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Query: UMLS:C0024530 (malaria)
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The artemisinin derivatives, dihydroartemisinin (DHA), artesunate, atemether and arteether, are currently used for treatment of malaria in artemisinin combination therapies (ACT) with longer half-life drugs. The demand is enormous--in 2005, the estimated global demand for one such ACT alone, artemether-lumifantrine, which constitutes about 70% of all current clinically-used ACTs, is for 120 million adult treatment courses. At 0.5 gm of artemether per total dose regimen, the amount of artemisinin required is approximately 114 tons. This has placed substantial stress on total artemisinin supplies world-wide, and considerable attention is being focussed on enhancing availability of artemisinin by improvement in horticultural practice and extraction of artemisinin from Artemisia annua. Artemisinic acid, which also occurs in A. annua, can be converted into artemisinin and is the ultimate target of a biotechnological approach, which if successful, will augment artemisinin supply in the future. The conversion of artemisinin into the known artemisinin derivatives, and problems with the methods are critically reviewed. Some attention is paid to mechanistic aspects which clarify stereochemistry. The current artemisinins are by no means ideal drugs. Artesunate in particular is incompatible with basic quinolines by virtue of proton transfer, and has intrinsic chemical instability. At pH 1.2, conversion to DHA is rapid, with t(1/2) 26 min, and at pH 7.4, t(1/2) is about 10 hours. With a pK(a) of 4.6, over 99% of artesunate will be ionized at pH 7.4, and thus uptake by passive diffusion from the intestinal tract will be minimal. Although a considerable effort has been vested in the search for new artemisinins, largely through functionalization of artemisinin at C-10, O-11 or at C-15 via artemisitene, or of DHA at C-10, deliberate enhancement of the 'druggability' of artemisinins by reducing lipophilicity, which at the same time will attenuate the neurotoxicity characteristic of the current derivatives, and enhance absorption, by and large has not been considered. A review of the various types of newer derivatives is given together with a consideration of medicinal chemistry aspects.
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PMID:From artemisinin to new artemisinin antimalarials: biosynthesis, extraction, old and new derivatives, stereochemistry and medicinal chemistry requirements. 1671 5

The infectivity of Plasmodium falciparum gametocytes after exposure in vitro to quinine, artesunate, and primaquine was assessed in Anopheles dirus, a major vector of malaria in Southeast Asia. Mature gametocytes (stage 5) of a Thai isolate of P. falciparum were exposed to the drugs for 24 h in vitro before membrane feeding to A. dirus. After 10 days, the mosquito midguts were dissected and the oocysts were counted. In this system, artesunate showed the most potent transmission-blocking activity; the mean (standard deviation [SD]) 50% and 90% effective concentrations (EC(50), and EC(90), respectively, in nanograms per milliliter) were 0.1 (0.02) and 0.4 (0.15), respectively. Transmission-blocking activity of quinine and primaquine was observed at relatively high concentrations (SDs): EC(50) of quinine, 642 (111) ng/ml; EC(50) of primaquine, 181 (23) ng/ml; EC(90) of quinine, 816 (96) ng/ml; EC(90) of primaquine, 543 (43) ng/ml. Artesunate both prevents the maturation of immature P. falciparum gametocytes and reduces the transmission potential of mature gametocytes. Both of these effects may contribute to reducing malaria transmission.
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PMID:Transmission-blocking activities of quinine, primaquine, and artesunate. 1672 47

Artesunate is a highly effective antimalarial and there is some evidence that it is also active against schistosome infections. We therefore investigated whether treatment with artesunate of acute malaria in Senegalese children had an impact on their level of infection with Schistosoma haematobium. Twenty-seven children who were entered into a clinical trial of antimalaria treatment were excreting S. haematobium eggs in their urine on the day of treatment. Fifteen children received a combination of a single dose of sulfadoxine/pyrimethamine together with three daily doses of artesunate (4 mg/kg); the remaining 12 children received three daily doses of amodiaquine and artesunate. The overall cure rate and reduction in the mean number of excreted eggs at 28 days post treatment were 92.6% and 94.5%, respectively. Our findings indicate that artesunate, in addition to being a very effective treatment for uncomplicated malaria, can also sharply reduce the S. haematobium loads harboured by pre-school African children.
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PMID:Antischistosomal efficacy of artesunate combination therapies administered as curative treatments for malaria attacks. 1676 98

Artesunate and mefloquine combination treatment has been used since 2000 in Cambodia as the first-line drug for the treatment of uncomplicated falciparum malaria. In order to assess its efficacy and safety, the national malaria control programme conducted 14 therapeutic efficacy studies with the drug combination between 2001 and 2004 at nine sites. In 2001 and 2002, co-blister packs of artesunate and mefloquine were used, whereas in 2003 and 2004, drugs were given individually from a bulk pack at a total dose of 12 mg/kg of artesunate and 25 mg/kg of mefloquine over 3 days. A total of 1025 patients were enrolled over the 4 years and 977 were follow-up during the period of 28 days. The PCR-corrected cure rates ranged from 85.7% to 100% with an overall cure rate of 95.8% (920/960). The studies in 2002 showed also that co-blister packs used on the basis of age and not on the basis of weight could lead to underdosed regimens but without any detectable effect on the treatment outcome. The follow-up period was extended from 28 to 42 days in three sites in 2004. A total of 219 among 255 were follow-up until day 42. The cure rate decreased but not significantly from 90.1% (73/81) with 28 days follow-up to 79.3% (46/58) with 42 days follow-up in Pailin, whereas the cure rate remained at 100% in the two other sites. Side effects were common, especially dizziness, but were mild and transient and patients recovered without any medical intervention.
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PMID:Surveillance of the efficacy of artesunate and mefloquine combination for the treatment of uncomplicated falciparum malaria in Cambodia. 1693 Feb 57

The choice of artemisinin-based combination that is being adopted for malaria treatment in sub-Saharan Africa may depend on several factors, including cost, efficacy, side effects, and simplicity of administration. We tested the hypothesis that artesunate-sulfamethoxypyrazine-pyrimethamine is as efficacious as the four-dose regimen of artemether-lumefantrine for treatment of Plasmodium falciparum malaria. The study was carried out during two transmission seasons (2003 and 2004) in Sotuba, Mali. Participants at least 6 months of age with uncomplicated P. falciparum malaria were randomly assigned to receive artesunate-sulfamethoxypyrazine-pyrimethamine or artemether-lumefantrine. Treatment efficacy was assessed using the World Health Organization 28-day protocol. A total of 606 (303 in each arm) patients were enrolled. The cure rate was higher for artesunate-sulfamethoxypyrazine-pyrimethamine than for artemether-lumefantrine (98.7% versus 89.6%; P < 0.0001). After correction for cases of re-infection, the cure rates were 100% and 99.0%, respectively (P = 0.08). No serious adverse events occurred. Artesunate-sulfamethoxypyrazine-pyrimethamine is well-tolerated and effective against P. falciparum malaria. It showed an additional benefit of preventing new infections.
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PMID:A randomized trial of artesunate-sulfamethoxypyrazine-pyrimethamine versus artemether-lumefantrine for the treatment of uncomplicated Plasmodium falciparum malaria in Mali. 1703 84

Artemisinin derivatives are potent antimalarial compounds that may have immunomodulatory properties. Artesunate (range 0.01-2 mirog/ml) or dihydroartemisinin (range 0.01-8 microg/ml; DHART) were added to peripheral blood mononuclear cells (PBMC) or whole blood (WB) cultures before or simultaneously upon stimulation with phytohemagglutinin (PHA), a T cell mitogen. Lymphoproliferation was then measured by 3[H]-thymidine incorporation, and CD4+ and CD8+ T cell activation was assessed by expression of CD69 or CD25 using flow cytometry. Reverse transcriptase polymerase chain reaction depicted PBMC mRNA production for interleukins 2, 4, 12, and 15, interferon-gamma, and tumor necrosis factor-alpha. Artesunate concentrations between 0.1-1.5 microg/ml reduced lymphoproliferation in PHA-stimulated PBMC and WB cultures in a generally dose-dependent manner; inhibition by DHART was similar. Removing artesunate from PBMC before PHA was added abolished the reduction. PBMCs cultured with artesunate or DHART simultaneously with PHA showed modestly reduced proportions of CD4+ and CD8+ T cells expressing CD69 and CD25. Artesunate had little effect on qualitative cytokine mRNA levels in PHA-stimulated PBMC cultures. Artesunate and DHART may diminish some PBMC responses to immunologic stimuli. Further work is warranted to define the mechanisms involved, and whether this affects malaria treatment.
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PMID:Artesunate and a major metabolite, dihydroartemisinin, diminish mitogen-induced lymphocyte proliferation and activation. 1733 24

Quinine and the artemisinin-derivative drugs artesunate and artemether are effective treatments for severe falciparum malaria. Trials comparing artemether with quinine have not demonstrated convincing evidence of a mortality advantage for artemether. The South East Asian Quinine Artesunate Malaria Trial (SEAQUAMAT), a multicenter, randomized, open-label trial in 1461 adults with severe malaria in Asia compared artesunate with quinine. Mortality was 15% in the artesunate group and 22% in the quinine group, a reduction of 34.7% (95% confidence interval: 18.5-47.6%) in the artesunate group, with almost all the benefit reported in those with high parasite counts. Artesunate should constitute first-line treatment for severe malaria in Asia. These results can probably be generalized to the treatment of severe malaria in adults from all areas, especially in those with hyperparasitemia. However, it is unclear whether these results can be generalized to children in Africa, who constitute the majority of those who die from severe malaria worldwide.
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PMID:Artesunate, artemether or quinine in severe Plasmodium falciparum malaria? 1740 35

Artemisinin combination therapies (ACTs) have recently been adopted as first-line therapy for Plasmodium falciparum infections in most malaria-endemic countries. In this study, we estimated the association between artesunate-mefloquine therapy failure and genetic changes in the putative transporter, pfmdr1. Blood samples were acquired from 80 patients enrolled in an 2004 in vivo efficacy study in Pailin, Cambodia, and genotyped for pfmdr1 copy number and haplotype. Having parasites with three or more copies of pfmdr1 before treatment was strongly associated with recrudescence (hazard ratio [HR] = 8.30; 95% CI: 2.60-26.43). This relationship was maintained when controlling for initial parasite density and hematocrit (HR = 7.91; 95% CI: 2.38-26.29). Artesunate-mefloquine treatment selected for increased pfmdr1 copy number, because isolates from recurrent episodes had higher copy numbers than the paired enrollment samples (Wilcoxon rank test, P = 0.040). pfmdr1 copy number should be evaluated further as a surveillance tool for artesunate-mefloquine resistance in Cambodia.
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PMID:Pfmdr1 and in vivo resistance to artesunate-mefloquine in falciparum malaria on the Cambodian-Thai border. 1742 63

Artesunate drug substance, for which a rectal capsule formulation is under development for the treatment of severe malaria, when heated at 100 degrees C for 39 h gives beta-artesunate, artesunate dimers, 9,10-anhydrodihydroartemisinin (glycal), a DHA beta-formate ester, and smaller amounts of other products that arise via intermediate formation of dihydroartemisinin (DHA) and subsequent thermal degradation. Solid DHA at 100 degrees C provides an epimeric mixture of a known peroxyhemiacetal, arising via ring opening to a hydroperoxide and re-closure, smaller amounts of a 3:1 mixture of epimers of a known tricarbonyl compound, and a single epimer of a new dicarbonyl compound. The latter arises via homolysis of the peroxide and an ensuing cascade of alpha-cleavage reactions which leads to loss of formic acid incorporating the C10 carbonyl group of DHA exposed by this 'unzipping' cascade. The tricarbonyl compound that arises via peroxide homolysis and extrusion of formic acid from a penultimate hydroxyformate ester incorporating C12 of the original DHA, is epimeric at the exocyclic 1''-aldehyde, and not in the cyclohexanone moiety. It is converted into the dicarbonyl compound by peroxide-induced deformylation. The dicarbonyl compound is not formed during anhydrous ferrous bromide mediated decomposition of DHA at room temperature, which provides the 1''-R epimer of the tricarbonyl compound as the dominant product; this equilibrates at room temperature to the 3:1 mixture of epimers of the tricarbonyl compound obtained from thermolysis. Each of artesunate and DHA decomposes readily under aqueous acidic conditions to provide significant amounts of the peroxyhemiacetal, which, like DHA, decomposes to the inert end product 2-deoxyartemisinin under acidic or basic conditions. DHA and the peroxyhemiacetal are the principal degradants in aged rectal capsule formulations of artesunate. TGA analysis and thermal degradation of DHA reveals a thermal lability which would pose a problem not only in relation to ICH stability testing guidelines, but in the use of DHA in fixed formulations currently under development. This thermolability coupled with the poor physicochemical properties and relative oral bioavailability of DHA suggests that it is inferior to artesunate in application as an antimalarial drug.
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PMID:Artesunate and dihydroartemisinin (DHA): unusual decomposition products formed under mild conditions and comments on the fitness of DHA as an antimalarial drug. 1769 24

Only a few drugs are available for the treatment of malaria. Artemisinin combination treatment is advocated because of its efficacy and to prevent the development of resistance. In the Netherlands, falciparum malaria is treated with atovaquone-proguanil or artemether-lumefantrine, both registered as 3-day treatments. In a recent study, 21 patients were treated with artemether-lumefantrine for 5 days. There are arguments in favour of a 5-day course: absorption of lumefantrine is dependent on food intake and the serum levels of lumefantrine are higher on day 7 after a 5-day course than after a 3-day course. As shown by studies in Thailand, the serum level is related to the relapse rate, although these studies revealed no difference in relapse rate between the 3- and 5-day courses. In endemic countries, short courses of treatment are favoured to further patient compliance. Artesunate for i.v. administration is urgently needed.
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PMID:[The treatment of falciparum malaria]. 1796 72


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