We assessed monthly doses of tafenoquine for preventing Plasmodium vivax and multidrug-resistant P. falciparum malaria. In a randomized, double-blind, placebo-controlled study, 205 Thai soldiers received either a loading dose of tafenoquine 400 mg (base) daily for 3 days, followed by single monthly 400-mg doses (n = 104), or placebo (n = 101), for up to 5 consecutive months. In volunteers completing follow-up (96 tafenoquine and 91 placebo recipients), there were 22 P. vivax, 8 P. falciparum, and 1 mixed infection. All infections except 1 P. vivax occurred in placebo recipients, giving tafenoquine a protective efficacy of 97% for all malaria (95% confidence interval [CI], 82%-99%), 96% for P. vivax malaria (95% CI, 76%-99%), and 100% for P. falciparum malaria (95% CI, 60%-100%). Monthly tafenoquine was safe, well tolerated, and highly effective in preventing P. vivax and multidrug-resistant P. falciparum malaria in Thai soldiers during 6 months of prophylaxis.

Artemisone (single oral dose, 10 mg/kg) cured non-immune Aotus monkeys of their Plasmodium falciparum infections when combined with mefloquine (single oral dose, 5 and 10 mg/kg, but not 2.5 mg/kg). In combination with amodiaquine (20 mg/kg/day), artemisone (10 mg/kg/day) given orally for 3 days cured all infected monkeys. 3-days treatment with artemisone (30 mg/kg/day) and clindamycin (100 mg/kg/day) was also curative.

In preclinical studies, artemisone (BAY 44-9585), a new artemisinin derivative, has been shown to possess enhanced efficacy over artesunate and does not possess the neurotoxicity characteristic of the current artemisinins. In a phase I program with double-blind, randomized, placebo-controlled, single- and multiple-ascending oral dose studies we evaluated the safety, tolerability, pharmacokinetics and ex vivo pharmacodynamic antimalarial activity of artemisone. Single-doses (10, 20, 30, 40 and 80 mg), and multiple-doses (40 and 80 mg daily x 3 days) of artemisone were administered orally to healthy subjects. Plasma concentrations of artemisone and its metabolites were measured by liquid chromatography/tandem mass spectrometry. Artemisone was well tolerated, with no serious adverse events and no clinical relevant changes in laboratory and vital parameters. The pharmacokinetics of artemisone over the 10 to 80 mg range demonstrated dose linearity. After the single 80 mg dose, artemisone had a geometric mean (range) maximum concentration of 140.2 ng/ml (80.6 - 391.0), a short elimination half-life (t(1/2)) of 2.79 h (1.56 - 4.88), a high oral clearance (CL/F) of 284.1 liters/h (106.7 - 546.7) and a large volume of distribution (V/F) of 14.50 liters/kg (3.21 - 51.58). Due to artemisone's short t(1/2), its pharmacokinetics was comparable after single- and multiple-dosing. Plasma samples taken after multiple-dosing showed marked ex vivo pharmacodynamic antimalarial activity against two multidrug-resistant Plasmodium falciparum lines. Artemisone equivalent concentrations measured by bioassay revealed higher activity than artemisone measured by LC/MS/MS, confirming the presence of active metabolites. Comparable to other artemisinin's, artemisone's t(1/2) is well suited for artemisinin-based combination therapy for the treatment of falciparum malaria.

Cynomolgus monkeys, as animal models of scrub typhus, are typically infected with Orientia tsutsugamushi by intradermal inoculation. However, the clinical and histological features at the O. tsutsugamushi inoculation sites, akin to "eschars" at chigger inoculation sites in humans, have not been fully characterized. We intradermally inoculated one medial thigh of six cynomolgus monkeys with semi-purified O. tsutsugamushi (Karp). Within 7 days, two animals developed scrub typhus-like eschars and four had dusky plaques, accompanied by inguinal lymphadenopathy. Biopsies of eschars and an enlarged regional lymph node resembled human disease and stained positively for O. tsutsugamushi by Giemsa, anti-Karp fluorescent antibody, or streptavidin alkaline phosphatase. O. tsutsugamushi-specific IgM and IgG antibody levels measured in both of two monkeys rose steadily after infection. This pilot study shows that cynomolgus intradermally inoculated with O. tsutsugamushi replicate the localized cutaneous pathogenesis of human scrub typhus infections, strengthening the value of this animal model.

Objectives To assess the antimalarial pharmacodynamics and pharmacokinetics of the novel dihydrofolate reductase (DHFR) inhibitor, JPC2056 and its principal active metabolite JPC2067 in cynomolgus monkeys using an in vivo-in vitro model. Methods In a two-phase crossover design, five cynomolgus monkeys were administered a single dose (20 mg/kg) and multiple doses (20 mg/kg daily for 3 days) of JPC2056. Plasma samples collected from treated monkeys were assessed for in vitro antimalarial activity against Plasmodium falciparum lines having wild-type (D6), double-mutant (K1) and quadruple-mutant (TM90-C2A) DHFR-thymidylate synthase (TS) and a P. falciparum line transformed with a Plasmodium vivax dhfr-ts quadruple-mutant allele (D6-PvDHFR). Plasma JPC2056 and JPC2067 concentrations were measured by LC-mass spectrometry. Results The mean inhibitory dilution (ID(90)) of monkey plasma at 3 h after drug administration against D6, K1 and TM90-C2A was, respectively, 1253, 585 and 869 after the single-dose regimen and 1613, 1120 and 1396 following the multiple-dose regimen. Less activity was observed with the same monkey plasma samples against the D6-PvDHFR line, with a mean ID(90) of 53 after multiple dosing. Geometric mean plasma concentrations of JPC2056 and JPC2067 at 3 h after drug administration were, respectively, 113 and 12 ng/mL after the single dose and 150 and 17 ng/mL after multiple dosing. The mean elimination half-life of JPC2056 was shorter than its metabolite after both regimens (single dose, 7.3 versus 11.8 h; multiple doses, 6.6 versus 11.1 h). Conclusions The high potency of JPC2056 against P. falciparum DHFR-TS quadruple-mutant lines provides optimism for the future development of JPC2056 for the treatment of malaria infections.

The population pharmacokinetics of tafenoquine were studied in Australian soldiers taking tafenoquine for malarial prophylaxis. The subjects (476 males, 14 females) received a loading dose of 200 mg tafenoquine base daily for 3 days, followed by a weekly dose of 200 mg tafenoquine for 6 months. Blood samples were collected from each subject after the last loading dose, then at weeks 4, 8, and 16. Plasma tafenoquine concentrations were determined by LC/MS/MS. Population modeling was performed with NONMEM using a one-compartment model. Typical values of the first-order absorption rate constant (Ka), clearance (CL/F) and volume of distribution (V/F) were 0.243 h(-1), 0.056 liters/h/kg and 23.7 liters/kg, respectively. The intersubject variability (coefficient of variation, CV%) in CL/F and V/F was 18%, and 22%, respectively. The interoccasion variability in CL/F was 18%, and the mean elimination half-life was 12.7 days. A positive linear association between weight and both CL/F and V/F was found, but this had insufficient impact to warrant dosage adjustments. Model robustness was assessed by a nonparametric bootstrap (200 samples). A degenerate visual predictive check indicated the raw data mirrored the post-dose concentration-time profiles simulated (n=1,000) from the final model. Individual pharmacokinetic estimates of tafenoquine did not predict prophylactic outcome to the drug in 4 subjects who relapsed with P. vivax malaria as they had similar pharmacokinetics to those who were free of malaria infection. No obvious pattern existed between the plasma tafenoquine concentrations and the pharmacokinetic parameter values in subjects with and without drug-associated moderate, or severe adverse events. This validated population pharmacokinetic model satisfactorily described the disposition and variability of tafenoquine when used for long-term malaria prophylaxis in a large cohort of soldiers on military deployment.

The standard adult treatment regimen for Plasmodium vivax malaria is chloroquine (1500mg over 3 d) plus primaquine (15 or 30mg daily for 14 d), but patient compliance tends to be poor with the lengthy course. Preliminary observations are reported on the efficacy of a shorter treatment course - artesunate (200mg twice a day for 2 d) plus primaquine (22.5mg base twice a day for 7 d)- given to 28 adult patients infected with P. vivax in Viet Nam. All patients responded quickly to treatment with mean (SD) parasite and fever clearance times of 14.2 (4.0) and 18.6 (8.4) h, respectively. The high dose of primaquine was generally well tolerated, and only one patient (3.6%) had a recurrence of parasitaemia during 28 d of follow-up. As most patients infected with Southeast Asian strains of P. vivax have their first relapse within 28 d after treatment with rapidly eliminated blood schizonticides, the absence of parasitaemia in the remaining 27 patients suggests that this drug regimen was active against both blood and liver stages. Further studies are needed to confirm that this rapidly acting, short artesunate-primaquine regimen can result in better patient compliance and treatment outcomes than the chloroquine-primaquine regimen.

Aims To evaluate the effects of gender, food and grapefruit juice on the pharmacokinetics of primaquine in healthy subjects. Methods In a randomized, two-phase cross-over study, 10 male and 10 female healthy Vietnamese subjects were administered 30 mg primaquine in the fasting state or with food, followed by administration of primaquine with grapefruit juice. Results The pharmacokinetics of primaquine were comparable between male and female subjects, with geometric mean ratios of C(max)= 0.89 [95% confidence interval (CI) 0.65, 1.22] and AUC = 0.80 (95% CI 0.56, 1.15). The mean CL/F of primaquine was slightly higher in males than in females [0.52 l h(-1) kg(-1)vs. 0.43 l h(-1) kg(-1), mean difference of 0.09 (95% CI -0.10, 0.28), P = 0.32]. When compared with fasting state values, food increased the geometric mean C(max) of primaquine by 26%(95% CI 12, 40) and the AUC by 14%(95% CI 3, 27). Similarly, grapefruit juice increased the geometric mean C(max) by 23%(95% CI 4, 45) and the AUC by 19%(95% CI 4, 37). Conclusions The disposition of primaquine was comparable between genders, suggesting no need to modify the dose of primaquine for malaria treatment or prophylaxis. Food increased the oral bioavailability of primaquine, which may lead to higher antimalarial efficacy. Grapefruit juice increased the bioavailability of primaquine, with marked interindividual differences suggesting that people should not take primaquine with grapefruit juice.

We assessed the prophylactic efficacy of azithromycin (250 mg/day) against malaria in 276 adults in western Thailand in a randomized, double-blind, placebo-controlled trial. After antimalarial suppressive treatment, volunteers were randomized in a 2:1 ratio to either the azithromycin or placebo, respectively. Study medication was given for an average of 74 days. The azithromycin group (n = 179) had five endpoint parasitemias (1 Plasmodium vivax and 4 P. falciparum), and the placebo group (n = 97) had 28 endpoint parasitemias (21 P. vivax, 5 P. falciparum, and 2 mixed infections). Adverse events and compliance and withdrawal rates were similar in both groups. The protective efficacy (PE) of azithromycin was 98% for P. vivax (95% confidence interval [CI]= 88-100%). There were too few cases to reliably estimate the efficacy of azithromycin for P. falciparum (PE =71%, 95% C =-14-94%). We conclude that daily azithromycin was safe, well-tolerated, and had a high efficacy for the prevention of P. vivax malaria.

Food has been reported to increase the bioavailability of mefloquine in healthy volunteers, but its role in increasing blood mefloquine concentrations in malaria patients treated with mefloquine is unclear. In this study, we compared blood mefloquine concentrations after the administration of artesunate (8 mg/kg) and mefloquine (15 mg/kg) over 12h with either a low-fat (approximately 3g of fat) or high-fat (approximately 30 g of fat) meal for the treatment of Plasmodium falciparum malaria in 12 Vietnamese patients. No statistical differences were detected in the following kinetic parameters between the low-fat (n=6) and high-fat (n=6) groups, respectively: maximum blood mefloquine concentrations (2838+/-531 ng/ml and 2556+/-657 ng/ml, 95% CI -486 to 1050 ng/ml, P=0.43) and the area under the blood mefloquine concentration versus time curves (246.8+/-58.3 microg.h/ml and 238.3+/-28.4 microg.h/ml, 95% CI -50.5 to 67.5 microg.h/ml, P=0.75). A fatty meal does not appear to increase the bioavailability of mefloquine in malaria patients and should not affect the response of malaria infections to treatment.

Tafenoquine is being developed for radical cure and post-exposure prophylaxis of Plasmodium vivax malaria. In an open-label study, 1512 Australian Defence Force personnel received one of three tafenoquine 3 d regimens [400mg once daily (od), 200mg twice daily (bid), 200mg od] or daily primaquine (22.5mg) plus doxycycline (100mg) over 14 d in Bougainville and in Timor-Leste for post-exposure prophylaxis. The relapse rate of subjects treated in Bougainville with tafenoquine (n=173) was 1.2%(200mg bidx3 d) and 2.3%(400mg odx3 d), while primaquine plus doxycycline (n=175) was 3.4%. For subjects treated in Timor-Leste with tafenoquine (n=636), the relapse rate was 4.9%(200mg odx3 d), 5.3%(200mg bidx3 d) and 11.0%(400mg odx3d), while primaquine plus doxycycline (n=289) was 10.0%. The most frequent adverse events reported across all groups were nausea, abdominal distress and diarrhoea. There was a dose-dependent reduction in adverse events with a reduced dose of tafenoquine, with the lowest dose (total 600mg over 3 d) producing rates of adverse events equivalent to that of primaquine plus doxycycline. The much shorter dosing regimen of tafenoquine should increase compliance, which is often suboptimal with primaquine after leaving an endemic area.[Australian New Zealand Clinical Trials Registry Number 12607000588493].

The population pharmacokinetics of tafenoquine were studied in Australian soldiers taking tafenoquine for malarial prophylaxis. The subjects (476 males, 14 females) received a loading dose of 200 mg tafenoquine base daily for 3 days, followed by a weekly dose of 200 mg tafenoquine for 6 months. Blood samples were collected from each subject after the last loading dose, then at weeks 4, 8, and 16. Plasma tafenoquine concentrations were determined by LC/MS/MS. Population modeling was performed with NONMEM using a one-compartment model. Typical values of the first-order absorption rate constant (Ka), clearance (CL/F) and volume of distribution (V/F) were 0.243 h(-1), 0.056 liters/h/kg and 23.7 liters/kg, respectively. The intersubject variability (coefficient of variation, CV%) in CL/F and V/F was 18%, and 22%, respectively. The interoccasion variability in CL/F was 18%, and the mean elimination half-life was 12.7 days. A positive linear association between weight and both CL/F and V/F was found, but this had insufficient impact to warrant dosage adjustments. Model robustness was assessed by a nonparametric bootstrap (200 samples). A degenerate visual predictive check indicated the raw data mirrored the post-dose concentration-time profiles simulated (n=1,000) from the final model. Individual pharmacokinetic estimates of tafenoquine did not predict prophylactic outcome to the drug in 4 subjects who relapsed with P. vivax malaria as they had similar pharmacokinetics to those who were free of malaria infection. No obvious pattern existed between the plasma tafenoquine concentrations and the pharmacokinetic parameter values in subjects with and without drug-associated moderate, or severe adverse events. This validated population pharmacokinetic model satisfactorily described the disposition and variability of tafenoquine when used for long-term malaria prophylaxis in a large cohort of soldiers on military deployment.

Malaria is the tropical disease most commonly imported into the UK, with 1500-2000 cases reported each year, and 10-20 deaths. Approximately three-quarters of reported malaria cases in the UK are caused by Plasmodium falciparum, which is capable of invading a high proportion of red blood cells and rapidly leading to severe or life-threatening multi-organ disease. Most non-falciparum malaria cases are caused by Plasmodium vivax; a few cases are caused by the other two species of Plasmodium: Plasmodium ovale or Plasmodium malariae. Mixed infections with more than 1 species of parasite can occur; they commonly involve P. falciparum with the attendant risks of severe malaria. Management of malaria depends on awareness of the diagnosis and on performing the correct diagnostic tests: the diagnosis cannot be excluded until 3 blood specimens have been examined by an experienced microscopist. There are no typical clinical features of malaria, even fever is not invariably present. The optimum diagnostic procedure is examination of thick and thin blood films by an expert to detect and speciate the malarial parasites; P. falciparum malaria can be diagnosed almost as accurately using rapid diagnostic tests (RDTs) which detect plasmodial antigens or enzymes, although RDTs for other Plasmodium species are not as reliable. The treatment of choice for non-falciparum malaria is a 3-day course of oral chloroquine, to which only a limited proportion of P. vivax strains have gained resistance. Dormant parasites (hypnozoites) persist in the liver after treatment of P. vivax or P. ovale infection: the only currently effective drug for eradication of hypnozoites is primaquine. This must be avoided or given with caution under expert supervision in patients with glucose-6-phosphate dehydrogenase deficiency (G6PD), in whom it may cause severe haemolysis. Uncomplicated P. falciparum malaria can be treated orally with quinine, atovaquone plus proguanil (Malarone) or co-artemether (Riamet); quinine is highly effective but poorly tolerated in prolonged dosage and is always supplemented by additional treatment, usually with oral doxycycline. ALL patients treated for P. falciparum malaria should be admitted to hospital for at least 24 h, since patients can deteriorate suddenly, especially early in the course of treatment. Severe falciparum malaria, or infections complicated by a relatively high parasite count (more than 2% of red blood cells parasitized), should be treated with intravenous therapy until the patient is well enough to continue with oral treatment. In the UK, the treatment of choice for severe or complicated malaria is currently an infusion of intravenous quinine. This may exacerbate hypoglycaemia that can occur in malaria; patients treated with intravenous quinine therefore require careful monitoring. Intravenous artesunate reduces high parasite loads more rapidly than quinine and is more effective in treating severe malaria in selected situations. It can also be used in patients with contra-indications to quinine. Intravenous artesunate is unlicensed in the EU. Assistance in obtaining artesunate may be sought from specialist tropical medicine centres, on consultation, for named patients. Patients with severe or complicated malaria should be managed in a high dependency or intensive care environment. They may require haemodynamic support and management of acute respiratory distress syndrome, disseminated intravascular coagulation, renal impairment/failure, seizures, and severe intercurrent infections including gram-negative bacteraemia/septicaemia. Falciparum malaria in pregnancy is more likely to be severe and complicated: the placenta contains high levels of parasites. Stillbirth or early delivery may occur and diagnosis can be difficult if parasites are concentrated in the placenta and scanty in the blood. The treatment of choice for falciparum malaria in pregnancy is quinine; doxycycline is contraindicated in pregnancy but clindamycin can be substituted for it, and is equally effective. Primaquine (for eradication of P. vivax or P. ovale hypnozoites) is contraindicated in pregnancy; after treatment for these infections a pregnant woman should take weekly chloroquine prophylaxis until after delivery when hypnozoite eradication can be considered. Children are over-represented in the incidence of malaria in the UK, probably because completely susceptible UK-born children accompany their overseas-born parents on visits to family and friends in endemic areas. Malaria in children (and sometimes in adults) may present with misleading symptoms such as gastrointestinal features, sore throat or lower respiratory complaints; the diagnosis must always be sought in a feverish or very sick child who has visited malaria-endemic areas. Children can be treated with most of the antimalarial regimens which are effective in adults, with appropriate dosage adjustment. Doxycycline plus quinine should not be given to children under 12 years as doxycycline is contraindicated in this age group, but clindamycin can be substituted for doxycycline, and pyrimethamine-sulfadoxine (Fansidar) may also be an effective substitute. An acute attack of malaria does not confer protection from future attacks: individuals who have had malaria should take effective anti-mosquito precautions and chemoprophylaxis during future visits to endemic areas.

In an open-label sequential cohort study, we compared gastrointestinal (GI) disturbances and plasma tafenoquine concentrations after administration of single-dose (400mg dailyx3 days; n=76 males, 11 females) and split-dose (200mg twice dailyx3 days; n=73 males, 13 females) tafenoquine regimens in healthy Australian Defence Force volunteers for post-exposure malaria prophylaxis. The female and male volunteers had comparable demographic characteristics (age, weight, height) in the single- and split-dose treatment groups. GI disturbances were generally mild and self-limiting for both groups. The frequency of nausea and abdominal distress was over two-fold higher in females than in males for both treatment groups. Reporting of GI disturbances in the single-dose group differed significantly between males and females, but this gender difference was not seen for the split-dose group. In those volunteers who experienced GI disturbances, the mean plasma tafenoquine concentrations 12h after the last dose of tafenoquine were approximately 1.3-fold higher in females than in males (means+/-SD: 737+/-118ng/ml vs. 581+/-113ng/ml). These preliminary findings suggest that further studies are required in a larger number of females to determine whether there is a need to reduce the dose of tafenoquine to minimise GI disturbances in females.

Molecular markers have been proposed as a method of monitoring malaria drug resistance and could potentially be used to prolong the life span of antimalarial drugs. Single nucleotide polymorphisms (SNPs) in the Plasmodium falciparum gene pfmdr1 and increased gene copy number have been associated with in vitro drug resistance but have not been well studied in vivo. In a prospective cohort study of malaria patients receiving mefloquine treatment on the Thai-Myanmar border, there was no significant association between either pfmdr1 SNPs or in vitro drug sensitivity and mefloquine resistance in vivo. Increased pfmdr1 gene copy number was significantly associated with recrudescence (relative risk 2.30, 95% CI 1.27-4.15). pfmdr1 gene copy number may be a useful surveillance tool for mefloquine-resistant falciparum malaria in Thailand.

Tafenoquine is an 8-aminoquiniline related to primaquine with pre-clinical activity against a range of malaria species. We treated two acute cases of vivax malaria with tafenoquine (800 mg over three days) alone, instead of conventional chloroquine (1500 mg over three days) and primaquine (420 mg over 14 days). In addition to the convenience of this regimen, the rapid parasite clearances observed, coupled with a good clinical response and lack of recrudescence or relapse, indicate that further investigation of tafenoquine in the treatment of vivax malaria is warranted.

The blood schizontocidal, pharmacodynamic interaction between tafenoquine (WR 238605--a 5-phenoxyprimaquine derivative--and chloroquine was investigated, using an in-vitro test for the inhibition of schizont maturation, in 15 fresh isolates of Plasmodium falciparum that originated from northwestern Thailand and neighbouring Myanmar. In this area the parasite is highly resistant to chloroquine. The geometric mean cut-off concentrations of schizont maturation for tafenoquine and chloroquine were 5261 nM and 7638 nM, respectively. With a mixture of tafenoquine and chloroquine, the mean cut-off concentration was 5252 nM, corresponding to 389 nM tafenoquine + 4863 nM chloroquine. Further analysis showed that the interaction between tafenoquine and chloroquine was additive within the range of EC20 and EC77. At concentrations higher than the EC77, interaction was moderately synergistic. While tafenoquine did not reverse the resistance to chloroquine to the degree of clinically relevant sensitivity, there was evidence that the blood schizontocidal efficacy of tafenoquine would be enhanced in the presence of chloroquine.

We assessed monthly doses of tafenoquine for preventing Plasmodium vivax and multidrug-resistant P. falciparum malaria. In a randomized, double-blind, placebo-controlled study, 205 Thai soldiers received either a loading dose of tafenoquine 400 mg (base) daily for 3 days, followed by single monthly 400-mg doses (n = 104), or placebo (n = 101), for up to 5 consecutive months. In volunteers completing follow-up (96 tafenoquine and 91 placebo recipients), there were 22 P. vivax, 8 P. falciparum, and 1 mixed infection. All infections except 1 P. vivax occurred in placebo recipients, giving tafenoquine a protective efficacy of 97% for all malaria (95% confidence interval [CI], 82%-99%), 96% for P. vivax malaria (95% CI, 76%-99%), and 100% for P. falciparum malaria (95% CI, 60%-100%). Monthly tafenoquine was safe, well tolerated, and highly effective in preventing P. vivax and multidrug-resistant P. falciparum malaria in Thai soldiers during 6 months of prophylaxis.