Cotrimoxazole

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