Trimethoprim-sulfamethoxazole (brand name Bactrim®) is a broad-spectrum antibiotic with excellent activity against most gram-negative organisms, Staphylococci infections, pneumonia, and coccidiosis in chickens. The sulfa class of antibiotics work by depriving the bacteria of the folic acid they need without interfering with the folic acid available to the host.
The sulfa or “sulfonamide” class of antibiotics has earned a special place in history as the very first antibiotics ever developed and for the first time in human history domination over bacterial infection became readily feasible.
Egg Withdrawal Period: Trimethoprim sulfamethoxazole should not be given to poultry producing eggs intended for human consumption in any country, due to the lack of studies on the duration of residues in the eggs of treated hens. Australia recommends 10-day withdrawal period for eggs.
Caution: Trimethoprim sulfamethoxazole can precipitate in urine forming crystals or even stones, leading to kidney damage and gout. This is typically a problem with prolonged use or acidified urine. Sulfa drugs should not be given to birds with liver or kidney problems.
Toxicity: The oral LD50 of sulfamethoxazole in mice and rats is 2300 mg/kg and 6200 mg/kg, respectively.