Cotrimoxazole is a fixed-dose combination of trimethoprim and sulfamethoxazole that acts as a bactericidal agent. It works by sequentially blocking folate metabolism through inhibiting the enzymes THFRase by trimethoprim and DHFRase by sulfamethoxazole. Cotrimoxazole is effective against various bacteria including S. typhi, serratia, and enterobacter. It has a spectrum of activity against both gram-positive and gram-negative bacteria. Common adverse effects include allergic reactions, megaloblastic anemia due to folate deficiency, and blood dyscrasias. It is used to treat urinary tract infections, respiratory tract infections, typhoid

1. CO-TRIMOXAZOLE
sravssmiling1521@gmail.com
Dr. KONERU NAGA SRAVANTHI,
ASSOCIATE PROFESSOR,
MALLA REDDY COLLEGE OF PHARMACY,
HYDERABAD.

2. • cotrimoxazole is fixed dose combination of
Trimethoprim and Sulfamethoxazole.
Mechanism of action
• Bactericidal
 Sequential block of folate metabolism
• Trimethoprim inhibits bacterial tetrahydrofolate
reductase (THFRase)
• Sulfamethoxazole inhibits bacterial dihydrofolate
reductase (DHFRase)
It is also active on S.typhi, serratia, Enterobacter,
Klebisella. Etc.,

3. Trimethoprim Sulfamethoxazole
Spectrum Bacteristatic Bacteristatic
Mechanism of action THFRase inhibition DHFRase inhibition
t1/2 Nearly 10 hr Nearly 10 hr
Dose ratio in cotrimoxazole 5 1
Plasma concetration ratio
in blood
20 1
Absorption Rapid Slow
BBB crossing Adequate poor
Plasma protein binding 40% 65%

4. Adverse Effects:
• All ADRS of Sulfonamides
• In folate deficiency: Megaloblastic Anaemia
• Blood Dyscrasias
• In renal disease: uremia develops
• In elderly:Bone marrow toxicity
• In pregnancy: Avoid the drug usage due to
teratogenic ris

5.  Uses:
• Urinary Infections
• Respiratory Tract Infections
• Typhoid
• Bacterial Diarrhoeas and dysentery
• Chancroid
References
K. D. Tripathi, “Essentials of Medical
Pharmacology,” 7th Edition, Jaypee Brothers
Medical Publishers (P) LTD, New Delhi, 2003;
706-707.

6. Further reading:
KDT - Essentials of Medical Pharmacology -7th
Edition-.pdf
https://dvmbooks.weebly.com/uploads/2/2/3
/6/22365786/2._goodman_and_gilman.pdf