No correlation was identified between vincristine clearance, vincristine neurotoxicity, age, sex or concomitant steroid therapy. The limited sampling methodology proved acceptable to patients and families and would be suitable for larger scale studies including a wider range of genotypic variants and more detailed prospective evaluation of neurotoxicity.

High rates of artemisinin-based combination therapy (ACT) failures in the treatment of Plasmodium falciparum malaria in Southeast Asia have led to triple-drug strategies to extend the useful life of ACTs. In this study, we determined whether methylene blue [MB; 3,7-bis(dimethylamino)phenothiazin-5-ium chloride hydrate] alters the pharmacokinetics of artesunate-amodiaquine (ASAQ) and enhances the ex vivo antimalarial activity of ASAQ. In an open-label, randomized crossover design, a single oral dose of ASAQ (200 mg AS/540 mg AQ) alone or with MB (325 mg) was administered to 15 healthy Vietnamese volunteers. Serial blood samples were collected up to 28 days after dosing. Pharmacokinetic properties of the drugs were determined by noncompartmental analysis. After drug administration, plasma samples from seven participants were assessed for ex vivo antimalarial activity against the artemisinin-sensitive MRA1239 and the artemisinin-resistant MRA1240 P. falciparum lines, in vitro. MB significantly increased the mean area under the curve of the active metabolite of AS, dihydroartemisinin (1,246 ± 473 versus 917 ± 405 ng·h/ml, P = 0.009) but did not alter the pharmacokinetics of AQ, AS, or desethylamodiaquine. Comparing the antimalarial activities of the plasma samples from the participants collected up to 48 h after ASAQ plus MB (ASAQ+MB) and ASAQ dosing against the MRA1239 and MRA1240 lines, MB significantly enhanced the blood schizontocidal activity of ASAQ by 2.0-fold and 1.9-fold, respectively. The ring-stage survival assay also confirmed that MB enhanced the ex vivo antimalarial activity of ASAQ against MRA1240 by 2.9-fold to 3.8-fold, suggesting that the triple-drug combination has the potential to treat artemisinin-resistant malaria and for malaria elimination. (This study has been registered in the Australian New Zealand Clinical Trials Registry [https://anzctr.org.au/] under registration number ACTRN12612001298808.)

The objective was to study the population pharmacokinetics of bound and unbound phenytoin in critically ill children, including influences on the protein binding profile. A population pharmacokinetic approach was used to analyze paired protein-unbound and total phenytoin plasma concentrations (n = 146 each) from 32 critically ill children (0.08-17 years of age) who were admitted to a pediatric hospital, primarily intensive care unit. The pharmacokinetics of unbound and bound phenytoin and the influence of possible influential covariates were modeled and evaluated using visual predictive checks and bootstrapping. The pharmacokinetics of protein-unbound phenytoin was described satisfactorily by a 1-compartment model with first-order absorption in conjunction with a linear partition coefficient parameter to describe the binding of phenytoin to albumin. The partitioning coefficient describing protein binding and distribution to bound phenytoin was estimated to be 8.22. Nonlinear elimination of unbound phenytoin was not supported in this patient group. Weight, allometrically scaled for clearance and volume of distribution for the unbound and bound compartments, and albumin concentration significantly influenced the partition coefficient for protein binding of phenytoin. The population model can be applied to estimate the fraction of unbound phenytoin in critically ill children given an individual's albumin concentration.

In vitro drug treatment with artemisinin derivatives, such as dihydroartemisinin (DHA), results in a temporary growth arrest (i.e., dormancy) at an early ring stage in Plasmodium falciparum. This response has been proposed to play a role in the recrudescence of P. falciparum infections following monotherapy with artesunate and may contribute to the development of artemisinin resistance in P. falciparum malaria. We demonstrate here that artemether does induce dormant rings, a finding which further supports the class effect of artemisinin derivatives in inducing the temporary growth arrest of P. falciparum parasites. In contrast and similarly to lumefantrine, the novel and fast-acting spiroindolone compound KAE609 does not induce growth arrest at the early ring stage of P. falciparum and prevents the recrudescence of DHA-arrested rings at a low concentration (50 nM). Our findings, together with previous clinical data showing that KAE609 is active against artemisinin-resistant K13 mutant parasites, suggest that KAE609 could be an effective partner drug with a broad range of antimalarials, including artemisinin derivatives, in the treatment of multidrug-resistant P. falciparum malaria. Over the last 2 decades, artemisinin-based combination therapies (ACTs) have been the most efficacious treatments against malaria and have contributed greatly to the decline in malaria mortality and morbidity (1, 2). Recent reports of falling efficacy rates of ACTs in Southeast Asia, as evidenced by increased treatment failures (3-5) and prolonged parasite clearance times following ACT treatment (6-11), are of great concern. Molecular markers of artemisinin resistance, K13 propeller mutations, have been identified (12, 13), and several recent reports suggest that resistance to the currently used ACTs is developing and spreading sooner than expected (14, 15). It remains unclear whether this resistance is a result of changes in the parasite molecular machinery required for the mode of action of artemisinin derivatives (16) or due to a recently described phenomenon of dormancy (growth retardation), where Plasmodium falciparum rings are able to survive dihydroartemisinin (DHA) treatment by undergoing a temporary growth arrest (17)(18)(19). Despite many unanswered questions about the role of dormancy, the importance of this phenomenon in the context of antimalarial chemotherapy and artemisinin resistance has become increasingly evident (17-23). Furthermore, the growth arrest of ring-stage parasites and their recovery rates observed in the in vitro ring survival assay (RSA) correlate strongly with parasite clearance half-lives after treatment of P. falciparum malaria with ACTs (22, 23), providing further support for the link between dormancy and treatment failures and possible resistance.Despite the concerns over emerging artemisinin resistance, ACTs still remain the treatment of choice for uncomplicated P. falciparum malaria (1). Therefore, to enhance or prolong the activity of ACTs against the emergence of resistance, it is important to d...

No abstract

Analytical methods for the quantification of the new 8-aminoquinoline antimalarial tafenoquine (TQ) in human blood, plasma and urine, and the 5,6-orthoquinone tafenoquine metabolite (5,6-OQTQ) in human plasma and urine have been validated. The procedure involved acetonitrile extraction of samples followed by ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Chromatography was performed using a Waters Atlantis T3 column with a gradient of 0.1% formic acid and acetonitrile at a flow rate of 0.5 mL per minute for blood and plasma. Urine analysis was the same but with methanol containing 0.1% formic acid replacing acetonitrile mobile phase. The calibration range for TQ and 5,6-OQTQ in plasma was 1 to 1200 ng/mL, and in urine was 10 to 1000 ng/mL. Blood calibration range for TQ was 1 to 1200 ng/mL. Blood could not be validated for 5,6-OQTQ due to significant signal suppression. The inter-assay precision (coefficient of variation %) was 9.9% for TQ at 1 ng/mL in blood (n = 14) and 8.2% for TQ and 7.1% for 5,6-OQTQ at 1 ng/mL in plasma (n = 14). For urine, the inter-assay precision was 8.2% for TQ and 6.4% for 5,6-OQTQ at 10 ng/mL (n = 14). TQ and 5,6-OQTQ are stable in blood, plasma and urine for at least three months at both −80 °C and −20 °C. Once validated, the analytical methods were applied to samples collected from healthy volunteers who were experimentally infected with Plasmodium falciparum to evaluate the blood stage antimalarial activity of TQ and to determine the therapeutic dose estimates for TQ, the full details of which will be published elsewhere. In this study, the measurement of TQ and 5,6-OQTQ concentrations in samples from one of the four cohorts of participants is reported. Interestingly, TQ urine concentrations were proportional to parasite recrudescence times post dosing To our knowledge, this is the first description of a fully validated method for the measurement of TQ and 5,6-OQTQ quantification in urine.

The pharmacokinetics (PK) and ex vivo activity (pharmacodynamics [PD]) of two artemisinin combination therapies (ACTs) (artemisinin-piperaquine [ARN-PPQ] [Artequick] and artesunate-amodiaquine [ARS-AQ] [Coarsucam]) in healthy Vietnamese volunteers were compared following 3-day courses of the ACTs for the preselection of the drugs for falciparum malaria therapy. For PK analysis, serial plasma samples were collected from two separate groups of 22 volunteers after ACT administration. Of these volunteers, ex vivo activity was assessed in plasma samples from seven volunteers who received both ACTs. The area under the concentration-time curve (AUC) was 3.6-fold higher for dihydroartemisinin (active metabolite of ARS) than that for ARN, whereas the AUC of desethylamodiaquine (active metabolite of AQ) was 2.0-fold lower than that of PPQ. Based on the 50% inhibitory dilution values of the volunteers' plasma samples collected from 0.25 to 3 hours after the last dose, the ex vivo activity of ARS-AQ was 2.9- to 16.2-fold more potent than that of ARN-PPQ against the drug-sensitive D6 line. In addition, at 1.5, 4.0, and 24 hours after the last dose, the ex vivo activity of ARS-AQ was 20.8-, 3.5-, and 8.5-fold more potent than that of ARN-PPQ against the ARN-sensitive MRA1239 line. By contrast, at 1.5 hours, the ex vivo activity of ARS-AQ was 5.4-fold more active than that of ARN-PPQ but had similar activities at 4 and 24 hours against the ARN-resistant MRA1240 line. The PK-PD data suggest that ARS-AQ possesses superior antimalarial activity than that of ARN-PPQ and would be the preferred ACT for further in vivo efficacy testing in multidrug-resistant falciparum malaria areas.

The new 2-aminomethylphenol, JPC-3210, has potent antimalarial activity against multidrug-resistant lines, low cytotoxicity, and high efficacy against murine malaria. Here we report on the pharmacokinetics of JPC-3210 in mice and monkeys and the results of screening assays, including the inhibition of cytochrome P450 (CYP450) isozymes. In mice, JPC-3210 was rapidly absorbed and had an extensive tissue distribution, with a brain tissue-to-plasma concentration ratio of about 5.4. JPC-3210 had a lengthy plasma elimination half-life of about 4.5 days in mice and 11.8 days in monkeys. JPC-3210 exhibited linear single-oral-dose pharmacokinetics across the dose range of 5 to 40 mg/kg of body weight with high oral bioavailability (∼86%) in mice. Systemic blood exposure of JPC-3210 was 16.6% higher in -infected mice than in healthy mice. studies with mice and human hepatocytes revealed little metabolism and the high metabolic stability of JPC-3210. The abundance of human metabolites from oxidation and glucuronidation was 2.0% and 2.5%, respectively. CYP450 studies in human liver microsomes showed JPC-3210 to be an inhibitor of CYP2D6 and, to a lesser extent, CYP3A4 isozymes, suggesting the possibility of a metabolic drug-drug interaction with drugs that are metabolized by these isozymes. studies showed that JPC-3210 is highly protein bound to human plasma (97%). These desirable pharmacological findings of a lengthy blood elimination half-life, high oral bioavailability, and low metabolism as well as high potency have led the Medicines for Malaria Venture to select JPC-3210 (MMV892646) for further advanced preclinical development.