What antibiotic can a pregnant woman take for a Proteus mirabilis (P. mirabilis) urinary tract infection (UTI)?

Antibiotic Treatment for Proteus mirabilis UTI in Pregnancy

For pregnant women with a Proteus mirabilis urinary tract infection, cephalexin (500mg four times daily for 7 days) is the recommended first-line antibiotic treatment due to its proven efficacy against P. mirabilis and established safety profile in pregnancy. 1, 2

First-Line Treatment Options

Cephalexin is the optimal choice for several reasons:

• FDA-approved for treating P. mirabilis infections during pregnancy 1
• Excellent safety profile in all trimesters of pregnancy 2
• Good urinary concentration with >90% excreted unchanged in urine 1
• Effective against P. mirabilis with minimal resistance patterns 1

Alternative First-Line Options:

1. Amoxicillin-clavulanic acid

   • High efficacy (100% sensitivity) against gram-positive bacteria and good activity against P. mirabilis 3
   • Safe in all trimesters of pregnancy

2. Nitrofurantoin (100mg twice daily for 5-7 days)

   • Highly effective for lower UTIs with 87.7% sensitivity against gram-negative bacteria 3, 2
   • Caution: Should be avoided in the first trimester if possible and near term (>36 weeks) due to risk of hemolytic anemia in G6PD-deficient neonates 2

3. Fosfomycin (3g single dose)

   • Convenient single-dose treatment 2
   • Good activity against most urinary pathogens including P. mirabilis
   • Safe throughout pregnancy

Antibiotics to Avoid in Pregnancy

• Trimethoprim-sulfamethoxazole: Contraindicated in first and third trimesters due to risk of neural tube defects and neonatal hyperbilirubinemia 2
• Fluoroquinolones: Contraindicated due to risk of cartilage damage and arthropathies 4
• Tetracyclines: Contraindicated due to risk of dental discoloration and bone growth inhibition 2

Treatment Duration and Follow-up

• Uncomplicated lower UTI: 5-7 days of therapy 2
• Complicated or upper UTI: 10-14 days of therapy 2
• Obtain follow-up urine culture 1-2 weeks after completing therapy to confirm cure 5
• Pregnant women with P. mirabilis UTIs require close monitoring due to the organism's urease activity and risk of stone formation 6

Special Considerations for P. mirabilis

P. mirabilis is a urease-producing bacterium that can increase urine pH, potentially leading to:

• Stone formation in the urinary tract 6
• Increased risk of pyelonephritis if untreated
• Potential for preterm labor if infection ascends to upper urinary tract 4

Clinical Pearls

• Asymptomatic bacteriuria should be treated in pregnant women, as recommended by European Association of Urology with a weak strength rating 6
• P. mirabilis infections may require imaging to rule out stone formation if symptoms persist or recur 6
• Adequate hydration is important to prevent stone formation with P. mirabilis infections
• Antibiotic resistance patterns should be monitored, as resistance rates to common antibiotics have been increasing 7

Treatment Algorithm

1. Confirm diagnosis: Positive urine culture with P. mirabilis
2. First-line therapy: Cephalexin 500mg four times daily for 7 days
3. If allergic to penicillins/cephalosporins: Use nitrofurantoin (avoid in first trimester and >36 weeks) or fosfomycin
4. For pyelonephritis: Hospitalization and IV antibiotics (ceftriaxone or ampicillin plus gentamicin) may be necessary
5. Follow-up culture: 1-2 weeks after completing therapy to confirm eradication

By following these evidence-based recommendations, clinicians can effectively treat P. mirabilis UTIs in pregnant women while minimizing risks to both mother and fetus.