EVIDENCE-BASED ANSWER
Trimethoprim/sulfamethoxazole (TMP/SMX) has a high success rate in eradicating bacteriuria for women with urinary tract infection and is compatible with breastfeeding (strength of recommendation: C, based on extrapolation from studies with nonlactating women and disease-oriented outcomes).
Quinolones (ciprofloxacin, ofloxacin) are effective and probably compatible with breastfeeding; however, their use has not been recommended by many investigators based on arthropathy in animal studies (SOR: C, based on extrapolation from case series and disease-oriented outcomes).
A 7-day course of nitrofurantoin has similar efficacy to TMP/SMX and is compatible with breastfeeding, but it should be avoided in populations at risk for glucose-6-phosphate dehydrogenase (G6PD) deficiency (also known as favism, most often found in patients of mediterranean or african descent) (SOR: C, extrapolation from studies in nonlactating women and disease-oriented outcomes).
Clinical commentary
An antibiotic that’s effective for mom and safe for baby is of paramount importance
Timothy Huber, MD
Oroville, Calif
Knowing the local resistance patterns can greatly aid in choosing a safe, effective antibiotic. Most local laboratories that do microbiology work either publish their antibiograms or make them available on a semiannual or annual basis. Keeping these readily available can be a time-saver when it comes to decision-making and writing a prescription.
Evidence summary
Urinary tract infections (UTIs) are common in reproductive-aged women. In lactating women, it’s important to select a therapy that is not only effective, but also safe for the breastfeeding infant. No studies in the literature address the safety or efficacy of UTI treatments in lactating women and their infants. Therefore, recommendations are extrapolated from studies of efficacy in the general population, studies of antibiotic penetration into breast milk, and effects of antibiotics given to infants directly.
How the efficacy of UTI treatments stack up
The best evidence for efficacy of UTI treatments comes from a 1999 meta-analysis of uncomplicated UTI in nonpregnant, nonlactating women.1 They found TMP/SMX to be the most widely studied antibiotic and to have a 93% bacterial eradication rate; it was therefore used as a standard for comparison of other treatments. Nitrofurantoin and quinolones (ofloxacin, ciprofloxacin, and others) had comparable eradication rates to TMP/SMX in the same study; 7-day courses of nitrofurantoin were more efficacious than shorter ones. TMP/SMX is not recommended if the local resistance rate is more than 10% to 20%.2
Three-day therapy for uncomplicated UTI is more effective than single-dose therapy and equal to longer courses for most antibiotics.1 A longer course (7 days) may be required for nitrofurantoin. Beta-lactams are associated with high levels of resistance and therefore not recommended in empiric treatment of UTI.2
A look at penetration into breast milk
Most of the data regarding antibiotic penetration into breast milk come from case series. One South African series measured breast milk levels of both trimethoprim and sulfamethoxazole among 50 Bantu women treated with TMP/SMX for various infections (including UTI).3 The women received 160 mg TMP and 800 mg SMX 2 or 3 times daily for up to 5 days. The average level of TMP in breast milk was 2 mcg/mL, and the level of SMX was 4.7 mcg/mL. Researchers calculated that the average breastfeeding infant would ingest only 1 mg of TMP and 2.5 mg of SMX per day. TMP/SMX is generally considered safe for infants in the absence of G6PD deficiency.
In a case series, 9 lactating mothers were given nitrofurantoin 100 mg orally every 6 hours for 1 day.4 On day 2, after a single 100 to 200 mg dose, drug levels in the breast milk 2 hours post-dose ranged from none (in 6 of the 9 women) to a maximum of 0.5 mcg/mL in one. Since even a very small amount of the drug may trigger a hemolytic reaction among G6PD-deficient individuals, the researchers called for caution when prescribing to mothers from high-risk populations.