Ketoconazole increases plasma concentrations of antimalarial mefloquine in healthy human volunteers

Genetic variation present in the CYP3A4 gene in Ni-Vanuatu and Kenyan populations in malaria endemicity

Cytochrome P450 3A4 (CYP3A4) enzyme is involved in the metabolism of about 30 % of clinically used drugs, including the antimalarials artemether and lumefantrine. CYP3A4 polymorphisms yield enzymatic variants that contribute to inter-individual variation in drug metabolism. Here, we examined CYP3A4 polymorphisms in populations from malaria-endemic islands in Lake Victoria, Kenya, and Vanuatu, to expand on the limited data sets. We used archived dried blood spots collected from 142 Kenyan and 263 ni-Vanuatu adults during cross-sectional malaria surveys in 2013 and 2005-13, respectively, to detect CYP3A4 variation by polymerase chain reaction (PCR) and sequencing. In Kenya, we identified 14 CYP3A4 single nucleotide polymorphisms (SNPs), including the 4713G (CYP3A4∗1B; allele frequency 83.9 %) and 19382A (CYP3A4∗15; 0.7 %) variants that were previously linked to altered metabolism of antimalarials. In Vanuatu, we detected 15 SNPs, including the 4713A (CYP3A4∗1A; 88.6 %) and 25183C (CYP3A4∗18; 0.6 %) variants. Additionally, we detected a rare and novel SNP C4614T (0.8 %) in the 5' untranslated region. A higher proportion of CYP3A4 genetic variance was found among ni-Vanuatu populations (16 %) than among Lake Victoria Kenyan populations (8 %). Our work augments the scarce data sets and contributes to improved precision medicine approaches, particularly to anti-malarial chemotherapy, in East African and Pacific Islander populations.

Triazole antifungal drug interactions-practical considerations for excellent prescribing

Systemic antifungal therapy is critical for reducing the mortality from many invasive and chronic fungal infections. Triazole antifungals are the most frequently prescribed antifungals but require attention to dosing and drug interactions. Nearly 600 severe drug-drug interactions and over 1100 moderate interactions requiring dose modifications are described or anticipated with systemic antifungal agents (see https://www.aspergillus.org.uk/antifungal-drug-interactions/). In this article, we address the common and less common, but serious, drug interactions observed in clinical practice with triazole antifungals, including a group of drugs that cannot be prescribed with all or most triazole antifungals (ivabradine, ranolazine, eplerenone, fentanyl, apomorphine, quetiapine, bedaquiline, rifampicin, rifabutin, sirolimus, phenytoin and carbamazepine). We highlight interactions with drugs used in children and new agents introduced for the treatment of haematological malignancies or graft versus host disease (midostaurin, ibrutinib, ruxolitinib and venetoclax). We also summarize the multiple interactions between oral and inhaled corticosteroids and triazole antifungals, and the strategies needed to optimize the therapeutic benefits of triazole antifungal therapy while minimizing potential harm to patients.

Mefloquine loaded niosomes as a promising approach for the treatment of acute and chronic toxoplasmosis

Toxoplasmosis is a disease with a worldwide distribution and significant morbidity and mortality. In search of effective treatment, mefloquine (MQ) was repurposed and loaded with niosomes to treat acute and chronic phases of toxoplasmosis in experimental mice. Mice were orally inoculated with 20 cysts of Toxoplasma gondii (ME 49 strain) for the acute model of infection and 10 cysts for the chronic model of infection. Infected mice were dosed with MQ solution or MQ-niosomes at 50 mg/kg/day, starting from the second day post-infection (PI) (acute model) or the fifth week PI (chronic model), and this was continued for six consecutive days. The effects of MQ solution and MQ-niosomes were compared with a pyrimethamine/sulfadiazine (PYR/SDZ) dosing combination as mortality rates, brain cyst number, inflammatory score, and immunohistochemical studies that included an estimation of apoptotic cells (TUNEL assays). In the acute infection model, MQ solution and MQ-niosomes significantly reduced the mortality rate from 45% to 25 and 10%, respectively, compared with infected untreated controls, and decreased the number of brain cysts by 51.5% and 66.9%, respectively. In the chronic infection model, cyst reduction reached 80.9% and 12.3% for MQ solution and MQ-niosomes treatments, respectively. MQ-niosomes significantly decreased inflammation induced by acute or chronic T. gondii infection. Additionally, immunohistochemical analysis revealed that MQ solution and MQ-niosomes significantly increased the number of TUNEL-positive cells in brain tissue, indicative of induction of apoptosis. Collectively, these results indicate that MQ-niosomes may provide a useful delivery strategy to treat both acute and chronic toxoplasmosis.

Itraconazole, a cytochrome P450 inhibitor, enhanced the efficacy of praziquantel against Schistosoma mansoni infection and alleviated liver injury in mice

Treatment of schistosomiasis is heavily reliant on the single antischistosomal drug praziquantel (PZQ). The use of synergistic drug-drug interactions is one possible solution, which could be used to mitigate PZQ's poor and variable bioavailability. Itraconazole (ITZ), a triazole antifungal agent, is a potent CYP3A inhibitor that can cause significant drug-drug interactions when used with CYP3A substrates. This study investigates the effect of ITZ as adjuvant therapy with PZQ on worm load, egg deposition and maturation, and the consequent histopathology and biochemical abnormalities in the liver during the immature and mature stages of Schistosoma mansoni (S. mansoni) infection. S. mansoni-infected mice were divided into five groups of eight-ten mice each: (I) infected untreated, (II) infected and treated with PZQ 3 weeks PI, (III) infected and treated with both ITZ and PZQ 3 weeks PI, (IV) infected and treated with PZQ 7 weeks PI, and (V) infected and treated with both ITZ and PZQ 7 weeks PI. All mice were killed by rapid decapitation 9 weeks PI. Data revealed that ITZ in combination with PZQ at both immature and mature stages improved the parasitological criteria of cure, and greatly reduced inflammation, granuloma and fibrotic tissue formation, and apoptosis versus PZQ alone. Furthermore, it showed the greatest impact on improving liver injury and oxidative stress markers. Notably, the effect was considerably stronger at the mature stage of S. mansoni infection. These findings support the notion that ITZ increased PZQ's antischistosomal activity by inhibiting CYP450 expression, potentially reducing PZQ metabolism and increasing systemic exposure.

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.

Drug interactions with antimalarial medications in older travelers: a clinical guide

Increasingly older adults are traveling to international destinations with malaria as a present risk. Surveillance systems indicate that older adults are more likely to suffer severe complications from malaria. The role of health care providers in selecting an appropriate medication for chemoprophylaxis or treatment of malaria in adults becomes more difficult as older adults undergo physiologic changes that alter the pharmacokinetic and pharmacodynamic nature of medications potentially causing increased drug interactions, adverse events and altered drug action. A comprehensive literature search from 1970 to present, with a focus on the past 10 years, was conducted on drug interactions, pharmacokinetic and pharmacodynamic effects on antimalarials in adults. It was determined that due to pharmacodynamic and pharmacokinetic changes in older adults, especially renal and cardiovascular, special attention should be given to this population of travelers in order to minimize the likelihood of adverse events or altered drug efficacy. Antimalarial drug-disease interactions in older adults can occur more often due to QT prolongation, exacerbation of hypoglycemia, decreased renal elimination and decreased hepatic metabolism. Older antimalarials have well-documented drug-drug interactions. Tafenoquine, a new antimalarial, requires glucose-6-phosphate dehydrogenase screening like primaquine and monitoring of new potential drug interaction with MATE1 and OCT2 substrates. While drug-drug interactions in older travelers may occur more often as a result of polypharmacy, data did not indicate adverse reactions or decreased drug efficacy is greater compared with younger adults. Overall, with the exception of recently approved tafenoquine, much is known about antimalarial drug and disease interactions, but new drugs are always being approved, requiring travel health providers to understand the pharmacokinetics and pharmacodynamics of antimalarial drugs to predict the impact on safety and efficacy in travelers. This guide provides travel health providers with valuable insights on potential outcomes associated with drug interactions in adults and recommended monitoring or drug regimen modification.

Development of a physiologically based pharmacokinetic model for mefloquine and its application alongside a clinical effectiveness model to select an optimal dose for prevention of malaria in young Caucasian children

AIMS

To predict the optimal chemoprophylactic dose of mefloquine in infants of 5-10 kg using physiologically based pharmacokinetic (PBPK) and clinical effectiveness models.

METHODS

The PBPK model was developed in Simcyp version 14.1 and verified against clinical pharmacokinetic data in adults; the final model, accounting for developmental physiology and enzyme ontogeny was then applied in the paediatric population. The clinical effectiveness model utilized real-world chemoprophylaxis data with stratification of output by age and including infant data from the UK population.

RESULTS

PBPK simulations in infant populations depend on the assumed fraction of mefloquine metabolized by CYP3A4 (0.47, 0.95) and on the associated CYP3A4 ontogeny (Salem, Upreti). However, all scenarios suggest that a dose of 62.5 mg weekly achieves or exceeds the exposure in adults following a 250 mg weekly dose and results in a minimum plasma concentration of 620 ng ml^-1 , which is considered necessary to achieve 95% prophylactic efficacy. The clinical effectiveness model predicts a 96% protective efficacy from mefloquine chemoprophylaxis at 62.5 mg weekly.

CONCLUSIONS

The PBPK and clinical effectiveness models are mutually supportive and suggest a prophylactic dose of 62.5 mg weekly in the Caucasian 5-10 kg infant population travelling to endemic countries. This dual approach offers a novel route to dose selection in a vulnerable population, where clinical trials would be difficult to conduct.

Alteration of the Disposition of Quinine in Healthy Volunteers After Concurrent Ciprofloxacin Administration

This study evaluated the effects of concurrent ciprofloxacin administration on the disposition of quinine in healthy volunteers. Quinine (600-mg single dose) was administered either alone or with the 11th dose of ciprofloxacin (500 mg every 12 hours for 7 days) to 15 healthy volunteers in a crossover fashion. Blood samples collected at predetermined time intervals were analyzed for quinine and its major metabolite, 3-hydroxquinine, using a validated high-performance liquid chromatographic method. Administration of quinine plus ciprofloxacin resulted in significant increases (P < 0.05) in the total area under the concentration-time curve, maximum plasma concentration (Cmax), and terminal elimination half-life (T1/2b) of quinine compared with values with quinine dosing alone (AUC: 27.93 ± 8.04 vs. 41.62 ± 13.98 h·mg/L; Cmax: 1.37 ± 0.24 vs. 1.64 ± 0.38 mg/L; T1/2b: 16.28 ± 2.66 vs. 21.43 ± 3.22 hours), whereas the oral plasma clearance markedly decreased (23.17 ± 6.49 vs. 16.00 ± 5.27 L/h). In the presence of ciprofloxacin, there was a pronounced decrease in the ratio of AUC (metabolite)/AUC (unchanged drug) and highly significant decreases in Cmax and AUC of the metabolite (P < 0.05). Ciprofloxacin may increase the adverse effects of concomitantly administered quinine, which can have serious consequences on the patient. Thus, a downward dosage adjustment of quinine seems to be necessary when concurrently administered with ciprofloxacin.

Pharmacokinetics of mefloquine and its effect on sulfamethoxazole and trimethoprim steady-state blood levels in intermittent preventive treatment (IPTp) of pregnant HIV-infected women in Kenya

Background

Intermittent preventive treatment in pregnancy with sulfadoxine/pyrimethamine is contra-indicated in HIV-positive pregnant women receiving sulfamethoxazole/trimethoprim prophylaxis. Since mefloquine is being considered as a replacement for sulfadoxine/pyrimethamine in this vulnerable population, an investigation on the pharmacokinetic interactions of mefloquine, sulfamethoxazole and trimethoprim in pregnant, HIV-infected women was performed.

Methods

A double-blinded, placebo-controlled study was conducted with 124 HIV-infected, pregnant women on a standard regimen of sulfamethoxazole/trimethoprim prophylaxis. Seventy-two subjects received three doses of mefloquine (15 mg/kg) at monthly intervals. Dried blood spots were collected from both placebo and mefloquine arms four to 672 h post-administration and on day 7 following a second monthly dose of mefloquine. A novel high-performance liquid chromatographic method was developed to simultaneously measure mefloquine, sulfamethoxazole and trimethoprim from each blood spot. Non-compartmental methods using a naïve-pooled data approach were used to determine mefloquine pharmacokinetic parameters.

Results

Sulfamethoxazole/trimethoprim prophylaxis did not noticeably influence mefloquine pharmacokinetics relative to reported values. The mefloquine half-life, observed clearance (CL/f), and area-under-the-curve (AUC_0→∞) were 12.0 days, 0.035 l/h/kg and 431 µg-h/ml, respectively. Although trimethoprim steady-state levels were not significantly different between arms, sulfamethoxazole levels showed a significant 53 % decrease after mefloquine administration relative to the placebo group and returning to pre-dose levels at 28 days.

Conclusions

Although a transient decrease in sulfamethoxazole levels was observed, there was no change in hospital admissions due to secondary bacterial infections, implying that mefloquine may have provided antimicrobial protection.

Pharmacokinetic interactions between artesunate-mefloquine and ritonavir-boosted lopinavir in healthy Thai adults

Background

Concomitant use of anti-malarial and antiretroviral drugs is increasingly frequent in malaria and HIV endemic regions. The aim of the study was to investigate the pharmacokinetic interaction between the anti-malarial drugs, artesunate-mefloquine and the antiretroviral drug, lopinavir boosted with ritonavir (LPV/r).

Methods

The study was an open-label, three-way, sequential, cross-over, pharmacokinetic study in healthy Thai adults. Subjects received the following treatments: Period 1: standard 3-day artesunate-mefloquine combination; Period 2 (2 months wash-out): oral LPV/r 400 mg/100 mg twice a day for 14 days; and, Period 3: artesunate-mefloquine and LPV/r twice a day for 3 days. Sixteen subjects (eight females) were enrolled and pharmacokinetic parameters were determined by non-compartmental analysis.

Results

In the presence of LPV/r, artesunate C_max and systemic exposure were significantly increased by 45–80 %, while the metabolic ratio of dihydroartemisinin to artesunate was significantly reduced by 72 %. In addition, mefloquine C_max and systemic exposure were significantly reduced by 19–37 %. In the presence of artesunate-mefloquine, lopinavir C_max was significantly reduced by 22 % but without significant change in systemic drug exposure. The 90 % CI of the geometric mean ratio (GMR) of AUC_0−∞ and C_max were outside the acceptable bioequivalent range for each drug. Drug treatments were generally well tolerated with no serious adverse events. Vertigo, nausea and vomiting were the most common adverse events reported.

Conclusion

The reduction in systemic exposure of all investigated drugs raises concerns of an increased risk of treatment failure rate in co-infected patients and should be further investigated.

Arteether resistance reversal by ketoconazole/fluconazole in rodent malaria parasite Plasmodium vinckei

Artemisinin and its derivative arteether (ART) are fast acting antimalarial drugs against chloroquine-resistant. There are several partner drugs that are identified as a potential drug for artemisinin combination therapy (ACT) to develop as the antimalarial drug. Limited studies have been carried out in ART drug combination that may have more promising as ACT for resistant Plasmodium parasite. Here, we are the first to show the ART drug resistance reversal in Plasmodium vinckei by using antifungal azole compounds ketoconazole (KTZ) and fluconazole (FCZ). Our previous study has shown that higher antioxidant enzyme, glutathione, and less hemozoin may be correlated with ART resistance in P. vinckei (PvAR). We further hypothesized that glutathione and heme catabolism may be interfered by KTZ and FCZ, resulting in an increased efficacy of ART in PvAR parasite. The results of present study demonstrate synergetic effect of KTZ and FCZ against PvAR parasite, since none of the mice developed infection up to day 10 after combination with ART. These results further showed that ED90 of ART was reduced from 17.23 to 2.19 and 2.56 mg/kg when used in combination with KTZ and FCZ, respectively. Resultant, activity enhancement index (AEI) of ART is significantly increased to 8.60 and 6.73 with partner agents. These studies propose the possibility of ART drug combination that may be helpful in prolonging the life of drug and a promising lead to reduce the chance of resistance development of artemisinin and its derivative.

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.

Interspecies allometric scaling of antimalarial drugs and potential application to pediatric dosing

Pharmacopeial recommendations for administration of antimalarial drugs are the same weight-based (mg/kg of body weight) doses for children and adults. However, linear calculations are known to underestimate pediatric doses; therefore, interspecies allometric scaling data may have a role in predicting doses in children. We investigated the allometric scaling relationships of antimalarial drugs using data from pharmacokinetic studies in mammalian species. Simple allometry (Y = a × W(b)) was utilized and compared to maximum life span potential (MLP) correction. All drugs showed a strong correlation with clearance (CL) in healthy controls. Insufficient data from malaria-infected species other than humans were available for allometric scaling. The allometric exponents (b) for CL of artesunate, dihydroartemisinin (from intravenous artesunate), artemether, artemisinin, clindamycin, piperaquine, mefloquine, and quinine were 0.71, 0.85, 0.66, 0.83, 0.62, 0.96, 0.52, and 0.40, respectively. Clearance was significantly lower in malaria infection than in healthy (adult) humans for quinine (0.07 versus 0.17 liter/h/kg; P = 0.0002) and dihydroartemisinin (0.81 versus 1.11 liters/h/kg; P = 0.04; power = 0.6). Interpolation of simple allometry provided better estimates of CL for children than MLP correction, which generally underestimated CL values. Pediatric dose calculations based on simple allometric exponents were 10 to 70% higher than pharmacopeial (mg/kg) recommendations. Interpolation of interspecies allometric scaling could provide better estimates than linear scaling of adult to pediatric doses of antimalarial drugs; however, the use of a fixed exponent for CL was not supported in the present study. The variability in allometric exponents for antimalarial drugs also has implications for scaling of fixed-dose combinations.

Population pharmacokinetics of mefloquine, piperaquine and artemether-lumefantrine in Cambodian and Tanzanian malaria patients

Background

Inter-individual variability in plasma concentration-time profiles might contribute to differences in anti-malarial treatment response. This study investigated the pharmacokinetics of three different forms of artemisinin combination therapy (ACT) in Tanzania and Cambodia to quantify and identify potential sources of variability.

Methods

Drug concentrations were measured in 143 patients in Tanzania (artemether, dihydroartemisinin, lumefantrine and desbutyl-lumefantrine), and in 63 (artesunate, dihydroartemisinin and mefloquine) and 60 (dihydroartemisinin and piperaquine) patients in Cambodia. Inter- and intra-individual variabilities in the pharmacokinetic parameters were assessed and the contribution of demographic and other covariates was quantified using a nonlinear mixed-effects modelling approach (NONMEM^®).

Results

A one-compartment model with first-order absorption from the gastrointestinal tract fitted the data for all drugs except piperaquine (two-compartment). Inter-individual variability in concentration exposure was about 40% and 12% for mefloquine. From all the covariates tested, only body weight (for all antimalarials) and concomitant treatment (for artemether only) showed a significant influence on these drugs’ pharmacokinetic profiles. Artesunate and dihydroartemisinin could not be studied in the Cambodian patients due to insufficient data-points. Modeled lumefantrine kinetics showed that the target day 7 concentrations may not be achieved in a substantial proportion of patients.

Conclusion

The marked variability in the disposition of different forms of ACT remained largely unexplained by the available covariates. Dosing on body weight appears justified. The concomitance of unregulated drug use (residual levels found on admission) and sub-optimal exposure (variability) could generate low plasma levels that contribute to selecting for drug-resistant parasites.

Ketoconazole, a cytochrome P(450) inhibitor can potentiate the antimalarial action of α/β arteether against MDR Plasmodium yoelii nigeriensis

The emergence of multidrug resistant (MDR) strains of Plasmodium falciparum in South East Asia and other tropical countries, is posing serious challenge for the international efforts to eradicate malaria. New drug target/ACT/non-ACT combinations need to be discovered to control the spread of MDR malaria. The present communication deals with antimalarial potential of a new combination comprising of ketoconazole (KTZ) (an antifungal/inhibitor of CYP3A4) and artemisinin derivative α/β arteether (ART). In vitro interactions of these drugs against chloroquine sensitive/resistant P. falciparum (Pf3D7/K1) have shown an overall additive interaction with mean sum fractional inhibitory concentrations (∑FICs) of 1.1±0.33 against 3D7 and 1.51±0.42 against K1 strains. Sub-curative doses of KTZ (150mg/kg×7 days) combined with ART (6.25-12.5mg/kg×5 days) both administered orally have shown 100% curative action against MDR P. yoelii nigeriensis in Swiss mice. Besides lower dose of KTZ (75mg/kg) which is non-curative itself, in combination with 12.5mg/kg×5 days of ART treatment, was also 100% curative. Further studies on mechanism of action of KTZ (150mg/kg single dose) have shown that significant inhibitory action of the antifungal drug is through very high level of suppression of CYP (nearly 90%) compared to that of healthy mice liver. The companion drug therapy comprising of KTZ together with ART (25mg/kg×1 dose) also produced more than 50% inhibitory effect on the CYP enzyme level. Since the ART is known to be rapidly metabolized by the liver cytochrome P450 (CYP) 3A4 to Dihydroquinghasu, the combined therapy with KTZ (a strong CYP 3A4 inhibitor) may influence the pharmacokinetics of ART and consequently slow down the drug metabolism and prolong the plasma life of the active drug, which would contribute to enhanced antimalarial action of ART against MDR P. yoelii nigeriensis.

Effect of single nucleotide polymorphisms in cytochrome P450 isoenzyme and N-acetyltransferase 2 genes on the metabolism of artemisinin-based combination therapies in malaria patients from Cambodia and Tanzania

The pharmacogenetics of antimalarial agents are poorly known, although the application of pharmacogenetics might be critical in optimizing treatment. This population pharmacokinetic-pharmacogenetic study aimed at assessing the effects of single nucleotide polymorphisms (SNPs) in cytochrome P450 isoenzyme genes (CYP, namely, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5) and the N-acetyltransferase 2 gene (NAT2) on the pharmacokinetics of artemisinin-based combination therapies in 150 Tanzanian patients treated with artemether-lumefantrine, 64 Cambodian patients treated with artesunate-mefloquine, and 61 Cambodian patients treated with dihydroartemisinin-piperaquine. The frequency of SNPs varied with the enzyme and the population. Higher frequencies of mutant alleles were found in Cambodians than Tanzanians for CYP2C9*3, CYP2D6*10 (100C → T), CYP3A5*3, NAT2*6, and NAT2*7. In contrast, higher frequencies of mutant alleles were found in Tanzanians for CYP2D6*17 (1023C → T and 2850C → T), CYP3A4*1B, NAT2*5, and NAT2*14. For 8 SNPs, no significant differences in frequencies were observed. In the genetic-based population pharmacokinetic analyses, none of the SNPs improved model fit. This suggests that pharmacogenetic data need not be included in appropriate first-line treatments with the current artemisinin derivatives and quinolines for uncomplicated malaria in specific populations. However, it cannot be ruled out that our results represent isolated findings, and therefore more studies in different populations, ideally with the same artemisinin-based combination therapies, are needed to evaluate the influence of pharmacogenetic factors on the clearance of antimalarials.

Influence of P-glycoprotein modulation on plasma concentrations and pharmacokinetics of orally administered prednisolone in dogs

OBJECTIVE

To evaluate the impact of modulation of the membrane-bound efflux pump P-glycoprotein (P-gp) on plasma concentrations of orally administered prednisolone in dogs.

ANIMALS

7 healthy adult Beagles.

PROCEDURES

Each dog received 3 treatments (control [no treatment], rifampicin [100 mg/d, PO, for 21 days, as an inducer of P-gp], and ketoconazole [100 mg/d, PO, for 21 days, as an inhibitor of P-gp]). A single dose of prednisolone (1 mg/kg, PO) was administered on day 8 of each treatment period. There was a 7-day washout period between subsequent treatments. Plasma concentrations of prednisolone were determined by use of a validated liquid chromatography-tandem mass spectrometry method. Duodenum and colon biopsy specimens were obtained endoscopically from anesthetized dogs and assessed for P-gp protein labeling via immunohistochemical analysis and mRNA quantification via real-time PCR assay. Total fecal collection was performed for evaluation of effects of P-gp modulation on digestion of nutrients.

RESULTS

Rifampicin treatment upregulated duodenal P-gp in dogs and significantly reduced the area under the plasma concentration-time curve of prednisolone. Ketoconazole typically downregulated expression of duodenal P-gp, with a subsequent increase in the area under the plasma concentration-time curve of prednisolone. There was a noticeable interindividual difference in response. Digestion of nutrients was not affected.

CONCLUSIONS AND CLINICAL RELEVANCE

Modulation of P-gp expression influenced plasma concentrations of prednisolone after oral administration in dogs. Thus, treatment response to prednisolone may be influenced by coadministration of P-gp-modulating medications or feed ingredients.

Clarithromycin, a cytochrome P450 inhibitor, can reverse mefloquine resistance in Plasmodium yoelii nigeriensis- infected Swiss mice

During the last 2 decades there have been numerous reports of the emergence of mefloquine resistance in Southeast Asia and nearly 50% resistance is reported in Thailand. A World Health Organization report (2001) considers mefloquine as an important component of ACT (artesunate+mefloquine) which is the first line of treatment for the control of uncomplicated/multi-drug resistant (MDR) Plasmodium falciparum malaria. In view of the emergence of resistance towards this drug, it is proposed to develop new drug combinations to prolong the protective life of this drug. Prior studies have suggested that mefloquine resistance can be overcome by a variety of agents such as ketoconazole, cyproheptadine, penfluridol, Icajine and NP30. The present investigation reports that clarithromycin (CLTR), a new macrolide, being a potent inhibitor of Cyt. P450 3A4, can exert significant resistance reversal action against mefloquine resistance of plasmodia. Experiments were carried out to find out the curative dose of CLTR against multi-drug resistant P. yoelii nigeriensis. Mefloquine (MFQ) and clarithromycin (CLTR) combinations have been used for the treatment of this MDR parasite. Different dose combinations of these two drugs were given to the infected mice on day 0 (prophylactic) and day 1 with established infection (therapeutic) to see the combined effect of these combinations against the MDR malaria infection. With a dose of 32 mg/kg MFQ and 225 mg/kg CLTR, 100% cure was observed, while in single drug groups, treated with MFQ or CLTR, the cure was zero and 40% respectively. Therapeutically, MFQ and CLTR combinations 32+300 mg/kg doses cleared the established parasitaemia on day 10. Single treatment with MFQ or CLTR showed considerable suppression of parasitaemia on day 14 but neither was curative. Follow-up of therapeutically treated mice showed enhanced anti-malarial action as reflected by their 100% clearance of parasitaemia. The present study reveals that CLTR is a useful antibiotic to be used as companion drug with mefloquine in order to overcome mefloquine resistance in plasmodia.

Effect of cytochrome P450 3A4 inhibitor ketoconazole on risperidone pharmacokinetics in healthy volunteers

WHAT IS KNOWN AND OBJECTIVE

Risperidone is an atypical antipsychotic agent used for the treatment of schizophrenia. It is mainly metabolized by human cytochrome P450 CYP2D6 and partly by CYP3A4 to 9-hydroxyrisperidone. Ketoconazole is used as a CYP3A4 inhibitor probe for studying drug-drug interactions. We aim to investigate the effect of ketoconazole on the pharmacokinetics of risperidone in healthy male volunteers.

METHODS

An open-label, randomized, two-phase crossover design with a 2-week washout period was performed in 10 healthy male volunteers. The volunteers received a single oral dose of 2mg of risperidone alone or in combination with 200mg of ketoconazole, once daily for 3days. Serial blood samples were collected at specific periods after ingestion of risperidone for a period of 96h. Plasma concentrations of risperidone and 9-hydroxyrisperidone were determined using a validated HPLC-tandem mass spectrometry method.

RESULTS AND DISCUSSION

After pretreatment with ketoconazole, the clearance of risperidone decreased significantly by 34·81±5·10% and the T(1/2) of risperidone increased significantly by 28·03±40·60%. The AUC(0-96) and AUC(0-∞) of risperidone increased significantly by 66·61± 43·03% and 66·54±39·76%, respectively. The Vd/f of risperidone increased significantly by 39·79±53·59%. However, the C(max) and T(max) of risperidone were not significantly changed, indicating that ketoconazole had minimal effect on the absorption of risperidone. The C(max) , T(max) and T(1/2) of 9-hydroxyrisperidone did not decrease significantly. However, the Cl/f of 9-hydroxyrisperidone increased significantly by 135·07± 124·68%, and the Vd/f of 9-hydroxyrisperidone decreased significantly by 29·47±54·64%. These changes led to a corresponding significant decrease in the AUC(0-96) and AUC(0-∞) of 9-hydroxyrisperidone by 47·76±22·39% and 48·49± 20·03%, respectively. Ketoconazole significantly inhibited the metabolism of risperidone through the inhibition of hepatic CYP3A4. our results suggest that besides CYP2D6, CYP3A4 contributes significantly to the metabolism of risperidone.

WHAT IS NEW AND CONCLUSION

The pharmacokinetics of risperidone was affected by the concomitant administration of ketoconazole. If a CYP3A4 inhibitor is used concomitantly with risperidone, it is necessary for the clinicians to monitor their patients for signs of adverse drug reactions.

Enhancement of the drug susceptibility of a triclabendazole-resistant isolate of Fasciola hepatica using the metabolic inhibitor ketoconazole

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) is altered by using the metabolic inhibitor, ketoconazole (KTZ) to inhibit the cytochrome P450 (CYP 450) system within Fasciola hepatica. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP 450 enzyme system was inhibited by a 2 h pre-incubation in KTZ (40 microM). Flukes were then incubated for a further 22 h in NCTC medium containing either KTZ; KTZ + nicotinamide adenine dinucleotide phosphate (NADPH; 1 nM); KTZ + NADPH + TCBZ (15 microg/ml); or KTZ + NADPH + triclabendazole sulphoxide (TCBZ.SO;15 microg/ml). Morphological changes resulting from drug treatment and following metabolic inhibition were assessed using scanning electron microscopy. After treatment with either TCBZ or TCBZ.SO alone, there was greater disruption to the TCBZ-susceptible isolate than the TCBZ-resistant isolate. However, co-incubation with KTZ and TCBZ/TCBZ.SO led to more severe surface changes to the TCBZ-resistant isolate than with each drug on its own, with greater swelling and blebbing of the tegument and even the loss of the apical plasma membrane in places. With the Cullompton isolate, there was limited potentiation of drug action in combination with KTZ, and only with TCBZ.SO. The results support the concept of altered drug metabolism within TCBZ-resistant isolates and indicate that this process may play a role in the development of drug resistance.

A microarray-based system for the simultaneous analysis of single nucleotide polymorphisms in human genes involved in the metabolism of anti-malarial drugs

Background

In order to provide a cost-effective tool to analyse pharmacogenetic markers in malaria treatment, DNA microarray technology was compared with sequencing of polymerase chain reaction (PCR) fragments to detect single nucleotide polymorphisms (SNPs) in a larger number of samples.

Methods

The microarray was developed to affordably generate SNP data of genes encoding the human cytochrome P450 enzyme family (CYP) and N-acetyltransferase-2 (NAT2) involved in anti-malarial drug metabolisms and with known polymorphisms, i.e. CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, and NAT2.

Results

For some SNPs, i.e. CYP2A6*2, CYP2B6*5, CYP2C8*3, CYP2C9*3/*5, CYP2C19*3, CYP2D6*4 and NAT2*6/*7/*14, agreement between both techniques ranged from substantial to almost perfect (kappa index between 0.61 and 1.00), whilst for other SNPs a large variability from slight to substantial agreement (kappa index between 0.39 and 1.00) was found, e.g. CYP2D6*17 (2850C>T), CYP3A4*1B and CYP3A5*3.

Conclusion

The major limit of the microarray technology for this purpose was lack of robustness and with a large number of missing data or with incorrect specificity.

In vitro antimalarial interactions between mefloquine and cytochrome P450 inhibitors

The treatment and control of malaria is becoming increasingly difficult due to resistance of Plasmodium falciparum strains resistance to commonly used antimalarials. Combination therapy is currently the strategy for combating multi-drug resistant falciparum malaria, through exploiting phamacodynamic synergistic effect and delaying the emergence of drug resistance. The objective of the present study was to investigate antimalarial activity of inhibitors of cytochrome P450 (CYP) enzyme including their interactions with the antimalarial mefloquine against chloroquine-resistant (K1) and chloroquine-sensitive (3D7) P. falciparum clones in vitro. Results showed IC(50) (drug concentration which produces 50% schizont maturation inhibition) values [mean (range)] of mefloquine against K1 and 3D7 clones to be 8.6 (8.0-9.3) and 12.1 (10.5-13.8) nM, respectively. The corresponding values for the IC(50) of quinidine were 32.2 (31.9-32.5) and 28.7 (28.4-29.0) nM, and for ketoconazole were 3.9 (3.7-4.1) and 4.8 (4.6-5.1) microM, respectively. Analysis of isobologram revealed a trend of decreasing of fraction IC(50) (FIC), which indicates synergistics of the either quinidine or ketoconazole with mefloquine for both chloroquine-resistant and chloroquine-sensitive clones.

General framework for the prediction of oral drug interactions caused by CYP3A4 induction from in vivo information

BACKGROUND

Induction of cytochrome P450 (CYP) 3A4 potentially reduces the blood concentrations of substrate drugs to less than one-tenth, which results in ineffective pharmacotherapy. Although the prediction of drug-drug interactions (DDIs) that are mediated by induction of CYP3A4 has been performed mainly on the basis of in vitro information, such methods have met with limited success in terms of their accuracy and applicability. Therefore, a realistic method for the prediction of CYP3A4-mediated inductive DDIs is of major clinical importance.

OBJECTIVE

The objective of the present study was to construct a robust and accurate method for the prediction of CYP3A4-mediated inductive DDIs. Such a method was developed on the basis of the principle applied for prediction of inhibitory DDIs in a previous report. A unique character of this principle is that the extent of alterations in the area under the plasma concentration-time curve (AUC) is predicted on the basis of in vivo information from minimal clinical studies without using in vitro data.

METHODS

The analysis is based on 42 DDI studies in humans reported in 37 published articles over the period 1983-2007. Kinetic analysis revealed that the reduction in the AUC of a substrate of CYP3A4 produced by consecutive administration of an inducer of CYP3A4 could be approximated by the equation 1/(1 + CRCYP3A4 * ICCYP3A4), where CRCYP3A4 is the ratio of the apparent contribution of CYP3A4 to the oral clearance of a substrate and ICCYP3A4 is the apparent increase in clearance of a substrate produced by induction of CYP3A4. Using this equation, the ICCYP3A4 was calculated for seven inducers (bosentan, carbamazepine, efavirenz, phenytoin, pioglitazone, rifampicin [rifampin], and St John's wort [hypericum]) on the basis of the reduction in the AUC of a coadministered standard substrate of CYP3A4, such as simvastatin, in ten DDI studies. The CRCYP3A4 was calculated for 22 substrates on the basis of the previously reported method from inhibitory DDI studies using a potent CYP3A4 inhibitor such as itraconazole or ketoconazole.

RESULTS

The proposed method enabled the prediction of AUC reduction by CYP3A4 induction with any combination of these substrates and inducers (total 154 matches). To assess the accuracy of the prediction, the AUC reductions in 32 studies were analysed. We found that the magnitude of the deviation between the mean values of the observed and predicted AUCs of all substrate drugs was <20% of the AUCs of the respective substrate drugs before administration of the inducers. In addition, rifampicin was found to be the most potent inducer among the compounds analysed in the present study, with an ICCYP3A4 value of 7.7, followed by phenytoin and carbamazepine, with values of 4.7 and 3.0, respectively. The ICCYP3A4 values of the other CYP3A4 inducers analysed in the present study were approximately 1 or less, which suggests that the AUCs of coadministered drugs may not be reduced to less than approximately half, even if the drug is metabolized solely by CYP3A4.

CONCLUSION

By using the method reported in the present study, the susceptibilities of a substrate drug of CYP3A4 to inductive DDIs can be predicted quantitatively. It was indicated that coadministration of rifampicin, phenytoin and carbamazepine may reduce plasma AUCs to less than half for a broad range of CYP3A4 substrate drugs, with CRCYP3A4 values greater than 0.13, 0.21 and 0.33, respectively.

Ketoconazole increases the plasma levels of ivermectin in sheep

The parasiticide ivermectin and the antifungal drug ketoconazole are drugs that interact with P-glycoprotein. We have tested the ability of ketoconazole at a clinical dose to modify the pharmacokinetics of ivermectin in sheep. Lacaune lambs were administered with a single oral dose of ivermectin alone at 0.2 mg/kg (n=5) or in combination with a daily oral dose of ketoconazole (10 mg/kg) given for 3 days before and 2 days after the ivermectin (n=5). The plasma kinetics of ivermectin and its metabolite were followed over 15 days by HPLC analysis. Co-administration of ketoconazole induced higher plasma concentrations of ivermectin, leading to a substantial increase in the overall exposure of the animals to the drug. Ketoconazole did not reduce the production of the main ivermectin metabolite but it may rather act by inhibiting P-glycoprotein, and thus increasing the absorption of ivermectin. The use of a P-gp reversing agent such as ketoconazole could be useful tool to optimize antiparasitic therapy in the face of the worldwide development of anthelmintic resistance.

Clinical pharmacology of artemisinin-based combination therapies

Malaria, a disease transmitted by the female Anopheles mosquito, has had devastating effects on human populations for more than 4000 years. Treatment of the disease with single drugs, such as chloroquine, sulfadoxine/pyrimethamine or mefloquine, has led to the emergence of resistant Plasmodium falciparum parasites that lead to the most severe form of the illness. Artemisinin-based combination therapies are currently recommended by WHO for the treatment of uncomplicated P. falciparum malaria. Artemisinin and semisynthetic derivatives, including artesunate, artemether and dihydroartemisinin, are short-acting antimalarial agents that kill parasites more rapidly than conventional antimalarials, and are active against both the sexual and asexual stages of the parasite cycle. Artemisinin fever clearance time is shortened to 32 hours as compared with 2-3 days with older agents. To delay or prevent emergence of resistance, artemisinins are combined with one of several longer-acting drugs--amodiaquine, mefloquine, sulfadoxine/pyrimethamine or lumefantrine--which permit elimination of the residual malarial parasites. The clinical pharmacology of artemisinin-based combination therapies is highly complex. The short-acting artemisinins and their long-acting counterparts are metabolized and/or inhibit/induce cytochrome P450 enzymes, and may thus participate in drug-drug interactions with multiple drugs on the market. Alterations in antimalarial drug plasma concentrations may lead to either suboptimal efficacy or drug toxicity and may compromise treatment.

Mefloquine-induced eosinophilic pneumonia

Mefloquine has been widely used for prophylaxis and treatment of patients with chloroquine-resistant malaria; the drug is usually well tolerated. Rarely, adverse effects may be severe, including gastrointestinal disturbances, neuropsychiatric reactions, cardiovascular manifestations, skin lesions, musculoskeletal symptoms, and bone marrow toxicity. We describe a 67-year-old woman with fever, dyspnea on exertion, peripheral blood eosinophilia, and diffuse pulmonary infiltrates on chest radiography. She had taken mefloquine for malaria prophylaxis for an 8-week trip to South Africa. A thorough work-up led to the diagnosis of eosinophilic pneumonia caused by the mefloquine. Her condition improved after the drug was discontinued. To our knowledge, this is the first report of mefloquine-induced eosinophilic pneumonia. Clinicians should be aware of this rare, potential adverse effect of mefloquine.

Rifampin, a cytochrome P450 3A inducer, decreases plasma concentrations of antipsychotic risperidone in healthy volunteers

BACKGROUND

Although cytochrome P450 (CYP) 2D6 is often thought to be the only CYP responsible for the metabolism of risperidone, many reports suggest that CYP3A may be involved too. Rifampin, a potent CYP3A inducer, has been known to markedly decrease plasma concentrations of various drugs, which are concomitantly administered during treatment.

OBJECTIVE

To examine the effect of rifampin on plasma concentrations of a single oral dose of risperidone in healthy Thai male volunteers.

METHODS

In an open, randomized two-phase crossover study, separated by a 2-week period, 10 healthy Thai male volunteers received a single oral dose of 4-mg risperidone alone or with 600 mg rifampin, orally once daily for 5 days. Serial blood samples were collected at specific time points for a 48-h period. Risperidone was measured in plasma using high performance liquid chromatography with ultraviolet detection. Pharmacokinetic parameters were determined by using non-compartmental analysis.

RESULTS

Co-administration with 600-mg rifampin once daily for 5 days was associated with a significant decrease in risperidone area under the curve (AUC(0-48)) and maximal concentration (C(max)) by 72% (157 x 49 +/- 48 x 80 vs. 42 x 66 +/- 7 x 81 ng/L/h; P<0 x 01) and 50% (32 x 44 +/- 6 x 05 vs. 16 x 16 +/- 2 x 73 ng/mL; P<0 x 05), respectively when compared with risperidone alone.

CONCLUSIONS

Rifampin when used concurrently with risperidone significantly decreases the plasma concentration of risperidone. Our results provide in vivo evidence of the involvement of CYP3A in the metabolism of risperidone, in addition to CYP2D6. Thus, co-administration of risperidone with CYP3A inducer(s), including rifampin should be recognized or avoided in clinical practice.

New concepts in antimalarial use and mode of action in dermatology

Although chloroquine, hydroxychloroquine and quinacrine were originally developed for the treatment of malaria, these medications have been used to treat skin disease for over 50 years. Recent clinical data have confirmed the usefulness of these medications for the treatment of lupus erythematosus. Current research has further enhanced our understanding of the pharmacologic mechanisms of action of these drugs involving inhibition of endosomal toll-like receptor (TLR) signaling limiting B cell and dendritic cell activation. With this understanding, the use of these medications in dermatology is broadening. This article highlights the different antimalarials used within dermatology through their pharmacologic properties and mechanism of action, as well as indicating their clinical uses. In addition, contraindications, adverse effects, and possible drug interactions of antimalarials are reviewed.

Lack of impact of artesunate on the disposition kinetics of sulfadoxine/pyrimethamine when the two drugs are concomitantly administered

OBJECTIVE

To determine the effect of artesunate (AT) on the disposition kinetics of sulfadoxine/pyrimethamine (SP) in humans.

METHODS

In a randomized cross-over study, 16 healthy volunteers were given a dose of three SP tablets containing 500 mg of sulfadoxine (SDX) and 25 mg of pyrimethamine (PYR) (=SP group), while the second arm received three SP tablets + two AT tablets of 200 mg in total followed by 100 mg AT for the next 4 days (SP+AT group). Blood samples (100 microl) were collected by means of a finger prick and dried on filter paper. The blood spots were wrapped in polythene folders and stored at room temperature until analysis. The samples were assayed using high-performance liquid chromatographic methods.

RESULTS

The peak concentration C(max)), time required to attain peak concentration (T(max)), half-life (t ((1/2))) and area under the plasma concentration-time curve (AUC) were determined. The C(max) of SDX were 92.9 and 98.9 microg/ml for the SP and SP+AT arms, respectively; for PYR, these were 0.86 and 0.79 microg/ml, respectively. The T(max) of SDX were 10 and 8 h for the SP and SP+AT arms, respectively; for PYR, these were 4.0 and 3.0 h, respectively. The AUC(0-288) of SDX were 15,840 and 18,876 microg/ml h for the SP and SP+AT arms, respectively; for PYR, they were 124 and 112 microg/ml h, respectively. The t ((1/2)) of values for SDX were 165 and 180 h for the SP and SP+AT arms, respectively; for PYR, these were 158 and 177 h, respectively. There was no statistically significant difference between the C(max), T(max), AUC(0-288) and t ((1/2)) between the two arms (p > 0.05).

CONCLUSION

Taking AT concomitantly with SP does not have any impact in the disposition of SP.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.

Malaria: Diagnosis and treatment of falciparum malaria in travelers during and after travel

Plasmodium falciparum is responsible for most of the mortality in travelers related to imported malaria. Problems that occur during travel include the inaccuracy of a microscopic diagnosis of malaria, both false positives and false negatives, when ill travelers seek care while abroad. A false positive diagnosis can result in unnecessary parenteral injections that carry a risk of transmission of blood-borne pathogens, receipt of potentially dangerous drugs such as halofantrine, or receipt of fake, counterfeit drugs. Increased morbidity and mortality are associated with delays in diagnosis and initiation of prompt treatment for falciparum malaria. Availability of expert microscopy to confirm the diagnosis of malaria is limited. The presence of splenomegaly and thrombocytopenia are strongly associated with malaria and would justify empiric treatment. The availability of atovaquone-proguanil, a safe and well tolerated oral drug, should prompt a reconsideration of current treatment recommendations that discourage empiric treatment on clinical suspicion alone.