Drug of the week - Cotrimoxazole
Meet this drug of the week’s duo of the pharmacy world - Sulfamethoxazole and Trimethoprim, better known by their ultimate team-name “Cotrimoxazole”
Keep reading to dive into their background, mechanism of action, clinical uses, side effects, drug interactions and crucial contraindications!
Background
Cotrimoxazole is a fixed dose combination antibiotic composed of trimethoprim and sulphamethoxazole, used to treat a variety of bacterial infections. It consists of one part trimethoprim to five parts sulfamethoxazole. It is sold under the trade names Bactrim, Cotrim and Septra.
Mechanism of action
- Cotrimoxazole produces the sequential block of bacterial folate metabolism i.e. its components -trimethoprim and sulfamethoxazole interfere with two successive steps in the folate metabolism pathway within bacteria.
- Trimethoprim and sulphamethoxazole inhibits dihydrofolate reductase and folate synthetase respectively.
- Blocking the folate metabolism will accelerate nucleotide depletion, resulting in a bactericidal effect (cell death).
Point to note**: Individually, both sulphamethoxazole and trimethoprim are bacteriostatic, but their combination i.e. cotrimoxazole becomes bactericidal against many organisms.**
Clinical uses
- Treatment of tonsillitis, pharyngitis, sinusitis, otitis media, chronic bronchitis, urinary tract infections and diarrheas.
- Used as an alternative drug for patients allergic to beta-lactam antibiotics and for chancroid.
Adverse effects
Include nausea, vomiting, stomatitis, headache, folate deficiency (megaloblastic anemia) and in some rare cases blood dyscrasias occur.
Contraindications
- Pregnancy: Trimethoprim being an antifolate, poses a teratogenic risk. Neonatal hemolysis and methemoglobinemia can occur
- Renal disease patients: Patients may develop uremia on consuming cotrimoxazole
Drug Interactions
- Enhances anticoagulant activity of warfarin
- Prolongs half-life of phenytoin
- Increases toxicity of methotrexate
Thank you to everyone who participated in this week’s polls and discussions! Looking forward to the next Drug of the Week series.
MBH/PS