Antimicrobial Drugs Part 1 by Prof CS Bhan

Antimicrobial Drugs Part 1 by Prof CS Bhan

Malaria is a severe infectious disease caused by Plasmodium parasites transmitted through infected Anopheles mosquitoes' bites. The disease remains a major health problem in many parts of the world, particularly in sub-Saharan Africa, Southeast Asia, and parts of South America. Antimalarial drugs have been essential in combating malaria. The role of Antimalarial drugs is critical in terms of both treatment and prevention of malaria. These drugs work by targeting different stages of the parasite's life cycle, including the liver and blood stages, to reduce the parasite load and alleviate symptoms Antimalarial agents have their origin from natural   quinine derivatives to contemporary synthetic medications.

These drugs operate through multiple mechanisms, -- such as inhibiting the growth of parasites, disrupting cellular functions, and interfering with vital metabolic pathways. Nevertheless, the rise of drug-resistant strains of Plasmodium, especially against chloroquine and artemisinin is a matter of concern and has created considerable obstacles for malaria control initiatives. Malaria remains one of the major health problems. Literature survey reveals that 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) was started in 1958.It achieved success and near complete disappearance of the disease in 1960s (from 75 million cases in 1950s to 0.1 million cases in 1960s). However, insecticidal pollution gave birth to insecticide resistance among mosquitoes and other factors, it staged a comeback in the mid-1970s (6.47 million cases in 1976. Conceding that eradication of malaria is not possible, NMEP was renamed National Antimalaria Programme (NAMP). Its area has now been broadened to include other vector borne diseases, and it is known as ‘National vector borne diseases control programme’ (NVBDCP). this programme has reported 1.8 million slide proven malaria cases in India. However, falciparum malaria cases are dominating causing more deaths. The WHO estimates that actual number of malaria cases in India is 6 times more.

Classification of Antimalarial Drugs

Antimalarial drugs can be Classified on the basis of following criteria-

Chemical Structure, 

Mechanism of Action, 

Therapeutic Function. 

A) CLASSIFICATION ON THE BASIS OF MECHANISM OF ACTION

Blood Schizonticides: Active against blood-stage parasites (e.g., Chloroquine, Artemisinin derivatives, Quinine, Mefloquine, Piperaquine).

Tissue Schizonticides: Target hypnozoites or pre-erythrocytic stages (e.g., Primaquine, Tafenoquine).

Gametocytocides: Destroy gametocytes, reducing transmission (e.g., Primaquine, some artemisinin derivatives).

Drug combinations, most notably Artemisinin-based Combination Therapies (ACTs), are essential. 

B) CHEMICAL 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. Sulphonamides and sulfone: Sulfoxide, Sulfamethopyrazine, Dapsone

8. Tetracyclines: Tetracycline, Doxycycline to thwart drug resistance and ensure high cure rates for P. falciparum infections.

10.Amino Alcohols: Halofantrine, Lumefantrine

11. Mannich Base: Pyronaridine

12. Naphthoquinones: Atovaquone

C) THERAPEUTIC CLASSIFICATION

Causal Prophylaxis—Target –Pre Erythrocytic Phase

Suppressive Prophylaxis ---Suppress the erythrocytic phase and thus attacks of malarial fever.

Clinical Cure----Terminate episodes of malaria

Radical Cure--Attack the Exo Erythrocytic Phase

Gametocidal –Eliminate Male and Female Gametes

The rationale behind using Antimalarial drugs in the treatment of Malaria is based on the following -

a) Prevention and Treatment of clinical attack of malaria.

b) Eradication of the parasite from the patient’s body.

c) Reduction of human reservoir of infection

d) Reduction of Transmission to mosquito.

Thanks for Reading