As a pharmacist, pregnant women will ask you about antibiotic safety for urinary tract infections (UTIs) partly due to new media headlines. A recent CDC report highlights that nitrofurantoin or TMP/SMX accounts for over 40% of prescribtion to treat a UTI in the first trimester and cautions about birth defects with these antibiotics. But this doesn't mean these medications must always be avoided. Balance benefits and risks of antibiotics for UTIs in pregnancy...
Nitrofurantoin (Uvamin Retard) in the first trimester is weakly linked to heart defects and cleft lip in a few studies, but other data suggest no association. Plus, its long history of seemingly safe use in pregnancy is reassuring and it has limited bacterial resistance. Feel comfortable using nitrofurantoin during most of pregnancy including the first trimester if necessary due to patient allergies, urine culture results, etc. But avoid it in the last month of pregnancy due to rare cases of hemolytic anemia in newborns.
TMP/SMX has more limitations. Trimethoprim in the first trimester is linked to heart or neural tube defects and sulfonamide use late in pregnancy raises concerns about dangerously high bilirubin in newborns. Save TMP/SMX for the second or early third trimester.
Beta-lactams are generally safe throughout pregnancy. Cephalexin (Ceporex) has good efficacy and can be dosed BID. Or depending on the bug, choose amoxicillin, ampicillin, etc. Fosfomycin (Monuril) can also be used in any trimester. It covers some resistant bugs and is just one dose. But it may not be covered by payers and many pharmacies don't stock it. The other options are prescribed for 3 to 7 days. Be aware there's no good data comparing efficacy of 3- or 5-day vs 7-day courses. Avoid quinolones. There's not enough data to say they're safe for a fetus, even though it seems okay to use quinolones if necessary in kids.
REFERENCES
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Ailes EC, Summers AD, Tran EL, Gilboa SM, Arnold KE, Meaney-Delman D, Reefhuis J. Antibiotics Dispensed to Privately Insured Pregnant Women with Urinary Tract Infections - United States, 2014. MMWR Morb Mortal Wkly Rep. 2018 Jan 12;67(1):18-22. Available at: https://www.cdc.gov/mmwr/volumes/67/wr/mm6701a4.htm?s_cid=mm6701a4_w
Glaser AP, Schaeffer AJ. Urinary Tract Infection and Bacteriuria in Pregnancy. Urol Clin North Am. 2015 Nov;42(4):547-60. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0094014315000452?via%3Dihub
Goldberg O, Koren G, Landau D, Lunenfeld E, Matok I, Levy A. Exposure to nitrofurantoin during the first trimester of pregnancy and the risk for major malformations. J Clin Pharmacol. 2013 Sep;53(9):991-5. Available at: https://accp1.onlinelibrary.wiley.com/doi/10.1002/jcph.139