In the context of treating a UTI in pregnancy, what is the dosing frequency for nitrofurantoin used for seven days?

• A. Twice daily
• B. Three times daily
• C. Four times daily
• D. Once daily

Answer: (C)

Nitrofurantoin works mainly in the urine, so keeping the drug concentration in the urinary tract above the level needed to stop bacteria (the MIC) most of the day is key. Because it has a short systemic half-life, dosing it four times a day helps maintain therapeutic urinary concentrations throughout the day, which improves the chances of clearing the infection when treating UTIs in pregnancy. A seven-day course with four daily doses (every 6 hours or so) provides continuous exposure in the urine, whereas less frequent dosing could let levels fall between doses and reduce effectiveness. Hence, four times daily is the regimen that best maintains urinary drug exposure over the course of therapy.