Famotidine

H2 Receptor Antagonist·Gastrointestinal - Acid Suppression

Treatment of gastric and duodenal ulcers, GORD, Zollinger-Ellison syndrome

PBSH2 ANTAGONISTPepzan, Pamacid20 mg tabletS4+1

Max Dose

80 mg/day

Half-life

3 h

CYP Inhibitor

NONE

Renal Adj.

DOSE RED.

Rapid Summary

Overview

Histamine H2 receptor antagonist. Highly effective acid-suppressor. Unlike its predecessor (Cimetidine), it has zero dangerous liver enzyme interactions, making it incredibly safe for polypharmacy.

Maximum Dose

Max 80 mg/day (e.g., 40 mg BD).

Clinical Focus

Predominantly renally cleared. Must halve the dose in severe kidney failure to prevent toxic CNS accumulation (delirium/seizures).

Bottom Line

Famotidine is an H2 receptor antagonist for acid suppression with fewer drug interactions than PPIs, but is less potent than PPIs and tolerance develops with regular use.

Formulation & Access

Brand Names

Pepzan, Pamacid

Oral Routes

Tablets (20 mg, 40 mg).

Parenteral

Ampoules (20 mg/2 mL) for IV use.

Prescribing & PBS

Unrestricted General Benefit (S4 for 40mg/IV). OTC (S2) for 20mg.

Indications & Use

Primary

PBSTGA

Treatment of gastric and duodenal ulcers, GORD, Zollinger-Ellison syndrome.

Off-Label

OFF

Refractory chronic urticaria (hives), adjunct in anaphylaxis protocols.

Clinical Place

Step-down therapy from PPIs. The preferred H2 antagonist worldwide after Ranitidine was recalled due to NDMA contamination.

Quick reference

Class & Role

H2 Receptor Antagonist — Histamine H2 receptor antagonist.

Route / Formulation

Tablets (20 mg, 40 mg). (Pepzan, Pamacid)

Usual Dose & Max

PO 20-40 mg BD or 40 mg NOCTE (Nighttime dosing is highly effective because histamine drives nocturnal acid secretion). Max 80 mg/day (e.g., 40 mg BD).

Key Indication Doses

GORD / Peptic Ulcer Disease: PO 20-40 mg BD or 40 mg NOCTE (Nighttime dosing is highly effective because histamine drives nocturnal acid secretion). Allergic Reactions (Off-Label): PO / IV 20 mg STAT (Acts as an H2 blocker to adjunct H1 blockers like cetirizine during anaphylaxis/hives). Renal Impairment: If eGFR < 50, reduce dose to 20 mg NOCTE or prolong the interval to 48 hours.

Best Uses

Famotidine is an H2 receptor antagonist for acid suppression with fewer drug interactions than PPIs, but is less potent than PPIs and tolerance develops with regular use.

Avoid / Cautions

Known hypersensitivity to H2 antagonists. Pregnancy Category B1.

Key Risks

Neurological: Confusion, delirium, hallucinations, agitation (Exclusively seen in elderly patients or those with unadjusted renal failure where the drug crosses the BBB). Gastrointestinal: Mild diarrhea or constipation. Haematological: RARE — Thrombocytopenia.

Key Interactions

Unlike Cimetidine (which violently blocks CYP450 enzymes and interacts with Warfarin/Phenytoin), Famotidine has ZERO effect on hepatic CYP enzymes. It is completely safe to mix. Drugs requiring an acidic gut to absorb (Ketoconazole, Iron) will fail to absorb properly.

Monitoring

Check eGFR in elderly patients before charting standard 40mg BD doses. If an elderly patient on Famotidine becomes acutely confused or delirious, withhold the drug immediately; it is likely neurotoxicity from renal accumulation.

Clinical Pearl

During severe anaphylaxis or full-body hives, blocking the H1 receptor (with Cetirizine/Promethazine) only solves half the problem. ~15% of histamine receptors in the skin and blood vessels are actually H2 receptors. Giving IV Famotidine provides total histamine blockade.

Access

Pepzan, Pamacid20 mg tablet

Brand: Pepzan, Pamacid
Formulation: Tablets (20 mg, 40 mg)

Famotidine

H2 Receptor Antagonist·Gastrointestinal - Acid Suppression

Treatment of gastric and duodenal ulcers, GORD, Zollinger-Ellison syndrome

PBSH2 ANTAGONISTPepzan, Pamacid20 mg tabletS4+1

Max Dose

80 mg/day

Half-life

3 h

CYP Inhibitor

NONE

Renal Adj.

DOSE RED.

Rapid Summary

Overview

Histamine H2 receptor antagonist. Highly effective acid-suppressor. Unlike its predecessor (Cimetidine), it has zero dangerous liver enzyme interactions, making it incredibly safe for polypharmacy.

Maximum Dose

Max 80 mg/day (e.g., 40 mg BD).

Clinical Focus

Predominantly renally cleared. Must halve the dose in severe kidney failure to prevent toxic CNS accumulation (delirium/seizures).

Bottom Line

Famotidine is an H2 receptor antagonist for acid suppression with fewer drug interactions than PPIs, but is less potent than PPIs and tolerance develops with regular use.

Formulation & Access

Brand Names

Pepzan, Pamacid

Oral Routes

Tablets (20 mg, 40 mg).

Parenteral

Ampoules (20 mg/2 mL) for IV use.

Prescribing & PBS

Unrestricted General Benefit (S4 for 40mg/IV). OTC (S2) for 20mg.

Indications & Use

Primary

PBSTGA

Treatment of gastric and duodenal ulcers, GORD, Zollinger-Ellison syndrome.

Off-Label

OFF

Refractory chronic urticaria (hives), adjunct in anaphylaxis protocols.

Clinical Place

Step-down therapy from PPIs. The preferred H2 antagonist worldwide after Ranitidine was recalled due to NDMA contamination.

Quick reference

Class & Role

H2 Receptor Antagonist — Histamine H2 receptor antagonist.

Route / Formulation

Tablets (20 mg, 40 mg). (Pepzan, Pamacid)

Usual Dose & Max

PO 20-40 mg BD or 40 mg NOCTE (Nighttime dosing is highly effective because histamine drives nocturnal acid secretion). Max 80 mg/day (e.g., 40 mg BD).

Key Indication Doses

Best Uses

Famotidine is an H2 receptor antagonist for acid suppression with fewer drug interactions than PPIs, but is less potent than PPIs and tolerance develops with regular use.

Avoid / Cautions

Known hypersensitivity to H2 antagonists. Pregnancy Category B1.

Key Risks

Key Interactions

Monitoring

Clinical Pearl

Access

Pepzan, Pamacid20 mg tablet

Brand: Pepzan, Pamacid
Formulation: Tablets (20 mg, 40 mg)