This drug is active against many urinary tract pathogens (but not Proteus or Pseudomonas), and resistance emerges slowly. Single daily doses of the drug can prevent recurrent urinary tract infections, and acidification of the urine enhances its activity. The drug is active orally and is excreted in the urine via filtration and secretion; toxic levels may occur in the blood of patients with renal dysfunction. Adverse effects of nitrofurantoin include gastrointestinal irritation, skin rashes, pulmonary infiltrates, phototoxicity, neuropathies, and hemolysis in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency.