Category C, D, X. According to babymed. Com: the category d antibiotics include tetracycline, doxycycline, Oxytetracycline in the 3rd trimester. Category x includes antibiotics that have shown fetal risk and / or abnormalities. Category x antibiotics include Isotretinoin and thalidomide. Also some category c drugs to be aware: sulfa, cipro, (ciprofloxacin) isoniazid, rifampin.