Cimetidine

Oral
Benign gastric and duodenal ulceration
Adult: 800 mg daily at bedtime or 400 mg bid for 4 weeks for duodenal ulcer, 6 weeks for gastric ulcer, and 8 weeks for NSAID-associated ulcer; may increase dose to 400 mg 4 times daily as necessary. Maintenance: 400 mg daily at bedtime or bid. Dosage recommendation may vary among countries or individual products. Refer to specific product guidelines.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily

Oral
Prophylaxis of gastrointestinal haemorrhage from stress ulceration
Adult: In critically ill patients: 200-400 mg 4-6 hourly via the oral or nasogastric route.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily.

Oral
Prophylaxis of acid aspiration during general anaesthesia
Adult: As tab: 400 mg given 90-120 minutes before induction of anaesthesia. In obstetric patients: 400 mg at the start of labour, may increase dose up to 400 mg 4 hourly if necessary. Max: 2,400 mg daily.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily.

Oral
Gastro-oesophageal reflux disease
Adult: 400 mg 4 times daily or 800 mg bid for 4-12 weeks.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily.

Oral
Hypersecretory conditions
Adult: 300 or 400 mg 4 times daily, may increase dose if necessary. Max: 2,400 mg daily. Doses are individualised according to patient's needs.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily

Oral
Zollinger-Ellison syndrome
Adult: 300 or 400 mg 4 times daily, may increase dose if necessary. Max: 2,400 mg daily. Doses are individualised according to patient's needs.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily

Oral
Pancreatic insufficiency
Adult: 800-1,600 mg daily in 4 divided doses, 60-90 minutes before meals.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily.

Oral
Short bowel syndrome
Adult: Initially, 400 mg bid, adjust dose according to response.
Renal impairment:

CrCl (ml/min)	Dosage Recommendation
0-15	200 mg bid.
16-30	200 mg tid.
31-50	200 mg 4 times daily.

Should be taken with food.

Patient with immunocompromised states, history of peptic ulcer. Possibility of gastric malignancy should be excluded prior to therapy. Do not use the syrup for the prophylaxis of acid aspiration. Renal and hepatic impairment. Elderly. Pregnancy and lactation. Monitoring Parameters Monitor gastric pH, CBC, renal function (to adjust dose), occult blood with GI bleeding; prothrombin time (in concomitant use with anticoagulants). Assess for signs of confusion.

Significant: Vitamin B¹² deficiency (prolonged use). Rarely, confusion; strongyloidiasis hyperinfection (immunocompromised patient). Gastrointestinal disorders: Diarrhoea. General disorders and administration site conditions: Fatigue. Musculoskeletal and connective tissue disorders: Myalgia. Nervous system disorders: Headache, dizziness, drowsiness. Reproductive system and breast disorders: Gynaecomastia. Skin and subcutaneous tissue disorders: Rashes.

Symptoms: CNS symptoms (e.g. unresponsiveness). Management: Supportive and symptomatic therapy. Administer activated charcoal if ingestion is within 1 hour. Induce vomiting or perform gastric lavage.

May inhibit certain CYP450 enzymes and increase the plasma concentration of warfarin-type coumarin anticoagulants (e.g. warfarin), TCAs (e.g. amitriptyline), class I antiarrhythmics (e.g. lidocaine), Ca channel blockers (e.g. nifedipine, diltiazem), oral sulfonylureas (e.g. glipizide), phenytoin, theophylline, metoprolol. Increased plasma concentration of procainamide, metformin, ciclosporin, and tacrolimus. Increased absorption of atazanavir. Decreased absorption of ketoconazole, itraconazole, posaconazole. May enhance the myelosuppressive effect of carmustine, fluorouracil, epirubicin.

Cimetidine competitively inhibits histamine at the H² receptor of the gastric parietal cells, thereby causing a decrease in gastric acid secretion, gastric volume and hydrogen ion concentration.
Onset: 1 hour.
Duration: 4-5 hours (80% reduction in gastric acid secretion after a 300 mg dose).
Absorption: Rapidly absorbed from the gastrointestinal tract. Food delays the rate and slightly decreases extent of absorption. Bioavailability: Approx 60-70%. Time to peak plasma concentration: 1-2 hours.
Distribution: Widely distributed. Crosses the placenta and enters breast milk. Volume of distribution: 1-1.5 L/kg. Plasma protein binding: Approx 20%.
Metabolism: Partially metabolised in the liver to sulfoxide and hydroxymethylcimetidine.
Excretion: Via urine (oral: approx 50%, IV: 75%) as unchanged drug; faeces. Elimination half-life: Approx 2 hours.

Oral: Store between 20-25°C.

Antacids, Antireflux Agents & Antiulcerants

A02BA01 - cimetidine ; Belongs to the class of H2-receptor antagonists. Used in the treatment of peptic ulcer and gastro-oesophageal reflux disease (GERD).