What should you know about first line antibiotics?

The choice depends on the infection site, likely bacteria, local prescribing practice, allergies, pregnancy, kidney function, previous antibiotic use, and test results. Antibiotics do not treat viruses, so they may not help illnesses such as many cases of acute bronchitis. A clinician may change the medicine when a swab, urine test, or other result identifies a different option. First-line does not mean suitable for every person or every infection.

Take the medicine exactly as prescribed and do not share leftover tablets. Check whether it should be taken with food and mention every medicine or supplement you use. Tell the prescriber about a penicillin or other drug allergy, pregnancy, diarrhoea, or kidney problems. Finish the prescribed course unless the clinician tells you to stop, and ask what to do after a missed dose. Nausea or loose stools can happen, but severe or persistent diarrhoea needs advice. Antibiotics are used for some infections such as cellulitis, chlamydia, gonorrhoea, and Helicobacter Pylori Infection, with different regimens for each.

Call emergency services for breathing difficulty, facial swelling, collapse, or a rapidly spreading rash after a dose. Contact a clinician urgently for severe diarrhoea, dehydration, confusion, or worsening infection. A painful red skin area that spreads, severe eye pain, or genital discharge needs assessment rather than self-treatment. Read about [Cellulitis](/conditions/cellulitis/) and [Conjunctivitis](/conditions/conjunctivitis/) for condition-specific guidance.

Ask what infection is being treated, why this medicine is the initial choice, when improvement should begin, and what result would prompt a change. Confirm interactions and the plan if symptoms do not improve.