COTRIMOXAZOLE

• Fixed drug combination of Sulfamethoxazole and Trimethoprim

MOA:

INTRODUCTION

• Both bacteriostatic (Individually)
  • Bactericidal – Combination 
• Both drugs have almost similar half-lives (10 Hrs)
• Maximum synergism for sensitive organism.
• Optimal synergism obtained at 5:1 dose ratio (e.g. 800 mg:160 mg)
• TMP crosses BBB and placenta 
  • SMZ doesn’t cross.
• TMP – more rapidly absorbed than SMZ
• TMP – 45% plasma protein bound
  • SMZ -65% bound

ANTIBACTERIAL SPECTRUM:

• Salmonella typhi, Serratia, Klebsiella Enterobacter, Yersinia & Pneumocystis jiroveci.
• Sulfonamides resistance strains of S. aureus, E. coli, gonococci, meningococci & H.influenzae.

RESISTANCE:

• Slow to develop
• By mutational changes or plasmid-mediated acquisition of DHFRase enzyme having lower affinity for inhibition.

USES:

• Uncomplicated lower urinary tract infection
• DOC grade IV vesicoureteric reflux with recurrent UTI Cotrimoxazole
• DOC for Cyclosporiasis & Isosporiasis (Protozoal infection).
• Cystitis.
• Chronic and recurrent urinary tract infections 
  • 3-10 days
• Respiratory tract infection – 
  • Lower and upper, chronic bronchitis, facio-maxillary infections, otitis media.
• Typhoid
• Bacterial diarrhoeas & dysentery: due to Campylobacter, E coli, Shigella etc.
• Pneumocystis jiroveci: Severe pneumonia – Prophylactic use in AIDS patients(CD4 count is less than 200) with neutropenia. 
  • Dose – DS tablet 4-6 times 2-3 weeks
• Chancroid – H. ducreyi
• Alternative to penicillin in agranulocytosis patients, septicaemia etc.

ADVERSE EFFECT:

• Nausea,  vomiting,  stomatitis, rash.
• Megaloblastic anaemia.
  • Folate deficiency.
  • Patients with marginal folate levels.
• Blood dyscrasias
• Pregnancy: 
  • Teratogenic risk
  • Neonatal haemolysis 
  • Methaemoglobinaemia
• Renal disease may develop uremia
• Fever.
• Risk of bone marrow toxicity – 
  • Especially in elderly
• Bone marrow hyperplasia.
• Among in AIDS patients with Pneumocystis jiroveci infection.

• With diuretics – Higher incidence of thrombocytopenia

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