CIMETIDINE

4g. Dosage should be reduced in patients with impaired renal function.

Adults:

The usual dosage is 400mg twice a day with breakfast and at bedtime. For patients with duodenal or benign gastric ulceration, a single daily dose of 800mg at bedtime is recommended. 6g/day) also with meals and at bedtime. Symptomatic relief is usually rapid.

Treatment should be given initially for at least four weeks (six weeks in benign gastric ulcer) eight weeks in ulcer associated with continued non-steroidal anti- inflammatory agents) even if symptomatic relief has been achieved sooner.

Most ulcers will have healed by that stage, but those which have not, will usually do so after a further course of treatment. Treatment may be continued for longer periods in those patients who may benefit from reduction of gastric secretion and the dosage may be reduced as appropriate to 400mg at bedtime or 400mg in the morning and at bedtime.

In patients with benign peptic ulcer disease, who have responded to the initial course, relapse may be prevented by continued treatment, usually with 400mg at bedtime; 400mg in the morning and at bedtime has also been used. In oesophageal reflux disease, 400mg four times a day, with meals and at bedtime, for four to eight weeks is recommended to heal oesophagitis and relieve associated symptoms.

g. Zollinger-Ellison syndrome) it may be necessary to increase the dose to 400mg four times a day, or in occasional cases further. Antacids can be made available to all patients until symptoms disappear. In the prophylaxis of haemorrhage from stress ulceration in seriously ill patients, doses of 200-400mg can be given every four to six hours by the oral route.

In patients thought to be at risk of acid aspiration syndrome an oral dose of 400mg can be given 90-120 minutes before induction of general anaesthesia or, in obstetric practice, at the start of labour. 4g. Cimetidine syrup should not be used.

The usual precautions to avoid acid aspiration should be taken. g. following substantial resection for Crohn's disease, the usual dosage range can be used according to individual response. To reduce degradation of pancreatic enzyme supplements, 800-1600mg a day may be given according to response in four divided doses, one to one and a half hours before meals.

Adverse experiences with cimetidine are listed below by system organ class and frequency. Frequencies are defined as: very common (>1/10), common (>1/100, <1/10), uncommon (>1/1000, <1/100), rare (>1/10000, <1/1000), very rare (<1/10000).

Blood and Lymphatic system disorders:

Uncommon: Leukopenia Rare: Thrombocytopenia, aplastic anaemia Very rare: Pancytopenia, agranulocytosis Immune system disorders: Very rare: Anaphylaxis. Anaphylaxis is usually cleared on withdrawal of the drug.

Psychiatric disorders Uncommon:

Depression, confusional states, hallucinations. Confusional states, reversible within a few days of withdrawing cimetidine, have been reported, usually in elderly or ill patients.

Nervous system disorders Common:

Headache, dizziness Cardiac disorders Uncommon: Tachycardia Rare: Sinus bradycardia Very rare: Heart block Gastrointestinal disorders Common: Diarrhoea Very rare: Pancreatitis. Pancreatitis cleared on withdrawal of the drug.

Hepatobiliary disorders Uncommon:

Hepatitis Rare: Increased serum transaminase levels. Hepatitis and increased serum transaminase levels cleared on withdrawal of the drug.

Skin and subcutaneous tissue disorders Common:

Skin rashes Very rare: Reversible alopecia and hypersensitivity vasculitis. Hypersensitivity vasculitis usually cleared on withdrawal of the drug.

Musculoskeletal and connective tissue disorders Common:

Myalgia Very rare: Arthralgia Renal and urinary disorders Uncommon: Increases in plasma creatinine Rare: Interstitial nephritis. Interstitial nephritis cleared on withdrawal of the drug. Small increases in plasma creatinine have been reported, unassociated with changes in glomerular filtration rate.

Patients with renal impairment require a lower dose of cimetidine than normal. Dosage should be reduced in patients with impaired renal function according to creatinine clearance. The following dosages are suggested: creatinine clearance of 0- 15ml per minute, 200mg twice a day; 15 to 30ml per minute, 200mg three times a day; 30 to 50ml per minute, 200mg four times a day; over 50ml per minute, normal dosage.

Cimetidine is removed by haemodialysis, but not to any significant extent by peritoneal dialysis. Clinical trials over six years' continuous treatment and more than 15 years' widespread use have not revealed unexpected adverse reactions related to long-term therapy.

Cimetidine can prolong the elimination of drugs metabolised by oxidation in the liver. The safety of prolonged use is not fully established and care should be taken to observe periodically patients given prolonged treatment. Care should be taken that patient with a history of peptic ulcer, particularly the elderly, being treated with cimetidine and a non-steroidal anti-inflammatory agent are observed regularly.

In patients on drug treatment or with illnesses that could cause falls in blood cell count, the possibility that H2-receptor antagonism could potentiate this effect should be borne in mind. Before initiating therapy with this preparation for any gastric ulceration, malignancy should be excluded by endoscopy and biopsy, if possible, because cimetidine tablets can relieve the symptoms and help the superficial healing of the gastric cancer.

The consequences of potential delay in diagnosis should be borne in mind especially in middle aged patients or over, with new or recently changed dyspeptic symptoms. Due to possible interaction with coumarins, close monitoring of prothrombin time is recommended when cimetidine is concurrently used.

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