Famotidine

Famotidine is a histamine H2 receptor antagonist used to treat conditions caused by excess stomach acid, including duodenal and gastric ulcers, gastro-oesophageal reflux disease (GORD), and Zollinger-Ellison syndrome.

It is also used for the prevention of NSAID-associated ulcers and for short-term symptomatic relief of heartburn and indigestion.

Famotidine competitively blocks histamine H2 receptors on gastric parietal cells, reducing both basal and stimulated acid secretion.

It is the most potent of the H2 receptor antagonists, being approximately 7-10 times more potent than ranitidine on a milligram-for-milligram basis, and has a duration of action of up to 12 hours.

While proton pump inhibitors (PPIs) have largely replaced H2 receptor antagonists for conditions requiring sustained acid suppression, famotidine retains important clinical roles.

It is particularly useful for intermittent heartburn, nocturnal acid breakthrough in patients already on a PPI, and for patients who prefer to avoid or cannot tolerate PPIs.

For ulcer treatment: take once daily at bedtime or twice daily (morning and evening). For GORD: take twice daily.

For symptomatic heartburn relief: take one tablet when symptoms occur, or before a meal that is likely to cause symptoms. Swallow tablets whole with water. Can be taken with or without food.

Duodenal ulcer: 40 mg at bedtime for 4-8 weeks. Gastric ulcer: 40 mg at bedtime for 4-8 weeks. GORD: 20 mg twice daily for 6-12 weeks. Maintenance: 20 mg at bedtime.

Symptomatic relief: 10-20 mg as needed. Zollinger-Ellison syndrome: starting dose 20 mg every 6 hours, adjusted to clinical response. Reduce dose in significant renal impairment.

Common (1 in 10 to 1 in 100): headache and dizziness. Uncommon (1 in 100 to 1 in 1,000): constipation, diarrhoea, nausea, dry mouth, and fatigue.

Rare (less than 1 in 1,000): elevated liver enzymes, rash, alopecia, and blood dyscrasias.

Very rare: QT prolongation (in patients with renal impairment receiving intravenous formulation), and severe hypersensitivity reactions.

The overall side effect profile is mild and famotidine is well tolerated by most patients.

Gastric malignancy should be excluded before starting treatment for gastric symptoms, as famotidine may mask symptoms of gastric cancer.

Dose reduction is required in moderate to severe renal impairment. Use with caution in patients with a history of QT prolongation. Long-term use may lead to vitamin B12 deficiency in some patients.

Rebound acid hypersecretion may occur following prolonged use and abrupt discontinuation.

Known allergy to famotidine or other H2 receptor antagonists. Caution in severe renal impairment (dose adjustment necessary).

Not recommended as first-line treatment for severe erosive oesophagitis (PPIs are more effective in this setting).