Which antibiotic is the best choice for treating a pregnant woman with a urinary tract infection?

Cephalexin is considered the best choice for treating a urinary tract infection in a pregnant woman due to its safety profile and effectiveness. The use of cephalosporins, such as cephalexin, is generally well tolerated during pregnancy and has not been associated with adverse fetal outcomes. This antibiotic is effective against the common pathogens responsible for UTIs, including E. coli.

Other antibiotics mentioned, such as trimethoprim-sulfamethoxazole, are usually avoided during the first trimester due to potential risks for the fetus and are associated with increased risk of kernicterus in newborns. Ciprofloxacin, a fluoroquinolone, is contraindicated during pregnancy due to concerns about potential effects on developing cartilage and bone. Erythromycin, while sometimes used, is not the first-line treatment for UTIs in pregnant patients and may not be as effective as cephalexin for this particular indication. Therefore, cephalexin is the preferred and safest choice for managing urinary tract infections in pregnant women.