Comparison of lumefantrine, mefloquine, and piperaquine concentrations between capillary plasma and venous plasma samples in pregnant women with uncomplicated falciparum and vivax malaria

Capillary samples offer practical benefits compared with venous samples for the measurement of drug concentrations, but the relationship between the two measures varies between different drugs. We measured the concentrations of lumefantrine, mefloquine, piperaquine in 270 pairs of venous plasma and concurrent capillary plasma samples collected from 270 pregnant women with uncomplicated falciparum or vivax malaria. The median and range of venous plasma concentrations included in this study were 447.5 ng/mL (8.81-3,370) for lumefantrine (day 7, n = 76, median total dose received 96.0 mg/kg), 17.9 ng/mL (1.72-181) for desbutyl-lumefantrine, 1,885 ng/mL (762-4,830) for mefloquine (days 3-21, n = 90, median total dose 24.9 mg/kg), 641 ng/mL (79.9-1,950) for carboxy-mefloquine, and 51.8 ng/mL (3.57-851) for piperaquine (days 3-21, n = 89, median total dose 52.2 mg/kg). Although venous and capillary plasma concentrations showed a high correlation (Pearson's correlation coefficient: 0.90-0.99) for all antimalarials and their primary metabolites, they were not directly interchangeable. Using the concurrent capillary plasma concentrations and other variables, the proportions of venous plasma samples predicted within a ±10% precision range was 34% (26/76) for lumefantrine, 36% (32/89) for desbutyl-lumefantrine, 74% (67/90) for mefloquine, 82% (74/90) for carboxy-mefloquine, and 24% (21/89) for piperaquine. Venous plasma concentrations of mefloquine, but not lumefantrine and piperaquine, could be predicted by capillary plasma samples with an acceptable level of agreement. Capillary plasma samples can be utilized for pharmacokinetic and clinical studies, but caution surrounding cut-off values is required at the individual level.CLINICAL TRIALSThis study is registered with ClinicalTrials.gov as NCT01054248.

In vitro hepatic metabolism of mefloquine using microsomes from cats, dogs and the common brush-tailed possum (Trichosurus vulpecula)

Feline infectious peritonitis (FIP) is a systemic, fatal, viral-induced, immune-mediated disease of cats caused by feline infectious peritonitis virus (FIPV). Mefloquine, a human anti-malarial agent, has been shown to inhibit FIPV in vitro. As a first step to evaluate its efficacy and safety profile as a potential FIP treatment for cats, mefloquine underwent incubation in feline, canine and common brush-tailed possum microsomes and phase I metabolism cofactors to determine its rate of phase I depletion. Tramadol was used as a phase I positive control as it undergoes this reaction in both dogs and cats. Using the substrate depletion method, the in vitro intrinsic clearance (mean ± S.D.) of mefloquine by pooled feline and common brush-tailed possum microsomes was 4.5 ± 0.35 and 18.25 ± 3.18 μL/min/mg protein, respectively. However, phase I intrinsic clearance was too slow to determine with canine microsomes. Liquid chromatography-mass spectrometry (LC-MS) identified carboxymefloquine in samples generated by feline microsomes as well as negative controls, suggesting some mefloquine instability. Mefloquine also underwent incubation with feline, canine and common brush-tailed possum microsomes and phase II glucuronidative metabolism cofactors. O-desmethyltramadol (ODMT or M1) was used as a positive control as it undergoes a phase II glucuronidation reaction in these species. The rates of phase II mefloquine depletion by microsomes by all three species were too slow to estimate. Therefore mefloquine likely undergoes phase I hepatic metabolism catalysed by feline and common brush-tailed possum microsomes but not phase II glucuronidative metabolism in all three species and mefloquine is not likely to have delayed elimination in cats with clinically normal, hepatic function.

Population pharmacokinetics of mefloquine given as a 3-day artesunate-mefloquine in patients with acute uncomplicated Plasmodium falciparum malaria in a multidrug-resistant area along the Thai-Myanmar border

BACKGROUND

Low mefloquine exposure has been shown to contribute to treatment failure in patients with uncomplicated falciparum malaria following a 3-day artesunate-mefloquine combination. The present study aimed to develop a population pharmacokinetic model for mefloquine based on whole blood concentration-time profiles of this target population for further dose optimization.

METHODS

A total of 129 Burmese patients aged above 15 years who presented with typical symptoms of malaria and had a blood smear positive for Plasmodium falciparum were included in the study. All were treated with the standard 3-day combination regimen of artesunate and mefloquine consisting of mefloquine for 2 days and artesunate for 3 days. Blood samples were collected before and at different time points after drug administration from different sub-groups of patients. Mefloquine concentrations were quantified in whole blood using high-performance liquid chromatography. A non-linear mixed-effect modelling approach was applied for population pharmacokinetic analysis using the NONMEM v7.3 software. Covariates investigated (body weight, gender, admission parasitaemia, and molecular markers of mefloquine resistance) were investigated in a step-wise manner using the SCM functionality in Perl-Speaks-NONMEM.

RESULTS

Population pharmacokinetic analysis of mefloquine was performed in all patients with a total of 653 samples. Whole blood mefloquine concentration-time profiles were described by a two-compartment disposition model. Of the covariates investigated, none was found to have a significant impact on the pharmacokinetics of mefloquine. Significant differences in maximum concentration (Cmax) and elimination half-life (t1/2) were found in patients who had treatment failure (36 cases) compared to patients with successful treatment (107 cases).

CONCLUSION

The study successfully describes the pharmacokinetics of mefloquine following a 2-day treatment of mefloquine as a part of a 3-day artesunate-mefloquine in patients with uncomplicated falciparum malaria from Thailand. A model has been developed which adequately describes the pharmacokinetics of mefloquine. More extensive clinical studies including both adults and children are needed to fully characterize the pharmacokinetics of mefloquine.

Activity of mefloquine and mefloquine derivatives against Echinococcus multilocularis

The cestode E. multilocularis causes the disease alveolar echinococcosis (AE) in humans. The continuously proliferating metacestode (larval stage) of the parasite infects mostly the liver and exhibits tumor-like growth. Current chemotherapeutical treatment options rely on benzimidazoles, which are rarely curative and have to be applied daily and life-long. This can result in considerable hepatotoxicity and thus treatment discontinuation. Therefore, novel drugs against AE are urgently needed. The anti-malarial mefloquine was previously shown to be active against E. multilocularis metacestodes in vitro, and in mice infected by intraperitoneal inoculation of metacestodes when administered at 100 mg/kg by oral gavage twice a week for 12 weeks. In the present study, the same dosage regime was applied in mice infected via oral uptake of eggs representing the natural route of infection. After 12 weeks of treatment, the presence of parasite lesions was assessed in a liver squeeze chamber and by PCR, and a significantly reduced parasite load was found in mefloquine-treated animals. Assessment of mefloquine plasma concentrations by HPLC and modeling using a two-compartment pharmacokinetic model with first-order absorption showed that >90% of the expected steady-state levels (Cmin 1.15 mg/L, Cmax 2.63 mg/L) were reached. These levels are close to concentrations achieved in humans during long-term weekly dosage of 250 mg (dose applied for malaria prophylaxis). In vitro structure-activity relationship analysis of mefloquine and ten derivatives revealed that none of the derivatives exhibited stronger activities than mefloquine. Activity was only observed, when the 2-piperidylmethanol group of mefloquine was replaced by an amino group-containing residue and when the trifluoromethyl residue on position 8 of the quinoline structure was present. This is in line with the anti-malarial activity of mefloquine and it implies that the mode of action in E. multilocularis might be similar to the one against malaria.

The use of a prodrug approach to minimize potential CNS exposure of next generation quinoline methanols while maintaining efficacy in in vivo animal models

The use of mefloquine (MQ) for antimalarial treatment and prophylaxis has diminished largely in response to concerns about its neurologic side effects. An analog campaign designed to maintain the efficacy of MQ while minimizing blood-brain barrier (BBB) penetration has resulted in the synthesis of a prodrug with comparable-to-superior in vivo efficacy versus mefloquine in a P. berghei mouse model while exhibiting a sixfold reduction in CNS drug levels. The prodrug, WR319670, performed poorly compared to MQ in in vitro efficacy assays, but had promising in vitro permeability in an MDCK-MDR1 cell line BBB permeability screen. Its metabolite, WR308245, exhibited high predicted BBB penetration with excellent in vitro efficacy. Both WR319670 and WR308245 cured 5/5 animals in separate in vivo efficacy studies. The in vivo efficacy of WR319670 was thought to be due to the formation of a more active metabolite, specifically WR308245. This was supported by pharmacokinetics studies in non-infected mice, which showed that both IV and oral administration of WR319670 produced essentially identical levels of WR319670 and WR308245 in both plasma and brain samples at all time points. In these studies, the levels of WR308245 in the brain were 1/4 and 1/6 that of MQ in similar IV and oral studies, respectively. These data show that the use of WR319670 as an antimalarial prodrug was able to maintain efficacy in in vivo efficacy screens, while significantly lowering overall penetration of drug and metabolites across the BBB.

Safety, efficacy and population pharmacokinetics of fixed-dose combination of artesunate-mefloquine in the treatment of acute uncomplicated Plasmodium falciparum malaria in India

BACKGROUND & OBJECTIVES

India has switched over to artemisinin-based combination therapy (ACT) for the treatment of acute uncomplicated Plasmodium falciparum malaria and the ACT used in the national programme is artesunate + sulphadoxine-pyrimethamine. Since the efficacy of ACT is dependent also on the partner drug, there is a need to evaluate and deploy multiple ACTs.

METHODS

This multicentre, single-arm, open-label clinical trial was carried out to assess the efficacy, safety and population pharmacokinetics of a fixed dose combination (FDC) artesunate mefloquine (ASMQ) in P. falciparum infected, Indian adults at Panjim, Goa, and Mangalore, Karnataka between December 2007 and November 2008.

RESULTS

A total of 77 patients (males 74) were screened and enrolled: 42 at Goa and 35 at Mangalore with a median age of 25 yr (range 18-55 yr). One patient failed in treatment on D53, a PCR proven new infection, seven developed recurrent vivax parasitaemia and 11 did not have a parasitological endpoint. By per protocol analysis, the D63 cure rate was 58/59 (98.3; 95% C.I. 90.9-99.9%), and 58/58, with PCR correction. ASMQ was well-tolerated and no serious adverse events were reported.

INTERPRETATION & CONCLUSION

The study showed that the ASMQ FDC was efficacious and well-tolerated for the treatment of acute, uncomplicated P. falciparum malaria in highly endemic, chloroquine resistant areas of Goa and Mangalore. It is a viable option for India.

Lysosomal disruption preferentially targets acute myeloid leukemia cells and progenitors

Despite efforts to understand and treat acute myeloid leukemia (AML), there remains a need for more comprehensive therapies to prevent AML-associated relapses. To identify new therapeutic strategies for AML, we screened a library of on- and off-patent drugs and identified the antimalarial agent mefloquine as a compound that selectively kills AML cells and AML stem cells in a panel of leukemia cell lines and in mice. Using a yeast genome-wide functional screen for mefloquine sensitizers, we identified genes associated with the yeast vacuole, the homolog of the mammalian lysosome. Consistent with this, we determined that mefloquine disrupts lysosomes, directly permeabilizes the lysosome membrane, and releases cathepsins into the cytosol. Knockdown of the lysosomal membrane proteins LAMP1 and LAMP2 resulted in decreased cell viability, as did treatment of AML cells with known lysosome disrupters. Highlighting a potential therapeutic rationale for this strategy, leukemic cells had significantly larger lysosomes compared with normal cells, and leukemia-initiating cells overexpressed lysosomal biogenesis genes. These results demonstrate that lysosomal disruption preferentially targets AML cells and AML progenitor cells, providing a rationale for testing lysosomal disruption as a novel therapeutic strategy for AML.

Use of mefloquine in children - a review of dosage, pharmacokinetics and tolerability data

BACKGROUND

Use of anti-malarial medication in children is hampered by a paucity of dosage, pharmacokinetic and tolerability data.

METHODS

Data on the use of mefloquine in children, particularly in young children weighing less than 20 kg, were reviewed using PubMed literature and reports on file.

RESULTS

Chemoprophylaxis data: Two studies with a total of 170 children were found. A simulated mefloquine plasma profile showed that doses to achieve protective chemoprophylaxis blood concentration of mefloquine of approximately 620 ng/mL (or 1.67 μmol/L) in children should be at least 5 mg/kg. This simulated plasma profile in children corresponds to that seen in adult travellers using a weekly prophylaxis dose of 250 mg. This reinforces current practice of using weight-based dosage for children. Clearance per body weight is higher in older children. For children who travel to malaria risk areas tablets can be broken and crushed as required. It is necessary to disguise the bitter taste of the drug. Treatment data: Mefloquine treatment (alone or in combination) data are available for more than 6000 children of all age and weight categories. The stereoselectivity and pharmacokinetic profile of mefloquine in children is similar to that observed in adults. There is higher clearance in older children (aged 5-12 years) compared to younger children (aged 6-24 months). Mefloquine treatment is well tolerated in infants (5-12 kg) but vomiting is a problem at high doses. This led to the use of a "split dose" regimen with 15 mg/kg initially, followed 12 hours later by 10 mg/kg. Mefloquine 125 mg has been used as intermittent preventive treatment (IPT) and was found to be efficacious in reducing episodes of malaria in a moderate-transmission setting but vomiting was a problem in 8% of children aged 2-11 months. Mefloquine is also used as a component of artemisinin combination therapy (ACT) in small children. The combination artesunate plus mefloquine is a WHO approved first-line treatment for uncomplicated malaria in Africa.

CONCLUSION

Currently available data provide a scientific basis for the use of mefloquine in small children in the chemoprophylaxis setting and as a part of treatment regimens for children living in endemic areas.

Radical curative efficacy of tafenoquine combination regimens in Plasmodium cynomolgi-infected Rhesus monkeys (Macaca mulatta)

BACKGROUND

Tafenoquine is an 8-aminoquinoline being developed for radical cure (blood and liver stage elimination) of Plasmodium vivax. During monotherapy treatment, the compound exhibits slow parasite and fever clearance times, and toxicity in glucose-6-phosphate dehydrogenase (G6PD) deficiency is a concern. Combination with other antimalarials may mitigate these concerns.

METHODS

In 2005, the radical curative efficacy of tafenoquine combinations was investigated in Plasmodium cynomolgi-infected naïve Indian-origin Rhesus monkeys. In the first cohort, groups of two monkeys were treated with a three-day regimen of tafenoquine at different doses alone and in combination with a three-day chloroquine regimen to determine the minimum curative dose (MCD). In the second cohort, the radical curative efficacy of a single-day regimen of tafenoquine-mefloquine was compared to that of two three-day regimens comprising tafenoquine at its MCD with chloroquine or artemether-lumefantrine in groups of six monkeys. In a final cohort, the efficacy of the MCD of tafenoquine against hypnozoites alone and in combination with chloroquine was investigated in groups of six monkeys after quinine pre-treatment to eliminate asexual parasites. Plasma tafenoquine, chloroquine and desethylchloroquine concentrations were determined by LC-MS in order to compare doses of the drugs to those used clinically in humans.

RESULTS

The total MCD of tafenoquine required in combination regimens for radical cure was ten-fold lower (1.8 mg/kg versus 18 mg/kg) than for monotherapy. This regimen (1.8 mg/kg) was equally efficacious as monotherapy or in combination with chloroquine after quinine pre-treatment to eliminate asexual stages. The same dose of (1.8 mg/kg) was radically curative in combination with artemether-lumefantrine. Tafenoquine was also radically curative when combined with mefloquine. The MCD of tafenoquine monotherapy for radical cure (18 mg/kg) appears to be biologically equivalent to a 600-1200 mg dose in humans. At its MCD in combination with blood schizonticidal drugs (1.8 mg/kg), the maximum observed plasma concentrations were substantially lower than (20-84 versus 550-1,100 ng/ml) after administration of 1, 200 mg in clinical studies.

CONCLUSIONS

Ten-fold lower clinical doses of tafenoquine than used in prior studies may be effective against P. vivax hypnozoites if the drug is deployed in combination with effective blood-schizonticidal drugs.

A randomized, double-blind, placebo-controlled study to investigate the safety, tolerability, and pharmacokinetics of single enantiomer (+)-mefloquine compared with racemic mefloquine in healthy persons

Racemic mefloquine is a highly effective antimalarial whose clinical utility has been compromised by its association with neuropsychiatric and gastrointestinal side effects. It is hypothesized that the cause of the side effects may reside in the (-) enantiomer. We sought to compare the safety, tolerability and pharmacokinetic profile of (+)-mefloquine with racemic mefloquine in a randomized, ascending-dose, double-blind, active and placebo-controlled, parallel cohort study in healthy male and female adult volunteers. Although differing in its manifestations, both study drugs displayed a substantially worse tolerability profile compared with placebo. The systemic clearance was slower for (-)-mefloquine than (+)-mefloquine. Thus, (+)-mefloquine has a different safety and tolerability profile compared with racemic mefloquine but its global safety profile is not superior and replacement of the currently used antimalarial drug with (+)-mefloquine is not warranted.

Impact of cerebral malaria on brain distribution of mefloquine

Cerebral malaria (CM) is the most severe complication of Plasmodium falciparum malaria. The aim of this study was to investigate the influence of CM on the cerebral uptake of mefloquine (MQ), in an experimental model of mice infected with Plasmodium berghei ANKA (PbA). Drug diffusion in brain is closely related to efflux pumps such as P-glycoprotein (P-gp/ABCB1/MDR1) and Breast Cancer Resistant Protein (BCRP/ABCG2), two major components of the blood-brain barrier (BBB) which can be modified by inflammation and/or infection. After a single IP dose, MQ concentrations were measured by liquid chromatography in blood and brains of mice infected with Plasmodium berghei ANKA and compared with that of non-infected mice. Our results show that MQ brain concentrations were decreased in CM mice versus healthy mice (0.77 versus 1.31 for brain/plasma concentrations). Although MQ is transported out of endothelial cells by P-glycoprotein, this result cannot be related to this transporter as we have previously shown that CM does not alter P-gp function (personal data). CM induces a reduction of MQ brain transport and, therefore, an increase of central toxicity due to MQ should not be expected during CM.

Pharmacokinetic determinants of the window of selection for antimalarial drug resistance

The selection and spread of antimalarial drug resistance pose enormous challenges to the health of people living in tropical countries. Most antimalarial drugs are slowly eliminated and so, following treatment in areas of endemicity, provide a gradient of concentrations to which newly acquired parasites are exposed. There is a variable period during which a new blood-stage infection with resistant malaria parasites can emerge from the liver and subsequently produce gametocyte densities sufficient for transmission while reinfection by sensitive parasites is still suppressed. This "window of selection" drives the spread of resistance. We have examined the factors which determine the duration of this window and, thus, the resistance selection pressure. The duration ranges from zero to several months and is dependent on the degree of parasite resistance, the slope of the concentration-effect relationship, and the elimination kinetics of the antimalarial drug. The time at which the window opens and the duration of opening are both linear functions of the terminal elimination half-life. Because of competition from sibling susceptible parasites, the greater risks of extinction with low starting numbers, and opening of the window only when blood concentrations have fallen below the MIC, the window of selection for de novo resistance is narrower than that for resistance acquired elsewhere. The windows were examined for the currently available antimalarials. Drugs with elimination half-lives of less than 1 day, such as the artemisinins and quinine, do not select for resistance during the elimination phase.

Liquid-phase microextraction combined with high-performance liquid chromatography for the enantioselective analysis of mefloquine in plasma samples

A simple and rapid method, which involves liquid-phase microextraction (LPME) followed by HPLC analysis using Chiralpak AD column and UV detection, was developed for the enantioselective determination of mefloquine in plasma samples. Several factors that influence the efficiency of three-phase LPME were investigated and optimized. Under the optimal extraction conditions, the mean recoveries were 33.2 and 35.0% for (-)-(SR-)-mefloquine and (+)-(RS)-mefloquine, respectively. The method was linear over 50-1500 ng/ml range. Within-day and between-day assay precision and accuracy were below 15% for both enantiomers at concentrations of 150, 600 and 1200 ng/ml. Furthermore, no racemization or degradation were seen with the method described.

An analytical method with a single extraction procedure and two separate high performance liquid chromatographic systems for the determination of artesunate, dihydroartemisinin and mefloquine in human plasma for application in clinical pharmacological studies of the drug combination

The combination of two sensitive, selective and reproducible reversed phase liquid chromatographic (RP-HPLC) methods was developed for the determination of artesunate (AS), its active metabolite dihydroartemisinin (DHA) and mefloquine (MQ) in human plasma. Solid phase extraction (SPE) of the plasma samples was carried out on Supelclean LC-18 extraction cartridges. Chromatographic separation of AS, DHA and the internal standard, artemisinin (QHS) was obtained on a Hypersil C4 column with mobile phase consisting of acetonitrile-0.05 M acetic acid adjusted to pH 5.2 with 1.0M NaOH (42:58, v/v) at the flow rate of 1.50 ml/min. The analytes were detected using an electrochemical detector operating in the reductive mode. Chromatography of MQ and the internal standard, chlorpromazine hydrochloride (CPM) was carried out on an Inertsil C8-3 column using methanol-acetonitrile-0.05 M potassium dihydrogen phosphate adjusted to pH 3.9 with 0.5% orthophosphoric acid (50:8:42, v/v/v) at a flow rate of 1.00 ml/min with ultraviolet detection at 284 nm. The mean recoveries of AS and DHA over a concentration range of 30-750 ng/0.5 ml plasma and MQ over a concentration of 75-1500 ng/0.5 ml plasma were above 80% and the accuracy ranged from 91.1 to 103.5%. The within-day coefficients of variation were 1.0-1.4% for AS, 0.4-3.4% for DHA and 0.7-1.5% for MQ. The day-to-day coefficients of variation were 1.3-7.6%, 1.8-7.8% and 2.0-3.4%, respectively. Both the lower limit of quantifications for AS and DHA were at 10 ng/0.5 ml and the lower limit of quantification for MQ was at 25 ng/0.5 ml. The limit of detections were 4 ng/0.5 ml for AS and DHA and 15 ng/0.5 ml for MQ. The method was found to be suitable for use in clinical pharmacological studies.

Pharmacokinetics of two paediatric artesunate mefloquine drug formulations in the treatment of uncomplicated falciparum malaria in Gabon

OBJECTIVES

Paediatric drug formulations of artemisinin combination therapies and pharmacokinetic data supporting their use in African children are urgently needed for the effective treatment of young children suffering from falciparum malaria in sub-Saharan Africa.

PATIENTS AND METHODS

In this study, the pharmacokinetic characteristics of a novel paediatric granule formulation of artesunate-mefloquine therapy were evaluated in comparison to the standard tablet formulation in the treatment of uncomplicated malaria in paediatric patients. Twenty-four patients were assigned to treatment according to body weight with either a fixed-dose paediatric granule co-formulation (10-20 kg body weight) or a free-dose co-blister tablet formulation of artesunate-mefloquine (>20-40 kg body weight).

RESULTS

Median values for C(max) (861 and 930 ng/mL), T(max) (1.5 and 1.5 h) and AUC(0-)(t) (2,050 and 2,470 ng.h/mL) were comparable for dihydroartemisinin in the two groups. Exploratory analysis of mefloquine plasma levels revealed a trend towards higher concentrations in the younger age group during the absorption phase (2,550 and 1,815 ng/mL, 54 h after initiation of treatment, respectively). Median mefloquine concentrations at day 28 were 197 and 343 ng/mL, respectively.

CONCLUSIONS

The pharmacokinetic characteristics of the two paediatric dosage forms, i.e. the novel fixed-dose co-formulation and the standard co-blister of artesunate-mefloquine show comparable results in the two treatment groups. The novel fixed-dose paediatric formulation is an interesting option for outpatient treatment of uncomplicated malaria in African children.

Pharmacokinetics of mefloquine with dihydroartemisinin as 2-day regimens in patients with uncomplicated falciparum malaria

The objective of this study was to investigate the pharmacokinetics of mefloquine (MQ) when given as 750 mg at two different times in combination regimens with dihydroartemisinin (DHA) in patients with acute uncomplicated falciparum malaria. A total of 12 Vietnamese patients (6 in each group) were randomized to receive two MQ-DHA regimens as follows: regimen-A: an initial oral dose of 300 mg DHA, followed by 750 mg MQ and 300 DHA 6 and 24 hours later; regimen-B: an initial dose of 300 mg DHA, followed by 300 mg DHA and 750 mg MQ at 24 hours. Both combination regimens were well tolerated. All patients responded well to treatment with no recrudescence during a 42 day follow-up period. The pharmacokinetics of MQ following both regimens were similar but pooled data from both groups suggest that the kinetics of MQ was different from that observed in Vietnamese healthy subjects reported in a previous study. The median (95% CI) time period for maintenance of whole blood MQ concentrations above 500 ng/ml was 16 (0-24) days. It was concluded that since no pharmacokinetic drug interaction was observed, MQ dose given 24 hours after an initial dose of DHA is a preferable combination treatment regimen with regard to patient compliance.

Population pharmacokinetics of mefloquine in military personnel for prophylaxis against malaria infection during field deployment

OBJECTIVE

The purpose of this study was to determine the population pharmacokinetics of mefloquine in healthy military personnel during prophylaxis for malaria infections.

METHODS

The subjects were 1,111 Australian soldiers participating in two studies: a randomised double-blinded study (group A, 161 subjects) and an open-label study (group B, 950 subjects). Following a loading dose (250 mg mefloquine base daily, 3 days), subjects received an oral weekly maintenance dose of 250 mg over 6 months. Blood was collected after the last split loading dose then at weeks 4, 8 and 16 for group A, and at weeks 13 and 26 for group B. Plasma mefloquine concentrations were measured by high-performance liquid chromatography (HPLC). Pharmacokinetic modelling was performed using NONMEM.

RESULTS

A two-compartment model with inter-occasion variability (IOV) for clearance satisfactorily described the pharmacokinetics. Typical values were clearance (CL/F, 2.09 l/h), central volume of distribution (V1/F, 528 l), absorption rate constant (KA, 0.24 h(-1)), inter-compartmental clearance (Q/F, 12.5 l/h), peripheral volume of distribution (V2/F, 483 l) and elimination half-life (t (1/2), 14.0 days). Weight had a positive influence on central volume but was insufficient to warrant dosage adjustments. The inter-individual variability (coefficient of variation, CV%) for CL/F and V1/F was 24.4% and 29.6%, respectively. The IOV for CL/F was 17.8%. The proportional residual error (CV%) for groups A and B was 11.5% and 19.5%, respectively, and the additive error standard deviation (SD) was 57 ng/ml and 149 ng/ml, respectively.

CONCLUSION

The typical parameter values were comparable with those estimated in much smaller cohorts of healthy subjects and in malaria patients treated with single-dose mefloquine. The lower unexplained variability in the blinded study suggested these subjects may have been more compliant in taking their medication than soldiers in the open-label study.

Utility of alkylaminoquinolinyl methanols as new antimalarial drugs

Mefloquine has been one of the more valuable antimalarial drugs but has never reached its full clinical potential due to concerns about its neurologic side effects, its greater expense than that of other antimalarials, and the emergence of resistance. The commercial development of mefloquine superseded that of another quinolinyl methanol, WR030090, which was used as an experimental antimalarial drug by the U.S. Army in the 1970s. We evaluated a series of related 2-phenyl-substituted alkylaminoquinolinyl methanols (AAQMs) for their potential as mefloquine replacement drugs based on a series of appropriate in vitro and in vivo efficacy and toxicology screens and the theoretical cost of goods. Generally, the AAQMs were less neurotoxic and exhibited greater antimalarial potency, and they are potentially cheaper than mefloquine, but they showed poorer metabolic stability and pharmacokinetics and the potential for phototoxicity. These differences in physiochemical and biological properties are attributable to the "opening" of the piperidine ring of the 4-position side chain. Modification of the most promising compound, WR069878, by substitution of an appropriate N functionality at the 4 position, optimization of quinoline ring substituents at the 6 and 7 positions, and deconjugation of quinoline and phenyl ring systems is anticipated to yield a valuable new antimalarial drug.

Population pharmacokinetic assessment of a new regimen of mefloquine used in combination treatment of uncomplicated falciparum malaria

A fixed artesunate-mefloquine combination, comprising three daily doses of 8 mg of mefloquine/kg of body weight and 4 mg of artesunate/kg, has been developed recently. This study was designed to construct a population pharmacokinetic model describing this new dosage regimen of mefloquine given as loose tablets together with artesunate. In two randomized trials in Thailand which evaluated the efficacy, safety, and tolerability of this new regimen, the members of a subgroup of 50 patients were randomized to have capillary blood sampling before treatment and at five randomly assigned time points during the 63-day follow-up period. Mefloquine levels in capillary whole blood were assayed by liquid chromatography with UV detection. A pharmacokinetic model for mefloquine was constructed using mixed-effects modeling. A one-compartment model with first-order absorption and elimination was selected to describe the kinetic properties of mefloquine. For capillary whole-blood mefloquine, the area under the concentration curve (AUC) was 40% higher than previous estimates for patients given the equivalent conventional-dose regimen (mefloquine given as 15 mg/kg and then 10 mg/kg on the second and third days of treatment). The half-life (t1/2) of the carboxylic acid metabolite was estimated as 26 days, and the metabolite was eliminated more slowly than the parent drug (population t1/2 estimate, 10.5 days). Splitting the 25 mg/kg dose of mefloquine into three doses of 8 mg/kg each resulted in improved oral bioavailability compared to the conventional split-dose regimen results. This new regimen is well tolerated and results in an equivalent therapeutic response.

El citocromo P-450 y la respuesta terapéutica a los antimaláricos

OBJECTIVES

To assess the relationship between the genetic and phenotypic factors linked to the cytochrome P-450 enzyme system and the response to the antimalarial drugs chloroquine, amodiaquine, mefloquine, and proguanil, as well as to determine how certain biological and social factors of the host influence the behavior of this enzymatic complex.

METHODS

We performed a systematic review of the medical bibliographic databases PubMed, Excerpta Medica, LILACS, and SciELO by using the following Spanish and English descriptors: "CYP-450" and "citocromo P-450" in combination with "proguanil" (and with "mefloquina," "cloroquina," and "amodiaquina"), "farmacocinética de proguanil" (and the same using "mefloquina," "cloroquina," and "amodiaquina"), "resistencia a proguanil" (and the same using "mefloquina," "cloroquina," and "amodiaquina"), "metabolismo," "farmacogenética," "enfermedad," "inflamación," "infección," "enfermedad hepática," "malaria," "nutrición," and "desnutrición." The same terms were used in English. The search included only articles published in Spanish, English, and Portuguese on or before 30 June 2005 that dealt with only four antimalarial drugs: amodiaquine, chloroquine, mefloquine, and proguanil.

RESULTS

Some genetic factors linked to human cytochrome P-450 (mainly its polymorphism), as well as other biological and social factors (the presence of disease itself, or of inflammation and infection, the use of antimalarials in their various combinations, and the patient's nutritional status) influence the behavior of this complex enzymatic system. It has only been in the last decade that the genetics of the cytochromes has been explored and that the mechanisms underlying some therapeutic interactions and aspects of drug metabolism have been uncovered, making it possible to characterize the biotransformation pathway of amodiaquine and chloroquine. Hopefully new research will help answer the questions that still remain, some of which pertain to the metabolism of other antimalarial drugs, the distribution in the population of the genetic alleles linked to the enzymes involved in their metabolism, the contribution of these genetic mutations to therapeutic failure, and the possibility of predicting the response to antimalarial therapy.

CONCLUSIONS

The therapeutic response to antimalarial drugs is a multifactorial process that is poorly understood, so that it is not possible to ascribe to a specific phenotype or genotype a role in the response to antimalarial therapy. Attention should be given to biological and social factors, such as diet, nutritional status, and inflammatory and infectious processes that are often present in areas where malaria is endemic.

Ketoconazole increases plasma concentrations of antimalarial mefloquine in healthy human volunteers

BACKGROUND

Antimalarial mefloquine has a structure related to quinine. The major metabolite of quinine is 3-hydroxyquinine formed by cytochrome P450 3A4 (CYP3A4). Ketoconazole, a potent inhibitor of CYP3A4, is known to markedly increase plasma concentrations of various co-administered drugs including quinine.

OBJECTIVE

To assess the effect of ketoconazole on plasma concentrations of mefloquine in healthy Thai male volunteers.

METHODS

In an open, randomized two-phase crossover study separated by a 1-month period, eight healthy Thai male volunteers received a single oral dose of 500 mg mefloquine alone or co-administration with 400 mg/day ketoconazole orally for 10 days. Serial blood samples were collected at specific time points for a 56-day period. Plasma mefloquine and mefloquine carboxylic metabolite concentrations during 56 days were measured by a modified and validated high-performance liquid chromatographic method with UV detection.

RESULTS

Co-administration with ketoconazole markedly increased the mean values of mefloquine AUC0-t, t(1/2), and Cmax when compared with mefloquine alone by 79% (P < 0.001), 39% (P < 0.05) and 64% (P < 0.001) respectively. The AUC0-t , and Cmax of mefloquine carboxylic acid metabolite were decreased by 28% (P < 0.05) and 31% (P < 0.05), respectively when compared with mefloquine alone.

CONCLUSIONS

Co-administration with ketoconazole increased plasma mefloquine concentrations in healthy human volunteers. One of possible mechanisms of the increase in plasma mefloquine concentrations may be the result of the inhibition of CYP3A4 by ketoconazole. In case of mefloquine is co-administered with ketoconazole, drug-drug interactions should be recognized and the dose of mefloquine should be adjusted to maximize the therapeutic efficacy and to reduce the cost of therapy.

Life-saving rectal artesunate for complicated malaria in children

We report the effectiveness of two regimens of rectal artesunate formulation in treating 13 Thai children with cerebral/complicated falciparum malaria. The drug was given at an initial dose of 40 mg/kg bodyweight, in 3 or 4 divided doses in the first 24 hours, followed by 10 mg/kg bodyweight once daily for three consecutive days. Mefloquine, at a dose of 15 mg/kg bodyweight was given orally at 72 hours after the initial dose of artesunate, followed by 10 mg/kg bodyweight 6 hours later. Three cases with cerebral malaria gained consciousness within 20 hours of artesunate administration. The median time required for reduction of parasitemia by 90% of the initial value (P90) in 13 children was 11.2 hours. No recrudescence was observed in any of the patients during the 28-day follow-up period. Plasma concentrations of artesunate and dihydroartemisinin (active plasma metabolite of artesunate) measured in two patients who received the high initial dose regimen (20 mg/ kg bodyweight) suggested rapid absorption and adequate plasma concentrations of both compounds following the administration of artesunate via the rectal route. Further studies for the optimized regimen of rectal artesunate in the treatment of cerebral/complicated childhood falciparum malaria in areas of multidrug resistance are warranted.

[Relative bioavailability of an optimised galenical formulation of mefloquine]

The bioequivalence of an optimised formulation of a generic mefloquine (Mephaquin Lactabs/Test) compared to the reference product under fed conditions was assessed in a GCP/ICH conformable study. A standard two-way randomised crossover design with a 9 week washout period between treatments was used. Blood samples for determination of mefloquine concentrations for calculation of Cmax and AUC were collected at pre-dose and at predefined intervals up to 2016 hours after administration of a single oral dose of 750 mg. A standard bioequivalence analysis was performed on the two one-sided t-test procedure for log-transformed Cmax and AUC. 90% confidence intervals were calculated for both parameters and evaluated against regulatory standards of 80-125% (T/R). Analysis of plasma for mefloquine concentration was performed using a validated LC/MS method with MS detection. The ratio of mean AUC and Cmax (T/R) was 1.015 and 1.044, respectively. The 90% confidence intervals were 95.8-109.3% for AUC and 98.2-110.5% for Cmax. Mephaquin produces plasma concentrations comparable to those after administration of the reference product. The 90% confidence intervals for AUC and Cmax are within the acceptable ranges for bioequivalence of 80-125%. Thus, the optimised galenical formulation of Mephaquin Lactabs is bioequivalent to the reference product.

Investigation of bioavailability, pharmacokinetics and safety of new pediatric formulations of artesunate and mefloquine

The bioavailability/pharmacokinetics of dihydroartemisinin and mefloquine following the oral doses of 4 mg/kg body weight artesunate (Cambodian Pharmaceutical Enterprise) given concurrently with 10 mg/kg body weight oral mefloquine artesunate (Cambodian Pharmaceutical Enterprise) were investigated in 15 healthy Cambodian male volunteers. Both formulations were generally well tolerated. Both produced satisfactory plasma/blood concentration-time profiles. Oral artesunate and mefloquine were rapidly absorbed from gastrointestinal tract with marked inter-individual variation. For the dihydroartemisinin, the median (95% Cl) Cmax of 748 (304-1,470) ng/ml was observed at 1.5 (0.3-3.0) hours (tmax) after drug administration. The median (95% CI) values for AUC0-infinity, lambda(z) and tl/2z were 1.673 (1.08-2.88) microg.h/ml, 0.54(0.24-1.1)/hour and 1.3 (0.6-2.9) hours, respectively. For mefloquine, a median (95% Cl) Cmax of 1,000 (591-1,500) ng/ml was observed at 4 (2-6) hours (tmax) after drug administration. The median (95% CI) value for AUC0-168h was 3.92 (2.88-7.02) microg.h/ml.

Pharmacokinetics of the four combination regimens of dihydroartemisinin/mefloquine in acute uncomplicated falciparum malaria

The pharmacokinetics of oral dihydroartemisinin and mefloquine were investigated in 40 patients (aged 16-30 y, weighing 45-60 kg) with acute uncomplicated falciparum malaria following the four combination regimens of dihydroartemisinin/ mefloquine [regimen-I: 300 mg dihydroartemisinin (h-0) plus 750 mg mefloquine (h-0); regimen-II: 300 mg dihydroartemisinin (h-0) plus 750 mg mefloquine (h-24); regimen-III: 300 mg dihydroartemisinin (h-0) plus 750 and 500 mg mefloquine (h-24 and 30); regimen-IV: 300 mg dihydroartemisinin (h-0) plus 750 and 500 mg mefloquine (h-0, 24)]. The four combination regimens were well tolerated. Patients in all treatment groups had a rapid initial response. However, 9 patients (4, 4, and 1 cases in regimens-I, II, and IV) had reappearance of parasitemia during the follow-up period. Significant changes in the pharmacokinetic parameters of both mefloquine and dihydroartemisinin were observed in patients with malaria compared with healthy subjects reported in a paralleled study. For mefloquine, Cmax (mg per dose), AUC0-day1 (mg per dose), and AUC0-day7 (mg per dose) were significantly higher in patients. Furthermore, tmax, was prolonged while V/F contracted and tl/2,z, MRT shortened in patients with malaria. For dihydroartemisinin, Cmax AUC, tmax and Vz/F were changed in the same direction as mefloquine, whereas t1/2z and MRT were prolonged. CL/F was also significantly reduced in patients with malaria. Absorption/disposition kinetics of oral dihydroartemisinin were similar among the various regimens. On the other hand, AUC0-day1 (mg per dose) of mefloquine after regimen-III was significantly higher than the other three regimens. Combination regimens with two divided doses of mefloquine (regimens-III and IV) resulted in a significantly delayed tmax (especially regimens-IV) compared with those with single dose regimens (regimens-I and II).

Artesunate with mefloquine at various intervals for non-severe Plasmodium falciparum malaria

To study the efficacy, tolerance, population pharmacokinetics and pharmacodynamics of artesunate followed by mefloquine at various intervals, 360 patients with Plasmodium falciparum malaria received 4 mg/kg of artesunate and thereafter 15 mg/kg of mefloquine simultaneously (group A), after 8 hours (after group B), and after 24 hours (group C). Three dosages were completed with placebo. Follow-up was 28 days. All patients recovered rapidly except one case of failure within the first 24 hours. Mefloquine pharmacokinetics was similar in the three regimens. Parasites reappeared in 26%, 26%, and 33% of the patients in groups A, B, and C, respectively. Early recrudescence was associated with high initial parasite density, slow parasite clearance, and rapid mefloquine clearance and low plasma concentrations at day 28. Mefloquine plasma concentrations all reached therapeutic ranges, suggesting reduced parasite sensitivity. In conclusion, there is no interaction between artesunate and mefloquine with respect to tolerance, efficacy, and pharmacokinetics. Single-dose combination therapy with artemisinin drugs and 15 mg/kg of mefloquine does not completely prevent parasite recurrence and may not prevent mefloquine resistance.

Cerebral uptake of mefloquine enantiomers with and without the P-gp inhibitor elacridar (GF1210918) in mice

1. Mefloquine is a chiral neurotoxic antimalarial agent showing stereoselective brain uptake in humans and rats. It is a substrate and an inhibitor of the efflux protein P-glycoprotein. 2. We investigated the stereoselective uptake and efflux of mefloquine in mice, and the consequences of the combination with an efflux protein inhibitor, elacridar (GF120918) on its brain transport. 3. Racemic mefloquine (25 mg kg(-1)) was administered intraperitoneally with or without elacridar (10 mg kg(-1)). Six to seven mice were killed at each of 11 time-points between 30 min and 168 h after administration. Blood and brain concentrations of mefloquine enantiomers were determined using liquid chromatography. 4. A three-compartment model with zero-order absorption from the injection site was found to best represent the pharmacokinetics of both enantiomers in blood and brain. (-)Mefloquine had a lower blood and brain apparent volume of distribution and a lower efflux clearance from the brain, resulting in a larger brain/blood ratio compared to (+)mefloquine. Elacridar did not modify blood concentrations or the elimination rate from blood for either enantiomers. However, cerebral AUC(inf) of both enantiomers were increased, with a stronger effect on (+)mefloquine. The efflux clearance from the brain decreased for both enantiomers, with a larger decrease for (+)mefloquine. 5. After administration of racemic mefloquine in mice, blood and brain pharmacokinetics are stereoselective, (+)mefloquine being excreted from brain more rapidly than its antipode, showing that mefloquine is a substrate of efflux proteins and that mefloquine enantiomers undergo efflux in a stereoselective manner. Moreover, pretreatment with elacridar reduced the brain efflux clearances with a more pronounced effect on (+)mefloquine.

Population pharmacokinetic and pharmacodynamic modelling of artemisinin and mefloquine enantiomers in patients with falciparum malaria

OBJECTIVES

The aims of this study were to investigate whether artemisinin influences the pharmacokinetics of mefloquine enantiomers or vice versa and to model the antiparasitic effect of these drugs alone and in combination in Plasmodium falciparum malaria patients.

METHODS

Forty-two male and female patients were randomised to treatment with either oral artemisinin 500 mg daily for 3 days followed by oral mefloquine 750 mg on day 4, oral artemisinin 500 mg daily for 3 days plus oral mefloquine 750 mg on day 1 or a single 750-mg oral dose of mefloquine. The data was modelled using NONMEM.

RESULTS

All patients were successfully treated regardless of treatment. The fastest parasite clearance rates were observed in patients receiving artemisinin together with mefloquine on the first day of treatment. A pharmacodynamic model based on the life cycle of P. falciparum successfully described the efficacy of artemisinin, mefloquine and the combination. The time artemisinin concentration stays above a minimum inhibitory concentration was estimated to 2.97 h (relative standard error 4.7 h). The two mefloquine enantiomers exhibited different pharmacokinetics, with an oral clearance of 3.51 (7.9) l/h and 0.602 (6.9) l/h for RS-mefloquine and SR-mefloquine, respectively. In patients receiving only artemisinin the first 3 days, artemisinin oral clearance was 6.9-fold higher the last day of treatment compared with the first day. There was no difference in the pharmacokinetics of mefloquine enantiomers when mefloquine was given alone, in combination with artemisinin or after a 3-day regimen of artemisinin. There was a tendency towards, although non-significant, higher artemisinin concentrations when artemisinin was given together with mefloquine compared with when given alone.

CONCLUSIONS

No significant pharmacokinetic interactions were observed after co-administration of artemisinin and mefloquine. The P. falciparum malaria pharmacodynamic model successfully described the antimalarial effect of artemisinin, mefloquine and a combination of the two drugs.

Pharmacokinetic-pharmacodynamic modelling of the antimalarial activity of mefloquine

Treatment protocols for the chemotherapy of malaria are usually acquired through clinical trials. Once pharmacokinetic and pharmacodynamic information becomes available, it is possible to use mathematical modelling for testing these protocols and, possibly, for improving them. In this report the case of monotherapy by mefloquine is analysed. Published pharmacokinetic and clinical results are used to derive the essential model parameters such as kill rate, parasite growth rates, drug sensitivity and the pharmacokinetic parameters. Good agreement is obtained between clinical results and simulated parasite numbers using the derived parameters. It is demonstrated that the 2 exponential kinetics of mefloquine elimination can be reduced to an operational single exponent for pharmacodynamic modelling by educated choice of sampling times of plasma drug concentration. It is deduced that a second drug dose, at a properly chosen time-interval, results in radical cure even when resistant parasites are present and at maximal parasite growth rates such as those found in non-immune patients. Finally, a table is provided for guiding the optimal choice of dosing intervals under different values of population pharmacokinetics, drug resistance and individual immunity parameters.

How can we do pharmacokinetic studies in the tropics?

Information regarding the pharmacokinetic (PK) and pharmacodynamic (PD) properties of a drug provides the basis for optimizing dosing. PK-PD information should be obtained from patients representative of the overall target population, but in many tropical hospitals or health care facilities it may be medically hazardous or logistically difficult for an ill patient or a young child to be sampled repeatedly. Traditional methods used to determine the pharmacokinetic properties of a drug require analysis of a large number of blood samples per subject. However, using modern statistical methods, sparse datasets (i.e. with assay results from only a few, or as little as one blood sample per subject) can now be analysed by a method termed 'the population approach'. Modern assay techniques can often be adapted to small blood volumes allowing finger prick blood samples to be taken. One of the major aims of the population approach is to distinguish and characterize patient and disease contributors to inter-individual variance in drug pharmacokinetics. The purpose of this paper is to explain the basis of the population approach, to highlight its advantages compared to traditional methods of analysis, and to review the application of the population approach to data from field studies of antimalarial drugs. The design of population pharmacokinetic studies is also discussed briefly. The principles discussed in the paper are also applicable to pharmacodynamic data.

Pharmacokinetic interaction between mefloquine and ritonavir in healthy volunteers

AIMS

To evaluate the pharmacokinetic interaction between ritonavir and mefloquine.

METHODS

Healthy volunteers participated in two separate, nonfasted, three-treatment, three-period, longitudinal pharmacokinetic studies. Study 1 (12 completed): ritonavir 200 mg twice daily for 7 days, 7 day washout, mefloquine 250 mg once daily for 3 days then once weekly for 4 weeks, ritonavir restarted for 7 days simultaneously with the last mefloquine dose. Study 2 (11 completed): ritonavir 200 mg single dose, mefloquine 250 mg once daily for 3 days then once weekly for 2 weeks, ritonavir single dose repeated 2 days after the last mefloquine dose. Erythromycin breath test (ERMBT) was administered with and without drug treatments in study 2.

RESULTS

Study 1: Ritonavir caused less than 7% changes with high precision (90% CIs: -12% to 11%) in overall plasma exposure (AUC(0,168 h)) and peak concentration (Cmax) of mefloquine, its two enantiomers, and carboxylic acid metabolite, and in the metabolite/mefloquine and enantiomeric AUC ratios. Mefloquine significantly decreased steady-state ritonavir plasma AUC(0,12 h) by 31%, Cmax by 36%, and predose levels by 43%, and did not affect ritonavir binding to plasma proteins. Study 2: Mefloquine did not alter single-dose ritonavir pharmacokinetics. Less than 8% changes in AUC and Cmax were observed with high variability (90%CIs: -26% to 45%). Mefloquine had no effect on the ERMBT whereas ritonavir decreased activity by 98%.

CONCLUSIONS

Ritonavir minimally affected mefloquine pharmacokinetics despite strong inhibition of CYP3A4 activity from a single 200 mg dose. Mefloquine had variable effects on ritonavir pharmacokinetics that were not explained by hepatic CYP3A4 activity or ritonavir protein binding.

Coadministration of mefloquine and chloroqine: use of a pharmacokinetic-based approach to reduce toxicity

A child with malaria from a chloroquine-resistant area received an accidental overdose of chloroquine administered by a parent. Application of pharmacokinetics permitted definitive treatment with mefloquine in a safe and effective manner.

Mefloquine pharmacokinetic-pharmacodynamic models: implications for dosing and resistance

Antimalarial resistance develops and spreads when spontaneously occurring mutant malaria parasites are selected by concentrations of antimalarial drug which are sufficient to eradicate the more sensitive parasites but not those with the resistance mutation(s). Mefloquine, a slowly eliminated quinoline-methanol compound, is the most widely used drug for the treatment of multidrug-resistant falciparum malaria. It has been used at doses ranging between 15 and 25 mg of base/kg of body weight. Resistance to mefloquine has developed rapidly on the borders of Thailand, where the drug has been deployed since 1984. Mathematical modeling with population pharmacokinetic and in vivo and in vitro pharmacodynamic data from this region confirms that, early in the evolution of resistance, conventional assessments of the therapeutic response </=28 days after treatment underestimate considerably the level of resistance. Longer follow-up is required. The model indicates that initial deployment of a lower (15-mg/kg) dose of mefloquine provides a greater opportunity for the selection of resistant mutants and would be expected to lead more rapidly to resistance than de novo use of the higher (25-mg/kg) dose.

Effect of rifampin on plasma concentrations of mefloquine in healthy volunteers

Mefloquine is a 4-quinolinemethanol compound structurally related to quinine. Quinine is mainly metabolized by the cytochrome P450 3A4 isozyme (CYP3A4), whereas rifampin, a potent inducer of CYP3A4, is known to markedly decrease plasma quinine concentration. Our aim was to study the effect of rifampin on the pharmacokinetics of mefloquine, and explore a possible role of CYP3A4 on mefloquine metabolism. In an open, two-phase crossover study, seven healthy Thai male volunteers received a single oral dose of 500 mg mefloquine alone, or 500 mg mefloquine plus a long-term administration of 600 mg rifampin. Blood samples were collected at specific time points over a 56-day period. Plasma mefloquine and its carboxylic acid metabolite were measured by HPLC for pharmacokinetic analysis. The results indicate that rifampin significantly decreased the area under the plasma concentration-time curve (AUC0 - infinity) of mefloquine by 68% (P < 0.01), maximum plasma concentration (Cmax) by 19% (P < 0.001), and elimination half-life (t1/2) by 63% (P < 0.01), whereas the time to reach Cmax (t(max)) of mefloquine was unaffected. The apparent oral clearance (CL) of mefloquine was significantly increased by 281% (P < 0.01). After administration of rifampin, the Cmax of the carboxylic acid metabolite of mefloquine was significantly increased by 47% (P < 0.05), whereas the t1/2 was significantly decreased by 39% (P < 0.01), and t(max) by 76% (P < 0.01). The AUC0 - infinity and CL of the mefloquine metabolite were increased by 30% and 25%, respectively, but were not significantly different from the control phase. The results indicate that rifampin reduces the plasma concentration of a single oral dose of 500 mg mefloquine by increasing metabolism of mefloquine in the liver and gut wall. The CYP3A4 isozyme most likely plays an important role in the enhanced metabolism of mefloquine. Simultaneous use of rifampin and mefloquine should be avoided to optimize the therapeutic efficacy of mefloquine and prevent the risk of Plasmodium falciparum resistance in malarial treatment.

Cardiac effects of co-artemether (artemether/lumefantrine) and mefloquine given alone or in combination to healthy volunteers

Co-artemether is an oral tablet of artemether (20 mg) and lumefantrine (120 mg) for the treatment of falciparum malaria. Administration in the presence of mefloquine is likely, as co-artemether may be used following failure of antimalarial prophylaxis or treatment with mefloquine.

OBJECTIVE

The effects on the QTc interval were compared among treatment with three doses of mefloquine (500, 250, 250 mg over 12 h) followed by six doses of co-artemether (6 x 4 tablets over 60 h) and either treatment alone. The study was performed in a randomised, double-blind, parallel group design in 14 healthy male subjects per dose group.

METHODS

Electrocardiograms (ECGs) were recorded before dosing and repeatedly thereafter. The Bazett formula was used to calculate the QTc interval. The maximum and average QTc intervals for the first, third and sixth dosing intervals of co-artemether treatment were compared among treatments. Drug plasma concentrations were determined at identical times with the ECG recordings for exploratory pharmacokinetic/pharmacodynamic evaluation.

RESULTS

No clinically relevant differences in the QTc interval were observed after sequential administration of mefloquine and co-artemether relative to either treatment given alone, and there were no clinically relevant study drug-related effects on the QTc interval after either treatment. Plasma drug measurements revealed adequate systemic exposure to artemether, dihydroartemisinin, lumefantrine and mefloquine, well in line with the clinical setting. No correlation between the length of the QTc interval and plasma drug concentrations was found for any of the compounds.

CONCLUSIONS

Untoward effects on the QTc interval are unlikely to occur when co-artemether is administered following prophylaxis or treatment with mefloquine.

Mefloquine pharmacokinetics in healthy subjects and in peptic ulcer patients after cimetidine administration

The pharmacokinetics of orally administered mefloquine were determined in six healthy male subjects and in six ulcer patients before and after a 3-day course of cimetidine (400 mg morning and evening). Peak plasma concentrations Cmax and AUC0-infinity were similarly and significantly (P < 0.05) increased after cimetidine pretreatement in both healthy subjects and peptic ulcer patients Cmax was increased by 42.4% and 20.5% while AUC0-infinity was increased by 37.5% in healthy and peptic ulcer subjects respectively. The values of t1/2ab absorption and t1/2 beta elimination, total crearance CLT/F and volume of distribution were altered to varying levels after cimetidine treatment but the changes were not statistically significant in both healthy and peptic ulcer subjects. The established long t1/2 beta and this apparent interaction between mefloquine and cimetidine which resulted in increased mefloquine plasma concentration might be of clinical significant in patients with neurological/psychiatric history.

Absence of significant pharmacokinetic and pharmacodynamic interactions between artemether and quinoline antimalarials

The study was carried out to investigate the pharmacokinetic and pharmacodynamic interactions between artemether (ARTEM) and quinoline antimalarials namely mefloquine (MQ), quinine (QN) and primaquine (PQ) when given concurrently. A randomised comparative, seven way cross-over design was performed in eight healthy male Thais following the administrations of seven drug regimens on seven occasions i.e. a single oral dose of ARTEM (300 mg), or MQ (750 mg), or QN (600 mg), or PQ (45 mg) alone, or the combination of ARTEM (300 mg) with MQ (750 mg), or QN (600 mg), or PQ (45 mg). All clinical and laboratory parameters were normal in all subjects, before, during and after the study. The eight subject experienced no adverse effect after ARTEM, QN, PQ alone regimens, or combination of ARTEM with QN and PQ. After administration of MQ in either occasion, 3 subjects had weakness, nausea, abdominal pain, and diarrhoea; one subject complained of dizziness. All symptoms were mild and occurred during the first day of MQ administration. The fitting of the concentration-time curves of ARTEM, QN and PQ, to a one-compartment model with first order absorption yielded satisfactory results in all subjects. The best fit model for MQ was two-compartment model with first order absorption. The pharmacokinetics of all investigated drug, when given alone or in combination were not significantly different.

Mefloquine concentration profiles during prophylactic dose regimens

A pharmacokinetic study with (malaria) prophylactic doses of mefloquine hydrochloride was conducted in 12 healthy adult subjects (Caucasians), 6 females and 6 males, mean age 29.2 +/- 6.4 years, mean weight 70.6 +/- 13.4 kg. Doses of 250 mg mefloquine were administered on days 0, 1, 7, 14, 21 and 28. Six subjects received a further 5 weekly doses of 250 mg mefloquine, the others 5 further weekly doses of 125 mg. After the third dose the protective threshold mefloquine concentration in blood plasma was achieved in all subjects. In female subjects, mean Cmin ss, Cmax ss and AUCd 0-35 were significantly higher than in males. After the fifth dose, mean Cmax in females reached 1692 ng/ml (4.48 mumol/l), equivalent to a high therapeutic concentration. This is apparently due to a generally lower body weight and a narrower volume of distribution in women. Adverse reactions were significantly more frequent in women than in men. Headache, anorexia, insomnia and vertigo were the most common side effects. The lesser tolerability of mefloquine in females may be due to the higher drug concentrations in this group. This may indicate the need for appropriate adjustment of the prophylactic dose regimen of mefloquine in females.

Pharmacokinetic and pharmacodynamic interactions of mefloquine and quinine

This study was carried out to investigate the pharmacokinetic and pharmacodynamic interactions between two antimalarial drugs, mefloquine and quinine. A randomized, comparative, three-way crossover study was performed in seven healthy male Thais after the administration of three drug regimens on three occasions i.e., a single oral dose of quinine sulfate (600 mg), mefloquine (750 mg) alone, or the combination of mefloquine (750 mg) and quinine (600 mg given 24 h after mefloquine). QTc interval was significantly prolonged in subjects following the combination regimen (at 2.5, 3, 4, 6, 8, 12, 18, 24 h after the quinine dose) but no abnormal clinical signs or symptoms were found. There were no significant changes in vital signs or routine laboratory values in any of the subjects. The pharmacokinetics of mefloquine and quinine were influenced by the presence of the other drug. Greater blood schizonticidal activities were collected from the sera of subjects on the combination regimen than from the sera of subjects the quinine or mefloquine regimens. The minimum inhibitory concentrations (MICs) of the equivalent concentrations (Eqs) of quinine or mefloquine, which completely inhibited the growth of the K1 strain of Plasmodium falciparum in vitro (MICs of quinine Eq and mefloquine Eq) were significantly lower in the sera of subjects on the combination regimens, than in the sera of subjects on mefloquine or quinine alone [MICs of quinine Eq: 41.2 (21.25-73.5) vs. 135 (118-150) ng/ml; MICs of mefloquine Eq: 18.2 (17-19.2) vs. 25.2 (24.4-26.8) ng/ml].

Pharmacokinetic interaction trial between co-artemether and mefloquine

Forty-two healthy subjects were randomized in a parallel three-group design trial to investigate potential electrocardiographic and pharmacokinetic interactions between the new antimalarial co-artemether, a combination of artemether and lumefantrine (both of which are predominantly metabolized through CYP3A4), and mefloquine, another antimalarial described as a substrate (and possible inhibitor) of CYP3A4. Subjects were assigned to one of the three possible treatment groups (i.e., co-artemether alone or mefloquine alone or the combination of both). The dosage was 1000 mg mefloquine (divided into three doses over 12 h) followed 12 h later by six applications of co-artemether (40 mg artemether+480 mg lumefantrine each) over 60 h. The study medications were generally well tolerated after all treatments. Concomitant administration with mefloquine caused statistically significant lower (around 30-40%) plasma concentrations of lumefantrine than when co-artemether was administered alone. Even if important, this decrease in lumefantrine exposure was considered unlikely to impact clinical efficacy given the wide therapeutic index of co-artemether and the usual high variability in lumefantrine plasma levels, mostly and more importantly influenced by food intake. However, patients should be encouraged to eat at dosing times to compensate for this decreased bioavailability. The pharmacokinetics of artemether, DHA or mefloquine were not affected. Artemether concentrations significantly decreased over doses, independently of mefloquine co-administration, while DHA concentrations slightly (not significantly) increased. Therefore, no clinically relevant risks due to pharmacokinetic drug-drug interaction are expected at the enzymatic level following co-administration of co-artemether with CYP3A4 substrates with similar affinity to that of mefloquine.

Pharmacokinetics and bioequivalence evaluation of three commercial tablet formulations of mefloquine when given in combination with dihydroartemisinin in patients with acute uncomplicated falciparum malaria

OBJECTIVE

To assess the pharmacokinetics and relative bioavailability/bioequivalence of three commercial tablet formulations of mefloquine, i.e. Lariam (reference formulation), Mephaquin 100 Lactab and Eloquin-250, when given sequentially after dihydroartemisinin in Thai patients with acute uncomplicated falciparum malaria.

METHODS

Twenty-nine Thai patients with acute uncomplicated falciparum malaria were randomised to receive an initial dose of 300 mg dihydroartemisinin, followed by 1250 mg mefloquine (at 24 h and 30 h after dihydroartemisinin) given as either Lariam (n=10 cases), Mephaquin (n=9 cases) or Eloquin-250 (n=10 cases). Serial blood samples were obtained up to day 42 after treatment with mefloquine. Mefloquine concentrations were determined in whole blood by means of ultraviolet high-performance liquid chromatography. The pharmacokinetic parameters of mefloquine were estimated using non-compartmental and compartmental analysis.

RESULTS

The three combination regimens were well tolerated. Patients in all treatment groups had a rapid initial response. However, nine patients (four and five cases in regimen containing Mephaquin 100 Lactab and Eloquin-250, respectively) had reappearance of parasitaemia during the follow-up period. Mefloquine from the three formulations showed significantly different pharmacokinetic and bioavailability metrics. Significantly lower peak plasma concentrations (C(max)) and areas under the plasma concentration-time curve (AUC; AUC(0-48h), AUC(0-7days), and total AUC) were observed with Mephaquin 100 Lactab than with the other two formulations. Mean values for relative bioavailability of the test to standard products were 49.1% (Mephaquin 100 Lactab) and 72.4% (Eloquine-250). Based on the criteria set, the bioavailability of the two test products (Mephaquin 100 Lactab and Eloquine-250) was considered non-equivalent to the reference product with respect to the rate (t(max), C(max)) and extent (AUC(0-48h), AUC(0-7days), total AUC) of mefloquine absorption.

Population pharmacokinetics of mefloquine in patients with acute falciparum malaria

OBJECTIVE

To construct a population pharmacokinetic model for mefloquine in the treatment of falciparum malaria.

BACKGROUND

Mefloquine is the treatment of choice for multidrug-resistant falciparum malaria. The factors that influence the pharmacokinetic properties of mefloquine in acute malaria are not well characterized.

METHODS

The pharmacokinetic properties of mefloquine were evaluated in 257 patients with acute falciparum malaria by use of nonlinear mixed-effects modeling. Two different oral dose regimens were used: (1) a split dose of 15 mg base/kg initially followed by 10 mg/kg 24 hours later (n = 159) and (2) a single dose of 25 mg/kg (n = 98). Mefloquine was combined with artesunate in 105 (41%) patients (74 received a split dose and 31 received a single dose).

RESULTS

Splitting the mefloquine dose increased the area under the concentration-time curve [AUC(0-infinity)] by 50% (95% confidence interval [CI], 36% to 65%) for monotherapy and by 20% (95% CI, 3% to 40%) for combined therapy. The apparent volume of distribution (V/F) was significantly lower in patients receiving split doses of mefloquine monotherapy (mean, 8.14 L/kg; 95% CI, 7.49 to 8.86 L/kg) compared with a single dose (mean, 20.37 L/kg; 95% CI, 16.26 to 25.51 L/kg). Patients who received mefloquine monotherapy and cleared parasitemia in less than 48 hours had a significantly higher AUC(0-infinity) independent of any confounders, compared with patients with slower parasite clearance (geometric mean [95% CI], 50,373 ng/mL x day [46,121 to 55,017 ng/mL x day] versus 45,583 ng/mL x day [42,306 to 49,125 ng/mL x day]).

CONCLUSIONS

The pharmacokinetic properties of mefloquine in malaria were relatively unaffected by demographic variables (other than body weight) or disease severity. If it is assumed that apparent clearance and volume of distribution are unaffected by dose regimen, then splitting the 25 mg/kg mefloquine dose improves oral bioavailability and the therapeutic response in the treatment of acute falciparum malaria.

Rapid absorption and clinical effectiveness of intragastric mefloquine in the treatment of cerebral malaria in African children

To obviate the lack of injectable quinine in a hospital in rural Burundi, mefloquine, only available as an oral formulation, was administered (25 mg/kg bodyweight) as a single dose by nasogastric tube to four small children with cerebral malaria. All patients recovered uneventfully after a mean coma duration of 20.5 h. Mefloquine was rapidly absorbed and therapeutic serum concentrations were achieved within a few hours in all subjects, with parasite reduction ratios after 48 h within the expected range for drug-sensitive parasites. These findings suggest that intragastric mefloquine deserves consideration whenever parenteral drugs are not available for the treatment of cerebral malaria.

Pharmacokinetic and pharmacodynamic interactions of mefloquine and dihydroartemisinin

Pharmacokinetic and pharmacodynamic interactions between dihydroartemisinin and mefloquine were investigated in 10 healthy Thai males. The study was of a three-way crossover design. Subjects were randomized to receive three drug regimens on three separate occasions as follows: regimen I: a single oral dose of 300 mg dihydroartemisinin; regimen II: a single oral dose of 750 mg mefloquine; regimen III: a single oral dose of 300 mg dihydroartemisinin, given concurrently with a single oral dose of 750 mg mefloquine. All regimens were well tolerated. Oral dihydroartemisinin was rapidly absorbed and disappeared from systemic circulation within 8-10 h. Mefloquine absorption and disposition were relatively slow processes. Pharmacokinetics of dihydroartemisinin and mefloquine when given concurrently were similar, except for the absorption rate of mefloquine which was faster in the presence of dihydroartemisinin. Pharmacodynamically, the combination of dihydroartemisinin and mefloquine resulted in a synergistic effect on ex vivo blood schizontocidal activity. Maximum activity (Amax) and area under effect-time curve (AUEC) of dihydroartemisinin and mefloquine were increased approximately two- and 20-fold (Amax), and four- and twofold, respectively, compared with each individual drug alone. AUEC of mefloquine during the first 24 h (AUEC 0-24 h) was increased approximately 50-fold in the presence of dihydroartemisinin.

Improved validated assay for the determination of mefloquine and its carboxy metabolite in plasma, serum and whole blood using solid-phase extraction and high-performance liquid chromatography

An improved high-performance liquid chromatography method using a low silanol activity octadecylsilica column and a solid-phase extraction technique is validated for the simultaneous analysis of mefloquine and its carboxy metabolite in whole blood, plasma and serum. An octadecylsilica column with high silanol activity is compared to a column of low activity in terms of pH dependent variability of chromatographic retention times for mefloquine and its carboxy metabolite. The low silanol activity column showed a relatively large mobile phase pH range where retention times for both components are consistent. The solid-phase extraction procedure consists of a simple protein precipitation step followed by sample concentration and extraction using a C18 membrane disk. The inter- and intra-assay variability for a therapeutic concentration of mefloquine (1000 ng/ml) is less than 2% in whole blood, plasma and serum while carboxymefloquine (1000 ng/ml) is 2.3% or less. At concentrations as low as 100 ng/ml the inter-assay variability is 6.2% or less for both analytes. This method shows a robust analytical procedure for the simultaneous analysis of mefloquine and its carboxy metabolite where precise measurements are useful in pharmacokinetic studies and in estimating drug compliance.

Pharmacokinetics of mefloquine combined with artesunate in children with acute falciparum malaria

Combining artemisinin or a derivative with mefloquine increases cure rates in falciparum malaria patients, reduces transmission, and may slow the development of resistance. The combination of artesunate, given for 3 days, and mefloquine is now the treatment of choice for uncomplicated multidrug-resistant falciparum malaria acquired on the western or eastern borders of Thailand. To optimize mefloquine administration in this combination, a prospective study of mefloquine pharmacokinetics was conducted with 120 children (4 to 15 years old) with acute uncomplicated falciparum malaria, who were divided into four age- and sex-matched groups. The patients all received artesunate (4 mg/kg of body weight/day orally for 3 days and mefloquine as either (i) a single dose (25 mg/kg) on day 2 with food, (ii) a split dose (15 mg/kg on day 2 and 10 mg/kg on day 3) with food, (iii) a single dose (25 mg/kg) on day 0 without food, or (iv) a single dose (25 mg/kg) on day 2 without food. Delaying administration of mefloquine until day 2 was associated with a mean (95% confidence interval) increase in estimated oral bioavailability of 72% (36 to 109%). On day 2 coadministration with food did not increase mefloquine absorption significantly, and there were no significant differences between patients receiving split- and single-dose administration. In combination with artesunate, mefloquine administration should be delayed until the second or third day after presentation.