ZANTAC
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ZANTAC (ZANTAC).
Competitive antagonist of histamine at H2 receptors on gastric parietal cells, reducing basal and stimulated gastric acid secretion.
| Metabolism | Metabolized by the liver via N-oxidation, S-oxidation, and N-demethylation; cytochrome P450 enzymes (CYP1A2, CYP2D6, and CYP3A4) may be involved; minimal first-pass metabolism. |
| Excretion | Renal: 30% unchanged (tubular secretion); hepatic metabolism to N-oxide, S-oxide, and desmethyl ranitidine; biliary/fecal: minimal. |
| Half-life | 2.5-3 hours (normal renal function); prolonged to 4-5 hours in elderly and up to 20 hours in severe renal impairment (CrCl < 30 mL/min). |
| Protein binding | 15% bound primarily to albumin. |
| Volume of Distribution | 1.4 L/kg (large, indicating extensive tissue distribution). |
| Bioavailability | Oral: 50-60% (first-pass hepatic metabolism); IM: 90-100%. |
| Onset of Action | Oral: 1 hour; IM: 15 minutes; IV: 5 minutes. |
| Duration of Action | Oral: 9-12 hours (acid suppression); IM/IV: 4-6 hours (dose-dependent). |
| Molecular Weight | 350.9 |
150 mg orally twice daily or 50 mg intravenously every 6-8 hours. Alternatively, 300 mg orally at bedtime.
| Dosage form | SYRUP |
| Renal impairment | For CrCl 15-50 mL/min: 150 mg orally every 24 hours or 50 mg intravenously every 12-24 hours. For CrCl <15 mL/min: 150 mg orally every 24 hours or 50 mg intravenously every 24-48 hours. |
| Liver impairment | No specific dose adjustment recommended for Child-Pugh A or B. For Child-Pugh C: reduce dose by 50% or extend dosing interval, e.g., 150 mg orally every 24 hours. |
| Pediatric use | 1-2 mg/kg/dose orally twice daily (max 300 mg/day) or 0.5-1 mg/kg/dose intravenously every 6-8 hours (max 50 mg/dose). |
| Geriatric use | Reduce dose to 150 mg orally once daily or extend interval due to age-related decline in renal function; monitor creatinine clearance. |
| 1st trimester | Limited human data; animal studies not indicative of fetal harm. Generally considered safe if clinically indicated. |
| 2nd trimester | No known teratogenic risk; use if benefit outweighs risk. |
| 3rd trimester | Safe; no increased risk of adverse outcomes. |
Clinical note
Comprehensive clinical and safety monograph for ZANTAC (ZANTAC).
| Placental transfer | Ranitidine crosses the placenta with cord blood concentrations similar to maternal plasma. |
| Breastfeeding | Ranitidine is excreted into breast milk in low concentrations (approximately 2-4% of maternal dose). Not expected to cause adverse effects in nursing infants. Consider using alternative agents with more safety data if prolonged use. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to ranitidine or any component of the formulationAcute porphyria
| Precautions | Risk of gastric malignancy (e.g., gastric cancer) due to symptomatic response masking underlying disease; risk of community-acquired pneumonia, particularly in elderly or immunocompromised; may increase serum creatinine levels; hepatotoxicity and pancreatitis reported; acute porphyria risk; reversible confusional states (especially in elderly, renal/hepatic impairment); adjust dose in renal impairment (creatinine clearance <50 mL/min); drug interactions with warfarin, procainamide, and triazolam. |
| Food/Dietary | No significant food interactions. Avoid excessive caffeine or alcohol intake as they may exacerbate symptoms. Take with or without food; food slightly delays absorption but does not affect total bioavailability. |
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| L2 (Safer) |
| Teratogenic Risk | ZANTAC (ranitidine) is classified as FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. In human pregnancy, data do not indicate increased risk of major malformations, but limited data are available for all trimesters. First trimester: No documented teratogenic effects, but caution advised due to limited data. Second and third trimesters: Safety supported for GERD treatment; no specific fetal risks identified. |
| Fetal Monitoring | No specific fetal monitoring required for standard use. Monitor for maternal side effects such as headache, dizziness, or gastrointestinal disturbances. In high-dose or long-term use, consider monitoring renal function. No routine fetal monitoring indicated. |
| Fertility Effects | No adverse effects on fertility reported in animal studies or human data. ZANTAC does not alter reproductive parameters. No evidence of impaired female fertility or male reproductive function. |
| Clinical Pearls | Ranitidine (Zantac) was withdrawn from the US market in 2020 due to NDMA impurities. Reserve for use only if formulary-restricted; consider famotidine as safer alternative. Dose adjustment required for CrCl <50 mL/min: reduce to 150 mg daily. May interfere with warfarin metabolism via CYP450; monitor INR. Rapid IV administration can cause bradycardia; infuse over 2 minutes or longer. |
| Patient Advice | Do not take this medication if you have a history of porphyria or acute intermittent porphyria. · Take ranitidine exactly as prescribed; do not take more than the maximum recommended dose. · Inform your doctor if you have kidney disease, as dose adjustment may be necessary. · Avoid alcohol and smoking, as they may worsen stomach acid conditions and reduce drug efficacy. · If you are pregnant, planning to become pregnant, or breastfeeding, discuss with your doctor. · Contact your doctor immediately if you experience chest pain, irregular heartbeat, or shortness of breath. · Do not use ranitidine for heartburn that has lasted for more than 2 weeks without medical advice. |