Cotrimoxazole is a WHO-approved antibiotic combination of sulphamethoxazole and trimethoprim, which possesses synergistic effects against bacteria due to its cidal action while reducing resistance development. It is effectively used for various infections including urinary tract, respiratory tract, and gastrointestinal infections, and is well-tolerated with some adverse effects like gastrointestinal disturbances and blood disorders. However, it is contraindicated during pregnancy.

1. Cotrimoxazole

2. Introduction
Cotrimoxazole is a World Health Organization (WHO)-approved fixed-dose combination of
sulphamethoxazole and trimethoprim in the ratio of 5:1.
The pharmacokinetic properties of these two drugs match each other almost closely;
hence they are selected for combination.
Optimum synergistic effect is seen at a concentration ratio of 20:1 (sulphamethoxazole to
trimethoprim) in blood and tissues.
The advantages of this combination are:
1. Individually, both are bacteriostatic but the combination has a cidal effect.
2. Chances of development of bacterial resistance are also greatly reduced.

3. Mechanism of action

4. Pharmacokinetics
• Administration: Oral and IV route
• Absorption: Well absorbed after oral administration
• Distribution: To various tissues Including the CSF and sputum
• Metabolism: In liver
• Excretion: Via urine

5. Adverse effects
Cotrimoxazole is well tolerated in most patients.
• Gastro-intestinal disturbance: nausea, vomiting, glossitis, stomatitis etc.
• Megaloblastic anaemia due to folate deficiency in alcoholic and malnourished
patients.
• Bone marrow suppression with leukopenia.
• Sometimes, neutropenia and thrombocytopenia

6. Uses
• Urinary tract infection: effective for the treatment of acute, chronic and
recurrent lower urinary tract infections (UTIs) due to gram-negative organisms
such as E. coli, Proteus and Enterobacter spp.
• Bacterial respiratory tract infections: effective for acute and chronic bronchitis
due to S. pneumoniae and H. influenzae. It is also useful for acute maxillary
sinusitis and otitis media.
• Bacterial diarrhoeas: used for GI infections due to shigella, E. coli an Salmonella
spp.
• Typhoid fever: Can be effective.
• P. jiroveci infections: Useful for the treatment as well as prophylaxis of P. jiroveci
pneumonia.
• Chancroid: effective.

7. Contraindications
• During pregnancy