CIMETIDINE HYDROCHLORIDE IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER
Clinical safety rating
safeNo significant drug interactions Can cause hypernatremia and fluid overload.
Competitive antagonist of histamine at H2 receptors on gastric parietal cells, reducing gastric acid secretion (basal and stimulated) by inhibiting cAMP production.
| Metabolism | Metabolized primarily in the liver via CYP450 enzymes, including CYP1A2, CYP2C19, CYP2D6, and CYP3A4; undergoes sulfoxidation and N-demethylation. |
| Excretion | Renal (75% as unchanged drug via glomerular filtration and tubular secretion); hepatic metabolism (25%); fecal (<10%). |
| Half-life | 2-3 hours in normal renal function, prolonged to >8 hours in severe renal impairment (CrCl <20 mL/min). |
| Protein binding | 13-25% bound to plasma proteins (albumin and alpha-1-acid glycoprotein). |
| Volume of Distribution | 1-2 L/kg, indicating extensive distribution into tissues, including liver, kidney, and gastric mucosa. |
| Bioavailability | Oral: 60-70% (first-pass metabolism); IM: 100% bioequivalent to IV. |
| Onset of Action | IV: within minutes; IM: ~15-30 minutes; oral: ~45-60 minutes. |
| Duration of Action | IV/IM: 4-6 hours (dose-dependent); oral: 4-6 hours (single dose), up to 12 hours with repeated dosing due to accumulation. |
| Molecular Weight | 252.34 |
300 mg intravenously every 6-8 hours or as continuous IV infusion at 37.5-50 mg/hour. Maximum 2400 mg/day.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 10-50 mL/min: 300 mg every 12 hours. CrCl <10 mL/min: 300 mg every 24 hours. |
| Liver impairment | No specific adjustment recommended. In severe hepatic impairment, reduce dose or prolong interval due to increased half-life; use with caution. |
| Pediatric use | Neonates: 5-10 mg/kg/day IV divided every 8-12 hours. Children: 20-40 mg/kg/day IV divided every 6 hours, max 800 mg/day. |
| Geriatric use | Reduce dose or prolong interval due to age-related renal impairment; consider creatinine clearance and adjust accordingly. |
| 1st trimester | Limited human data; animal studies show no teratogenicity, but avoid unless clearly needed. |
| 2nd trimester | Limited human data; appears safe based on available evidence, but use caution. |
| 3rd trimester | Avoid near term due to risk of neonatal tachycardia, CNS depression, and potential H2 receptor blockade in the fetus. |
Clinical note
No significant drug interactions Can cause hypernatremia and fluid overload.
| FDA category | Animal |
| Placental transfer | Crosses the placenta; fetal plasma concentrations reach 0.5–1.0 times maternal levels. |
| Breastfeeding | Cimetidine is excreted into breast milk in concentrations similar to maternal plasma. Infant exposure is low but may cause gastric pH changes and H2 blockade. Monitor infant for irritability or GI effects. Use lowest effective dose. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Cimetidine crosses the placenta. First trimester: No increased risk of major malformations in human studies, but animal studies show fetal effects at high doses. Second and third trimesters: Risk of transient neonatal hepatic dysfunction and possible androgen anti-androgen effects; use only if clearly needed. |
| Fetal Monitoring | Monitor maternal liver function tests and renal function periodically. Assess for signs of cimetidine toxicity (confusion, gynecomastia). Fetal surveillance with ultrasound for growth and well-being if used chronically during second/third trimesters. |
| Fertility Effects | In males, cimetidine may cause reversible gynecomastia, reduced sperm count, and impaired fertility due to anti-androgenic effects. In females, no significant fertility impairment reported, but prolactin elevation may occur. |
■ FDA Black Box Warning
No FDA boxed warning for cimetidine hydrochloride.
| Common Effects | fluid replacement |
| Serious Effects |
Hypersensitivity to cimetidine or any componentConcomitant use with theophylline, warfarin, phenytoin, or other drugs with narrow therapeutic index metabolized via CYP450 (due to significant CYP inhibition)
| Precautions | May cause confusion and delirium, especially in elderly or renally impaired patients; dose adjustment required for renal impairment., Potential for drug interactions due to inhibition of CYP450 enzymes; monitor for interactions with warfarin, theophylline, phenytoin, lidocaine, and others., Avoid rapid intravenous administration to prevent cardiac arrhythmias (bradycardia, hypotension)., Reversible gynecomastia and impotence may occur with prolonged use., Neutropenia and thrombocytopenia reported rarely. |
| Food/Dietary | Avoid alcohol, caffeine, and spicy foods as they may exacerbate gastric irritation. Cimetidine can increase caffeine levels; limit caffeine intake. No significant food-drug interactions, but a high-protein meal may delay absorption when given orally, though IV route bypasses this. |
| Clinical Pearls | Cimetidine is a potent inhibitor of CYP450 enzymes, notably CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. Monitor for drug interactions, especially with warfarin, theophylline, phenytoin, and lidocaine. Adjust doses of these drugs when co-administered. Cimetidine can cause confusion in elderly patients, particularly with high doses or renal impairment. Administer IV slowly over at least 20 minutes to avoid hypotension and cardiac arrhythmias. In renal impairment (CrCl <30 mL/min), reduce dose to 300 mg q12h. For acid suppression, IV route is reserved for when oral therapy is not feasible. |
| Patient Advice | Do not stop taking this medication abruptly without consulting your doctor. · Report any signs of confusion, especially if you are elderly or have kidney problems. · Avoid smoking, as it can increase stomach acid and reduce drug effectiveness. · Notify your doctor if you are taking blood thinners (e.g., warfarin), asthma medications (e.g., theophylline), or seizure medications (e.g., phenytoin). · This medication may cause dizziness or drowsiness; avoid driving until you know how it affects you. · Do not take over-the-counter pain relievers like ibuprofen or aspirin unless approved by your doctor, as they can worsen stomach issues. |
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