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All about: Cimetidine

Big Image Pronouncation: (sigh-MET-ih-deen)
Class: Histamine H 2 antagonist

Trade Names:
Cimetidine
- Tablets 300 mg
- Tablets 400 mg
- Tablets 800 mg
- Liquid 300 mg (as hydrochloride) per 5 mL
- Injection 150 mg (as hydrochloride) per mL

Trade Names:
Cimetidine in 0.9% Sodium Chloride
- Injection, premixed 6 mg (as hydrochloride) per mL

Trade Names:
Tagamet HB
- Tablets 200 mg

Apo-Cimetidine (Canada)
Gen-Cimetidine (Canada)
Novo-Cimetine (Canada)
Nu-Cimet (Canada)

Mechanism of Action

Pharmacology

Reversibly and competitively blocks histamine at H 2 receptors, particularly those in gastric parietal cells, leading to inhibition of gastric acid secretion.

Pharmacokinetics

Absorption

Oral

Rapidly absorbed. T max is 45 to 90 min. 60% to 70% bioavailable.

Distribution

13% to 25% protein bound. Vd is 0.8 to 1.2 L/kg. Crosses the placenta and is excreted in breast milk.

Metabolism

Following oral administration, cimetidine is extensively metabolized with the sulfoxide being the major metabolite.

Elimination

The t ½ is about 2 h.

Oral

48% is excreted unchanged in the urine.

IV/IM

About 75% is excreted unchanged in the urine.

Special Populations

Renal Function Impairment

Drug accumulation may occur in those with severe renal failure. Dosage adjustment may be necessary.

Indications and Usage

Management of duodenal ulcer; treatment of gastroesophageal reflux disease (GERD), including erosive esophagitis; therapy for benign gastric ulcer; treatment of pathologic hypersecretory conditions; prevention of upper GI bleeding.

Unlabeled Uses

Prevention of aspiration pneumonia and stress ulcers; herpes virus infection; chronic idiopathic urticaria; anaphylaxis (relieves dermatologic symptoms only); dyspepsia; used before anesthesia to prevent aspiration pneumonitis; treatment of hyperparathyroidism and control of secondary hyperparathyroidism in chronic hemodialysis patient; treatment of chronic viral warts in children.

Contraindications

Hypersensitivity to cimetidine or other H 2 antagonists.

Dosage and Administration

Duodenal Ulcer (Active)
Adults

PO 800 mg at bedtime for 4 to 6 wk.

Alternate regimens

PO 300 mg 4 times daily with meals and at bedtime or 400 mg twice daily.

Maintenance Therapy

PO 400 mg at bedtime.

Active Benign Gastric Ulcer
Adults

PO 800 mg at bedtime.

GERD
Adults

PO 1600 mg daily in divided doses (800 mg or 400 mg) for 12 wk, although some patients may require chronic therapy.

Pathologic Hypersecretory Conditions
Adults

PO 300 mg 4 times daily w/meals and at bedtime. If needed, 300 mg doses may be given more often (max, 2400 mg/day).

Prevention of Upper GI Bleeding
Adults

Continuous IV infusion of 50 mg/h. For hospitalized patients with pathologic hypersecretory conditions or intractable ulcers, or patients unable to take PO medication.

Usual dose

IM/IV 300 mg every 6 h to 8 h (max 2400 mg/day).

General Advice

  • Dilute IV dose (300 mg) in 0.9% normal saline, D5W, or other compatible solution to a total of 20 mL. Inject slowly over at least 5 min.
  • For intermittent IV infusion, dilute 300 mg in at least 50 mL of compatible solution; infuse over at least 20 min (continuous IV infusion is usually preceded by a loading dose).
  • Do not add drugs or additives to mixture. Stop other inline drugs while administering, and flush lines before and after administration.
  • Product may be added to standard TPN solutions.

Storage/Stability

Store premixed products at room temperature. Discard any unused mixed solutions after 48 h. Store oral doseform between 15° to 30°C (59° to 86°F).

Drug Interactions

Antacids, anticholinergics, metoclopramide

May decrease absorption of cimetidine.

Benzodiazepines, caffeine, calcium channel blockers, carbamazepine, chloroquine, labetalol, lidocaine, metoprolol, metronidazole, moricizine, pentoxifylline, phenytoin, propranolol, quinidine, quinine, sulfonylureas, theophyllines, triamterene, tricyclic antidepressants, warfarin

Cimetidine may reduce metabolism and increase serum concentration and pharmacologic/toxic effects of these drugs.

Carmustine

Bone marrow toxicity may be enhanced.

Cigarette smoking

Reversed cimetidine's effects on suppression of nocturnal gastric secretion.

Ferrous salts, indomethacin, fluconazole, ketoconazole, tetracyclines

Cimetidine may decrease absorption of these drugs.

Hydantoins

Hydantoin levels may increase.

Narcotic analgesics

Toxic effects (eg, respiratory depression) may be increased.

Procainamide

Levels of procainamide and its active metabolite may increase.

Tocainide

Cimetidine may decrease the pharmacologic effects of tocainide.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Cardiac arrhythmias.

CNS

Headache; somnolence; fatigue; dizziness; confusional states; hallucinations.

Dermatologic

Exfoliative dermatitis or erythroderma; alopecia; rash; erythema multiforme; epidermal necrolysis.

GI

Diarrhea.

Genitourinary

Impotence; loss of libido.

Respiratory

Bronchospasm.

Miscellaneous

Gynecomastia; hypersensitivity reactions; transient pain at injection site; reversible exacerbation of joint symptoms with pre-existing arthritis, including gouty arthritis.

Precautions

Pregnancy

Category B .

Lactation

Excreted in breast milk.

Children

Safety and efficacy not established.

Elderly

May have reduced renal function; decreased Cl may occur.

Hypersensitivity

Rare cases of anaphylaxis have occurred as well as rare episodes of hypersensitivity.

Renal Function

Decreased Cl may occur; reduced dosage may be needed.

Hepatic Function

Use caution; decreased Cl may occur.

Gastric malignancy

Symptomatic relief with cimetidine does not preclude gastric malignancy.

Antiandrogenic effect

Gynecomastia may occur, especially in patients treated for pathologic hypersecretory states.

Rapid IV administration

Has been followed by rare instances of cardiac arrhythmias and hypotension.

Reversible CNS effects

Mental confusion, agitation, psychosis, depression, anxiety, hallucinations, and disorientation have occurred, predominantly in severely ill patients. Advanced age and pre-existing liver or renal disease appear to be contributing factors.

Patient Information

  • Counsel patients to stop smoking, since smoking reduces ulcer-healing efficacy of cimetidine.
  • Instruct patients to keep appointments for laboratory testing and health care provider follow-up.
  • Instruct patients to report to health care provider immediately any black tarry stools, coffee-ground emesis, abdominal pain or confusion.
  • Counsel patients regarding need for lifestyle changes, stress reduction programs and dietary modifications (eg, avoid spicy foods and alcohol).

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