TAGAMET
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TAGAMET (TAGAMET).
Competitive antagonist of histamine H2 receptors on gastric parietal cells, inhibiting gastric acid secretion. Also reduces pepsin and intrinsic factor secretion.
| Metabolism | Primarily hepatic via CYP1A2, CYP2C19, CYP2D6, and CYP3A4. Also undergoes renal tubular secretion. About 40-50% of the drug is excreted unchanged in urine. |
| Excretion | Renal: 50-70% unchanged; hepatic metabolism: ~30%; biliary/fecal: minor (<5%) |
| Half-life | Terminal elimination half-life: 2-3 hours (normal renal function); prolonged to 5-10 hours in moderate renal impairment (CrCl <30 mL/min) and up to 20-30 hours in anuria |
| Protein binding | 15-20% (primarily to albumin; minimal binding to alpha-1-acid glycoprotein) |
| Volume of Distribution | 1-2 L/kg; indicates extensive tissue distribution (e.g., kidney, liver, lungs, skin) with low CNS penetration due to polarity |
| Bioavailability | Oral: 60-70% (variable with first-pass metabolism; food delays absorption but does not affect extent); IM: 90-100% |
| Onset of Action | Oral: 30-60 minutes (histamine H2 blockade); IV: within 5 minutes; IM: 15-30 minutes |
| Duration of Action | Oral: 4-6 hours (acid suppression); IV/IM: 4-5 hours; dose adjustment needed for renal impairment to avoid accumulation |
400 mg orally twice daily or 800 mg orally at bedtime for duodenal ulcer; 300 mg IV/IM every 6-8 hours.
| Dosage form | SOLUTION |
| Renal impairment | CrCl 20-40 mL/min: 300 mg every 8 hours; CrCl <20 mL/min: 300 mg every 12 hours. |
| Liver impairment | No specific Child-Pugh based adjustment; use with caution in severe impairment. |
| Pediatric use | 20-40 mg/kg/day orally in divided doses every 6 hours; maximum 800 mg/day. |
| Geriatric use | Reduce dose if renal function impaired; monitor for confusion. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for TAGAMET (TAGAMET).
| Breastfeeding | Cimetidine is excreted into breast milk; M/P ratio approximately 5:1. Peak milk levels occur 1-2 hours after dose. Use with caution; consider alternatives, especially when nursing a preterm or jaundiced infant due to potential for hepatic enzyme inhibition and CNS effects. |
| Teratogenic Risk | Cimetidine crosses the placenta. First trimester: Limited human data, animal studies show no teratogenicity; risk cannot be excluded (FDA Pregnancy Category B changed to use-specific labeling). Second/Third trimester: No evidence of fetal harm in human studies; avoid high doses due to potential anti-androgenic effects in male fetuses (in animal studies, not confirmed in humans). |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to cimetidine or any component of the formulation.
| Precautions | May cause confusional states, especially in elderly or severely ill patients. Avoid rapid IV administration (may cause hypotension or cardiac arrhythmias). May inhibit cytochrome P450 metabolism of other drugs (e.g., warfarin, theophylline, phenytoin). Risk of ventricular arrhythmias and QT prolongation. Use with caution in patients with renal or hepatic impairment. May cause vitamin B12 deficiency with long-term use. Reversible impotence and gynecomastia with high doses. Mask symptoms of gastric malignancy. |
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| Fetal Monitoring | Monitor maternal liver function tests, renal function, and complete blood count periodically. Monitor infant for potential adverse effects if used during lactation: diarrhea, drowsiness, or irritability. |
| Fertility Effects | Cimetidine has anti-androgenic properties in males: reported gynecomastia, reduced sperm count, and impotence with chronic high doses. In females, limited evidence of menstrual irregularities. Effects are reversible upon discontinuation. |