Composition of Pepcid (Famotidine)
Pepcid is made of the active ingredient famotidine (N'-(aminosulfonyl)-3-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]propanimidamide) with molecular formula C8H15N7O2S3 and inactive ingredients including hypromellose, microcrystalline cellulose, magnesium stearate, modified corn starch, polydextrose, polyethylene glycol, talc, sodium starch glycolate, titanium dioxide and triacetin. 1
Active Ingredient Details
Famotidine is a histamine-2 (H2) receptor antagonist that works by blocking the action of histamine on stomach cells, thereby reducing the production of stomach acid. It is a white to pale yellow crystalline compound with the following solubility properties:
- Freely soluble in glacial acetic acid
- Slightly soluble in methanol
- Very slightly soluble in water
- Practically insoluble in ethanol 1
Pharmacological Properties
Famotidine is a highly selective and potent H2-receptor antagonist:
- Approximately 20-50 times more potent than cimetidine
- About 8 times more potent than ranitidine on a weight basis 2, 3
- Has a longer duration of action than both cimetidine and ranitidine 4
Formulation
Pepcid tablets are available in two main strengths:
- 20 mg tablets
- 40 mg tablets 1
Both formulations contain the same inactive ingredients that serve various functions:
- Binding agents (microcrystalline cellulose)
- Disintegrants (sodium starch glycolate)
- Lubricants (magnesium stearate)
- Film coating components (hypromellose, polyethylene glycol, titanium dioxide, triacetin)
- Fillers and other excipients (modified corn starch, polydextrose, talc) 1
Clinical Significance
Famotidine's chemical composition gives it several advantages:
- Unlike cimetidine, famotidine does not interact with the cytochrome P-450 hepatic enzyme system, avoiding many drug interactions 3, 4
- Its higher potency allows for lower dosing while maintaining efficacy 2
- The compound structure enables a longer duration of action, making once-daily dosing effective for many indications 5
Safety Profile
The chemical structure of famotidine contributes to its favorable safety profile:
- Overall incidence of side effects is only 1.2-2% in post-marketing studies 3
- Does not have the antiandrogenic effects occasionally reported with cimetidine 2
- Common side effects, when they do occur, include headache, dizziness, constipation, and diarrhea 4
Understanding the composition of Pepcid is important as it explains both its therapeutic efficacy and its safety profile compared to other H2-receptor antagonists.