Class Explorer · Anti-infectives
Urinary antiseptics
Agents that concentrate in urine and act there. They treat the bladder and nothing else, which is both their strength and their hard limit.
Members
Also in this class: Fosfomycin · Methenamine. Full pages arrive as the library grows.
Compare the members
Nitrofurantoin
- Site of action
- Bladder urine only
- Hard limit
- Not for pyelonephritis or CrCl < 30
Shared across the class
- Indications
- Uncomplicated cystitis · UTI prophylaxis
- Adverse effects
- Nausea · Brown urine, harmless · Pulmonary reactions and neuropathy on long-term use
- Contraindications
- Creatinine clearance below roughly 30 mL/min · Pyelonephritis or suspected bacteraemia · Term pregnancy and G6PD deficiency
- Monitoring
- Symptom resolution · Long-term prophylaxis: pulmonary symptoms and liver enzymes
What makes each agent different
- Nitrofurantoin needs adequate renal function to reach therapeutic urinary concentrations, which is why renal impairment makes it both ineffective and more toxic at the same time.
It achieves no useful tissue concentration anywhere. Prescribing it for pyelonephritis treats the urine while the kidney gets on with the infection.
The one antibiotic whose contraindication in renal impairment is about efficacy first and toxicity second.
Last reviewed 2026-08-16 · Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed.