SMZ/TMP Tablets for Dogs, Cats and Horses. Sulfamethoxazole and trimethoprim is an antibiotic used to treat a wide range of infections in horses, dogs, cats and other species of animals. SMZ/TMP Tablets may be used to treat bacterial and protozoal infections. SMZ/TMP may be used in horses where control of bacterial infections is required during treatment of acute strangles, respiratory tract infections, acute urogenital infections, wound infections and abscesses. Sulfamethoxazole and trimethoprim.