Pharmacology of cotrimoxazole. Pharmacodynamics, pharmacokinetics, adverse effects, uses and contraindications of cotrimoxazole.

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