ABSTRACT

Mefloquine was evaluated as an alternative for intermittent preventive treatment of malaria in pregnancy (IPTp) due to increasing resistance against the first-line drug sulfadoxine-pyrimethamine (SP). This study determined the pharmacokinetic characteristics of the mefloquine stereoisomers and the metabolite carboxymefloquine (CMQ) when given as IPTp in pregnant women. Also, the relationship between plasma concentrations of the three analytes and cord samples was evaluated, and potential covariates influencing the pharmacokinetic properties were assessed. A population pharmacokinetic analysis was performed with 264 pregnant women from a randomized controlled trial evaluating a single and a split-dose regimen of two 15-mg/kg mefloquine doses at least 1 month apart versus SP-IPTp. Both enantiomers of mefloquine and its carboxy-metabolite (CMQ), measured in plasma and cord samples, were applied for pharmacokinetic modelling using NONMEM 7.3. Both enantiomers and CMQ were described simultaneously by two-compartment models. In the split-dose group, mefloquine bioavailability was significantly increased by 5%. CMQ induced its own metabolism significantly. Maternal and cord blood concentrations were significantly correlated (r2 = 0.84) at delivery. With the dosing regimens investigated, prophylactic levels are not constantly achieved. A modeling tool for simulation of the pharmacokinetics of alternative mefloquine regimens is presented. This first pharmacokinetic characterization of mefloquine IPTp indicates adequate exposure in both mefloquine regimens; however, concentrations at delivery were below previously suggested threshold levels. Our model can serve as a valuable tool for researchers and clinicians to develop and optimize alternative dosing regimens for IPTp in pregnant women.

INTRODUCTION

Women in regions where malaria is endemic are particularly vulnerable to malaria in pregnancy and the early postpartum period (13). Intermittent preventive treatment in pregnancy (IPTp) is an effective prevention strategy against malaria in pregnancy in combination with insecticide-treated bed nets (4, 5). The effectiveness of sulfadoxine-pyrimethamine (SP)—the current standard drug for IPTp—is increasingly threatened due to an increasing frequency and level of drug-resistant Plasmodium falciparum isolates (6). Mefloquine (MQ)—an aryl amino alcohol antimalarial that has been used in the treatment and chemoprophylaxis of malaria for more than 25 years—has been considered a potential alternative drug for IPTp. Important characteristics include its favorable safety during pregnancy and high efficacy in sub-Saharan Africa (710). Importantly, its pharmacokinetic characteristics as a long-half-life drug make it particularly suitable as a prophylactic agent (11).
The exact mechanism of action of mefloquine has not been fully understood. It was originally hypothesized that mefloquine interferes with hemoglobin digestion inside the parasite’s food vacuole (12). However, studies have shown that intensive transport of mefloquine from the parasite cytoplasm into the food vacuole via Pgh-1 does not increase efficacy. Rather, this transporter seems to be the main reason for mefloquine resistance (13). Wong et al. demonstrated that (+)-mefloquine is a protein synthesis inhibitor which binds to the 80S ribosome (13). Since only the (+)-mefloquine was found in the cryo-electron microscopy (cryo-EM) structure of the P. falciparum 80S (Pf80S)-mefloquine complex, they suggest that the (–)-mefloquine may be a key factor for inhibiting other molecular targets (13). The presumption of different mechanisms of action for the mefloquine enantiomers corresponds with findings from the literature in which different antimalarial activities of the two enantiomers were detected (14). In contrast, the major metabolite carboxymefloquine (CMQ) has no antimalarial activity at all (15).
Mefloquine has recently been evaluated as alternative preventive drug for IPTp in pregnant women in sub-Saharan Africa. This large multicenter trial (MIPPAD trial; ClinicalTrials registration no. NCT0081121) was designed as a randomized controlled clinical trial comparing mefloquine with standard SP-IPTp in four African countries. IPTp was administered twice during pregnancy in this study, following World Health Organization (WHO) recommendations at that time. Mefloquine dosing was performed either as a 1-day, single-dose administration (15 mg/kg of body weight) or as a split-dose regimen (7.5 mg/kg of body weight on two consecutive days) in order to explore potential benefits in tolerability due to splitting drug administration (16, 17).
The pharmacokinetics (PK) of mefloquine have been well characterized for the treatment of pregnant women with clinical malaria by various dosing regimens (18, 19). These data indicated pharmacokinetic profiles similar to those of nonpregnant individuals, although one study suggested faster clearance of mefloquine during pregnancy (19). However, no data exist to date on the pharmacokinetics of mefloquine when administered as IPTp, a prevention strategy administered to asymptomatic and noninfected pregnant women. To improve our understanding of mefloquine IPTp, a pharmacokinetic study was conducted in a subsample of participants enrolled in the main clinical trial at the Gabonese study sites.
The objectives of this study were to determine the pharmacokinetic characteristics of the mefloquine stereoisomers and the metabolite CMQ when given as IPTp to pregnant women by using a population pharmacokinetic approach, to describe the relationship between plasma concentrations of the three analytes and cord samples, and to assess potential covariates influencing the pharmacokinetic properties.

RESULTS

Study population and data set.

A total of 1,180 pregnant women were recruited into the main clinical trial (MIPPAD trial) at the Gabonese study centers in Lambaréné and Fougamou. Among those, 263 agreed to participate in the pharmacokinetic study and were assigned to rich-PK (n = 37) or sparse-PK (n = 226) sampling protocols. Participants were on average 24 years old, their mean gestational age at study entry was 17.8 weeks, and their body weight ranged from 39 to 108 kg (mean, 58 kg) (Table 1). The demographic characteristics of the PK cohort did not differ significantly from those of the main trial population. Further, no difference was observable between the rich- and sparse-PK or the full- and split-dose populations.
TABLE 1
TABLE 1 Demographics of the study population at baseline (n = 263)
CharacteristicMean (SD)MedianRange
Age (yr)24.0 (6.75)22.014–44
Body mass index (kg/m²)23.2 (3.91)22.415.6–41.7
Body wt (kg)58.3 (10.8)55.939.3–108
Gestational age (wks)17.8 (5.85)19.08–28
Hemoglobin concn (g/dl]10.2 (1.38)10.35.7–14.7
In total, 924 (–)mefloquine, 923 (+)mefloquine, and 924 CMQ concentrations in blood from 263 participants (129 with the full-dose and 134 with the split-dose regimen) were available. Overall, cord samples were available from 126 women at birth. The number of plasma samples below the lower limit of quantification (LLOQ) ranged from 5.2% to 21.2%. Among (+)mefloquine cord blood samples at delivery, the number was higher, at 75.4% (see Table S1 in the supplemental material). Twenty-six women (10 split-dose and 16 full-dose patients) attended only the first dosing interval. While the majority of study participants contributed 3.5 blood samples for the sparse pharmacokinetic analysis, 37 patients (12 single-dose and 25 split-dose patients) agreed to provide 5 to 14 samples (median, 11) to obtain a “rich” pharmacokinetic profile.
For single- and split-dose regimens, substantial interpatient variability was observed in the mefloquine pharmacokinetic profiles of the enantiomers and the metabolite CMQ for the rich-PK subgroup, which was most striking during the absorption and early distribution phases (Fig. 1). Many of the mefloquine pharmacokinetic profiles were characterized by a sharp rise in mefloquine concentrations, double and multiple peaks, and a second, slow increase after 1 week. No significant difference in the concentration-time profiles was observable between the full- and split-dose groups.
FIG 1
FIG 1 Observed individual plasma concentration-time profiles of (–)mefloquine, (+)mefloquine, and the metabolite carboxymefloquine, separated by dose group. Each line indicates one individual subject. The blue dashed lines reflect the LLOQ.
There was evidence of accumulation of the maximum concentrations and predose levels, defined as an increase from the first to the second IPTp administration. The median maximum concentrations following the first IPTp administration were observed at 611 nmol/liter (interquartile range [IQR], 376 to 954 nmol/liter), 357 nmol/liter (IQR, 144 to 624 nmol/liter), and 402 nmol/liter (IQR, 245 to 613 nmol/liter) for (–)MQ, (+)MQ, and CMQ, respectively. Congruently, the median maximum observed concentrations were higher after the second IPTp administration: 881 nmol/liter (IQR, 311 to 1,132 nmol/liter) and 465 nmol/liter (IQR, 173 to 722 nmol/liter nmol/liter) for (–)MQ and CMQ, respectively. For (+)MQ, no increase was observed, with a median of 341 nmol/liter (IQR, 24 to 572 nmol/liter). At the first IPTp administration, the predose levels were mostly below the LLOQ. Before the second IPTp administration, the median predose levels were increased, at 274 nmol/liter (IQR, 198 to 395 nmol/liter), 13.7 nmol/liter (IQR, 5.6 to 27.5 nmol/liter), and 261 nmol/liter (IQR, 200 to 398 nmol/liter) for (–)MQ, (+)MQ, and CMQ, respectively.

Population PK model.

A combined population pharmacokinetic model, describing the plasma and cord concentrations of the (+) and (–) enantiomers of mefloquine and its metabolite CMQ well, was developed. The final structural PK model is shown in Fig. 2; parameter estimates are provided in Table 2. Goodness-of-fit plots (see Fig. S2 in the supplemental material) showed that these data were well described by the final PK model. A visual predictive check (VPC) stratified by analyte and matrix showed a good descriptive performance with neither bias nor under- or overestimation of the model variability (see Fig. S3 in the supplemental material).
FIG 2
FIG 2 Schematic representation of the final PK model of (–)mefloquine [(–)MQ] (red), (+)mefloquine [(+)MQ] (blue), and the metabolite carboxymefloquine (CMQ) (black). Cord compartments are represented by ellipses color-coded by compound. The metabolizing enzyme pool is displayed in orange. Due to increased CMQ concentrations, PXR binding mediates the induction of the enzymatic RNA, followed by an increased enzyme pool. The amount of enzyme in the enzyme pool is linearly linked to the CMQ clearance (the higher the enzyme pool, the higher the CMQ clearance). Solid arrows indicate mass transfer between the compartments; dashed arrows indicate processes without a significant mass transfer. VCentral, volume of distribution in the central compartment; VPeriph, volume of distribution in the peripheral compartment.
TABLE 2
TABLE 2 Estimated parameter values for the final PK model
ParametereValue90% CIaDescription
Fixed effects
    Ka(–)MQ (1/h)0.1570.023–0.303First-order absorption rate constant for (–)MQ
    Vcentral,(–)MQ/F (liters)b476132–801Apparent volume of distribution central compartment for (–)MQ
    Q(–)MQ/F (liters/h)85.712.8–120.5Intercompartmental clearance of (–)MQ
    Vperipheral,(–)MQ/F (liters)860657–1,173Apparent volume of distribution peripheral compartment for (–)MQ
    CL(–)MQ/F (liters/h)1.491.38–1.60Apparent clearance of (–)MQ
    Ka(+)MQ (1/h)0.2090.032–0.329First-order absorption rate constant for (+)MQ
    Vcentral,(+)MQ/F (liters)b814252–1,230Apparent volume of distribution central compartment for (+)MQ
    Q(+)MQ/F (liters/h)14122.2–182Intercompartmental clearance of (+)MQ
    Vperipheral,(+)MQ/F (liters)1,070808–1,492Apparent volume of distribution peripheral compartment for (+)MQ
    CL(+)MQ/F (liters/h)8.287.55–9.28Apparent clearance of (+)MQ
    Vcentral,CMQ/F (liters)47.87.6–62.0Apparent volume of distribution central compartment for CMQ
    QCMQ/F (liters/h)16.811.9–20.1Intercompartmental clearance of CMQ
    Vperipheral,CMQ/F (liters)968657–1,063Apparent volume of distribution peripheral compartment for CMQ
    CLCMQ/F (liters/h)1.120.78–2.58Apparent clearance of CMQ
    Emax3.380.54–5.07Maximum induction of synthesis rate
    EC50 (nmol/liter)2.45FIXcCMQ concn achieving half-maximum induction effect
    Kdeg (1/h)0.004530.00144–0.6433Elimination rate of metabolizing enzyme pool
    WTexponent1.330.42–2.48Effect of wt on V1,(–)MQ/F and V1,(+)MQ/F
    SPLIT1.051.01–1.16Effect of split dose on relative bioavailability
    CORD1FIXcRatio of drug concentration in cord blood to that in plasma
Random effects: interindividual variability
    IIV Vcentral,MQ (%CV)11980.3–189IIV on volume of distribution central compartment for (–)MQ and (+)MQ
    IIV CLMQ (%CV)34.633.7–47.3IIV on clearance of (–)MQ and (+)MQ
    IIV CLCMQ (%CV)42.739.4–55.6IIV on clearance of CMQ
Random effects: residual variabilityd
    PRV(–)MQ plasma (%)29.927.6–34.8Proportional residual error for (–)MQ in plasma
    ARV(–)MQ plasma (± nmol/liter)5313.4–69.9Additive residual error for (–)MQ in plasma
    PRV(+)MQ plasma (%)38.535.7–45.4Proportional residual error for (+)MQ in plasma
    ARV(+)MQ plasma (± nmol/liter)128.4–17.5Additive residual error for (+)MQ in plasma
    PRVCMQ plasma (%)24.821.5–35.6Proportional residual error for CMQ in plasma
    ARVCMQ plasma (± nmol/liter)638.6–94.8Additive residual error for CMQ in plasma
    PRV(–)MQ cord (%)3922.6–47.1Proportional residual error for (–)MQ in cord
    ARV(–)MQ cord (± nmol/liter)291.2–36.4Additive residual error for (–)MQ in cord
    PRV(+)MQ cord (%)18048.2–257Proportional residual error for (+)MQ in cord
    ARV(+)MQ cord (± nmol/liter)21.7–3.7Additive residual error for (+)MQ in cord
    PRVCMQ cord (%)40.237.6–55.9Proportional residual error for CMQ in cord
    ARVCMQ cord (± nmol/liter)10.1–5.8Additive residual error for CMQ in cord
a
90% CI, ninety percent bootstrap confidence interval based on 250 replicates.
b
V1,(–),(+)MQ/F – individual = V1,(–),(+)MQ/F × (individual weight/55)WTexponent.
c
Parameters were fixed to the respective value and were not estimated by the algorithm.
d
PRV, proportional residual variability; ARV, additive residual variability.
e
/F, over bioavailability.

(i) Mefloquine PK model.

Plasma concentration-time profiles of the enantiomers of mefloquine were best described by two-compartment disposition models. Absorption of (–)MQ and (+)MQ was best described by a first-order process, where the absorption half-life was similar for both enantiomers [4.4 h for (–)MQ and 3.3 h for (+)MQ). Implementation of an enterohepatic circulation process (20) or other modifications of the absorption process (e.g., lag time, parallel absorption process) did not improve the model significantly, presumably due to the low number of samples obtained during the absorption phase. Covariate analysis revealed that the relative bioavailability under the split-dose regimen was statistically significantly increased by 5%. The total volume of distribution was large, with 1,330 liters and 1,884 liters for (–)MQ and (+)MQ, respectively. Covariate analysis demonstrated further that body weight at baseline had a significant effect on the central volumes of distribution of both enantiomers. The effect on the volume of distribution was modelled allometrically centered around the median body weight of 55 kg with an estimated exponent of 1.33, where an increased body weight resulted in increased volumes of distribution. A more complex model incorporating the change of body weight during gestation did not improve the model significantly. Both enantiomers were metabolized by a first-order clearance process into CMQ, where the clearance of (+)MQ was estimated to be about 5-fold higher than that of (–)MQ. Since the interindividual variabilities (IIVs) were highly correlated for the volumes and clearance processes for both enantiomers, a common IIV was established on the central volumes of distribution and the clearance of both enantiomers. The IIVs were estimated to be moderate (coefficient of variation [%CV], 35) and high (%CV, 120) for the clearances and central volumes of distribution, respectively.

(ii) CMQ PK model.

The plasma concentration-time profiles of the metabolite CMQ were also best described by a two-compartment disposition model. The total volume of distribution was estimated to be large, at 1,015.8 liters, but the central volume of distribution was estimated to be between 10- and 20-fold lower than those of the mefloquine enantiomers. CMQ clearance was best described by a first-order process but was significantly (P < 0.0001) autoinduced by its own plasma concentrations. This process was included in the model by two consecutive turnover models, where the first model echoes the transcription process of metabolizing enzymes. The zero-order synthesis rate was induced by CMQ concentrations in the plasma using a proportional maximum-effect (Emax) model, where the maximum induction was estimated as a 3.38-fold increase of the synthesis rate and the 50% effective concentration (EC50) was determined at 2.45 nmol/liter. The second turnover model reflects the metabolizing enzyme pool. The zero-order synthesis rate was influenced by the amount in the precursor compartment. The half-life of the metabolizing enzyme pool was estimated at 152 h. A moderate IIV (%CV, 43) was established on the CMQ clearance.

(iii) Transplacental distribution.

Median plasma concentrations at delivery were 85 nmol/liter (IQR, 43 to 163 nmol/liter), 8.3 nmol/liter (IQR, 6.3 to 31.3 nmol/liter), and 35.6 nmol/liter (IQR, 23 to 69 nmol/liter) for (–)MQ, (+)MQ, and CMQ, respectively. In cord blood, median concentrations were similar, with 95 nmol/liter (IQR, 38 to 172 nmol/liter), 8.2 nmol/liter (IQR, 6.7 to 39 nmol/liter), and 39 nmol/liter (IQR, 25 to 71 nmol/liter) for (–)MQ, (+)MQ, and CMQ, respectively (n = 128). The ratio of drug concentrations in cord blood to those in maternal blood as an indicator of transplacental drug distribution was 0.98 (IQR, 0.77 to 1.30), 0.97 (IQR, 0.78 to 1.32), and 1.02 (IQR, 0.78 to 1.32) for (–)MQ, (+)MQ, and CMQ, respectively. Nonparametric analysis revealed a highly statistically significant correlation between maternal and cord blood drug concentrations (Fig. 3) (r2 = 0.84; P < 0.0001). Cord concentrations were also included in the PK model. Several structural models were tested, including a time delay using effect compartments. Finally, cord samples were best described by a direct correlation with the respective plasma concentrations. For all three analytes, the same “cord-to-plasma” factor was sufficient, estimated at 0.984 and in the final model fixed at 1 without losing descriptive performance.
FIG 3
FIG 3 Observed plasma concentrations versus observed cord concentrations upon delivery of the analytes (–)mefloquine, (+)mefloquine, and their metabolite carboxymefloquine. Solid lines represent the line of identity.

Simulations.

Simulations were performed to visualize the complex pharmacokinetics and the effect of covariates using the final PK model. If a fixed dose of 825 mg is administered, which is the absolute dose for a typical study participant in this study (15 mg/kg at a body weight of 55 kg), the effect of body weight on the plasma concentration-time profiles is negligible (Fig. 4). If mefloquine is administered in a body-weight-adjusted manner, a body-weight-dependent increase in exposure can be observed (see Fig. S4 in the supplemental material). The effect of a split-dose regimen on the plasma concentration-time profiles is negligible (see Fig. S5 in the supplemental material). If 1,000 mg mefloquine is administered as a loading dose, followed by a maintenance dose of 250 mg once weekly, steady-state trough values above 500 ng/ml total mefloquine can be achieved quickly for patients weighing less than 64 kg (Fig. 5).
FIG 4
FIG 4 Simulation of fixed-dose administration of the complete 825 mg of mefloquine (full dose) on day 1 and day 50. Median plasma concentration-time profiles of subjects with various body weights (WT; given in kilograms) are shown. The upper dashed reference line indicates 620 ng/ml (equal to 1,638 nmol/liter); the lower dashed reference line indicates 500 ng/ml (equal to 1,321 nmol/liter).
FIG 5
FIG 5 Simulation of a fixed-dose administration of 1,000 mg mefloquine as a loading dose on day 1 and 250 mg once weekly to subjects with various body weights (WT; given in kilograms). The upper dashed reference line indicates 620 ng/ml (equal to 1,638 nmol/liter); the lower dashed reference line indicates 500 ng/ml (equal to 1,321 nmol/liter).

DISCUSSION

This is the first study evaluating the enantioselective pharmacokinetics of mefloquine and its metabolite carboxymefloquine when given as IPTp to pregnant African women. This information is useful for fully understanding the efficacy findings and for deciding on the most efficacious dosing regimen. These data indicate that mefloquine administered as IPTp at 15 mg/kg shows considerable interpatient variability in concentration-time profiles in peripheral blood. As in previous reports, considerable fluctuations of concentrations of both mefloquine enantiomers during the first days after administration were commonly observed in both full- and split-dose regimens (21). This may be explained by variability in drug absorption and a complex interplay between saturated absorption pathways, distribution, and enterohepatic recirculation.
Despite the variability in the observed data, a robust and descriptive population pharmacokinetic model was developed. To our knowledge, this is the first time that the pharmacokinetics for both enantiomers and the major metabolite carboxymefloquine was modeled simultaneously in plasma and cord samples. For all three analytes, a two-compartment disposition model described the concentration-time profiles best. This is in line with the literature, where two-compartment models were applied for total mefloquine and the enantiomers (22, 23). Even though both enantiomers could be described by the same structural model, a marked difference was observable in the clearance parameters between the two enantiomers. This was reflected in significantly faster elimination of the (+) enantiomer than of the (–) enantiomer, which is also described in the literature (2325).
Mefloquine enantiomers showed a high volume of distribution, considerably higher than the previously published 10 liters/kg for Thai pregnant women suffering from malaria and treated with the same dose of mefloquine (18). Similarly, a (–)MQ terminal half-life significantly shorter than that in the Gabonese study population (173 h compared to ∼620 h) was reported in the above-cited study (18). This discrepancy may be at least partly explained by the fact that mefloquine was given for the treatment of pregnant women suffering from clinical malaria, as opposed to asymptomatic and presumably aparasitemic women in the present study. It was previously hypothesized that differences in the elimination of mefloquine may be explained by a reduced enterohepatic circulation leading to a shorter elimination half-life in individuals suffering from acute disease (18, 2628). However, in male patients with falciparum malaria, the elimination half-life of (–)MQ was in the same range, at ∼750 h.
Population pharmacokinetic analysis confirmed a beneficial effect on exposure of splitting the mefloquine dose into two doses at intervals of 24 h. The relative bioavailability was estimated to be increased by ∼5% in the split-dose group. The effect is smaller than that in other studies, where increases in mefloquine exposure as high as 50% were reported (26). A mechanistic explanation could be provided by saturation of intestinal or hepatic uptake processes, including membrane transporters, after administration of the full mefloquine dose. However, it is still unknown whether mefloquine is also a substrate of specific uptake transporters, such as organic anion/cation transporters or organic anion-transporting proteins (29). In the context of the clinical trial, and based on the fact that malaria-related outcomes did not differ between mefloquine dosing regimens, the observed difference in mefloquine bioavailability between the two dosing regimens may have only limited clinical significance. This was also confirmed by simulations showing a negligible difference in the concentration-time profiles of the two regimens. These study data therefore indicate that single-dose IPTp regimens of mefloquine—with all their advantages from a programmatic point of view—may lead to adequate drug exposure.
Covariate analysis revealed also that body weight has a significant effect on the volume of distribution of both mefloquine enantiomers, where a higher body weight results in an increased volume of distribution. This effect has also been described in other analyses (23) and is not unexpected for a compound with large volumes of distribution. Nevertheless, simulations have shown that the effect of body weight on mefloquine exposure is negligible if a fixed dose is administered. If mefloquine is dosed according to body weight, a body-weight-dependent increase in exposure can be detected, which is only related to the higher absolute dose administered and has no physiological basis. It should therefore be considered whether dosing based on body weight is truly justified or whether a fixed dose would be preferable given its programmatic advantages.
In our analysis, the major metabolite carboxymefloquine was included in the comprehensive mefloquine PK model. In vitro studies showed recently that carboxymefloquine induces drug-metabolizing enzyme and transporter expression by activation of the pregnane X receptor (PXR) (30). In the reported analysis, the induction effect was strong and comparable to that of rifampin, one of the most potent and clinically relevant inducers of metabolizing enzymes and drug transporters. Our analysis showed, for the first time, that carboxymefloquine also has the potential to induce metabolizing processes in vivo. We revealed that CMQ induces its own metabolism up to 4-fold in a time-dependent manner. To our knowledge, it is unclear how CMQ is metabolized, and further research is required. But it should be highlighted that currently only a few human drug-drug interaction studies with mefloquine are available, focusing on cytochrome P450 (CYP) inhibition. Our study reveals that an in vivo drug-drug interaction potential exists for CMQ as an inducer of PXR and should be investigated more closely in the context of the clinical application of mefloquine.
A longer SP-IPTp than the previously endorsed two-dose regimen is now recommended to provide effective prophylactic activity during the second and third trimesters of pregnancy (31). To further investigate the potential duration of preventive efficacy, proposed thresholds for effective prophylactic activity have been collated from published literature. Several differing thresholds of plasma mefloquine concentrations for chemoprophylaxis, ranging from 500 ng/ml to 620 ng/ml, have been proposed (32, 33). These estimates correlated with plasma mefloquine concentrations used for curative therapy in individuals with recrudescent infections in Thailand before the development of mefloquine resistance, ranging from 546 ng/ml to 730 ng/ml (1,400 to 1,900 nmol/liter) (34). These proposed prophylactic levels were in the range of peak mefloquine concentrations in this study, but simulations showed that no constant concentration levels above the thresholds could be achieved. However, peak drug concentrations reported by others for pregnant women after the administration of a single dose of 15 mg/kg mefloquine were in a similar range, and this regimen, when used as IPTp, proved to be highly efficacious (18, 35). Simulations showed that a mefloquine loading dose of 1,000 mg, followed by maintenance dosing of 250 mg, would lead to adequate exposure, with trough levels above 500 ng/ml. A Web-based exposure simulator of the model presented is available online at www.mefloquine.de, allowing researchers and clinicians interested in mefloquine to develop and optimize alternative dosing regimens for IPTp.
Due to the long half-life of mefloquine, blood concentrations were detectable at birth. However, these concentrations were well below the above-mentioned threshold for chemoprophylaxis, indicating that a higher frequency of dosing may be needed to provide adequate protection during the entire period of pregnancy. At delivery, median mefloquine concentrations were within a similar range in maternal blood and in cord blood, and a high level of correlation between paired maternal and cord blood samples was demonstrated. It may therefore be speculated that drug exposure in the fetus closely follows the concentration-time profile of the cord and the pregnant mother. This hypothesis is further supported by a human placenta perfusion model indicating a constant fetal-maternal mass ratio for mefloquine at 120 min of drug exposure, and similar data have been reported for chloroquine in pregnant women in Papua New Guinea (36, 37).
The limitations of this study include a proportion of participants not fully complying with the blood sampling schedule due to loss to follow-up or premature withdrawal from the clinical trial. This is partly explained by the challenge of repeated blood sampling in pregnant women. In addition, the complex initial absorption and distribution phase could not be considered in the PK model due to the limited number of sampling time points. However, the number and scheduling of blood samples obtained during the study were adequate to yield reliable PK estimates as confirmed by bootstrapping analysis, a procedure that provides reassurance for the robustness and generalizability of the reported findings.
MQ-IPTp has been proven to be highly efficacious against malaria, but its use as standard IPTp regimen is currently precluded due to poor tolerability. This pharmacokinetic analysis confirms that mefloquine is an antimalarial with complex initial absorption and early distribution phases, a high volume of distribution, and a long half-life in asymptomatic, apparently healthy pregnant women from sub-Saharan Africa. Transplacental distribution measures indicate comparable drug exposure of the fetus. Given the programmatic problems associated with unsupervised drug intake, the reported minor increase in the relative bioavailability of mefloquine as a full-dose regimen most likely does not justify the recommendation of a split-dose regimen for IPTp. The major metabolite carboxymefloquine was identified as a potent inducer of metabolizing enzymes in vivo and should be monitored more closely in the future to avoid drug-drug interactions. More-frequent dosing of mefloquine may be required to provide adequate prophylactic drug levels throughout pregnancy and until delivery. Despite problems in the tolerability of mefloquine when administered as IPTp, these pharmacokinetic data and the online exposure simulator provided can serve as valuable tools for researchers and clinicians interested in alternative dosing regimens of mefloquine.

MATERIALS AND METHODS

Study region and population.

This study was an ancillary study of a large multinational randomized, controlled clinical trial (MIPPAD [Malaria in Pregnancy Preventive Alternative Drugs]; ClinicalTrials registration no. NCT0081121, Pan African Clinical Trials registration no. PACTR2010020001429343). The clinical trial had the objective of investigating the efficacy, tolerability, and safety of mefloquine as a potential candidate drug alternative to SP as IPTp in sub-Saharan Africa. The pharmacokinetic study was performed at the two study centers in Gabon: the Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, in the province of Moyen Ogooue, and the Centre de Recherches Médicales de Fougamou, Regional Hospital of Fougamou, in the neighboring province of La Ngounie. Both study regions are rural communities in the tropical rainforest, characterized by a tropical Central African climate (38). P. falciparum is the main causative agent for human malaria, with high in vitro resistance to chloroquine and SP and in vitro susceptibility to mefloquine (39).

Study design.

All participants in the MIPPAD trial allocated to the mefloquine IPTp arm were eligible for inclusion in this study. The main inclusion criteria were attendance for a first antenatal care visit between 13 and 28 weeks of gestation, and exclusion criteria were human immunodeficiency virus (HIV) infection and allergy to study drugs. After recruitment to the main trial, pregnant women were fully informed about the conduct of the pharmacokinetics study and all study-related procedures and were invited to participate in that study.
All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The study was approved by the responsible ethics committee (Comité d’Ethique de Lambaréné), and written informed consent was provided by all participants.
Details on the design and conduct of the MIPPAD trial are reported in a separate article (16). In brief, participants were randomly allocated to one of three IPTp regimens, consisting of SP (a single dose of 3 tablets), single-dose mefloquine (15 mg/kg), or split-dose mefloquine (7.5 mg/kg/day on two consecutive days). IPTp was administered at the earliest visit during the second trimester (13 to 28 weeks of gestation). A second dose of IPTp was administered at least 1 month after the first IPTp administration. Pregnant women were followed up until 1 month postpartum, and offspring were revisited until their first birthday.
Information on the sampling schedule for pharmacokinetic analysis, bioanalytics, and the pharmacokinetic analysis and statistical considerations is provided in the supplemental material.

ACKNOWLEDGMENTS

We acknowledge the contributions of Mesküre Capan, Moritz Fürstenau, Mario Jäckle, Christian Kleine, Joachim Melser, Ulla Schipulle, Meike Schlie, Julia Schwing, Florian Thol, and Malte Witte to the conduct of the study. We gratefully acknowledge the participation of the pregnant women in this pharmacokinetic study.
The main clinical trial (MIPPAD) was funded by grants from EDCTP (EDCTPIP.07.31080.002) and BMBF (FKZ 01KA0803) and by the Malaria in Pregnancy Consortium, which is funded through a grant from the Bill and Melinda Gates Foundation to the Liverpool School of Tropical Medicine. Additional funding was received by from the DFG (grant KE 1629/1-1), BMBF (grant 01KA1011), European Commission Horizon 2020 UPGx program (grant 668353), and Robert Bosch Foundation (Stuttgart, Germany).
We have no conflicts of interest to declare.
M.R., G.M.-N., M.S., P.G.K., and R.K. wrote the manuscript. M.R., G.M.-N., R.G., M.S., P.G.K., C.M., and R.K. designed the research. M.R., G.M.-N., R.Z.M., D.A.-D., A.B., J.-R.M., H.W., P.-B.M., and J.-G.W. performed the research and contributed to the writing of the manuscript. U.H., M.G., T.L., M.S., and R.K. analyzed the data.

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Information & Contributors

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Published In

cover image Antimicrobial Agents and Chemotherapy
Antimicrobial Agents and Chemotherapy
Volume 63Number 2February 2019
eLocator: 10.1128/aac.01113-18

History

Received: 31 May 2018
Returned for modification: 18 July 2018
Accepted: 8 November 2018
Published online: 29 January 2019

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Keywords

  1. Plasmodium falciparum
  2. malaria
  3. mefloquine
  4. population pharmacokinetics
  5. pregnancy

Contributors

Authors

Michael Ramharter
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Department of Tropical Medicine, Bernhard Nocht Institute for Tropical Medicine & I. Department of Medicine University Medical Center Hamburg-Eppendorf, Hamburg, Germany
Matthias Schwab
Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany
Department of Clinical Pharmacology, University Hospital, Tübingen, Germany
Ghyslain Mombo-Ngoma
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Department of Tropical Medicine, Bernhard Nocht Institute for Tropical Medicine & I. Department of Medicine University Medical Center Hamburg-Eppendorf, Hamburg, Germany
Département de Parasitologie, Université des Sciences de la Santé, Libreville, Gabon
Rella Zoleko Manego
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Department of Tropical Medicine, Bernhard Nocht Institute for Tropical Medicine & I. Department of Medicine University Medical Center Hamburg-Eppendorf, Hamburg, Germany
Ngounié Medical Research Centre, Fougamou, Gabon
Daisy Akerey-Diop
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Arti Basra
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Jean-Rodolphe Mackanga
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Heike Würbel
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Jan-Georg Wojtyniak
Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany
Clinical Pharmacy, Saarland University, Saarbrücken, Germany
Raquel Gonzalez
Barcelona Centre for International Health Research (CRESIB, Hospital Clínic—Universitat de Barcelona), Barcelona, Spain
Ute Hofmann
Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany
Department of Clinical Pharmacology, University Hospital, Tübingen, Germany
Mirjam Geditz
Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany
Department of Clinical Pharmacology, University Hospital, Tübingen, Germany
Pierre-Blaise Matsiegui
Ngounié Medical Research Centre, Fougamou, Gabon
Peter G. Kremsner
Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
Institut für Tropenmedizin, Universität Tübingen, Tübingen, Germany
Clara Menendez
Barcelona Centre for International Health Research (CRESIB, Hospital Clínic—Universitat de Barcelona), Barcelona, Spain
Reinhold Kerb
Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany
Department of Clinical Pharmacology, University Hospital, Tübingen, Germany
Thorsten Lehr
Clinical Pharmacy, Saarland University, Saarbrücken, Germany

Notes

Address correspondence to Michael Ramharter, [email protected].
M.R., M.S., C.M., R.K., and T.L. contributed equally to this work.

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