TAGAMET HB
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TAGAMET HB (TAGAMET HB).
Competitive antagonist at histamine H2 receptors, inhibiting gastric acid secretion by blocking the action of histamine on parietal cells in the stomach.
| Metabolism | Primarily hepatic via CYP1A2, CYP2C19, CYP2D6, and CYP3A4; also renal excretion of unchanged drug. |
| Excretion | Renal (70% unchanged via glomerular filtration and tubular secretion), fecal (less than 10%), biliary (minor). |
| Half-life | 2–3 hours (normal renal function), prolonged to 5–6 hours in moderate renal impairment, up to 20 hours in severe impairment; requires dose adjustment in CrCl <30 mL/min. |
| Protein binding | 20–25% (primarily to albumin). |
| Volume of Distribution | 0.8–1.4 L/kg (increased in renal failure, indicating potential accumulation in tissues). |
| Bioavailability | Oral: 60–70% (reduced by antacids; food slightly increases absorption). |
| Onset of Action | Oral: 45–60 minutes (peak effect at 1–2 hours). |
| Duration of Action | 4–6 hours (acid suppression); up to 8 hours for 12-hour control of heartburn. |
200-400 mg orally twice daily or 800 mg orally at bedtime.
| Dosage form | TABLET |
| Renal impairment | GFR 10-50 mL/min: reduce dose by 50% or increase interval to 12 hours. GFR <10 mL/min: reduce dose by 75% or increase interval to 18-24 hours. |
| Liver impairment | No specific Child-Pugh based adjustments required; use with caution in severe impairment. |
| Pediatric use | Children <16 years: not recommended. Children ≥16 years: same as adult dosing. |
| Geriatric use | Consider reduced dosing due to age-related renal impairment; monitor for confusion. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for TAGAMET HB (TAGAMET HB).
| Breastfeeding | Cimetidine is excreted into human breast milk with a milk-to-plasma ratio of approximately 4.6 to 12. Concentrations in milk are higher than maternal plasma. Peak milk levels occur 2-3 hours after a dose. The potential for gastric acid suppression, CNS effects, or inhibition of drug metabolism in the nursing infant exists. Caution is advised; the American Academy of Pediatrics considers cimetidine to be usually compatible with breastfeeding but recommend monitoring the infant for adverse effects. |
| Teratogenic Risk | Cimetidine crosses the placenta. In the first trimester, limited human data do not show an increased risk of major congenital malformations. In the second and third trimesters, no teratogenic effects have been reported, but cimetidine can cause transient neonatal liver enzyme elevation and may theoretically suppress fetal gastric acid secretion. Risk cannot be excluded; use only if clearly needed. |
■ FDA Black Box Warning
No FDA boxed warning for TAGAMET HB.
| Serious Effects |
Hypersensitivity to cimetidine or any component of the formulation.
| Precautions | Avoid use in patients with difficulty swallowing, or if symptoms persist for more than 2 weeks. May cause confusion, especially in elderly or renally impaired patients. Potential for drug interactions due to CYP450 inhibition. |
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| Fetal Monitoring | Monitor liver function tests (LFTs) and renal function during pregnancy. In neonates exposed near term, observe for potential adverse effects such as bradycardia, hypotension, or CNS depression. No specific fetal monitoring required beyond standard prenatal care. |
| Fertility Effects | Cimetidine has antiandrogenic effects; in males, it can cause gynecomastia, impotence, and decreased sperm count. In females, it may cause menstrual irregularities and galactorrhea. These effects are reversible upon discontinuation. The impact on human fertility is not fully characterized but potential for impairment exists. |