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Chapter: Medicinal Chemistry : Antimalarials

Antimalarials: Halofantrine, Artemether (Larither, Paluther) and Artether, Artesunate (Asunate, Ultera, Falcigo), Mefloquine


Antimalarials - Synthesis and Drug Profile

Micellaneous

 

Halofantrine


Metabolism: The drug is metabolized by N-dealkylation to desbutyl halofantrine by CYP3A4. The metabolites appear to be several folds more active than the parent drug.


Synthesis


Properties and uses: Halofantrine is a white or almost white powder, practically insoluble in water, soluble in methanol, and sparingly soluble in alcohol. Structurally, halofentrine differs from all other antimalarial drugs and belongs to the latest generation of antimalarials. It is a good example of a drug design that incorporates bioisosteric principles evidenced by the tri-fluoro methyl moiety. It is schizonticidal and has no effect on the sporozoite, gametocyte, or hepatic stages. It is effective in the treatment and prophylaxis of chloroquine and multidrug resistant P. falciparum.

Assay: It is as assayed by adopting Liquid chromatography technique.

 

Artemether (Larither, Paluther) and Artether


Synthesis


Dose: The administered dose for acute uncomplicated falciparum malaria in the case of adults is 80 mg daily to be taken with lumefantrine 480 mg daily. Doses to be taken at diagnosis and repeated after 8,  24, 36, 48, and 60 h. Total doses are six. For a child, the daily dose based on the body weight is as follows: 5–14 kg: 20 mg ; 15–24 kg: 40 mg with lumefantrine 240 mg; 25–34 kg; 60 mg with lumefantrine 360 mg and more than 34 kg; 80 mg with lumefantrine 480 mg. Doses to be taken at diagnosis and repeated after 8, 24, 36, 48, and 60 h and the total doses are 6.

 

Artesunate (Asunate, Ultera, Falcigo)


Synthesis


Dose: The dose in the case of falciparum malaria for adults is 2.4 mg/kg via IM or IV administration to be repeated after 12 h and 24 h later; then, once daily thereafter. For a child, the dose is 2.4 mg/kg via IM or IV administration and to be repeated after 12 h and 24 h later; then, once daily thereafter.

 

Mefloquine


Metabolism of mefloquine: It is metabolized through CYP3A4 oxidation to its major inactive metabolite called carboxy mefloquine and rest of the amount is excreted unchanged in urine.


Properties and uses: Mefloquine hydrochloride is a white or slightly yellow crystalline powder, very slightly soluble in water, soluble in methanol and in alcohol. It is used as an antimalarial agent.

Assay: Dissolve the sample in anhydrous formic acid, add acetic anhydride and titrate with 0.1 M perchloric acid. Determine the end-point potentiometrically.

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