Trimethoprim : Clinical Uses, Mechanism of Action and Side Effects


Mechanism of Action of Trimethoprim (An Anti-Malarial Drug):

Trimethoprim is chemically related to the antimalarial drug pyrimethamine. Both the drugs, trimethoprim and pyrimethamine are folate antagonists.

Trimethoprim resembles the pteridine moiety of the folate and it resembles the bacterial dihydrofolate reductase. This enzyme is more sensitive to trimethoprim than the enzyme present in the human beings.

Trimethoprim is bacteriostatic in nature and inhibits the growth of common bacterial pathogens.

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Trimethoprim is mixed with sulfonamides (sulfamethoxazole), this combination is called as co-trimoxazole.

The upstream from the dihydrofolate reductase potentiates the action of the trimethoprim. Its use is restricted in the UK for the treatment of Pneumocystis carinii pneumonia, toxoplasmosis and nocardiasis.

Mechanism of Action of Trimethoprim

Mechanism of Action of Trimethoprim

Administration of Trimethoprim:

Trimethoprim is administered orally and is fully absorbed in the gastrointestinal tract.

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Trimethoprim gets widely distributed throughout the tissues and the body fluids. Its concentration will be more in the lungs and kidneys and very high concentration in the cerebrospinal fluid.

Elimination of the trimethoprim by the kidney increases with the decreasing urinary pH.

Adverse Effects of Trimethoprim:

  • Nausea
  • Vomiting
  • Blood disorders
  • Skin rashes
  • Folate deficiency
  • Megaloblastic anaemia
Megaloblastic anameia results due to folate deficiency and can be prevented by giving folinic acid.

Clinical Uses of Trimethoprim:

  • Trimethorpim is used for urinary tract infections.
  • Trimethoprim is used for respiratory tract infections.
  • Trimethoprim is also employed in Pneumocystis carinii infection.
  • Trimethoprim is used for treating Pneumonia in AIDS patients.
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