Antimalarial

Antimalarial

Antimalarials are a class of medications used to prevent and treat malaria, a disease caused by Plasmodium parasites transmitted through the bites of infected Anopheles mosquitoes. Malaria is a significant public health challenge, particularly in tropical and subtropical regions.

History

The use of antimalarial drugs dates back centuries, with the bark of the Cinchona tree being used by indigenous peoples in South America to treat fevers. The active ingredient, quinine, was isolated in the 19th century and became the first effective treatment for malaria.

Types of Antimalarials

Antimalarial drugs can be classified into several categories based on their chemical structure and mechanism of action:

1. Quinolines

• Chloroquine: Once the mainstay of antimalarial treatment, chloroquine is now largely ineffective in many parts of the world due to resistance.
• Quinine: Used primarily for severe malaria and in areas where chloroquine resistance is prevalent.
• Mefloquine: Effective against chloroquine-resistant strains but associated with neuropsychiatric side effects.

2. Antifolates

• Pyrimethamine: Often used in combination with sulfadoxine (as in Fansidar) for treatment and prevention.
• Proguanil: Commonly used in combination with atovaquone (as in Malarone) for prophylaxis and treatment.

3. Artemisinin Derivatives

• Artemether: Used in combination therapies (e.g., artemether-lumefantrine) for treating uncomplicated malaria.
• Artesunate: Preferred for severe malaria, often administered intravenously.

4. Antibiotics

• Doxycycline: Used for prophylaxis and in combination with other antimalarials for treatment.
• Clindamycin: Sometimes used in combination with quinine.

Mechanism of Action

Antimalarials work by targeting different stages of the Plasmodium life cycle:

• Blood Schizonticides: These drugs, such as chloroquine and artemisinin derivatives, act on the asexual blood stages of the parasite.
• Tissue Schizonticides: Drugs like primaquine target the liver stages of the parasite, preventing relapses in Plasmodium vivax and Plasmodium ovale infections.
• Gametocytocides: These drugs, including primaquine, target the sexual stages of the parasite, reducing transmission.

Resistance

Resistance to antimalarial drugs is a major challenge in malaria control. Plasmodium falciparum has developed resistance to many drugs, including chloroquine and sulfadoxine-pyrimethamine. The emergence of artemisinin resistance in Southeast Asia is particularly concerning.

Prevention

Antimalarials are used for prophylaxis in travelers to endemic areas. The choice of drug depends on the resistance patterns in the destination region. Common prophylactic regimens include:

• Atovaquone-proguanil
• Doxycycline
• Mefloquine

Side Effects

Antimalarials can have various side effects, ranging from mild gastrointestinal disturbances to severe neuropsychiatric effects. Monitoring and managing these side effects is crucial in treatment.

Future Directions

Research is ongoing to develop new antimalarials and combination therapies to overcome resistance. Vaccines, such as the RTS,S vaccine, are also being developed to provide additional tools in the fight against malaria.

See Also

• Malaria
• Plasmodium
• Anopheles