Doxific 100 mg Doxific 100 mg is an injectable antibiotic containing doxycycline. It is used against a range of bacterial infections by interfering with the bacteria's ability to make essential proteins needed for growth and multiplication. It may be used when an injectable form of doxycycline is appropriate, including for certain respiratory, urinary, skin, eye, intestinal and other bacterial infections. The injection is administered by a healthcare professional.