COTRIMOXAZOLE The fixed dose combination of trimethoprim and sulfamethoxazole is called cotrimoxazole. T rimethoprim is a diaminopyrimidine related to the antimalarial drug pyrimethamine which selectively inhibits bacterial dihydrofolate reductase (DHFRase). Uses: Though cotrimoxazole is still widely used, its popularity in the treatment of systemic infections has declined. Common indications are: 1 . Urinary tract infections Most acute uncomplicated infections respond rapidly. Single dose therapy with 4 tablets of cotrimoxazole has been recommended for acute cystitis. Courses of 3-l 0 days have been advised for lower and upper urinary tract infections, according to associated features. It is specially valuable for chronic and recurrent cases and in prostatitis, because trimethoprim is concentrated in prostate. 2. Respiratory tract infections Both upper and lower respiratory tract infections, including chronic bronchitis and facio-maxillary infection, otitis media caused by gram positive cocci and H influenzae respond well 3. Typhoid: Initially cotrimoxazole was an effect alten1ative to chloramphenicol. However, in many areas resistant S typlri have appeared, and now it is seldom used Sensitive strains of S typhi respond to one DS tab BD for 2 weeks. 4. Bacterial diarrhoeas and dysentery Cotrimoxazole may be used for severe and invasive infections by Campylobacter, E. coli, Shigella Y. enterocolitica . Though response rate is lower than previously, and fluoroquinolone are more commonly used, it is effective in ampicillin resistant cases. 5. Pneumocystis jiroveci causes severe pnemonia in neutropenic and AIDS patients. Cotrimoxazole has prophylactic as well as therapeutic value, but high doses are needed. One DS tab 4-6 times/ day for 2-3 weeks may be curative,but adverse effects necessitate discontinuation in upto 20%cases. One DS tab. daily has been used for prophylaxis and is better tolerated. 6. Chancroid Cotrimoxazole (800 + 160 mg) BD for 7 days is a 3rd choice inexpensive alternative to ceftriaxone, erythromycin or ciprofloxacin. 7. Cotrimoxazole is an effective alternative to penicillin for protecting agranulocytosis patients and treating respiratory and other infections in them. Intensive parenteral cotrirnoxazole therapy has been used successfully in septicaemias, but other drugs are more commonly employed now. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:686,687