What antibiotic is appropriate for a pregnant woman with a urinary tract infection (UTI)?

From the Guidelines

Nitrofurantoin is the most appropriate antibiotic for pregnant women with urinary tract infections (UTIs), typically prescribed at 100mg twice daily for 5-7 days, though it should be avoided in the third trimester. For pregnant women with UTIs, nitrofurantoin, amoxicillin-clavulanate, or cephalexin are typically recommended first-line antibiotics 1. These medications are considered safe during pregnancy and effectively treat most uncomplicated UTIs. Fosfomycin (3g single dose) is another option for uncomplicated cases. Trimethoprim-sulfamethoxazole should be avoided in the first trimester due to potential birth defects and near delivery because of neonatal jaundice risks. Fluoroquinolones and tetracyclines are contraindicated throughout pregnancy. Some key points to consider when treating UTIs in pregnant women include:

• The optimal duration of antimicrobial therapy for treatment of bacteriuria in pregnant women has not been determined, but current recommendations for a 4- to 7-day duration of antimicrobial therapy are reasonable 1.
• A Cochrane review from 2015 found that 7 days of therapy was more effective than a single dose in preventing the adverse outcome of lower birth weight, but no differences in pyelonephritis or preterm delivery were observed between the 2 study arms 1.
• Prompt treatment is essential as untreated UTIs can lead to pyelonephritis, which increases risks of preterm labor and low birth weight.
• Pregnant women should increase fluid intake, urinate frequently, and complete the full antibiotic course even if symptoms improve quickly. It's also important to note that the Infectious Diseases Society of America recommends screening for bacteriuria by urine culture at least once in early pregnancy 1.

From the FDA Drug Label

1. 1 Pregnancy Teratogenic Effects: Reproduction studies have been performed in mice and rats at doses up to 2000 mg/kg (3 and 6 times the 3 g human dose, based on body surface area). There was no evidence of harm to the fetus due to amoxicillin. There are, however, no adequate and well-controlled studies in pregnant women Because animal reproduction studies are not always predictive of human response, amoxicillin should be used during pregnancy only if clearly needed.

Amoxicillin can be used during pregnancy if clearly needed, as there is no evidence of harm to the fetus in animal studies, but no adequate and well-controlled studies in pregnant women have been conducted 2.

From the Research

Antibiotic Treatment for Urinary Tract Infections in Pregnancy

• The appropriate antibiotic for treating urinary tract infections (UTIs) in pregnancy is a subject of several studies and guidelines 3, 4, 5.
• According to a 1994 study, amoxicillin and trimethoprim/sulfamethoxazole are effective in treating UTIs in pregnancy, with cure rates of approximately 80% and greater than 80%, respectively 3.
• The same study recommends separating pregnant subjects with UTIs into two groups: those with asymptomatic bacteriuria who can be treated with a single dose of an antimicrobial, and those with symptomatic UTI who can be treated with amoxicillin 500 mg tid for three days 3.
• A 2012 study emphasizes the importance of screening for bacteriuria in pregnant women and treating it to prevent the development of acute pyelonephritis and its negative effects on the fetus 4.
• The selection of an appropriate antimicrobial agent should be based on the result of urine culture and the safety of the drug for both the woman and the fetus 4, 5.
• A 2022 literature review of international guidelines found concordance between guidelines regarding several aspects of antibiotic treatment for UTIs in pregnancy, but also areas of discordance, such as the use of fluoroquinolones 5.
• Other studies discuss the importance of correct diagnosis, diagnostic measures, and the use of antibiotics such as nitrofurantoin, fosfomycin, and pivmecillinam in treating UTIs 6, 7.

Considerations for Antibiotic Choice

• The choice of antibiotic should be based on the susceptibility of the organism, the safety of the drug for the fetus, and the potential for resistance 3, 4, 6.
• Amoxicillin, trimethoprim/sulfamethoxazole, and nitrofurantoin are commonly recommended antibiotics for treating UTIs in pregnancy 3, 4, 5.
• Fluoroquinolones are not recommended for use in pregnancy due to the potential risk of harm to the fetus 4, 5.
• The duration of treatment should be based on the severity of the infection and the response to treatment, with a typical duration of 3-5 days 3, 7.