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
