Nitrofurantoin typically starts working within a few hours to a day after you begin taking it, with peak antibacterial concentrations in the urine reached within about 30 minutes to a few hours depending on the formulation

. In terms of symptom relief for urinary tract infections (UTIs), many people notice improvement within 24 hours of starting nitrofurantoin, and symptoms are usually resolved after about 3 to 5 days of treatment

. However, it is important to complete the full prescribed course (often around 5 to 6 days for uncomplicated UTIs) even if symptoms improve sooner, to ensure the infection is fully cleared and to prevent recurrence or resistance

. For complicated UTIs, treatment may be longer (up to 10-14 days), but response to nitrofurantoin should still be noticeable within 1-2 days

. In summary:

• Nitrofurantoin reaches effective urine concentrations rapidly, within 30 minutes to a few hours after dosing

• Symptom improvement usually occurs within 24 hours

• Full course is typically 5-6 days for uncomplicated UTIs; longer for complicated infections

• Always finish the entire prescribed course even if feeling better

This ensures effective bacterial eradication and reduces the risk of infection returning or developing resistance.