Antibiotics target some bacterial infections; they do not treat cold or flu viruses. A useful question is what infection a prescription is intended to treat, rather than which medicine is strongest. Unnecessary use contributes to resistance. Never borrow another person's prescription, and disclose pregnancy, breastfeeding and other medicines. Follow your own instructions; ask a pharmacist about missed doses instead of doubling up yourself. Digestive side effects can occur, but mouth or throat swelling and breathing difficulty after medication may indicate a severe allergic reaction. Seek emergency help immediately rather than waiting for a routine appointment.