Can Macrobid (nitrofurantoin) be used safely to treat an uncomplicated urinary tract infection in a 22‑week‑gestation pregnant woman with normal renal function?

Nitrofurantoin (Macrobid) for UTI at 22 Weeks Gestation

Nitrofurantoin 100 mg twice daily for 7 days is safe and appropriate for treating uncomplicated urinary tract infection at 22 weeks gestation, provided the patient has normal renal function and no suspicion of pyelonephritis. 1, 2

First-Line Treatment Recommendation

• Nitrofurantoin monohydrate/macrocrystals 100 mg orally twice daily for 7 days is the preferred first-line agent for uncomplicated lower UTI during the second trimester of pregnancy. 1, 2

• The 7-day duration (rather than the 5-day course used in non-pregnant women) ensures complete eradication of infection during pregnancy, when treatment failure carries significantly higher maternal and fetal risks. 2

• Nitrofurantoin achieves excellent urinary concentrations and has minimal teratogenic risk throughout pregnancy, with a retrospective analysis of 91 pregnancies showing no fetal toxicity or drug-related adverse events. 3

Critical Safety Considerations

• Do not use nitrofurantoin if pyelonephritis is suspected (fever, flank pain, costovertebral angle tenderness), because it does not achieve therapeutic blood concentrations needed for upper urinary tract infections. 1

• Nitrofurantoin is contraindicated only in the last 4 weeks of pregnancy (≥36 weeks) due to theoretical risk of hemolytic anemia in the newborn, but is safe at 22 weeks gestation. 4

• Confirm normal renal function before prescribing, as nitrofurantoin is contraindicated in any degree of renal impairment (creatinine clearance <60 mL/min). 4

Mandatory Diagnostic Steps

• Obtain urine culture before initiating antibiotics to guide therapy and confirm the diagnosis, as screening for pyuria alone has only 50% sensitivity for identifying bacteriuria in pregnant women. 1, 2

• Start empiric nitrofurantoin immediately without waiting for culture results, as delaying treatment increases the risk of progression to pyelonephritis. 1

• Perform follow-up urine culture 1–2 weeks after completing treatment to confirm bacteriologic cure, as recurrence is common (20–35% risk of progression to pyelonephritis if untreated). 2

Alternative Antibiotics if Nitrofurantoin Cannot Be Used

• Cephalexin 500 mg four times daily for 7–14 days is the preferred alternative if nitrofurantoin is contraindicated or not tolerated. 1, 2

• Fosfomycin trometamol 3 g single dose is an acceptable alternative for uncomplicated lower UTI, though clinical data for second trimester use are more limited than for nitrofurantoin. 1

• Avoid trimethoprim-sulfamethoxazole in the first trimester (teratogenic risk due to folic acid antagonism) and it is contraindicated in the third trimester (risk of neonatal hyperbilirubinemia). 1, 2

• Avoid fluoroquinolones throughout pregnancy due to potential adverse effects on fetal cartilage development. 1

Clinical Context: Why Treatment Is Urgent

• Untreated bacteriuria increases pyelonephritis risk 20–30 fold, from 1–4% with treatment to 20–35% without treatment. 1, 2

• Treatment reduces premature delivery and low birth weight infants in pregnant women with UTI. 1

• Even asymptomatic bacteriuria must be treated during pregnancy, as it carries significant risk for progression to pyelonephritis and adverse pregnancy outcomes. 1, 2

Common Pitfalls to Avoid

• Do not use shorter courses (3-day or single-dose regimens) in pregnancy, as they show lower bacteriuria clearance rates and higher recurrence. 2

• Do not perform surveillance urine testing or treat asymptomatic bacteriuria repeatedly after the initial screen-and-treat approach, as this fosters antimicrobial resistance. 1

• Do not use nitrofurantoin for Proteus mirabilis infections, as this organism is intrinsically resistant; switch to cephalexin if culture identifies Proteus. 1