Cimetidine

cimetidine

(sye met' i deen)

Apo-Cimetidine (CAN), Gen-Cimetidine (CAN), Novo-Cimetine (CAN), Nu-Cimet (CAN), Tagamet, Tagamet HB, Tagamet HB Suspension

Pregnancy Category B

Drug class

Histamine₂ (H₂) antagonist

Therapeutic actions

Inhibits the action of histamine at the histamine₂ (H₂) receptors of the stomach, inhibiting gastric acid secretion and reducing total pepsin output.

Indications

·        Short-term treatment and maintenance of active duodenal ulcer

·        Short-term treatment of benign gastric ulcer

·        Treatment of pathologic hypersecretory conditions (Zollinger-Ellison syndrome)

·        Prophylaxis of stress-induced ulcers and acute upper GI bleeding in critical patients

·        Treatment of erosive GERD

·        OTC use: Relief of symptoms of heartburn, acid indigestion, sour stomach

Contraindications and cautions

·        Contraindicated with allergy to cimetidine.

·        Use cautiously with impaired renal or hepatic function, lactation, pregnancy.

Available forms

Tablets—100, 200, 300, 400, 800 mg; liquid—300 mg/5 mL; injection—150 mg/mL; injection premixed—300 mg/5 mL 0.9% Nacl

Dosages

ADULTS

·        Active duodenal ulcer: 800 mg PO hs or 300 mg PO qid at meals and hs or 400 mg PO bid; continue for 4–6 wk unless healing is demonstrated by endoscopy. For intractable ulcers, 300 mg IM or IV q 6–8 hr.

·        Maintenance therapy for duodenal ulcer: 400 mg PO hs.

·        Active benign gastric ulcer: 300 mg PO qid at meals and hs or 800 mg hs.

·        Pathologic hypersecretory syndrome: 300 mg PO qid at meals and hs, or 300 mg IV or IM q 6 hr. Individualize doses as needed; do not exceed 2,400 mg/day.

·        Erosive GERD: 1,600 mg PO in divided doses bid–qid for 12 wk.

·        Prevention of upper GI bleeding: Continuous IV infusion of 50 mg/hr. Do not treat beyond 7 days.

·        Heartburn, acid indigestion: 200 mg as symptoms occur; up to 4 tablets/24 hr. Do not take maximum dose for > 2 wk.

PEDIATRIC PATIENTS

Not recommended for children < 12 yr.

GERIATRIC PATIENTS OR PATIENTS WITH IMPAIRED RENAL FUNCTION

Accumulation may occur. Use lowest dose possible, 300 mg PO or IV q 12 hr; may be increased to q 8 hr if patient tolerates it and levels are monitored; if creatinine clearance < 30 mL/min, give 25 mg/hr IV for prevention of upper GI bleed.

Pharmacokinetics

Route	Onset	Peak
Oral	Varies	1–1.5 hr
IV, IM	Rapid	1–1.5 hr

Metabolism: Hepatic; T_1/2: 2 hr

Distribution: Crosses placenta; enters breast milk

Excretion: Urine

IV facts

Preparation: For IV injections, dilute in 0.9% sodium chloride injection, 5% or 10% dextrose injection, lactated Ringer's solution, 5% sodium bicarbonate injection to a volume of 20 mL. Solution is stable for 48 hr at room temperature. For IV infusions, dilute 300 mg in at least 50 mL of 5% dextrose injection or one of above listed solutions.

Infusion: Inject by direct injection over not less than 2 min; by infusion, slowly over 15–20 min.

Incompatibilities: Incompatible with aminophylline, barbiturate in IV solutions; pentobarbital sodium and pentobarbital sodium and atropine in the same syringe.

Adverse effects

·        CNS: Dizziness, somnolence, headache, confusion, hallucinations, peripheral neuropathy; symptoms of brain stem dysfunction (dysarthria, ataxia, diplopia)

·        CV: Cardiac arrhythmias, cardiac arrest, hypotension (IV use)

·        GI: Diarrhea

·        Hematologic: Increases in plasma creatinine, serum transaminase

·        Other: Impotence (reversible), gynecomastia (in long-term treatment), rash, vasculitis, pain at IM injection site

Interactions

Drug-drug

·        Increased risk of decreased white blood cell counts with antimetabolites, alkylating agents, other drugs known to cause neutropenia

·        Increased serum levels and risk of toxicity of warfarin-type anticoagulants, phenytoin, beta-adrenergic blocking agents, alcohol, quinidine, lidocaine, theophylline, chloroquine, certain benzodiazepines (alprazolam, chlordiazepoxide, diazepam, flurazepam, triazolam), nifedipine, pentoxifylline, TCAs, procainamide, carbamazepine when taken with cimetidine

Nursing considerations

Assessment

·        History: Allergy to cimetidine, impaired renal or hepatic function, lactation

·        Physical: Skin lesions; orientation, affect; pulse, baseline ECG (continuous with IV use); liver evaluation, abdominal examination, normal output; CBC, LFTs, renal function tests

Interventions

·        Give drug with meals and hs.

·        Decrease doses in renal and liver dysfunction.

·        Administer IM dose undiluted deep into large muscle group.

·        Arrange for regular follow-up, including blood tests to evaluate effects.

Teaching points

·        Take drug with meals and at bedtime; therapy may continue for 4–6 weeks or longer.

·        Take antacids as prescribed, and at recommended times.

·        Inform your health care provider about your cigarette smoking habits. Cigarette smoking decreases the drug's effectiveness.

·        Have regular medical follow-up care to evaluate your response to drug.

·        Report sore throat, fever, unusual bruising or bleeding, tarry stools, confusion, hallucinations, dizziness, muscle or joint pain.

Adverse effects in Italic are most common; those in Bold are life-threatening.