Phenazopyridine (Azo) Safety in Pregnancy for UTI Symptom Relief
Phenazopyridine is classified as FDA Pregnancy Category B and can be used during pregnancy for symptomatic relief of UTI-related dysuria, but it should only be used as a short-term adjunct (maximum 2 days) alongside appropriate antibiotic therapy, not as standalone treatment. 1
FDA Safety Classification
- The FDA drug label indicates that reproduction studies in rats at doses up to 50 mg/kg/day revealed no evidence of impaired fertility or harm to the fetus due to phenazopyridine. 1
- However, there are no adequate and well-controlled studies in pregnant women, so the drug should be used during pregnancy only if clearly needed. 1
- No information is available on the appearance of phenazopyridine or its metabolites in human milk, which is an important consideration for breastfeeding. 1
Critical Clinical Context: UTIs in Pregnancy Require Antibiotic Treatment
All bacteriuria in pregnancy—whether symptomatic or asymptomatic—must be treated with antibiotics, not just symptomatic relief agents. 2, 3
- Pregnant women with untreated asymptomatic bacteriuria have a 20-30-fold increased risk of developing pyelonephritis compared to women without bacteriuria. 2, 4
- Without antibiotic treatment, pyelonephritis develops in 20-35% of pregnant women with bacteriuria, compared to only 1-4% when treated. 2, 4
- Untreated UTIs are associated with premature delivery, low birth weight infants, and other adverse maternal and fetal outcomes. 2, 4, 5
Appropriate Use of Phenazopyridine in Pregnancy
If phenazopyridine is used, it should only serve as a bridge for symptomatic relief during the first 24-48 hours while waiting for antibiotics to take effect:
- The primary treatment must be appropriate antibiotics such as nitrofurantoin, fosfomycin trometamol, amoxicillin, or third-generation cephalosporins (cefixime). 2, 6, 7
- Phenazopyridine only provides symptomatic relief of dysuria, urgency, and frequency—it does not treat the underlying infection. 1
- Duration should be limited to 2 days maximum, as prolonged use increases risk of accumulation, especially given the physiological changes in renal function during pregnancy. 1
Important Safety Precautions
- Monitor for yellowish discoloration of skin or sclera, which may indicate accumulation due to impaired renal excretion and necessitates discontinuation. 1
- Warn patients that phenazopyridine produces reddish-orange discoloration of urine and may stain fabric and contact lenses. 1
- The drug may interfere with urinalysis based on spectrometry or color reactions, which could complicate follow-up testing. 1
Common Pitfall to Avoid
Never use phenazopyridine as monotherapy or allow it to delay appropriate antibiotic treatment. The physiological changes of pregnancy (ureteral compression by the enlarging uterus after 20 weeks, urinary stasis, physiological hydronephrosis) create an environment that promotes ascending infections. 4 Any delay in antibiotic therapy significantly increases the risk of progression to pyelonephritis with its associated maternal and fetal complications. 2, 4
Recommended Antibiotic Options for UTI in Pregnancy
- First-line oral options: Nitrofurantoin, fosfomycin trometamol (single dose), or amoxicillin for 4-7 days. 2, 8, 6, 7
- Alternative oral options: Third-generation cephalosporins such as cefixime. 6, 7
- For pyelonephritis: Amoxicillin combined with an aminoglycoside, third-generation cephalosporins, or carbapenems (parenteral). 5