THERAPEUTIC ACTIONS ã…¡ H2 antagonists or H2-blocker inhibit the action of histamine at the H2 receptors of the stomach, inhibiting gastric acid secretion and reducing total pepsin output; the resultant decrease in acid allows healing of ulcerated areas. See additional notes Peptic Ulcer; assessment and management and Dyspepsia.
PHARMACOLOGY
| Table (1). Pharmacology of H2RA | |
|---|---|
| COMMENT | |
| Indications |
|
| Contraindications and cautions | Contraindicated with allergy to H2 antagonists, impaired renal or hepatic function |
| Pregnancy category | Category B (safe during pregnancy) |
| Adverse effects | CNS: Dizziness, somnolence, headache, confusion, hallucinations, peripheral neuropathy, symptoms of brain stem dysfunction (dysarthria, ataxia, diplopia) CV: Cardiac arrhythmias, arrest; hypotension (IV use) GI: Diarrhea Hematologic: Increases in plasma creatinine, serum transaminase Other: Impotence (reversible with drug withdrawal), gynecomastia (long-term treatment), rash, vasculitis, pain at IM injection site |
| Interactions |
|
CLINICAL CONSIDERATIONS
| Table (2). Clinical considerations of H2RA | |
|---|---|
| COMMENT | |
| Assessment | History: Allergy to H2 antagonists, impaired renal or hepatic function, lactation. Physical: Skin lesions; orientation, affect; pulse, baseline ECG (continuous with IV use); liver evaluation, abdominal examination, normal output; CBC, LFTs, renal function tests. |
| Interventions | Administer drug with food and at bedtime. Decrease doses in renal and hepatic impairment. Administer IM dose undiluted, deep into large muscle group. Ensure ready access to bathroom. Provide comfort measures for rash, headache. Establish safety measures if CNS changes occur (side rails, accompany patient). Arrange for regular follow-up, including liver and renal function tests, to evaluate effects. |
TEACHING POINTS
(1) Take these drugs with food and at bedtime; therapy may continue for 4–6 weeks or longer. (2) Take antacids exactly as prescribed; be careful of the time. (3) Inform your health care provider about your cigarette smoking habits. (4) Cigarette smoking decreases the effectiveness of these drugs. (5) Have regular medical follow-up while on this drug to evaluate your response. (6) Report sore throat, fever, unusual bruising or bleeding, tarry stools, confusion, hallucinations, dizziness, muscle or joint pain.DOSING
See, Table (3) recommended oral dosing of H2 antagonist for patients with normal renal function. See cimetidine, famotidine, nizatidine and ranitidine for prescribing information (from priscriber's digital reference [PDR]). Ranitidine (Zantac) withdrawn from market in 2020.
| Table (3). Recommended oral dosing of H2 antagonist for patients with normal renal function | |||
|---|---|---|---|
| Medication | Maintenance, duodenal ulcer | Active ulcer | GERD/erosive esophagitis |
| Cimetidine (Tagamet) | 400 mg HS | 800 mg HS (can divide BID for duodenal ulcer) up to 1600 mg HS (duodenal) or 300 mg QID (gastric) | 1600 mg divided BID or QID |
| Famotidine (Antodine) | 20 mg HS | 40 mg HS (can divide BID for duodenal ulcer) | 20 mg BID (GERD); 20 or 40 mg BID (erosive esophagitis) |
| Nizatidine (Nizatect) | 150 mg HS | 300 mg HS (duodenal ulcers) or divided BID (duodenal or gastric ulcers) | 150 mg BID |
| Ranitidine (Zantac) | 150 mg HS | 300 mg HS (duodenal ulcer) or 150 mg BID (duodenal or gastric ulcer) | 150 mg BID (GERD); 150 mg QID (erosive esophagitis) |
| Abbreviations: BID=twice daily; CrCl=creatinine clearance; GERD=gastroesophageal reflux disease; HS=at bedtime; QID=four times daily | |||
REFERENCES
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Lexicomp, www.lexicomp.com
Nugent, C.C. and Terrell, J.M. (2019). H2 Blockers. [online] Nih.gov. Available at: https://www.ncbi.nlm.nih.gov/books/NBK525994
UpToDate, www.uptodate.com