng/ml and an AUC0-∞ of 1,404 ng·h/ml. AR-DHA exhibited a Cmax of 34/119 ng/ml and an AUC0-∞ of 168/382 ng·h/ml, respectively. For LR, Cmax and AUC0-∞ were 6,757 ng/ml and 210 μg·h/ml, respectively. For AQ and its active metabolite, desethylamodiaquine (DEAQ), the Cmaxs were 5.2 ng/ml and 235 ng/ml, respectively, and the AUC0-∞s were 39.3 ng·h/ml and 148 μg·h/ml, respectively. Comparison of the findings of the present study to previously published data for adults suggests that the level of exposure to LR is lower in children than in adults and that the level of AQ-DEAQ exposure is similar in children and adults. For the artemisinin derivatives, differences between children and adults were variable and drug specific. The PK results generated for children must be considered to optimize the dosing strategies for these widely utilized ACT regimens.

Impact of the Method of G6PD Deficiency Assessment on Genetic Association Studies of Malaria Susceptibility

Background Clinical association studies have yielded varied results regarding the impact of glucose-6-phosphate dehydrogenase (G6PD) deficiency upon susceptibility to malaria. Analyses have been complicated by varied methods used to diagnose G6PD deficiency. Methodology/Prinicipal Findings We compared the association between uncomplicated malaria incidence and G6PD deficiency in a cohort of 601 Ugandan children using two different diagnostic methods, enzyme activity and G6PD genotype (G202A, the predominant East African allele). Although roughly the same percentage of males were identified as deficient using enzyme activity (12%) and genotype (14%), nearly 30% of males who were enzymatically deficient were wild-type at G202A. The number of deficient females was three-fold higher with assessment by genotype (21%) compared to enzyme activity (7%). Heterozygous females accounted for the majority (46/54) of children with a mutant genotype but normal enzyme activity. G6PD deficiency, as determined by G6PD enzyme activity, conferred a 52% (relative risk [RR] 0.48, 95% CI 0.31–0.75) reduced risk of uncomplicated malaria in females. In contrast, when G6PD deficiency was defined based on genotype, the protective association for females was no longer seen (RR = 0.99, 95% CI 0.70–1.39). Notably, restricting the analysis to those females who were both genotypically and enzymatically deficient, the association of deficiency and protection from uncomplicated malaria was again demonstrated in females, but not in males (RR = 0.57, 95% CI 0.37–0.88 for females). Conclusions/Significance This study underscores the impact that the method of identifying G6PD deficient individuals has upon association studies of G6PD deficiency and uncomplicated malaria. We found that G6PD-deficient females were significantly protected against uncomplicated malaria, but this protection was only seen when G6PD deficiency is described using enzyme activity. These observations may help to explain the discrepancy in some published association studies involving G6PD deficiency and uncomplicated malaria.

Biochemical and immunological mechanisms by which sickle cell trait protects against malaria

Sickle cell trait (HbAS) is the best-characterized genetic polymorphism known to protect against falciparum malaria. Although the protective effect of HbAS against malaria is well known, the mechanism(s) of protection remain unclear. A number of biochemical and immune-mediated mechanisms have been proposed, and it is likely that multiple complex mechanisms are responsible for the observed protection. Increased evidence for an immune component of protection as well as novel mechanisms, such as enhanced tolerance to disease mediated by HO-1 and reduced parasitic growth due to translocation of host micro-RNA into the parasite, have recently been described. A better understanding of relevant mechanisms will provide valuable insight into the host-parasite relationship, including the role of the host immune system in protection against malaria.

Molecular Evaluation of the Natural History of Asymptomatic Parasitemia in Ugandan Children

We assessed the prevalence and natural history of malarial parasitemia by use of microscopy and polymerase chain reaction (PCR) in 314 asymptomatic children in Kampala, Uganda. The prevalence of asymptomatic parasitemia was 17% by microscopy and 47% by PCR. Children with parasitemia identified by microscopy had a 5-fold higher rate of subsequent symptomatic malaria, compared with children without detectable parasitemia. Children with parasitemia identified by PCR alone had a similar rate of subsequent symptomatic malaria, compared with children without detectable parasitemia. Among microscopy-positive children who later developed symptomatic malaria, 47% had strains identical to those identified at enrollment, and the proportion of symptomatic episodes due to persistent strains remained high for 3 months. Among the PCR-positive/microscopy-negative children, only 17% had identical genotyping patterns at the onset of symptomatic malaria, with most of these episodes occurring during the first month. Asymptomatic parasitemia detected by microscopy, but not by PCR, strongly predicted subsequent clinical malaria, often due to persistent infection.

Concomitant efavirenz reduces pharmacokinetic exposure to the antimalarial drug artemether-lumefantrine in healthy volunteers.

Background:The antiretroviral drug efavirenz (EFV) and the antimalarial artemisinin-based combination therapy artemether–lumefantrine (AL) are commonly co-administered to treat HIV and malaria. EFV is a known inducer of cytochrome P450 3A4, which converts artemether to dihydroartemisinin (DHA) that is also active and metabolizes longer acting lumefantrine (LR). A study in healthy volunteers was completed to address the concern that EFV impacts AL pharmacokinetics (PKs). Methods:Adults received AL (80/480 mg twice daily) for 3-days before and during EFV co-administration (600 mg daily for 26 days) with intensive PK for artemether, DHA, and LR conducted after the last AL dose for each period. EFV PK was evaluated with and without AL. PK parameters were estimated using noncompartmental methods. Results:Twelve subjects completed the 2-period study. PK exposure for artemether, DHA, and LR [as estimated by the area under the concentration time curve (AUClast)] decreased or trended toward decrease with EFV, compared with when administered alone [−51% (P = 0.084), −46% (P = 0.005), and −21% (P = 0.102), respectively]. Day-7 LR levels, previously deemed predictive of treatment success, were 46% lower (P = 0.002) with EFV, but the LR half-life was unchanged. EFV PK exposure was minimally altered after AL co-administration [AUC0–24 hrs decreased by 17% (P = 0.034)]. Conclusions:Exposure to DHA, but not LR, was significantly lower during EFV-AL co-administration compared with that during administration of AL alone. These findings may have implications for the treatment efficacy of AL, particularly in children. However, the observed modest changes probably do not warrant dosage adjustment during co-administration of AL with EFV.