Gender-specific distribution of mefloquine in the blood following the administration of therapeutic doses.

BACKGROUND: The objectives of the study were to elucidate the gender-specific distribution of mefloquine in cellular and fluid blood compartments when given at therapeutic dosage, to assess its correlation with the occurrence of treatment-related adverse events, and to explore the necessity of adjusting treatment guidelines for females. METHODS: The distribution of mefloquine following the administration of standard therapeutic doses (1,250 mg mefloquine in split dose) to 22 healthy Caucasian volunteers was assessed in whole blood, serum, plasma, red blood cells (RBCs), white blood cells, and platelets using high performance liquid chromatography. RESULTS: Plasma mefloquine concentrations after 14 hours were considerably higher in female subjects than in males (2,778 vs 1,017 ng/ml at H14), concordant with a significantly higher frequency, duration, and severity of adverse reactions. However, mean drug concentrations of RBC appeared slightly higher in male volunteers (857 vs 719 ng/ml). At H48, a similar situation prevailed, and at H168 the mefloquine concentrations in plasma continued to be higher in females compared to males (1,353 vs 666 ng/ml), while the concentrations of RBC were similar in females (389 vs 375 ng/ml). Since the observations relate to healthy individuals, they do not take into account selective uptake of mefloquine by Plasmodium-infected erythrocytes as in the case of therapeutic drug use. CONCLUSION: Although plasma mefloquine concentrations in female healthy volunteers are considerably higher and the concentrations of the RBCs are initially lower compared to males, they do not seem to justify an adjustment of treatment guidelines for mefloquine in female Caucasian individuals.

Investigation of the in vitro gender-specific partitioning of mefloquine in malarial infected red blood cells and plasma.

The investigation of gender-specific partitioning of the antimalarial drug mefloquine to cellular and fluid blood compartments was performed using blood collected from a female and male healthy subject that were infected with Plasmodium falciparum PCM2 clone and spiked with mefloquine (0.25, 1, and 5 µM). Mefloquine concentrations in red cells of both female and male subjects were significantly higher than plasma, which suggests an intensive uptake by red cells. This was supported by a high ratio of mefloquine concentrations in the parasitized and non-parasitized red cells of about 4-fold. Gender-specific partitioning of mefloquine in parasitized blood was seen only in plasma where significantly higher concentrations were observed in female compared with male plasma. Down-adjusting the therapeutic dose of mefloquine in female patients with malaria is not advisable because mefloquine concentrations in the target cellular compartment are similar in both genders.

Activity of selected phytochemicals against Plasmodium falciparum.

According to the WHO, in 2008, there were 247 million reported cases of malaria and nearly one million deaths from the disease. Parasite resistance against first-line drugs, including artemisinin and mefloquine, is increasing. In this study the plant-derived compounds aglafolin, rocaglamid, kokusaginine, arborine, arborinine and tuberostemonine were investigated for their anti-plasmodial activity in vitro. Fresh Plasmodium falciparum isolates were taken from patients in the area of Mae Sot, north-western Thailand in 2008 and the inhibition of schizont maturation was determined for the respective compounds. With inhibitory concentrations effecting 50%, 90% and 99% inhibition (IC(50), IC(90) and IC(99)) of 60.95 nM, 854.41 nM and 7351.49 nM, respectively, rocaglamid was the most active of the substances, closely followed by aglafoline with 53.49 nM, 864.55 nM and 8354.20 nM. The activity was significantly below that of artemisinin, but moderately higher than that of quinine. Arborine, arborinine, tuberostemonine and kokusaginine showed only marginal activity against P. falciparum characterized by IC(50) and IC(99) values higher than 350 nM and 180 µM, respectively, and regressions with relatively shallow slopes S>14.38. Analogues of rocaglamid and aglafoline merit further exploration of their anti-plasmodial activity.

Global challenges of changing epidemiological patterns of malaria.

In the absence of secular climatic changes, the global challenges of changing epidemiological patterns of malaria have to be induced by man, i.e. by a disturbance of the equilibrium between man, vector and the parasite in an environment conducive to the natural transmission of the pathogen. There are many ways of attempting such a disturbance, from the use of personal protection to the use of diagnostic and remedial antiplasmodial treatment, up to the application of vector control measures for the elimination of breeding places, larviciding and the use of intradomestic insecticides. This will be done by looking at the parasites responsible for the specific infection, and considering the various arthropod hosts and the human hosts, before the comprehensive treatment of the environmental features. This will be followed by a section on the quantitative epidemiology. The various tools of intervention and their relative efficacy precede the section on common denominators of previously malarious countries having achieved and maintained malaria-free status. Similarly, the reasons for failing the declared goal of eliminating malaria sets the new scene for the global challenges ahead of us in the endeavour of future attempts at eliminating malaria.

Sensitivity of Plasmodium vivax to chloroquine, mefloquine, artemisinin and atovaquone in north-western Thailand.

Excepting tropical Africa, where Plasmodium falciparum prevails, Plasmodium vivax is the most frequent cause of malaria in Asia and Latin America. First reliable reports of chloroquine resistance came in 1989 from the area of the distribution of the Chesson-strain of P. vivax. Since then, reports also came from other areas of the world. This study had the objective of measuring the sensitivity of P.vivax to chloroquine and potential alternative compounds in western Thailand. The study was performed in 2008 in Mae Sot, Tak Province, and followed the method of Tasanor. The IC(50) and IC(90) values for chloroquine were 167 nM and 5445 nM, those for mefloquine were 139 nM and 5282 nM, those for artemisinin were 32 nM and 466 nM, and those for atovaquone 30 nM and 650 nM. The values for chloroquine indicate the existing or imminent occurrence of specific resistance. High prevalence of mefloquine resistance precludes its alternative use. However, atovaquone, in combination with proguanil, may be a possible alternative.

Distribution of mefloquine in the blood of Thai patients with acute uncomplicated falciparum malaria following administration of therapeutic doses of artesunate.

PURPOSE: The study objectives to investigate the distribution of the antimalarial drug mefloquine (MQ) in cellular and fluid blood compartments when given at therapeutic dosage with artesunate and to investigate an eventual association with the occurrence of treatment-related adverse events in Thai patients with acute uncomplicated falciparum malaria. METHODS: MQ distribution following administration of standard therapeutic doses (1,250 mg MQ in split dose) with artesunate to 20 Thai patients with acute uncomplicated falciparum malaria was assessed in whole blood, serum, plasma, red blood cells (RBC), white blood cells (WBC), and platelets using high -performance liquid chromatography. RESULTS: All patients responded to treatment without reappearance of parasitemia during the 42-day follow-up period. There was no significant gender difference in MQ levels. The chronological change in MQ levels in all blood components, including ratios of plasma to serum, whole blood, RBC, platelets or WBC were similar and parallel in both genders. MQ concentrations at 14 and 168 h, in descending order, in both male and female patients were as follow: WBC > platelets > plasma > serum > whole blood > RBC. Gender-specific whole blood, serum, and RBC concentrations were similar at all time points, with median ratios of plasma:whole blood, plasma:serum, and plasma:RBC of 0.84:1.21, 1.09:1.64, and 1.59:3.79, respectively. Plasma vs whole blood and plasma vs RBC MQ concentrations showed a highly significant correlation, with r = 0.923 and 0.867, respectively. No association between occurrence of treatment-related adverse events and MQ concentrations in various blood components/fluids was observed in either gender. CONCLUSIONS: Based on these observations, gender-specific therapeutic MQ dose adjustment is obviously not required.

Clinical and molecular characterization of a near fatal case of human babesiosis in Austria.

A previously healthy febrile patient with travel history to Nicaragua showed rapid clinical deterioration with hemodynamic shock and anuria. Diagnosis of severe malaria was established based on intra-erythrocytic parasites and antimalarial treatment was initiated. However, upon reevaluation Babesia microti infection was suspected and molecular characterization by polymerase chain reaction and sequence analysis was performed.

Pharmacodynamic interaction between lumefantrine and desbutyl-benflumetol in Plasmodium falciparum in vitro.

The pharmacodynamic interaction between lumefantrine and monodesbutyl-benflumetol has been investigated in 44 fresh isolates of patients with a Plasmodium falciparum infection from the region of Mae Sot (Thailand). Both substances proved to be effective against parasite maturation within the test concentration range, with monodesbutyl-benflumetol being effective at a lower concentration than lumefantrine. Synergism between the two substances was evaluated with a combination of lumefantrine and monodesbutyl-benflumetol at a ratio of 4.25:1. The geometric mean values for complete inhibition of schizont maturation were 1035.7 nM for lumefantrine, 655 nM for monodesbutyl-benflumetol and 222.5 nM for the combination of both. An analysis for interaction according to the method of Berenbaum indicates a moderate synergism at the IC(50), which gets stronger with increasing ICs and reaches the highest level at the IC(99). The geometric mean of the sums of the FIC(50) is 0.73, of the FIC(90) it is 0.37 and of the FIC(99) it is 0.25.

Synergism between pyronaridine and retinol in Plasmodium vivax in vitro.

Estimates of the annual number of infections with Plasmodium vivax reach 391 million. So far the blood-schizontocidal therapy with chloroquine remained effective in most parts of the world, but reports about emerging resistance are increasing. The study had the objective of determining the pharmacodynamic interaction between pyronaridine and retinol in Plasmodium vivax, since pyronaridine is a potential alternative for chloroquine and an earlier study had shown strong synergism between pyronaridine and retinol in Plasmodium falciparum. The study was conducted at the Malaria Clinic of Mae Sot, Tak Province, Thailand, near the border to Myanmar. The in vitro observations followed the method of Tasanor. Successful tests were performed with 44 isolates. The mean IC(50), IC(90) and IC(99) values for pyronaridine were 9.8, 2069.6 and 162446.5 nM. The mean IC(50), IC(90) and IC(99) values for the combinations with retinol (corresponding to the 50th, 65th and 80th percentile of the physiological retinol levels in healthy adults) were 1.7, 542.8 and 59379.5 nM for pyronaridine + retinol "low", for the combination with retinol "medium" they were 0.5, 313.7 and 58891.4 nM and for the combination with retinol "high" they were 0.2, 96.7 and 16754.3 nM. These results suggest strong synergism between the two substances.

Synergism between mefloquine and artemisinin and its enhancement by retinol in Plasmodium falciparum in vitro.

Following the advent of mefloquine resistance in Plasmodium falciparum in Thailand in the 1990s, the combined treatment of falciparum malaria with artesunate and mefloquine was found to be highly effective in treating and curing the patients in the affected areas. Monitoring of the clinical-parasitological response and of the in vitro sensitivity of P. falciparum was systematically conducted in order to detect any signs of failure of this type of artemisinin-based combination treatment (ACT). In earlier observations the in vitro activity of artemisinin was found to be significantly enhanced when combined with retinol. The same applies to mefloquine. In order to check whether the synergism between artemisinin and mefloquine was maintained in the presence of retinol, the pharmacodynamic interaction of the three compounds was investigated in the western border area of Thailand. Successful parallel tests with mefloquine, artemisinin, retinol, mefloquine-artemisinin 5:1 as well as mefloquine-artemisinin (5:1) + retinol low, medium and high were obtained with 43 fresh parasite isolates. The retinol concentrations in the low, medium and high formulations corresponded to the 50th, 65th and 80th percentile of the physiological mean concentrations in the blood of healthy adults. The IC(50), IC(90) and IC(99) values for mefloquine alone showed a further increase over the data of 2008. In the combinations with artemisinin and retinol moderate synergism was observed at the IC(50), but synergism increased strongly at the IC(90) and the IC(99).

Sensitivity to artemisinin, mefloquine and quinine of Plasmodium falciparum in northwestern Thailand.

The increasing drug resistance of Plasmodium falciparum is a worldwide problem. The objective of the study was the assessment of the in vitro activity of artemisinin, mefloquine and quinine, in an area where P. falciparum is multi-drug resistant. The sensitivity tests were based on measuring the drug-dependent inhibition of schizont maturation. For the 43 successfully tested isolates the mean effective concentrations (IC(50) and IC(90)) for artemisinin were 0.0081 and 0.1372 µM, respectively. For mefloquine the IC(50) was 0.1260 µM and the IC(90) was 3.7345 µM. Quinine showed an IC(50) of 0.2155 µM and an IC(90) of 2.5040 µM. All tested drugs showed a significant reduction in the effectiveness, compared with the results of former years. This suggests a further rise of resistance of local P. falciparum, which is alarming especially for artemisinin and quinine.

Frequency distribution of antimalarial drug resistance alleles among Plasmodium falciparum isolates from Gezira State, central Sudan, and Gedarif State, eastern Sudan.

In 2004, Sudan adopted artesunate + sulfadoxine/pyrimethamine (SP) combination as the first-line drug, in response to the high level of falciparum resistance to antimalarials. In 2007, a molecular study on antimalarial resistance linked genes, pfcrt, pfmdr1, pfdhfr, pfdhps, and pfATPase6, was conducted on 198 isolates from central and eastern Sudan. We observed a high frequency of point mutations at almost all loci analyzed, mainly of pfcrt 76T (72.7%), pfdhfr 51I (75.3%), and pfdhfr 108N (72.7%) alleles. The MARK III in vitro test for chloroquine sensitivity in 45 P. falciparum isolates showed that 37.8% of the isolates were low resistant and 6.7% were fully resistant. This study represents the most recent molecular investigation on antimalarial resistance in this area after the adoption of artemisinin-based combination therapy (ACT), and underlines the importance of the analysis of SP resistance evolution to monitor the efficacy of ACT therapy in endemic areas.

Thrombocyte counts in mice after the administration of papaya leaf suspension.

Following up a popular use of crude leaf preparations from Carica papaya for the treatment of dengue infections, a suspension of powdered Carica papaya leaves in palm oil has been investigated for its effect on thrombocyte counts in mice, administering by gavage 15 mg of powdered leaves per kg body weight to 5 mice. Equal numbers of animals received corresponding volumes of either palm oil alone or physiological saline solution. Thrombocyte counts before and at 1, 2, 4, 8, 10, 12, 24, 48 and 72 hours after dosing revealed significantly higher mean counts at 1, 2, 4, 8, 10 and 12 after dosing with the C. papaya leaf formulation as compared to the mean count at hour 0. There was only a non-significant rise of thrombocyte counts in the group having received saline solution, possibly the expression of a normal circadian rhythm in mice. The group having received palm oil only showed a protracted increase of platelet counts that was significant at hours 8 and 48 and obviously the result of a hitherto unknown stimulation of thrombocyte release. The results call for a dose-response investigation and for extending the studies to the isolation and identification of the C. papaya substances responsible for the release and/or production of thrombocytes.

Activity of Eurycoma longifolia root extract against Plasmodium falciparum in vitro.

The habitats of Eurycoma longifolia Jack, a slender tree, are jungles in Malaysia and Indonesia. It belongs to the family Simaroubaceae and is a source of quassinoids with anabolic, antimalarial and cytostatic activity. In this study, conducted during 2008 in Mae Sot, Thailand, a standardized extract of E. longifolia containing three major quassinoids, eurycomanone (1), 13,21-dihydroeurycomanone (2) and 13alpha(21)-epoxyeurycomanone (3) was evaluated for antiplasmodial activity against Plasmodium falciparum and its activity has been compared with that of artemisinin, using 38 fresh parasite isolates and assessment of inhibition of schizont maturation. The IC(50), IC(90) and IC(99) values for artemisinin were 4.30, 45.48 and 310.97 microg/l, and those for the root extract from E. longifolia 14.72, 139.65 and 874.15 microg/l respectively. The GMCOC for artemisinin was 337.81 mug/l, and for the plant extract it was 807.41 microg/l. The log-concentration probit regressions were parallel. The inhibitory activity of the E. longifolia extract was higher than that expected from the three quassinoids isolated from the plant, suggesting synergism between the quassinoids or the presence of other unidentified compounds.

Pharmacodynamic interaction between mefloquine and retinol in Plasmodium falciparum in vitro.

Mefloquine, a 4-quinolinemethanol derivative, was introduced in Thailand after Plasmodium falciparum had acquired almost universal resistance to the 4-aminoquinolines and antifols. However, also resistance to mefloquine has become an increasing problem, but artemisinin-based combination therapy (ACT) with mefloquine and artesunate remained until recently sufficiently effective. Since synergistic interaction between quinine, another 4-quinolinemethanol, with retinol was observed earlier, the investigations were expanded to mefloquine. The interaction between mefloquine and retinol at concentrations equal to the 50(th), 65(th) and 80(th) percentile of the physiological retinol levels in healthy adults was determined in 37 fresh isolates of P. falciparum. The mean IC(50), IC(90) and IC(99) values for mefloquine were 1.76, 9.81 and 39.78 microM, those for mefloquine + retinol "low" 0.33, 1.37 and 4.33 microM, those for mefloquine + retinol "medium" 0.29, 1.15 and 3.48 microM, and those for mefloquine + retinol "high" 0.20, 0.85 and 2.70 microM. Evidence for strong synergism between mefloquine and retinol in P. falciparum was highly significant.

Synergism between pyronaridine and retinol in Plasmodium falciparum in vitro.

Pyronaridine, a naphthyridine derivative and Mannich base, is a highly active blood schizontocide and currently being explored as partner in artemisinin-based combination therapy (ACT). In this study, carried out 2008 in Mae Sot, Thailand, the activity of pyronaridine was found to be compromised, obviously as the result of mono-therapy in an adjacent area. The pyronaridine sensitivity and the interaction between pyronaridine and retinol at concentrations corresponding to the 50th, 65th and 80th percentile of the physiological retinol levels in healthy adults were assessed in 38 fresh isolates of P. falciparum. The mean IC50, IC90 and IC99 values for pyronaridine were 12.7, 201.4 and 3084.2 nM, those for pyronaridine + retinol "low" 1.2, 14.0 and 102.6 nM, those for pyronaridine + retinol "medium" 0.6, 7.4 and 54.8 nM, and those for pyronaridine + retinol "high" 0.9, 8.2 and 47.8 nM. There was significant evidence of strong synergism between pyronaridine and retinol against P. falciparum.

From malaria control to eradication: The WHO perspective.

Efforts to control malaria have been boosted in the past few years with increased international funding and greater political commitment. Consequently, the reported malaria burden is being reduced in a number of countries throughout the world, including in some countries in tropical Africa where the burden of malaria is greatest. These achievements have raised new hopes of eradicating malaria. This paper summarizes the outcomes of a World Health Organization's expert meeting on the feasibility of such a goal. Given the hindsight and experience of the Global Malaria Eradication Programme of the 1950s and 1960s, and current knowledge of the effectiveness of antimalarial tools and interventions, it would be feasible to effectively control malaria in all parts of the world and greatly reduce the enormous morbidity and mortality of malaria. It would also be entirely feasible to eliminate malaria from countries and regions where the intensity of transmission is low to moderate, and where health systems are strong. Elimination of malaria requires a re-orientation of control activity, moving away from a population-based coverage of interventions, to one based on a programme of effective surveillance and response. Sustained efforts will be required to prevent the resurgence of malaria from where it is eliminated. Eliminating malaria from countries where the intensity of transmission is high and stable such as in tropical Africa will require more potent tools and stronger health systems than are available today. When such countries have effectively reduced the burden of malaria, the achievements will need to be consolidated before a programme re-orientation towards malaria elimination is contemplated. Malaria control and elimination are under the constant threat of the parasite and vector mosquito developing resistance to medicines and insecticides, which are the cornerstones of current antimalarial interventions. The prospects of malaria eradication, therefore, rest heavily on the outcomes of research and development for new and improved tools. Malaria control and elimination are complementary objectives in the global fight against malaria.

In vitro drug sensitivity testing in Plasmodium vivax.

The possibility of short-term in vitro cultivation, i.e. growth of asexual erythrocytic stages up to the stage of mature schizonts, permits in principle the development of drug sensitivity tests also for Plasmodium vivax. In the absence of a sequestration of erythrocytes carrying the advanced stages of schizogony, asexual parasites of all stages may be seen in the peripheral blood of patients infected with P. vivax. This precludes schizont maturation tests since schizont development will be unduly influenced by the number of advanced trophozoites. A test system reflecting the age composition of the parasite population and its progression without and under the influence of inhibitors was found to yield precise results also in the higher IC ranges. The population-based test procedure would also permit the identification of any stage-specific impact of antimalarial agents.

Malariological baseline survey and in vitro antimalarial drug resistance in Gulu district, Northern Uganda.

A comprehensive, representative malaria survey has been carried out in a population of internally displaced persons (IDP) in the district of Gulu, Northern Uganda. It included 74 households and 390 persons, and covered socio-economic and environmental information, individual physical data, malaria and the drug sensitivity of Plasmodium falciparum. The prevalence of infections with Plasmodium falciparum was 54.4% at a geometric mean asexual parasitaemia of 229/microl blood, typical for hyperendemic conditions. P. falciparum turned out to be highly resistant to chloroquine and amodiaquine. It showed also reduced sensitivity against lumefantrine and artemisinin, obviously the result of the liberal use of the lumefantrine-artemether combination without evidence-based indication.