H2-receptor antagonist
Cimetidine
Brand names: Tagamet
Adult dose
Dose: PUD: 400mg BD or 800mg nocte for 4–8 weeks. GORD: 400mg QDS
Route: PO
Frequency: BD-QDS
Clinical pearls
- Largely superseded by PPIs and ranitidine alternatives; significant CYP inhibition is the key safety issue
Contraindications
- Hypersensitivity
Side effects
- Headache
- Diarrhoea
- Gynaecomastia (anti-androgen effect)
- Confusion in elderly
- Reversible thrombocytopenia
Interactions
- Major: inhibits CYP1A2/2C9/2D6/3A4 — raises warfarin, phenytoin, theophylline, lidocaine, ciclosporin levels
- Reduces ketoconazole/itraconazole absorption (raises gastric pH)
Reference: BNF; https://bnf.nice.org.uk/drugs/cimetidine/. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Pathways
- Lower Gastrointestinal Bleed · BSG 2019; NICE NG141
- Variceal Upper GI Bleed · BSG 2015; Baveno VII (2022)
- Spontaneous Bacterial Peritonitis (SBP) · BSG / EASL 2018
- Hepatorenal Syndrome · EASL 2018; ICA 2015
- Hepatic Encephalopathy · EASL 2014; West Haven criteria
- Clostridioides difficile Colitis · NICE NG199 (2021); IDSA/SHEA 2021