Resistance, antimalarials

The success of quinine inspired the search for other antimalarials. The greatest impetus for the development of synthetic dmgs came this century when the two World Wars intermpted the supply of cinchona bark to the combatants. A stmcturally related 4-quinolinemethanol is mefloquine (65, Lariam [51773-92-3]) which now serves as an effective alternative agent for chloroquine-resistant P. falciparum. This is a potent substance that requires less than one-tenth the dose of quinine to effect cures. There are some untoward side effects associated with this dmg such as gastrointestinal upset and dizziness, but they tend to be transient. Mefloquine is not recommended for use by those using beta-blockers, those whose job requires fine coordination and spatial discrimination, or those with a history of epilepsy or psychiatric disorders. A combination of mefloquine with Fansidar (a mixture of pyrimethamine and sulfadoxine) is known as Fansimef but its use is not recommended. Resistance to mefloquine has been reported even though the compound has not been in wide use. 

Quinones and naphthoquinones were explored during the World War 11 Antimalarial Dmg Program. Now that chloroquine resistance is a serious problem, compounds of this group such as menoctone (76) are being reinvestigated. 

Quinacrine (49) is an acridine that was used extensively from the mid-1920s to the end of World War 11. It acts much like chloroquine and is reasonably effective. Because it causes the skin to turn yellow and, in high doses, causes yellow vision, the dmg is no longer in use as an antimalarial. Pyronaridine (77), a 1-azaacridine developed in China, appears to be effective against mefloquine-resistant, but not entirely against chloroquine-resistant, strains of P falciparum. 

In connection with studies on anthnalarial compounds, simpler mimics of artemisinin based on substituted 1,2,4-trioxepanes were examined. Examples include the 1,2,4-trioxepanes 152, 153 and 154, with the seven-membered ring being made by acid catalysed condensation of the appropriate ketone with the hydroxy hydroperoxide 151. Unfortunately the 1,2,5-trioxepanes were not active as antimalarials in vitro (up to 1000 nM) probably due to their resistance to Fe(II)-mediated degradation <06BMCL6124>. 

Malaria is still one of the world s most devastating infectious diseases. An estimated 270 million people are affected by the parasite every year, and close to 2 million children die. The most deadly species, Plasmodium falciparum, has become widely resistant to most of the available antimalarial drugs such as quinolines. 

Malaria parasite has developed resistance to many of these so-called quinoline antimalarials rendering them completely obsolete. This situation has forced the use of combination regimens that consists of a mixture of two or more antimalarial active ingredients this approach has proven to work better than monotherapies, but often is only a temporary soulu-tion. Nevertheless, quinine remains a very effective drug, with only few treatment failures or resistance reported around the globe. 

Since that time, artemisinin has been used successfully in many thousand malaria patients throughout the world including those infected with both cldoroquine-sensitive and chloroquine-resistant strains of P falciparum. Artemisinin has progressively estabhshed itself as one of the most potent and effective antimalarial dmg, and is primarily recommended in the treatment of multidrug-resistant strains of P. falciparum. However, the therapeutic... 

Fidock DA, Eastman RT, Ward SA, Meshnick SR. (2008) Recent highlights in antimalarial drug resistance and chemotherapy research. Trends Parasitol 24 537-544. 

Antimalarial drug choice takes into account tolerability and plasmodial resistance. 

Artemisinin ( qinghaosu ) (18), a sesquiterpene lactone antimalarial compound with an endoperoxide group, discovered in the Peoples Republic of China as a constituent of Artemisia annua L., has created great interest in the biomedical community, owing to its unique mechanism of action on the heme complex. Artemisinin serves as an option for the treatment of chloroquine (4l)-resistant malaria and is used in some Asian countries as an antimalarial. However, the use of artemisinin as a single agent anti-malarial is a potential risk since the malaria parasite may become resistant to this compound class. 

Quinidine (6) and quinine (7) are diastereomeric quinoline alkaloids obtained from Cinchona spp. Quinidine (6) is included in many pharmacopeias for its antiarrhythmic effects.Quinine was the first antimalarial drug and served as an effective remedy for this deadly infectious disease in colonial times, making European settlement in many tropical and subtropical parts of the world possible.Owing to the development of resistance to synthetic antimalarials, quinine is still reverted to some extent for this... 

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