Antimalarial Drugs

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Chapter: Essential pharmacology : Antimalarial Drugs

These are drugs used for prophylaxis, treatment and prevention of relapses of malaria.


ANTIMALARIAL DRUGS

 

These are drugs used for prophylaxis, treatment and prevention of relapses of malaria.

 

Malaria, caused by 4 species of the protozoal parasite Plasmodium, is endemic in most parts of India and other tropical countries. It is one of the major health problems. As per latest WHO estimates there are 300–500 million new clinical cases globally and >1 million deaths occur due to malaria each year, 90% of which are in Africa. In India the National Malaria Eradication Programme (NMEP), started in 1958, achieved near complete disappearance of the disease in 1960s (from 75 million cases in 1950s to 0.1 million cases in 1960s). However, due to the development of insecticide resistance among mosquitoes and other factors, it staged a comeback in the mid 1970s (6.47 million cases in 1976), and continues to prevail in endemic/subendemic proportions in different areas. Conceding that eradication of malaria is not possible, NMEP was renamed National Antimalaria Programme (NAMP). Its scope has now been widened to include other vector borne diseases, and it is called ‘National vector borne diseases control programme’ (NVBDCP). For the year 2005, the NVBDCP has reported 1.8 million slide proven malaria cases in India, out of which ~ 44% were falciparum malaria with 963 deaths. The WHO estimates that actual number of malaria cases in India is 6 times more, i.e. ~12 million.

 

The bark of Cinchona tree, growing in Peru, was introduced in Europe in the early 17th century as a cure for fevers. Later it was realized to be a specific remedy for malaria. Quinine, isolated from Cinchona bark in 1820, replaced the crude preparation and continued to be the major antimalarial drug till 1942. The world’s supply of Cinchona bark for producing quinine was met by Java and neighbouring countries. This was cut off from the Germans during World War I and from the Allies during World War II. Due to enormous military importance of malaria and its treatment, intense activity was initiated for the development of antimalarial drugs. Mepacrine was produced in Germany in 1926 and extensively field tested by the Allies during World War II. Chloroquine was produced in USA soon after as a less toxic alternative to mepacrine. It had already been synthesized and used by Germans in 1934 as ‘Resochin’. Proguanil was introduced in 1945 by the British as a well tolerated clinical curative.

 

None of the above drugs were found to be capable of preventing relapses in vivax malaria. Pamaquine was the first 8aminoquinoline to be tested in Germany in the 1920s. However, no attention was paid to it because of its poor schizontocide action. This class of drugs was retested during World War II as radical curative and Primaquine emerged as the most desirable drug. Pyrimethamine was produced in 1951 under a planned postwar research programme for antimalarial drugs. The important additions of the recent years are Mefloquine, Artemisinin and its derivatives/congeners, pyronaridine and few other synthetic compounds for resistant falciparum malaria.

 

Classification

 

1. 4-Aminoquinolines: Chloroquine, Amodiaquine, Piperaquine.

2. Quinoline-methanol:  Mefloquine.

3. Cinchona alkaloid: Quinine, Quinidine

4. Biguanides: Proguanil (Chloroguanide), Chlorproguanil

5. Diaminopyrimidines:  Pyrimethamine

6. 8-Aminoquinoline:   Primaquine, Bulaquine

7. Sulfonamides and sulfone: Sulfadoxine, Sulfamethopyrazine, Dapsone

8. Tetracyclines: Tetracycline, Doxycycline

9. Sesquiterpine Lactones : Artesunate, Artemether, Arteether

10.Amino Alcohols: Halofantrine, Lumefantrine

11. Mannich Base: Pyronaridine

12. Naphthoquinone: Atovaquone

 

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