Cotrimoxazole (Sulphamethoxazole + Trimethoprim)
Cotrimoxazole is indicated in-
- Respiratory tract infections: Acute and chronic bronchitis, bronchiectasis, lobar and bronchopneumoniae, pneumocystis carinii pneumonitis, otitis media and sinusitis.
- Genito-urinary tract infections: Urethritis, cystitis, prostatitis, pyelonephritis, gonorrhoea.
- Skin infections: Pyoderma, abscess and wound infections.
- Other bacterial infections: Acute and chronic osteomyelitis, acute brucellosis, septicaemias, nocardiosis and other infections caused by susceptible organisms.
Anti-diarrhoeal Antimicrobial drugs, Sulphonamides & Trimethoprim
Cotrimoxazole is a mixture of the sulphonamides sulphamethoxazole with trimethoprim in the proportions of 5 to 1. The two components act synergistically to produce a bactericidal or bacteriostatic action against a wide range of gram-positive and gram-negative organism and some protozoa.
Cotrimoxazole is a mixture of the sulphonamides sulphamethoxazole with trimethoprim in the proportions of 5 to 1. The two components act synergistically to produce a bactericidal or bacteriostatic action against a wide range of gram-positive and gram-negative organisms and some protozoa. It is also active against pneumocystis carinii. Sulphamethoxazole inhibits the enzyme dihydropteroate reductase, which catalyzes the reduction of folic acid to dihydrofolic acid whilst trimethoprim prevents the reduction of dihydrofolic acid to tetrahydrofolic acid by competitive inhibition of dihydrofolate reductase, thereby interfering with cell replication.
Both drugs are rapidly and almost completely absorbed from the bowel reaching peak plasma concentrations 1-4 hours after ingestion. Sulphamethoxazole is 65% and trimethoprim is 40% protein bound.
Dosage & Administration
Cotrimoxazole double strength tablet: Over 12 years
- For mild to moderate infections: 1 tablet twice daily.
- For severe infections: 1.5 tablets twice daily.
- Long term therapy (>14 days): 0.5 tablet twice daily.
- Gonorrhoea: 2 tablets every 12 hours for two days or 2.5 tablets followed by a further dose of 2.5 tablets after 8 hours.
Cotrimoxazole tablet: over 12 years
- For mild to moderate infections: 2 tablets twice daily.
- For severe infections: 2 tablets thrice daily.
- Long term therapy: (>14 days): 1 tablet twice daily.
Cotrimoxazole suspension: Under 12 years
- 6-12 years: 2 teaspoonful twice daily.
- 6 month-5 years: 1 teaspoonful twice daily.
- 6 weeks-6 months: 0.5 teaspoonful twice daily.
Hypersensitivity to trimethoprim or sulphonamides, Patients with documented megaloblastic anaemia due to folate deficiency, Patients showing marked liver parenchymal damage, blood dyscrasia, severe renal insufficiency, glucose 6-phosphate dehydrogenase deficiency.
At the recommended dose side effects are rare and mild. About 75% of the untoward effects involve the skin. Exfoliative dermatitis, Stevens-Johnson syndrome and toxic epidermal necrolysis (Lyell’s syndrome) are rare. Nausea and vomiting constitute the bulk gastrointestinal reactions. Diarrhoea, glossitis, and stomatitis are uncommon. Hematological reactions include various types of anemia, granulocytopenia, purpura and agranulocytosis.
Pregnancy & Lactation
Pregnancy category-D. Pregnancy and during the nursing period, because sulphonamides pass the placenta and are excreted in the breast milk and may cause kernicterus.
Prolonged full dose treatment with sulfamethoxazole-trimethoprim combination is associated with the risk of macrocytic anaemia due to the drug’s interference in the conversion of Folic acid into Folinic acid. If this occurs, it can be reversed by giving Folinic acid. Care should be taken when giving this combination to diabetic patients receiving sulphonylurea drug for possible potentiation of action of sulphonylurea
Symptoms: Dizziness, nausea, vomiting, rashes, headache, ataxia, drowsiness, dysuria, facial swelling, weakness and confusion, bone marrow depression, slight elevations of serum aminotransferases.
Management: Supportive and symptomatic treatment. Empty stomach immediately by inducing emesis or by lavage. Observe the patient for at least 4 hr and monitor urea and electrolytes with FBC. Give fluids to maintain a good urine output. May give Ca leucovirin 5-10 mg/day to counteract any adverse effects of trimethoprim on bone marrow or Ca folinate 3-6 mg for 5-7 days orally or by IM inj.