ZANTAC 75
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ZANTAC 75 (ZANTAC 75).
Competitive inhibitor of histamine at H2 receptors on gastric parietal cells, reducing basal and stimulated gastric acid secretion.
| Metabolism | Hepatic via CYP450 (minor), primarily N-oxidation and N-demethylation; renal excretion of unchanged drug and metabolites. |
| Excretion | Renal (60-70% as unchanged drug), hepatic metabolism (30-40% as N-oxide, S-oxide, and desmethyl metabolites), with fecal excretion accounting for <10%. |
| Half-life | Terminal elimination half-life is 2.5-3 hours. In elderly patients or those with renal impairment (CrCl <50 mL/min), half-life may extend to 4-6 hours, requiring dose adjustment. |
| Protein binding | Approximately 15% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | 1.0-1.5 L/kg (indicates extensive extravascular distribution, with tissue concentrations exceeding plasma). |
| Bioavailability | Oral: 50-60% (due to first-pass metabolism; bioavailability increases in hepatic impairment). |
| Onset of Action | Oral: 30-60 minutes (peak effect at 1-2 hours for gastric acid suppression). |
| Duration of Action | 5-12 hours (single dose suppresses basal and stimulated gastric acid secretion for at least 12 hours at therapeutic doses). |
75 mg orally once daily or 150 mg orally once daily for heartburn; up to 300 mg/day for duodenal ulcer or GERD.
| Dosage form | TABLET |
| Renal impairment | CrCl 30-50 mL/min: 50% of normal dose or increased dosing interval; CrCl <30 mL/min: 150 mg every 24 hours or 75 mg every 12 hours. |
| Liver impairment | No dose adjustment required for mild to moderate hepatic impairment; severe impairment (Child-Pugh C): reduce dose by 50% or increase dosing interval. |
| Pediatric use | For GERD in children ≥1 month: 2-4 mg/kg orally twice daily; maximum 300 mg/day. For duodenal ulcer in children ≥1 month: 2-4 mg/kg orally twice daily; maximum 300 mg/day. For heartburn in children ≥12 years: 75 mg orally once or twice daily. |
| Geriatric use | May require dose reduction due to age-related renal impairment; consider starting at 75 mg orally once daily and titrate based on renal function and tolerability. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ZANTAC 75 (ZANTAC 75).
| Breastfeeding | Ranitidine is excreted in human breast milk with M/P ratio approximately 2.5:1. Peak milk concentration occurs 4-6 hours after maternal dose. Use with caution; consider timing of breastfeeding to minimize infant exposure. |
| Teratogenic Risk | FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; limited human data show no increased risk of major malformations. Caution in third trimester due to potential for histamine H2-receptor antagonist effects on neonatal gastric pH. |
| Fetal Monitoring |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to ranitidine or other H2 receptor antagonists; acute porphyria (relative contraindication).
| Precautions | May mask symptoms of gastric malignancy; adjust dose in renal impairment; risk of community-acquired pneumonia; rare hepatitis; confusion in elderly; drug interactions (e.g., warfarin, procainamide). |
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| No specific maternal-fetal monitoring required beyond routine pregnancy care. Monitor for maternal adverse effects (headache, dizziness, gastrointestinal disturbances). |
| Fertility Effects | No significant effects on fertility in animal studies. Human data on fertility impact are lacking. |