Which of the following antibiotics is CONTRAINDICATED (not safe) during pregnancy due to its adverse effects on fetal tooth development?

Tetracycline and its derivatives (doxycycline, minocycline) are contraindicated in pregnancy (particularly after the 4th month) and in children under 8 years of age because they chelate calcium and deposit in developing teeth and bones. This causes permanent intrinsic yellow-brown-gray staining (tetracycline staining) and enamel hypoplasia. Tetracyclines are FDA Pregnancy Category D (risk to fetus demonstrated). Amoxicillin (penicillin class) and azithromycin (macrolide, generally considered compatible with pregnancy) are safe to use. Clindamycin is sometimes used in pregnancy when other options are not suitable.