Bactrim in patients with Cystic Fibrosis

Q: The dose of oral trimethoprim-sulfamethoxazole (Bactrim) in patients with Cystic Fibrosis (CF) should be adjusted to? (select one) 

 A) Increase the dose 
B) Decrease the dose 


Answer: A

The dose of oral trimethoprim-sulfamethoxazole in patients with Cystic fibrosis need to be increased by almost 50 percent. This is due to the fact that hepatic clearance of sulfamethoxazole is increased in these patients due to accelerated acetylation. Also, clearance of trimethoprim via kidney gets enhanced. The reason for this renal effect is not clear.

#pharmacology



Reference:

Reed MD, Stern RC, Bertino JS Jr, et al. Dosing implications of rapid elimination of trimethoprim-sulfamethoxazole in patients with cystic fibrosis. J Pediatr 1984; 104:303.