What is the appropriate antibiotic regimen for treating an acute episode of diverticulitis in an outpatient setting?

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Posted: 16 August 2025Updated: 16 August 2025 Guideline-Aligned (High Confidence) Clinically Reviewed
Dr Kola Tytler MBBS CertHE MBA MRCGPClinical Lead • iatroX

For an outpatient treatment of an acute episode of diverticulitis, the recommended antibiotic regimen is co-amoxiclav 500/125 mg three times daily for 5 days .

Alternatively, if penicillin allergy or co-amoxiclav is unsuitable, options include cefalexin 500 mg twice or three times daily for 5 days plus metronidazole 400 mg three times daily for 5 days .

Other alternatives are trimethoprim 200 mg twice daily for 5 days plus metronidazole 400 mg three times daily for 5 days .

Use of ciprofloxacin in combination with metronidazole is also an option, but only if switching from IV ciprofloxacin with specialist advice, with ciprofloxacin 500 mg twice daily for 5 days .

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