One of least toxic , but it can produce GI disturbance. It is not able to penetrate most Gram negatives, but it is effective against Legionella and some Neisseria . F. Inhibitors of Nucleic Acid Synthesis 1. Sulfonamides Fig 20.6. The sulfa drugs block folic acid synthesis by competitive inhibition with PABA, a component of folic acid.
Folic acid is needed to make purines .
Selective toxicity is maintained because animals cannot make their own folic acid but must take it in with food, preformed by bacteria or by plants. Rifampicin or rifampin. Can cause liver damage. Group of synthetic analogues of nalidixic acid. Block DNA gyrase.