Trimethoprim (TMP) is an antibiotic used in the treatment of urinary tract infections due to susceptible strains, acute exacerbations of chronic bronchitis in adults, and superficial ocular infections, and it is combined with other agents for the treatment of toxoplasmosis. The mechanism of action of TMP is through inhibition of folic acid reductase to tetrahydrofolate, thereby inhibiting microbial growth. The drug is known by a variety of trade names including Proloprim®, Trimanyl®, Uretrim®, Primsol®, and many others. TMP combined with sulfamethoxazole given orally at low doses to hamsters caused embryotoxicity and malformations in rats and rabbits administered higher doses on 7 or 8 days during organogenesis. In the human, several reports suggested that TMP may have teratogenic potential. TMP is a polar molecule of average size. It is slightly hydrophilic and can participate in hydrogen bonding as both an acceptor and donor.