This quinolone drug acts against many gram-negative organisms (but not Proteus or Pseudomonas) by mechanisms that may involve acidification or inhibition of DNA gyrase. Resistance emerges rapidly. The drug is active orally and is excreted in the urine partly unchanged and partly as the inactive glucuronide. Toxic effects include gastrointestinal irritation, glycosuria, skin rashes, phototoxicity, visual disturbances, and CNS stimulation. Nitrofurantoin may antagonize the action of nalidixic acid.