Released August 2007 - The Indian Society for Parasitology

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16 Gupta and SinglaPyrimethamine: It is also a slow-acting bloodschizonticide like proguanil, but its action iscomparatively faster and more potent than that ofproguanil. It does not eliminate the pre-erythrocyticphase of P. falciparum. Therefore, it is not a radicalcurative. However, extended treatment causesexhaustion of secondary tissue phases of P. vivaxleading to suppressive cure. In combination withsulphonamides, it is used to treat clinical attacks ofmalaria.Primaquine: Primaquine is the most important drugused for the radical cure of relapsing malaria. It is a poorblood schizonticide, but has marked efficacy againstprimary as well as secondary tissue phases of malarialparasite. Primaquine differs from all other antimalarialsin being highly active against gametocytes andhypnozoites. Its mechanism of action is not clearlyknown. It is readily absorbed orally and the mostsignificant side-effect is dose-related hemolysis andmethemoglobinemia, especially in persons with G-6PD deficiency. As foetus is also G-6 PD deficient, itsuse is not advised during pregnancy.Artemisinin compounds: Artemisinin is the activeprinciple of the plant Artemisia annua, used in Chinesetraditional medicine as 'Quinghaosu.' It is asesquiterpine lactone active against P. falciparum-resistant to all other antimalarial drugs as well assensitive strains. The mechanism of action ofartemisinin is not definitely known. The endo-peroxidebridge in its molecule appears to interact with heme inmalaria parasite, which results in the release of a highlyreactive free-radical that binds membrane proteins,causes lipid peroxidation, damages endoplasmicreticulum and ultimately leads to parasite lysis.It is a potent and rapid blood schizonticide. Severalderivatives of artemisinin have been produced, ofwhich three are marketed in India: water solubleartesunate, oil soluble artemether and arteether(developed in India). Artesunate preparations areavailable as Falcigo, Falcyanate and Arnatecommercially, whereas artemether is available asPaluther and Larither. These compounds are used totreat severe malaria and show very rapid parasiteclearance. However, the duration of action is short andrecrudescence rate is high, when these are used alone inshort courses. Therefore, monotherapy needs to beextended beyond the disappearance of parasite toprevent recrudescence. So far, no artemisinin resistanceamong P. falciparum has been noted. Arteether is thecompound developed in India, and has been releasedschizonticide, but its action is slower than chloroquine.It is effective against both chloroquine-sensitive and -resistant strains of malaria parasites. It is also aneffective suppressive prophylactic for multi-drugresistant P. falciparum and other types of malarias.Mefloquine-resistance among P. falciparum strains hasbecome common in Thailand, Combodia andMyanmar, but is sporadic in Africa, South America andMiddle East. Because it is not used extensively in India,mefloquine-resistance is not a problem here yet.Resistance to mefloquine causes cross-resistance toquinine and halofantrine also (Ter Kuile Fo et al., 1993;Mockenhaupt, 1995).Mepacrine: It is a blood schizonticide that is moretoxic and less effective than chloroquine. It is obsoleteas an antimalarial, but is still marketed.Quinine: The first known effective antimalarial wasquinine, often referred to as the Jesuit's bark. It is thelevo rotatory alkaloid obtained from the bark of theSouth American Cinchona sp. plant. It first rose tothprominence in the 17 century when, in the apocryphalthstory the 4 Condessa (Countess) de Chinchon wascured from malaria while staying in Lima (Gardiner etal., 2005). It is a blood schizonticide for all species ofPlasmodium. It is also less effective and more toxic thanchloroquine. It is effective in terminating an acuteattack of falciparum malaria, but does not preventrecrudescence completely, so, there is incompleteclearance of parasites from the body. It also does not acton pre-erythrocytic stages and on hypnozoites ofrelapsing malaria, but kills the gametes of P. vivax. Itsuse primarily is restricted to the chloroquine-resistantstrains of Plasmodia where it is used orally. Intravenouspreparation is used for complicated/cerebral malariaeven for chloroquine-sensitive strains. Its main sideeffectis cinchonism, in which patient exhibits ringingin the ears, nausea, vomiting, headache, mentalconfusion, vertigo etc. Signs and symptoms ofcinchonism gradually disappear as the drug is stopped.Quinine still remains an effective antimalarial drug,although resistance to it has been reported in Indochina,South East Asia and Brazil (Tripathi, 2003).Proguanil: Proguanil, also known as chloroguanide, isa slow-acting blood schizonticide. It is also causalprophylactic for P. falciparum. Proguanil inhibits theplasmodial dihydrofolate reductase (DHFR) enzyme.Currently, it is used in combination with chloroquinefor malaria prophylaxis in areas with low levelchloroquine-resistance against P. falciparum. It canalso be given during pregnancy.
Antimalarial agents17for institutional use only. It is used for efficacious agents is the need of the hour, optimizationcomplicated/cerebral malaria in areas with of existing agents by new dosing regimen as well aschloroquine-resistant P. falciparum (Tripathi, 2003). combination therapy with pre-existing agents has goneOther derivatives available are dihydroartemisinin, a long way. Combination therapy offers variousartelinate and artemotil (injectable artemether). Major advantages: it improves the antimalarial efficacy anddrawback with artemisinin compounds is their cost. provides synergistic antiparasitic action along withTherefore, many synthetic derivatives of artemisinin decreasing the chances of the development ofare under development and production. Artemisone is resistance. Combination therapy also shortens theone such metabolically stable, semi-synthetic duration of treatment, and in turn increases compliancederivative of artemisinin (Olliaro and Taylor, 2003). (Kremsner and Krishna, 2004).B. Lumefantrine is a fluoromethanol compound, whichis being tried as a fixed combination tablet withartemether and is marketed under the name of Riamet orCoartem. Riamet is available in developed, non-endemic countries for use by travellers, whereasCoartem is marketed in malaria endemic areas. The sixdoseregimen is highly efficacious against MDR P.Halofantrine: It is a phenanthrene methanol bloodschizonticidehaving activity comparable tomefloquine. It has been especially recommended foruse in areas with multi-drug resistant (MDR) P.falciparum infections. It is also effective againstresistant strains of P. vivax. But it is not active againstgametocytes or hepatic stages of malarial parasite.Serious side-effects in the form of severe, potentiallyfatal cardiac conduction abnormalities have beendocumented (Nosten et al., 1993).Atovaquone: This recently produced synthetichydroxy naptha-quinone is a rapidly acting bloodschizonticide for P. falciparum and other Plasmodia. Itcollapses plasmodial mitochondrial membranes andinterferes with ATP production. When used singly,development of resistance is rapid due to a single point-mutation in cytochrome b gene and so, presently, it islicensed for use as an antimalarial, only in combinationwith proguanil as 'Malarone'. As this drug is costly, costfactor limits its wide-spread use and is predominantlyused by the travellers to Southeast Asia, confrontedwith MDR parasites (Hyde, 2005). It can be givenduring pregnancy, and is being distributed throughdonation programmes (Bloland et al., 1997; Foege,1997).Tetracyclines: Tetracyclines are ribosomal inhibitors.They are weak blood schizonticide and also act on preerythrocyticstages of P. falciparum. Tetracyclines arebasically used for chloroquine-resistant falciparummalaria, in combination with quinine orpyrimethamine- sulfadoxine (Bloland, 2001).Clindamycin: Clindamycin is given to patients unableto take tetracyclines. In combination with quinine, itcan increase the efficacy of treatment and alsodecreases the duration of treatment, which furtherreduces the likelihood of the development of resistanceand quinine associated side-effects.Combination drugs: Although, for successfulantimalarial therapy, development of newer andAntifolate combination drugs: Such drugs are variouscombinations of dihydrofolate reductase inhibitors(proguanil, chlorproguanil, pyrimethamine,trimethoprim) and sulfa drugs (dapsone, sulfalene,sulfamethoxazole, sulfadoxine). They exhibit supra-additive synergistic effect due to sequential block ofDHFsynthetase and DHFRase, and are primarily usedfor clinical cure of P. falciparum, especially the strainswhich are chloroquine-resistant. Typical combinationsinclude sulfadoxine/pyrimethamine (Fansidar),sulfalene/ pyrimethamine (Metakeflin) andsulfamethoxazole/trimethoprim (Co-trimoxazole).However, these next generation antimalarial drugsfared even worse. Resistance to Fansidar developedwithin a year of its introduction into Thailand and isnow widespread (White, 1992). Resistance to sulfapyrimethaminehas been found to a limited extent inIndia, and that too mainly in North-East states.However, resistance to sulfa-pyrimethamine is sohighly prevalent in South East Asia, South America andSouthern Africa that it precludes its clinical use(Bloland, 2001). Fansimef or MSP, a combination ofmefloquine, sulfadoxine and pyrimethamine, wasdeveloped but not used eventually due to possiblesevere adverse reactions, this combination can cause.Newer drug combinations: A. A new antifolate drugcombination, which is currently used, primarily inAfrica, is a combination of chlorproguanil and dapsone(Lapdap). It has been found to be a much more potentdrug, with efficacy more than that of Fansidar. Itsbenefits include a greater cure rate, less chances of thedevelopment of resistance and comparatively less cost(Watkins et al., 1997).
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70 Ravindran and WilliamsTable I. C
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The Indian Society for Parasitology
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