Which medication should be avoided when treating a UTI in a pregnant woman due to potential harm to the fetus?

Doxycycline should be avoided when treating a urinary tract infection (UTI) in a pregnant woman due to its potential harm to the developing fetus. This antibiotic belongs to the tetracycline class, which is known to interfere with the normal development of bones and teeth in fetuses and young children. Doxycycline can bind to calcium, which can lead to permanent discoloration of teeth and inhibition of bone growth if it is administered during pregnancy. This makes it particularly contraindicated during this critical period of fetal development when the structures for teeth and bone are forming.

In contrast, the other options—Nitrofurantoin, Amoxicillin, and Cephalexin—are generally considered safer alternatives for treating UTIs in pregnant women. While Nitrofurantoin should be used cautiously in late pregnancy due to potential effects on fetal hemoglobin synthesis, it is still often prescribed early in pregnancy. Amoxicillin and Cephalexin are both commonly prescribed antibiotics that have a better safety profile during pregnancy, making them appropriate choices for UTI treatment in this population.