They may also have teratogenic effects of a similar nature and are therefore contraindicated during pregnancy. Decreases DNA function, inhibiting bacterial protein synthesis and replication. Resistance is rare. A urinary antiseptic, by the metabolites formaldehyde and ammonia. May cause crystalluria and stone formation.
Many bacteria are unable to take up exogenous folic acid.
Mammalian cells do not synthesis folate, consequently the sulphonamides have no effect in humans. Trimethoprim shows selectivity for bacterial DHF reductase at low doses, although some inhibition may occur at high doses. Sulphadoxine may also be used in the treatment of malaria. Trimethoprim is used almost exclusively in combination with a sulphonamide. The combination results in synergistic activity and is often seen in the treatment of UTI, RTI, OM, and Pneumocystis pneumonia.