Recommended Dosage of Cimetidine for Adults
The recommended adult oral dosage of cimetidine is 800 mg once daily at bedtime for most conditions, with alternative regimens of 400 mg twice daily or 300 mg four times daily depending on the specific condition being treated. 1
Standard Dosing Regimens
- For duodenal ulcer treatment, 800 mg once daily at bedtime is the preferred regimen, providing high healing rates, maximal pain relief, decreased potential for drug interactions, and optimal patient convenience 1
- Alternative regimens include 400 mg twice daily (morning and bedtime) or 300 mg four times daily with meals and at bedtime 1, 2
- For maintenance therapy of duodenal ulcer, the recommended dose is 400 mg at bedtime 1
- For active benign gastric ulcer, 800 mg once daily at bedtime or 300 mg four times daily with meals and at bedtime 1, 3
Condition-Specific Dosing
- For erosive gastroesophageal reflux disease (GERD): 1600 mg daily in divided doses (800 mg twice daily or 400 mg four times daily) for 12 weeks 1
- For pathological hypersecretory conditions (such as Zollinger-Ellison Syndrome): 300 mg four times daily with meals and at bedtime; may require up to 2400 mg per day in some patients 1
- For anaphylaxis management (as an H2-blocker adjunct): 4 mg/kg intravenously for adults 4
Special Populations
- For patients with severely impaired renal function: 300 mg every 12 hours orally or by intravenous injection; frequency may be increased to every 8 hours with caution if needed 1
- For hemodialysis patients: dosing should ideally be timed to coincide with the end of hemodialysis 1
- For patients with both renal and hepatic impairment: further dose reductions may be necessary 1
Pharmacokinetic Considerations
- Cimetidine has a high systemic clearance (500-600 ml/min), primarily through renal clearance 5
- Elimination half-life is approximately 2 hours 5
- Bioavailability is about 60% in healthy subjects and around 70% in patients with peptic ulcer disease 5
- When taken with food, absorption is delayed but the overall extent of absorption remains unchanged 5
Efficacy of Different Dosing Regimens
- Once-daily bedtime dosing (800 mg) has been shown to be as effective as or superior to twice-daily dosing (400 mg twice daily) for duodenal ulcer healing 2
- In one study, 84% of patients with duodenal ulcer healed after four weeks with once-daily dosing compared to 68% with twice-daily dosing (p<0.05) 2
- For gastric ulcer, once-daily bedtime dosing (800 mg) achieved healing rates similar to those seen with twice-daily and four-times-daily regimens 3
Common Pitfalls and Caveats
- Simultaneous administration of oral cimetidine and antacids is not recommended as antacids may interfere with cimetidine absorption 1, 6
- Cimetidine can interact with numerous medications as it inhibits CYP2C9, CYP2D6, and CYP3A4 enzymes 4
- Concomitant use with certain medications (e.g., dofetilide) is contraindicated due to potential drug interactions 4
- For patients who are heavy smokers (≥1 pack/day) with endoscopically demonstrated ulcers larger than 1 cm, 1600 mg at bedtime may achieve more rapid healing 1