Antibiotics and ulcerative colitis

Because antibiotics can also cause diarrhoea and alter gut bacteria, new bowel symptoms during or after a course should be discussed with the prescribing clinician.

Ulcerative colitis is inflammation of the colon driven by an abnormal immune response, not an illness that an antibiotic normally clears. Medicines that control inflammation are therefore central to treating a flare.

An antibiotic may be appropriate when testing or examination points to a separate bacterial infection, or when the clinical team is concerned about a complication. Stool tests can help distinguish infection from active inflammation because both can produce frequent loose or bloody stools.

Before starting treatment, tell the prescriber about your colitis medicines, recent antibiotic use, allergies, pregnancy or breastfeeding, and any previous severe antibiotic-related diarrhoea. Take the medicine according to the label and do not share it or use leftovers.

Continue your usual ulcerative colitis treatment unless the clinical team tells you to change it. Record changes in stool frequency, bleeding, pain, fever and hydration; this gives the team concrete information if reassessment is needed.

Contact your care team promptly for distinctly worsening diarrhoea, increasing blood in stool, fever, persistent vomiting, new severe abdominal pain, or symptoms that begin after an antibiotic. Assessment may include stool testing and a review of both infection and colitis activity.

Seek urgent care for a markedly swollen abdomen, severe continuous pain, fainting, confusion, very little urine, inability to drink, heavy rectal bleeding, or breathing difficulty. A widespread rash, facial swelling, wheeze or breathing problem after a dose may represent a serious allergic reaction.

Ask what infection or complication the antibiotic is intended to treat, whether a stool sample is needed first, how the medicine interacts with your current treatment, and what change should trigger an early review. If your symptoms could represent a flare, ask who should adjust your anti-inflammatory treatment and how follow-up will be arranged.