Pepcid
Pepcid
Generic Name
Pepcid
Mechanism
Famotidine competitively inhibits histamine binding to the H₂ receptors on gastric parietal cells, thereby blocking the Gs‑protein–mediated stimulation of adenylyl cyclase.
• ↓ cAMP → ↓ potassium channel activation → ↓ chloride secretion
• Result: decreased gastric acidity and reduced parietal‑cell H⁺/K⁺‑ATPase activity.
Pharmacokinetics
| Parameter | Data | Notes |
| Absorption | ~70 % oral bioavailability, peak plasma conc. (t_max) 1–2 h | Rapid absorption and high oral bioavailability. |
| Distribution | Volume of distribution ~5 L/kg; protein binding ~65 % | Minimal distribution to adipose tissue. |
| Metabolism | Minimal hepatic metabolism (∼10 %); a small portion via CYP1A2 | Predominantly excreted unchanged. |
| Elimination | Renal excretion 60–70 % unchanged; half‑life 2–3 h (shorter in pregnancy) | Dose adjustment needed in renal impairment. |
| Drug‑Drug Interactions | Inhibits CYP1A2 → ↑ levels of clozapine, sulfonamides; displaces warfarin from binding sites | Monitor for toxicity with interacting agents. |
Indications
- Peptic ulcer disease (PUD) → healing, ulcer prevention, GERD symptom control
- Gastro‑esophageal reflux disease (GERD) → nocturnal reflux, Hiatal hernia.
- Zollinger‑Ellison syndrome (in conjunction with PPIs)
- H. pylori eradication – adjunct in triple‑therapy regimens.
Contraindications
- Hypersensitivity to famotidine or any excipient.
- Severe renal impairment (CrCl <15 mL/min) → switch to ranitidine or observe closely.
- Adverse drug reactions: hypokalemia, hypotension, CNS effects (dizziness, confusion) in elderly.
Warnings
• Use with caution in patients with hepatic disease; monitor liver enzymes.
• Avoid concomitant use of drugs with narrow therapeutic index (e.g., clopidogrel) unless necessary—adjust dose or monitor.
Dosing
| Population | Dose | Form | Frequency | Route | Comments |
| Adult (PUD, GERD) | 20 mg BID or 40 mg daily | Oral capsule/tablet | BID/Daily | PO | Start high‑dose BP or GERD 48 h → taper. |
| Adult (maintenance) | 10 mg nightly | Oral | QHS | PO | For chronic GERD or ulcer prophylaxis. |
| Pediatric (≥3 mo) | 0.2 mg/kg/d (max 15 mg) | Oral | BID | PO | Weight‑adjusted for safety. |
| Renal impairment | Reduce by 50 % if CrCl 30–50 mL/min | Oral | BID | PO | Dose adjustment critical. |
Administration tips
• Take 30 min before meals or 1 h after when used for ulcer healing.
• Tablets may be crushed for nasogastric tube delivery; tablets should not be crushed for sublingual use.
Adverse Effects
- Common: headache, dizziness, constipation or diarrhea, nausea.
- Serious:
- Hypotension (especially with β‑blockers); hold dose if symptomatic.
- Electrolyte disturbances (hypokalemia, hyperkalemia in renal disease).
- Liver dysfunction: ALT/AST ↑ >3× ULN—rare.
- Neuropsychiatric: confusion, hallucinations in elderly.
- Allergic reactions: rash, urticaria, anaphylaxis (rare).
Monitoring
- Renal function (CrCl/eGFR) every 3 months in chronic users.
- Serum electrolytes in elderly or patients on diuretics.
- Liver enzymes if chronic therapy >6 months.
- Drug levels for interacting agents (e.g., warfarin INR, clozapine levels).
- Symptom assessment: acid‑reflux score, ulcer healing endoscopy if indicated.
Clinical Pearls
1. Use on Demand – For GERD patients with infrequent symptoms, an as‑needed (PRN) dose can reduce overall exposure and cost.
2. Triple‑Therapy Synergy – When used in H. pylori regimens, famotidine’s rapid onset complements PPIs, providing more immediate acid suppression.
3. Renal Dosing – In patients with CrCl 30–50 mL/min, a 10 mg BID regimen yields adequate acid control while minimizing accumulation.
4. Drug–Interaction Awareness – Famotidine can increase clozapine levels; monitor for seizures or sedation.
5. Elderly Sensitivities – Dose reduction to 10 mg nightly often sufficient for maintenance; monitor for CNS side‑effects.
6. VAS Score Paradox – Despite strong acid suppression, 30% of GERD patients remain symptomatic; consider motility agents or surgical options.
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• References
1. Katz PO, et al. *Journal of Clinical Gastroenterology* 2023;57(4):342‑348.
2. Brown S, et al. *Pharmacology & Therapeutics* 2022;219:107878.
3. FDA Prescribing Information – *Famotidine* 2024.