Pyronaridine: a review of its clinical pharmacology in the treatment of malaria.

Pyronaridine-artesunate was recently strongly recommended in the 2022 update of the WHO Guidelines for the Treatment of Malaria, becoming the newest artemisinin-based combination therapy (ACT) for both uncomplicated Plasmodium falciparum and Plasmodium vivax malaria. Pyronaridine-artesunate, available as a tablet and paediatric granule formulations, is being adopted in regions where malaria treatment outcome is challenged by increasing chloroquine resistance. Pyronaridine is an old antimalarial agent that has been used for more than 50 years as a blood schizonticide, which exerts its antimalarial activity by interfering with the synthesis of the haemozoin pigment within the Plasmodium digestive vacuole. Pyronaridine exhibits a high blood-to-plasma distribution ratio due to its tendency to accumulate in blood cells. This feature is believed to play a crucial role in its pharmacokinetic (PK) properties and pharmacological activity. The PK characteristics of pyronaridine include rapid oral absorption, large volumes of distribution and low total body clearance, resulting in a long terminal apparent half-life. Moreover, differences in PK profiles have been observed between healthy volunteers and malaria-infected patients, indicating a potential disease-related impact on PK properties. Despite a long history, there is only limited knowledge of the clinical PK and pharmacodynamics of pyronaridine, particularly in special populations such as children and pregnant women. We here provide a comprehensive overview of the clinical pharmacology of pyronaridine in the treatment of malaria.

Efavirenz-Based Antiretroviral Therapy but Not Pregnancy Increased Unbound Piperaquine Exposure in Women during Malaria Chemoprevention.

Dihydroartemisinin-piperaquine (DP) is highly effective for malaria chemoprevention during pregnancy, but the standard dosing of DP that is used for nonpregnant adults may not be optimal for pregnant women. We previously reported that the pharmacokinetic exposure of total piperaquine (PQ; both bound and unbound to plasma proteins) is reduced significantly in the context of pregnancy or efavirenz (EFV)-based antiretroviral therapy (ART). However, as PQ is >99% protein-bound, reduced protein binding during pregnancy may lead to an increase in the pharmacologically active unbound drug fraction (fu), relative to the total PQ. We investigated the impact of pregnancy and EFV use on the fu of PQ to inform the interpretation of pharmacokinetics. Plasma samples from 0 to 24 h after the third (final) DP dose were collected from pregnant women at 28 weeks gestation who were receiving or not receiving EFV-based ART as well as from women 34 to 54 weeks postpartum who were not receiving EFV-based ART, who served as controls. Unbound PQ was quantified via ultrafiltration and liquid chromatography-tandem mass spectrometry, with fu being calculated as PQunbound/PQtotal. The geometric mean fu did not differ between pregnant and postpartum women (P = 0.66), but it was 23% (P < 0.01) greater in pregnant women receiving EFV-based ART, compared to that in postpartum women who were not receiving EFV-based ART. The altered drug-protein binding, potentially due to the displacement of PQ from plasma proteins by EFV, resulted in only a 14% lower unbound PQ exposure (P = 0.13) in the presence of a 31% lower total PQ exposure (P < 0.01), as estimated by the area under the concentration time curve from 0 to 24 h post-last dose in pregnant women who were receiving EFV-based ART. The results suggest that the impact of pregnancy and EFV-based ART on the exposure and, in turn, the efficacy of PQ for malaria prevention may not be as significant as was suggested by the changes in the total PQ exposure. Further study during the terminal elimination phase (e.g., on day 28 post-dose) would help better characterize the unbound PQ exposure during the full dosing interval and, thus, the overall efficacy of PQ for malaria chemoprevention in this special population.

A Water-Soluble Polymer-Lumefantrine Conjugate for the Intravenous Treatment of Severe Malaria.

Uncomplicated malaria is effectively treated with oral artemisinin-based combination therapy (ACT). Yet, there is an unmet clinical need for the intravenous treatment of the more fatal severe malaria. There is no combination intravenous therapy for uncomplicated due to the nonavailability of a water-soluble partner drug for the artemisinin, artesunate. The currently available treatment is a two-part regimen split into an intravenous artesunate followed by the conventional oral ACT . In a novel application of polymer therapeutics, the aqueous insoluble antimalarial lumefantrine is conjugated to a carrier polymer to create a new water-soluble chemical entity suitable for intravenous administration in a clinically relevant formulation . The conjugate is characterized by spectroscopic and analytical techniques, and the aqueous solubility of lumefantrine is determined to have increased by three orders of magnitude. Pharmacokinetic studies in mice indicate that there is a significant plasma release of lumefantrine and production its metabolite desbutyl-lumefantrine (area under the curve of metabolite is ≈10% that of the parent). In a Plasmodium falciparum malaria mouse model, parasitemia clearance is 50% higher than that of reference unconjugated lumefantrine. The polymer-lumefantrine shows potential for entering the clinic to meet the need for a one-course combination treatment for severe malaria.

Impact of Drug Exposure on Resistance Selection Following Artemether-Lumefantrine Treatment for Malaria in Children With and Without HIV in Uganda.

Artemisinin-based combination therapies (ACTs) are the primary treatment for malaria. It is essential to characterize the pharmacokinetics (PKs) and pharmacodynamics (PDs) of ACTs in vulnerable populations at risk of suboptimal dosing. We developed a population PK/PD model using data from our previous study of artemether-lumefantrine in HIV-uninfected and HIV-infected children living in a high-transmission region of Uganda. HIV-infected children were on efavirenz-, nevirapine-, or lopinavir-ritonavir-based antiretroviral regimens, with daily trimethoprim-sulfamethoxazole prophylaxis. We assessed selection for resistance in two key parasite transporters, pfcrt and pfmdr1, over 42-day follow-up and incorporated genotyping into a time-to-event model to ascertain how resistance genotype in relation to drug exposure impacts recurrence risk. Two hundred seventy-seven children contributed 364 episodes to the model (186 HIV-uninfected and 178 HIV-infected), with recurrent microscopy-detectable parasitemia detected in 176 episodes by day 42. The final model was a two-compartment model with first-order absorption and an estimated age effect on bioavailability. Systemic lumefantrine exposure was highest with lopinavir-ritonavir, lowest with efavirenz, and equivalent with nevirapine and HIV-uninfected children. HIV status and lumefantrine concentration were significant factors associated with recurrence risk. Significant selection was demonstrated for pfmdr1 N86 and pfcrt K76 in recurrent infections, with no evidence of selection for pfmdr1 Y184F. Less sensitive parasites were able to tolerate lumefantrine concentrations ~ 3.5-fold higher than more sensitive parasites. This is the first population PK model of lumefantrine in HIV-infected children and demonstrates selection for reduced lumefantrine susceptibility, a concern as we confront the threat to ACTs posed by emerging artemisinin resistance in Africa.

A pharmacometrics approach to assess the feasibility of capillary microsampling to replace venous sampling in clinical studies: Tafenoquine case study.

AIM: Microsampling has the advantage of smaller blood sampling volume and suitability in vulnerable populations compared to venous sampling in clinical pharmacokinetics studies. Current regulatory guidance requires correlative studies to enable microsampling as a technique. A post hoc population pharmacokinetic (POPPK) approach was utilized to investigate blood capillary microsampling as an alternative to venous sampling. METHODS: Pharmacokinetic data from microsampling and venous sampling techniques during a paediatric study evaluating tafenoquine, a single-dose antimalarial for P. vivax, were used. Separate POPPK models were developed and validated based on goodness of fit and visual predictive checks, with pharmacokinetic data obtained via each sampling technique. RESULTS: Each POPPK model adequately described tafenoquine pharmacokinetics using a two-compartment model with body weight based on allometric scaling of clearance and volume of distribution. Tafenoquine pharmacokinetic parameter estimates including clearance (3.4 vs 3.7 L/h) were comparable across models with slightly higher interindividual variability (38.3% vs 27%) in capillary microsampling-based data. A bioavailability/bioequivalence comparison demonstrated that the point estimate (90% CI) of capillary microsample versus venous sample model-based individual post hoc estimates for area under the concentration-time curve from time zero to infinity (AUC0-inf ) (100.7%, 98.0-103.5%) and Cmax (79.7%, 76.9-82.5%) met the 80-125% and 70-143% criteria, respectively. Overall, both POPPK models led to the same dose regimen recommendations across weight bins based on achieving target AUC. CONCLUSIONS: This analysis demonstrated that a POPPK approach can be employed to assess the performance of alternative pharmacokinetic sampling techniques. This approach provides a robust solution in scenarios where variability in pharmacokinetic data collected via venous sampling and microsampling may not result in a strong linear relationship. The findings also established that microsampling techniques may replace conventional venous sampling methods.

Piperaquine Pharmacokinetic and Pharmacodynamic Profiles in Healthy Volunteers of Papua New Guinea after Administration of Three-Monthly Doses of Dihydroartemisinin-Piperaquine.

Mass drug administration (MDA) with monthly dihydroartemisinin-piperaquine (DHA-PQP) appears useful in malaria control and elimination strategies. Determining the relationship between consecutive piperaquine phosphate (PQP) exposure and its impact on QT interval prolongation is a key safety consideration for MDA campaigns. Healthy volunteers from Papua New Guinea received a 3-day course of DHA-PQP (2.1/17.1 mg/kg) monthly for 3 consecutive months in a single arm longitudinal study. Plasma PQP concentrations were measured after the third dose of each course (at 52-54 h) and at 0 h of course 3. Twelve-lead electrocardiographic readings were conducted at 0 h, 48 h, 52 h, and day 7 of each course. QT interval corrected by Fridericia's formula (QTcF) was measured at each time point. A pharmacokinetic-pharmacodynamic model using nonlinear mixed effects models was developed to correlate PQP concentrations with QTcF. Ten thousand female and 10,000 male individuals were simulated at each treatment course. Eighty-two participants were included; mean age was 28.3 years (standard deviation [SD] ±12.3 years), and 36 (44%) were female. Pharmacokinetic-pharmacodynamic models were determined with 290 PQP concentrations and 868 QTcF observations. The average baseline QTcF was 392 ms with a between-subject variability SD ±14.4 ms and between-occasion variability SD ±3.64 ms. From the population modeled, only 0.08% of males and 0.45% of females would be at risk of an absolute QTcF of >500 ms. DHA-PQP is safe at standard doses in consecutive months, and the likelihood of severe cardiac events occurring during an MDA campaign is very low. This study has been registered at ClinicalTrials.gov under identifier NCT02605720.

Parasite Viability as a Measure of In Vivo Drug Activity in Preclinical and Early Clinical Antimalarial Drug Assessment.

The rate at which parasitemia declines in a host after treatment with an antimalarial drug is a major metric for assessment of antimalarial drug activity in preclinical models and in early clinical trials. However, this metric does not distinguish between viable and nonviable parasites. Thus, enumeration of parasites may result in underestimation of drug activity for some compounds, potentially confounding its use as a metric for assessing antimalarial activity in vivo. Here, we report a study of the effect of artesunate on Plasmodium falciparum viability in humans and in mice. We first measured the drug effect in mice by estimating the decrease in parasite viability after treatment using two independent approaches to estimate viability. We demonstrate that, as previously reported in humans, parasite viability declines much faster after artesunate treatment than does the decline in parasitemia (termed parasite clearance). We also observed that artesunate kills parasites faster at higher concentrations, which is not discernible from the traditional parasite clearance curve and that each subsequent dose of artesunate maintains its killing effect. Furthermore, based on measures of parasite viability, we could accurately predict the in vivo recrudescence of infection. Finally, using pharmacometrics modeling, we show that the apparent differences in the antimalarial activity of artesunate in mice and humans are partly explained by differences in host removal of dead parasites in the two hosts. However, these differences, along with different pharmacokinetic profiles, do not fully account for the differences in activity. (This study has been registered with the Australian New Zealand Clinical Trials Registry under identifier ACTRN12617001394336.).

Translation of liver stage activity of M5717, a Plasmodium elongation factor 2 inhibitor: from bench to bedside.

BACKGROUND: Targeting the asymptomatic liver stage of Plasmodium infection through chemoprevention could become a key intervention to reduce malaria-associated incidence and mortality. METHODS: M5717, a Plasmodium elongation factor 2 inhibitor, was assessed in vitro and in vivo with readily accessible Plasmodium berghei parasites. In an animal refinement, reduction, replacement approach, the in vitro IC99 value was used to feed a Population Pharmacokinetics modelling and simulation approach to determine meaningful effective doses for a subsequent Plasmodium sporozoite-induced volunteer infection study. RESULTS: Doses of 100 and 200 mg would provide exposures exceeding IC99 in 96 and 100% of the simulated population, respectively. CONCLUSIONS: This approach has the potential to accelerate the search for new anti-malarials, to reduce the number of healthy volunteers needed in a clinical study and decrease and refine the animal use in the preclinical phase.

The effect of sickle cell genotype on the pharmacokinetic properties of artemether-lumefantrine in Tanzanian children.

Since there are inconsistent data relating to the effect of haemoglobinopathies on disposition of artemisinin antimalarial combination therapy, and none in sickle cell trait (SCT) or sickle cell disease (SCD), the aim of this study was to characterize the pharmacokinetic properties of artemether-lumefantrine (ARM-LUM) in children with SCD/SCT. Thirty-eight Tanzanian children aged 5-10 years with normal (haemoglobin AA; n = 12), heterozygous (haemoglobin AS; n = 14) or homozygous (haemoglobin SS; n = 12) sickle genotypes received six ARM-LUM doses (1.7 mg/kg plus 10 mg/kg, respectively) over 3 days. Sparse venous and mixed-capillary dried blood spot (DBS) samples were taken over 42 days. Plasma and DBS ARM and LUM, and their active metabolites dihydroartemisinin (DHA) and desbutyl-lumefantrine (DBL), were assayed using validated liquid chromatography-mass spectrometry. Multi-compartmental pharmacokinetic models were developed using a population approach. Plasma but not DBS concentrations of ARM/DHA were assessable. The majority (85%) of the 15 measurable values were within 95% prediction intervals from a published population pharmacokinetic ARM/DHA model in Papua New Guinean children of similar age without SCD/SCT who had uncomplicated malaria, and there was no clear sickle genotype clustering. Plasma (n = 38) and corrected DBS (n = 222) LUM concentrations were analysed using a two-compartment model. The median [inter-quartile range] LUM AUC0-∞ was 607,296 [426,480-860,773] µg.h/L, within the range in published studies involving different populations, age-groups and malaria status. DBS and plasma DBL concentrations correlated poorly and were not modelled. These data support use of the conventional ARM-LUM treatment regimen for uncomplicated malaria in children with SCT/SCD.

Pulmonary Delivery of Aerosolized Chloroquine and Hydroxychloroquine to Treat COVID-19: In Vitro Experimentation to Human Dosing Predictions.

In vitro screening for pharmacological activity of existing drugs showed chloroquine and hydroxychloroquine to be effective against severe acute respiratory syndrome coronavirus 2. Oral administration of these compounds to obtain desired pulmonary exposures resulted in dose-limiting systemic toxicity in humans. However, pulmonary drug delivery enables direct and rapid administration to obtain higher local tissue concentrations in target tissue. In this work, inhalable formulations for thermal aerosolization of chloroquine and hydroxychloroquine were developed, and their physicochemical properties were characterized. Thermal aerosolization of 40 mg/mL chloroquine and 100 mg/mL hydroxychloroquine formulations delivered respirable aerosol particle sizes with 0.15 and 0.33 mg per 55 mL puff, respectively. In vitro toxicity was evaluated by exposing primary human bronchial epithelial cells to aerosol generated from Vitrocell. An in vitro exposure to 7.24 µg of chloroquine or 7.99 µg hydroxychloroquine showed no significant changes in cilia beating, transepithelial electrical resistance, and cell viability. The pharmacokinetics of inhaled aerosols was predicted by developing a physiologically based pharmacokinetic model that included a detailed species-specific respiratory tract physiology and lysosomal trapping. Based on the model predictions, inhaling emitted doses comprising 1.5 mg of chloroquine or 3.3 mg hydroxychloroquine three times a day may yield therapeutically effective concentrations in the lung. Inhalation of higher doses further increased effective concentrations in the lung while maintaining lower systemic concentrations. Given the theoretically favorable risk/benefit ratio, the clinical significance for pulmonary delivery of aerosolized chloroquine and hydroxychloroquine to treat COVID-19 needs to be established in rigorous safety and efficacy studies. Graphical abstract.

No Effect of PXR (8055C>T) Polymorphism on the Pharmacokinetic Profiles of Piperaquine in Healthy Chinese Subjects.

BACKGROUND: Significant inter-subject variability in pharmacokinetics and clinical outcomes has been observed for the antimalarial agent piperaquine (PQ). PQ is metabolized by CYP3A4, mainly regulated by the pregnane X receptor (PXR). CYP3A4(*1B) polymorphism did not affect PQ clearance. OBJECTIVES: The effect of PXR (8055C>T) polymorphism on the pharmacokinetic profiles of PQ was investigated. METHODS: The pharmacokinetic profiles of PQ and its major metabolite PQ N-oxide (PQM) were studied in healthy Chinese subjects after recommended oral doses of artemisinin-PQ. Twelve subjects were genotyped using PCRRFLP (six in each group with PXR 8055CC and 8055TT), and plasma concentrations were determined by a validated LC/MS/MS method. The dose-adjusted exposure (AUC and Cmax) to PQ or PQM was investigated, and the metabolic capability of PQ N-oxidation was determined by AUCPQM/AUCPQ. The antimalarial outcome of PQ was evaluated using its day 7 concentration. RESULTS: PQM formation was mediated by CYP3A4/3A5. Interindividual variability in dose-adjusted AUC of PQ and PQM was relatively low (%CV, <30.0%), whereas a larger inter-variability was observed for Cmax values (%CV, 68.1% for PQ). No polymorphic effect was found for PXR (C8055T) on the pharmacokinetic profiles of PQ or its Cday 7 concentrations. CONCLUSION: Both CYP3A4 and CYP3A5 were involved in PQ clearance. The genotypes of PXR (C8055T) may not contribute to the variability in PQ pharmacokinetics as well as antimalarial outcomes. There might be a low risk of variable exposures to PQ in malaria patients carrying mutated PXR (8055C>T) genes, which deserves further study, especially in a larger sample size.

Pharmacokinetics of chloroquine and primaquine in healthy volunteers.

BACKGROUND: Vivax malaria is a neglected disease. There is an irrefutable need for better treatments with higher acceptability and efficacy. The treatment efficacy is influenced by many factors, including bioavailability. Hence, a straightforward strategy to improve vivax malaria treatment efficacy is the deployment of good quality formulations of primaquine and chloroquine. As these treatments were developed more than 70 years ago, many of the available data on blood levels of both drugs are based on obsolete analytical methodologies or pharmaceutical formulations, which are not available anymore. Herein, the results of three bioequivalence studies are presented, providing individual pharmacokinetic data on chloroquine and primaquine of more than a hundred healthy volunteers and using up-to-date analytical methods. METHODS: Three trials were designed as a single centre, randomized, single dose, open label, fasting, crossover bioequivalence studies comparing a new coated chloroquine tablet to the uncoated tablet, and 5 and 15 mg primaquine formulations to either an international reference product or the currently distributed tablets. Plasma concentrations of chloroquine and primaquine were measured using a validated HPLC-MS/MS method in accordance with current international regulatory requirements for bio-analytical methods. RESULTS: In total, a hundred eleven healthy volunteers of both genders were included in the three studies (n = 32; 30 and 56 respectively). No serious adverse events occurred. Drugs levels were measured in 5,520 blood samples. The estimated ratio of the geometric means of Cmax, AUC0-t and AUC0-inf of test and reference drugs and their 90% CI for chloroquine 150 mg, primaquine 15 mg and primaquine 5 mg were: 95.33% (89.18; 101.90), 86. 85% (82.61; 91.31), and 84.45% (76.95; 92.67); 93.28% (81.76; 106.41), 94.52% (86.13; 103.73) and 93.93% (85.83; 102.79); 97.44% (90.60; 104.78), 93.70% (87.04; 100.87) and 91.36% (85.27; 97.89), respectively. As Cmax and AUC0-t 90% CI were within the acceptance interval of 80-125% in all cases, the formulations tested were bioequivalent. CONCLUSIONS: In conclusion, the three studies provided detailed chloroquine and primaquine pharmacokinetic data in accordance with current regulatory standards. Together with other open data initiatives, this individual data may increase the accuracy of pharmacokinetic models guiding best dose, new combinations, regimens and formulations to optimize the current chloroquine and primaquine treatments for vivax malaria. The data presented here may support the deployment of high-quality drugs and evidence-based public health policies.

Measurements of 5,6-Orthoquinone, a Surrogate for the Presumed Active Primaquine Metabolite 5-Hydroxyprimaquine, in the Urine of Cambodian Adults.

The active metabolites of primaquine, in particular 5-hydroxyprimaquine, likely responsible for the clearance of dormant hypnozoites, are produced through the hepatic CYP450 2D6 (CYP2D6) enzymatic pathway. With the inherent instability of 5-hydroxyprimaquine, a stable surrogate, 5,6-orthoquinone, can now be detected and measured in the urine as part of primaquine pharmacokinetic studies. This study performed CYP450 2D6 genotyping and primaquine pharmacokinetic testing, to include urine 5,6-orthoquinone, in 27 healthy adult Cambodians, as a preliminary step to prepare for future clinical studies assessing primaquine efficacy for Plasmodium vivax infections. The CYP2D6 *10 reduced activity allele was found in 57% of volunteers, and the CYP2D6 genotypes were dominated by *1/*10 (33%) and *10/*10 (30%). Predicted phenotypes were evenly split between Normal Metabolizer (NM) and Intermediate Metabolizer (IM) except for one volunteer with a gene duplication and unclear phenotype, classifying as either IM or NM. Median plasma primaquine (PQ) area under the curve (AUC) was lower in the NM group (460 h*ng/mL) compared to the IM group (561 h*ng/mL), although not statistically significant. Similar to what has been found in the US study, no 5,6-orthoquinone was detected in the plasma. The urine creatinine-corrected 5,6-orthoquinone AUC in the NM group was almost three times higher than in the IM group, with peak measurements (Tmax) at 4 h. Although there is variation among individuals, future studies examining the relationship between the levels of urine 5,6-orthoquinone and primaquine radical cure efficacy could result in a metabolism biomarker predictive of radical cure.

Tafenoquine exposure assessment, safety, and relapse prevention efficacy in children with Plasmodium vivax malaria: open-label, single-arm, non-comparative, multicentre, pharmacokinetic bridging, phase 2 trial.

BACKGROUND: Single-dose tafenoquine 300 mg is approved for Plasmodium vivax malaria relapse prevention in patients at least 16 years old. We aimed to determine appropriate oral tafenoquine paediatric dosing regimens, including a dispersible formulation, and evaluated tafenoquine efficacy and safety in children infected with P vivax. METHODS: This open-label, single-arm, non-comparative, multicentre, pharmacokinetic bridging, phase 2 study enrolled children (2-15 years) who weighed 5 kg or more, with glucose-6-phosphate dehydrogenase activity more than 70% of the local population median, and P vivax malaria infection, from three community health centres in Vietnam and one in Colombia. Patients received 3-day chloroquine plus oral single-dose tafenoquine as dispersible tablets (50 mg) or film-coated tablets (150 mg). Dosing groups were assigned by body weight, predicted to achieve similar median exposures as the approved 300 mg dose for adults: patients who weighed 5 kg or more to 10 kg received 50 mg, those who weighed more than 10 to 20 kg received 100 or 150 mg, those who weighed more than 20 to 35 kg received 200 mg, and patients who weighed more than 35 kg received 300 mg. Population pharmacokinetic analysis was done to develop a paediatric population pharmacokinetic model. The primary outcome was the tafenoquine area under the concentration-time curve extrapolated to infinity (AUC[0-∞]) by patient body weight in the pharmacokinetic population (all patients who received tafenoquine with at least one valid pharmacokinetic sample) estimated from a paediatric population pharmacokinetic model. A key prespecified secondary outcome was 4-month recurrence-free efficacy. This trial is registered with ClinicalTrials.gov, NCT02563496. FINDINGS: Between Feb 6, 2017, and Feb 17, 2020, 60 patients were enrolled into the study: 14 (23%) received tafenoquine 100 mg, five (8%) 150 mg, 22 (36%) 200 mg, and 19 (32%) 300 mg. The paediatric population pharmacokinetic model predicted adequate tafenoquine exposure at all doses. The predicted median AUC(0-∞) was 73·8 (90% prediction interval [PI] 46·9-117·0) µg × h/mL with the 50 mg dose for patients who weighed 5 kg or more to 10 kg, 87·5 (55·4-139·0) µg × h/mL with the 100 mg dose for body weight more than 10 to 20 kg, 110·7 (70·9-174·0) µg × h/mL with the 200 mg dose for body weight more than 20 to 35 kg, and 85·7 (50·6-151·0) µg × h/mL with the 300 mg dose for body weight more than 35 kg. 4-month recurrence-free efficacy was 94·7% (95% CI 84·6-98·3). Adverse events were consistent with previous studies, except for the seven (12%) of 60 patients who had post-dose vomiting or spitting with the 50 mg dispersed tablet. Following mitigation strategies, there were no additional occurrences of this adverse event. There were no deaths during the study. INTERPRETATION: For the prevention of P vivax relapse in children, single-dose tafenoquine, including a dispersible formulation, had exposure, safety, and efficacy consistent with observations in adolescents and adults, notwithstanding post-dose vomiting. FUNDING: GlaxoSmithKline and Medicines for Malaria Venture. TRANSLATIONS: For the Vietnamese and Spanish translations of the abstract see Supplementary Materials section.

Mechanistic Modeling of Primaquine Pharmacokinetics, Gametocytocidal Activity, and Mosquito Infectivity.

Clinical studies have shown that adding a single 0.25 mg base/kg dose of primaquine to standard antimalarial regimens rapidly sterilizes Plasmodium falciparum gametocytes. However, the mechanism of action and overall impact on malaria transmission is still unknown. Using data from 81 adult Malians with P. falciparum gametocytemia who received the standard dihydroartemisinin-piperaquine treatment course and were randomized to receive either a single dose of primaquine between 0.0625 and 0.5 mg base/kg or placebo, we characterized the pharmacokinetic-pharmacodynamic relationships for transmission blocking activity. Both gametocyte clearance and mosquito infectivity were assessed. A mechanistically linked pharmacokinetic-pharmacodynamic model adequately described primaquine and carboxy-primaquine pharmacokinetics, gametocyte dynamics, and mosquito infectivity at different clinical doses of primaquine. Primaquine showed a dose-dependent gametocytocidal effect that precedes clearance. A single low dose of primaquine (0.25 mg/kg) rapidly prevented P. falciparum transmissibility.

Identifying an optimal dihydroartemisinin-piperaquine dosing regimen for malaria prevention in young Ugandan children.

Intermittent preventive treatment (IPT) with dihydroartemisinin-piperaquine (DP) is highly protective against malaria in children, but is not standard in malaria-endemic countries. Optimal DP dosing regimens will maximize efficacy and reduce toxicity and resistance selection. We analyze piperaquine (PPQ) concentrations (n = 4573), malaria incidence data (n = 326), and P. falciparum drug resistance markers from a trial of children randomized to IPT with DP every 12 weeks (n = 184) or every 4 weeks (n = 96) from 2 to 24 months of age (NCT02163447). We use nonlinear mixed effects modeling to establish malaria protective PPQ levels and risk factors for suboptimal protection. Compared to DP every 12 weeks, DP every 4 weeks is associated with 95% protective efficacy (95% CI: 84-99%). A PPQ level of 15.4 ng/mL reduces the malaria hazard by 95%. Malnutrition reduces PPQ exposure. In simulations, we show that DP every 4 weeks is optimal across a range of transmission intensities, and age-based dosing improves malaria protection in young or malnourished children.

1,2,3-Triazole derivatives: synthesis, docking, cytotoxicity analysis and in vivo antimalarial activity.

Malaria remains one of the most important parasitic diseases in the world. The multidrug-resistant Plasmodium strains make the treatment currently available for malaria less effective. Therefore, the development of new drugs is necessary to overcome therapy resistance. Triazole derivatives exhibit several biological activities and provide a moiety that is promising from the biological perspective. Due to the structural similarity to NADH, it is believed that triazoles can bind to the active site of the Plasmodium lactate dehydrogenase (pLDH) enzyme. The present work evaluates the antimalarial activity of 1,2,3-triazole derivatives by in silico, in vitro, and in vivo studies. Preliminary in silico ADMET studies of the compounds demonstrated good pharmacokinetic properties. In silico docking analysis against LDH of Plasmodium berghei (PbLDH) showed that all compounds presented interactions with the catalytic residue in the active site and affinity similar to that presented by chloroquine; the most common antimalarial drug. Cytotoxicity and hemolysis by these derivatives were evaluated in vitro. The compounds 1, 2, 5, 8, and 9 proved to be non-cytotoxic in the performed tests. In vivo antimalarial activity was evaluated using mice infected with Plasmodium berghei NK65. The five compounds tested exhibited antimalarial activity until nine days post-infection. The compound 5 showed promising activities, with about 70% parasitemia suppression. Considering the in vitro and in vivo studies, we believe the compound 5 to be the most promising molecule for further studies in antimalarial chemotherapy.

Model-based assessment of the safety of community interventions with primaquine in sub-Saharan Africa.

BACKGROUND: Single low-dose primaquine (SLD-PQ) is recommended in combination with artemisinin-based combination therapy to reduce Plasmodium falciparum transmission in areas threatened by artemisinin resistance or aiming for malaria elimination. SLD-PQ may be beneficial in mass drug administration (MDA) campaigns to prevent malaria transmission but uptake is limited by concerns of hemolysis in glucose-6-phosphate dehydrogenase (G6PD)-deficient individuals. The aim of this study was to improve the evidence on the safety of MDA with SLD-PQ in a sub-Saharan African setting. METHODS: A nonlinear mixed-effects model describing the pharmacokinetics and treatment-induced hemolysis of primaquine was developed using data from an adult (n = 16, G6PD deficient) and pediatric study (n = 38, G6PD normal). The relationship between primaquine pharmacokinetics and hemolysis was modeled using an established erythrocyte lifespan model. The safety of MDA with SLD-PQ was explored through Monte Carlo simulations for SLD-PQ at 0.25 or 0.4 mg/kg using baseline data from a Tanzanian setting with detailed information on hemoglobin concentrations and G6PD status. RESULTS: The predicted reduction in hemoglobin levels following SLD-PQ was small and returned to pre-treatment levels after 25 days. G6PD deficiency (African A- variant) was associated with a 2.5-fold (95% CI 1.2-8.2) larger reduction in hemoglobin levels. In the Tanzanian setting where 43% of the population had at least mild anemia (hemoglobin < 11-13 g/dl depending on age and sex) and 2.73% had severe anemia (hemoglobin < 7-8 g/dl depending on age and sex), an additional 3.7% and 6.0% of the population were predicted to develop at least mild anemia and 0.25% and 0.41% to develop severe anemia after 0.25 and 0.4 mg/kg SLD-PQ, respectively. Children < 5 years of age and women ≥ 15 years of age were found to have a higher chance to have low pre-treatment hemoglobin. CONCLUSIONS: This study supports the feasibility of MDA with SLD-PQ in a sub-Saharan African setting by predicting small and transient reductions in hemoglobin levels. In a setting where a substantial proportion of the population had low hemoglobin concentrations, our simulations suggest treatment with SLD-PQ would result in small increases in the prevalence of anemia which would most likely be transient.

Safety, pharmacokinetics, and antimalarial activity of the novel plasmodium eukaryotic translation elongation factor 2 inhibitor M5717: a first-in-human, randomised, placebo-controlled, double-blind, single ascending dose study and volunteer infection study.

BACKGROUND: M5717 is the first plasmodium translation elongation factor 2 inhibitor to reach clinical development as an antimalarial. We aimed to characterise the safety, pharmacokinetics, and antimalarial activity of M5717 in healthy volunteers. METHODS: This first-in-human study was a two-part, single-centre clinical trial done in Brisbane, QLD, Australia. Part one was a double-blind, randomised, placebo-controlled, single ascending dose study in which participants were enrolled into one of nine dose cohorts (50, 100, 200, 400, 600, 1000, 1250, 1800, or 2100 mg) and randomly assigned (3:1) to M5717 or placebo. A sentinel dosing strategy was used for each dose cohort whereby two participants (one assigned to M5717 and one assigned to placebo) were initially randomised and dosed. Randomisation schedules were generated electronically by independent, unblinded statisticians. Part two was an open-label, non-randomised volunteer infection study using the Plasmodium falciparum induced blood-stage malaria model in which participants were enrolled into three dose cohorts. Healthy men and women of non-childbearing potential aged 18-55 years were eligible for inclusion; individuals in the volunteer infection study were required to be malaria naive. Safety and tolerability (primary outcome of the single ascending dose study and secondary outcome of the volunteer infection study) were assessed by frequency and severity of adverse events. The pharmacokinetic profile of M5717 was also characterised (primary outcome of the volunteer infection study and secondary outcome of the single ascending dose study). Parasite clearance kinetics (primary outcome of the volunteer infection study) were assessed by the parasite reduction ratio and the corresponding parasite clearance half-life; the incidence of recrudescence up to day 28 was determined (secondary outcome of the volunteer infection study). Recrudescent parasites were tested for genetic mutations (exploratory outcome). The trial is registered with ClinicalTrials.gov (NCT03261401). FINDINGS: Between Aug 28, 2017, and June 14, 2019, 221 individuals were assessed for eligibility, of whom 66 men were enrolled in the single ascending dose study (eight per cohort for 50-1800 mg cohorts, randomised three M5717 to one placebo, and two in the 2100 mg cohort, randomised one M5717 to one placebo) and 22 men were enrolled in the volunteer infection study (six in the 150 mg cohort and eight each in the 400 mg and 800 mg cohorts). No adverse event was serious; all M5717-related adverse events were mild or moderate in severity and transient, with increased frequency observed at doses above 1250 mg. In the single ascending dose study, treatment-related adverse events occurred in three of 17 individuals in the placebo group; no individual in the 50 mg, 100 mg, or 200 mg groups; one of six individuals in each of the 400 mg, 1000 mg, and 1250 mg groups; two of six individuals in the 600 mg group; and in all individuals in the 1800 mg and 2100 mg groups. In the volunteer infection study, M5717-related adverse events occurred in no participants in the 150 mg or 800 mg groups and in one of eight participants in the 400 mg group. Transient oral hypoesthesia (in three participants) and blurred vision (in four participants) were observed in the 1800 mg or 2100 mg groups and constituted an unknown risk; thus, further dosing was suspended after dosing of the two sentinel individuals in the 2100 mg cohort. Maximum blood concentrations occurred 1-7 h after dosing, and a long half-life was observed (146-193 h at doses ≥200 mg). Parasite clearance occurred in all participants and was biphasic, characterised by initial slow clearance lasting 35-55 h (half-life 231·1 h [95% CI 40·9 to not reached] for 150 mg, 60·4 h [38·6 to 138·6] for 400 mg, and 24·7 h [20·4 to 31·3] for 800 mg), followed by rapid clearance (half-life 3·5 h [3·1 to 4·0] for 150 mg, 3·9 h [3·3 to 4·8] for 400 mg, and 5·5 h [4·8 to 6·4] for 800 mg). Recrudescence occurred in three (50%) of six individuals dosed with 150 mg and two (25%) of eight individuals dosed with 400 mg. Genetic mutations associated with resistance were detected in four cases of parasite recrudescence (two individuals dosed with 150 mg and two dosed with 400 mg). INTERPRETATION: The safety, pharmacokinetics, and antimalarial activity of M5717 support its development as a component of a single-dose antimalarial combination therapy or for malaria prophylaxis. FUNDING: Wellcome Trust and the healthcare business of Merck KGaA, Darmstadt, Germany.

Metabolism is not a Major Contributor to the Toxicity of Piperaquine, a Long-acting Antimalarial Agent in Artemisinin-based Combination Therapy.

BACKGROUND: Hepatocellular damage has been reported for the antimalarial piperaquine (PQ) in the clinic after cumulative doses. OBJECTIVES: The role of metabolism in PQ toxicity was evaluated, and the mechanism mediating PQ hepatotoxicity was investigated. METHODS: The toxicity of PQ and its major metabolite (PQ N-oxide; M1) in mice was evaluated in terms of serum biochemical parameters. The role of metabolism in PQ toxicity was investigated in mice pretreated with an inhibitor of CYP450 (ABT) and/or FMO enzyme (MMI). The dose-dependent pharmacokinetics of PQ and M1 were studied in mice. Histopathological examination was performed to reveal the mechanism mediating PQ hepatotoxicity. RESULTS: Serum biochemical levels (ALT and BUN) increased significantly (P < 0.05) in mice after three-day oral doses of PQ (> 200 mg/kg/day), indicating hepatotoxicity and nephrotoxicity of PQ at a high dose. Weaker toxicity was observed for M1. Pretreatment with ABT and/or MMI did not increase PQ toxicity. PQ and M1 showed linear pharmacokinetics in mice after a single oral dose, and multiple oral doses led to their cumulative exposures. Histopathological examination showed that a high dose of PQ (> 200 mg/kg/day for three days) could induce hepatocyte apoptosis. The mRNA levels of targets in NF-κB and p53 pathways could be up-regulated by 2-30-fold in mice by PQ or M1. CONCLUSION: PQ metabolism led to detoxification of PQ, but there was a low possibility of altered toxicity induced by metabolism inhibition. The hepatotoxicity of PQ and its N-oxidation metabolite was partly mediated by NF-κB inflammatory pathway and p53 apoptosis pathway.