Citidine

Citidine is a histamine H2-receptor antagonist which rapidly inhibits both basal and stimulated gastric secretion of acid and reduces pepsin output.

Citidine is indicated in the treatment of duodenal and benign gastric ulceration, including that associated with non-steroidal anti-inflammatory agents, recurrent and stomal ulceration, oesophageal reflux disease and other conditions where reduction of gastric acid by Citidine has been shown to be beneficial: persistent dyspeptic symptoms with or without ulceration, particularly meal-related upper abdominal pain, including such symptoms associated with non-steroidal anti-inflammatory agents; the prophylaxis of gastrointestinal haemorrhage from stress ulceration in critically ill patients; before general anaesthesia in patients thought to be at risk of acid aspiration (Mendelson's) syndrome, particularly obstetric patients during labour; to reduce malabsorption and fluid loss in the short bowel syndrome; and in pancreatic insufficiency to reduce degradation of enzyme supplements. Citidine is also recommended in the management of the Zollinger-Ellison syndrome.

Citidine is a histamine H₂-receptor antagonist which rapidly inhibits both basal and stimulated gastric secretion of acid and reduces pepsin output.

Citidine is indicated in the treatment of duodenal and benign gastric ulceration, including that associated with non-steroidal anti-inflammatory agents, recurrent and stomal ulceration , oesophageal reflux disease and other conditions where reduction of gastric acid by Citidine has been shown to be beneficial: persistent dyspeptic symptoms with or without ulceration, particularly meal-related upper abdominal pain, including such symptoms associated with non-steroidal anti-inflammatory agents; the prophylaxis of gastrointestinal haemorrhage from stress ulceration in seriously ill patients ; before general anaesthesia in patients thought to be at risk of acid aspiration (Mendelson's Syndrome), particularly obstetric patients during labour ; to reduce malabsorption and fluid loss in the short bowel syndrome; and in pancreatic insufficiency to reduce degradation of enzyme supplements. Citidine is also recommended in the management of the Zollinger-Ellison syndrome.

Cimetidine is indicated in the treatment of duodenal and benign gastric ulceration, including that associated with non-steroidal anti-inflammatory agents, recurrent and stomal ulceration, oesophageal reflux disease and other conditions where reduction of gastric acid by cimetidine has been shown to be beneficial: persistent, dyspeptic symptoms with or without ulceration, particularly meal-related upper abdominal pain, including such symptoms associated with non-steroidal anti-inflammatory agents; the prophylaxis of gastro-intestinal haemorrhage from stress ulceration in seriously ill patients; before general anaesthesia in patients thought to be at risk of acid aspiration (Mendelson's) syndrome, particularly obstetric patients during labour; to reduce malabsorption and fluid loss in the short bowel syndrome; and in pancreatic insufficiency to reduce degradation of enzyme supplements. Cimetidine is also recommended in the management of the Zollinger-Ellison syndrome.

The total daily dose should not normally exceed 2.4g. Dosage should be reduced in patients with impaired renal function.

Adults: The usual dosage is 400mg twice a day with breakfast and at bedtime. Alternatively for patients with duodenal or benign gastric ulceration, a single daily dose of 800mg at bedtime can be used. Other effective regimens are 200mg three times a day with meals and 400mg at bedtime (1.0g/day) and, if inadequate, 400mg four times a day (1.6g/day) also with meals and at bedtime.

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 in those who have responded to treatment, for example 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.

In patients with very high gastric acid secretion (e.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.

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. While such a risk persists, a dose of up to 400mg may be repeated at four hourly intervals as required up to the usual daily maximum of 2.4g. The usual precautions to avoid acid aspiration should be taken.

In the short bowel syndrome, e.g. following substantial resection for Crohn's disease, the usual dosage range (see above) 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.

Elderly: The normal adult dosage may be used unless renal function is markedly impaired.

Children: Experience in children is less than that in adults. In children more than one year old, Citidine 25-30mg/kg body weight per day in divided doses may be administered.

The use of Citidine in infants under one year old is not yet fully evaluated; 20mg/kg body weight per day in divided doses has been used.

Administration: Oral; the tablets should be swallowed with a drink of water.

For oral administration.

The total daily dose by any route should not normally exceed 2.4g. Dosage should be reduced in patients with impaired renal function (see Special warnings and precautions for use)

Adults:

Oral: 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. Other effective regimens are 200mg three times a day with meals and 400mg at bedtime (1.0g/day) and, if inadequate, 400mg four times a day (1.6g/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, 400 mg four times a day, with meals and at bedtime, for four to eight weeks is recommended to heal oesophagitis and relieve associated symptoms. In patients with very high gastric acid secretion (e.g. Zollinger-Ellison syndrome) it may be necessary to increase the dose to 400mg four times a day or in occasional cases further. Since Citidine may not give immediate symptomatic relief, 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. While such a risk persists, a dose of up to 400mg may be repeated (parenterally if appropriate) at four hourly intervals as required up to the usual daily maximum of 2.4g.

Citidine syrup should not be used. The usual precautions to avoid acid aspiration should be taken.

In the short bowel-syndrome e.g. following substantial resection for Crohn's disease, the usual dosage range (see above) 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.

Elderly:

The normal adult dosage may be used unless renal function is markedly impaired.

Children:

Experience in children is less than that in adults. In children more than one year old, Citidine 25-30mg/kg body weight per day in divided doses may be administered by oral route.

The use of Citidine in infants under one year old is not fully evaluated, 20mg/kg body weight per day in divided doses has been used.

For oral administration only.

The total daily dose should not exceed 2.4g. Dosage should be reduced in patients with impaired renal function (see Special warnings and precautions for use)

Adults: For patients with duodenal or benign gastric ulceration, a single daily dose of 800mg at bedtime is recommended. Otherwise the usual dosage is 400mg twice a day with breakfast and at bedtime. Other effective regimens are 200mg three times a day with meals and 400mg at bedtime (1.0g/day) and, if inadequate, 400mg four times a day (1.6g/day) also with meals and at bedtime.

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 in those who have responded to treatment, for example 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.

In patients with very high gastric acid secretion (e.g. Zollinger-Ellison syndrome) it may be necessary to increase the dose to 400mg four times a day, or in occasional cases further. Since cimetidine may not give immediate symptomatic relief, 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.

In the short bowel syndrome, e.g. following substantial resection for Crohn's disease, the usual dosage range (see above) can be used according to individual response.

Treatment should be avoided before general anaesthesia and in management of labour.

To reduce degradation of pancreatic enzyme supplements, 800-1600mg a day may be given according to response in four divided doses, 1- 1½ hours before meals.

Elderly:

The normal adult dosage may be used unless renal function is markedly impaired (See special warnings and precautions for use).

Children:

Experience in children is less than that in adults.

In children more than one year old, cimetidine 25-30mg/kg body weight per day in divided doses may be administered by the oral route.

The use of cimetidine in infants under one year old is not fully evaluated; 20mg/kg body weight per day in divided doses has been used.

Hypersensitivity to Cimetidine.

Hypersensitivity to Citidine or to any other of the tablet ingredients listed.

Hypersensitivity to cimetidine or any of the other ingredients listed.

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 of over six years' continuous treatment and more than 15 years' widespread use have not revealed unexpected adverse reactions related to long-term therapy

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 patients with a history of peptic ulcer, particularly the elderly, being treated with cimetidine and a non-steroidal anti-inflammatory agent are observed regularly.

Before initiating therapy with this preparation for any gastric ulceration, malignancy should be excluded by endoscopy and biopsy, if possible, because Citidine 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.

Co-administration of therapeutic agents with a narrow therapeutic index, such as phenytoin or theophylline, may require dosage adjustment when starting or stopping concomitantly administered cimetidine.

Adults:

Oral: 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. Other effective regimens are 200mg three times a day with meals and 400mg at bedtime (1.0g/day) and, if inadequate, 400mg four times a day (1.6g/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, 400 mg four times a day, with meals and at bedtime, for four to eight weeks is recommended to heal oesophagitis and relieve associated symptoms. In patients with very high gastric acid secretion (e.g. Zollinger-Ellison syndrome) it may be necessary to increase the dose to 400mg four times a day or in occasional cases further. Since Citidine may not give immediate symptomatic relief, 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. While such a risk persists, a dose of up to 400mg may be repeated (parenterally if appropriate) at four hourly intervals as required up to the usual daily maximum of 2.4g.

Citidine syrup should not be used. The usual precautions to avoid acid aspiration should be taken.

In the short bowel-syndrome e.g. following substantial resection for Crohn's disease, the usual dosage range (see above) 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.

Elderly:

The normal adult dosage may be used unless renal function is markedly impaired.

Children:

Experience in children is less than that in adults. In children more than one year old, Citidine 25-30mg/kg body weight per day in divided doses may be administered by oral route.

The use of Citidine in infants under one year old is not fully evaluated, 20mg/kg body weight per day in divided doses has been used.

Hypersensitivity to Citidine or to any other of the tablet ingredients listed.

Dosage should be reduced in patients with impaired renal function according to creatinine clearance. The following doses are suggested : Creatinine clearance of 0 to l5ml 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 50 ml per minute, normal dosage. Citidine 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.

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 patients with a history of peptic ulcer, particularly the elderly, being treated with Citidine and a non-steroidal anti-inflammatory agent are observed regularly.

Before initiating therapy with this preparation for any gastric ulceration, malignancy should be excluded by endoscopy and biopsy, if possible, because Citidine 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 Citidine is concurrently used.

Co-administration of therapeutic agents with a narrow therapeutic index, such as phenytoin or theophylline, may require dosage adjustment when starting or stopping concomitantly administered Citidine.

Lactose: This product contains lactose. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicinal product.

Adults: For patients with duodenal or benign gastric ulceration, a single daily dose of 800mg at bedtime is recommended. Otherwise the usual dosage is 400mg twice a day with breakfast and at bedtime. Other effective regimens are 200mg three times a day with meals and 400mg at bedtime (1.0g/day) and, if inadequate, 400mg four times a day (1.6g/day) also with meals and at bedtime.

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 in those who have responded to treatment, for example 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.

In patients with very high gastric acid secretion (e.g. Zollinger-Ellison syndrome) it may be necessary to increase the dose to 400mg four times a day, or in occasional cases further. Since cimetidine may not give immediate symptomatic relief, 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.

In the short bowel syndrome, e.g. following substantial resection for Crohn's disease, the usual dosage range (see above) can be used according to individual response.

Treatment should be avoided before general anaesthesia and in management of labour.

To reduce degradation of pancreatic enzyme supplements, 800-1600mg a day may be given according to response in four divided doses, 1- 1½ hours before meals.

Elderly:

The normal adult dosage may be used unless renal function is markedly impaired (See special warnings and precautions for use).

Children:

Experience in children is less than that in adults.

In children more than one year old, cimetidine 25-30mg/kg body weight per day in divided doses may be administered by the oral route.

The use of cimetidine in infants under one year old is not fully evaluated; 20mg/kg body weight per day in divided doses has been used.

Hypersensitivity to cimetidine or any of the other ingredients listed.

Dosage should be reduced in patients with impaired renal function according to creatinine clearance. The following dosages are suggested: creatinine clearance of 0 to 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 of over six years' continuous treatment and more than 15 years' widespread use have not revealed unexpected adverse reactions related to long-term therapy. The safety of prolonged use is not, however, fully established and care should be taken to observe periodically patients given prolonged treatment.

Before initiating therapy with this preparation for any gastric ulceration, malignancy should be excluded by endoscopy and biopsy if possible, because cimetidine treatment can mask the symptoms and allow transient healing of gastric cancer. The potential delay in diagnosis should particularly be borne in mind in patients of middle age and over with new or recently changed dyspeptic symptoms.

Care should be taken that patients with a history of peptic ulcer, particularly the elderly, being treated with cimetidine and a non-steroidal anti-inflammatory agent are observed regularly.

Ingredients in the formulation

The product contains sunset yellow E110 which may cause allergic reactions including asthma. Allergy is more common in those people who are allergic to aspirin.

Cimetidine 200mg/5ml Oral Solution contains methyl and propyl hydroxybenzoates (preservatives) which may cause allergic reactions (possibly delayed).

The product also contains liquid maltitol. Patients with rare hereditary problems of fructose intolerance should not take this medicine.

Contained in this product is propylene glycol which may cause alcohol-like symptoms

None known.

None known

Not applicable.

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. The increases do not progress with continued therapy and disappear at the end of therapy.

Reproductive system and breast disorders

Uncommon: Gynaecomastia and reversible impotence. Gynaecomastia is usually reversible upon discontinuation of cimetidine therapy. Reversible impotence has been reported particularly in patients receiving high doses (e.g. in Zollinger-Ellison Syndrome). However, at regular dosage, the incidence is similar to that in the general population.

Very rare: Galactorrhoea

General disorders and administration site conditions

Common: Tiredness

Very rare: Fever. Fever cleared on withdrawal of the drug.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard.

Adverse experiences with Citidine 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 Citidine, 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. The increases do not progress with continued therapy and disappear at the end of therapy.

Reproductive system and breast disorders

Uncommon: Gynaecomastia and reversible impotence. Gynaecomastia is usually reversible upon discontinuation of Citidine therapy. Reversible impotence has been reported particularly in patients receiving high doses (e.g. in Zollinger-Ellison Syndrome). However, at regular dosage, the incidence is similar to that in the general population.

Very rare: Galactorrhoea

General disorders and administration site conditions

Common: Tiredness

Very rare: Fever. Fever cleared on withdrawal of the drug.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard.

Over 56 million patients have been treated with cimetidine world-wide and adverse reactions have been infrequent.

Blood and the lymphatic system disorders

Thrombocytopenia and leucopenia, including agranulocytosis (see Special warnings and precautions for use), reversible on withdrawal of treatment, have been reported rarely; pancytopenia and aplastic anaemia have been reported very rarely.

Immune

In common with other H₂-receptor antagonists, there have been very rare reports of anaphylaxis. Rare cases of hypersensitivity vasculitis have been reported. These usually clear on withdrawal of the drug.

Endocrine Disorders

Gynaecomastia has been reported and is always reversible on discontinuing treatment. There have been rare reports of acute pancreatitis which is reversible on withdrawal of treatment.

Psychiatric Disorders

Reversible confusional states have occurred, usually in elderly or already very ill patients, e.g. those with renal failure.

Hallucination has been reported rarely.

Depression has been reported infrequently.

Cardiac

There are rare reports of sinus bradycardia, tachycardia and heart block which are all reversible on withdrawal of treatment.

Hepato-biliary disorders

Biochemical or biopsy evidence of reversible liver damage has been reported occasionally as have rare cases of hepatitis.

Musculoskeletal, connective tissue and bone disorders

There have been rare reports of myalgia and arthralgia which is reversible on withdrawal of treatment.

Renal and Urinary Disorders

Isolated increases of plasma creatinine have been of no clinical significance.

There have been very rare reports of interstitial nephritis which is reversible on withdrawal.

Reproductive system and breast disorders

Reversible impotence has also been very rarely reported but no causal relationship has been established at usual therapeutic doses.

General Disorders

Diarrhoea, dizziness or rash, usually mild or transient, and tiredness have been reported.

There are rare reports of fever and headache which are reversible on withdrawal of treatment.

Alopecia has been reported but no causal relationship has been established.

Acute overdosage of up to 20g has been reported several times with no significant ill-effects. Induction of vomiting and/or gastric lavage may be employed together with symptomatic and supportive therapy.

Acute overdosage of up to 20 grams has been reported several times with no significant ill effects. Induction of vomiting and/or gastric lavage may be employed together with symptomatic and supportive therapy.

Acute overdosage of up to 20g has been reported several times with no significant ill effects. Induction of vomiting and/or gastric lavage may be employed together with symptomatic and supportive therapy.

Cimetidine, one of the H2 blockers is a reversible, competitive antagonist of the actions of histamine on H2 receptors. It is highly selective in its action and is virtually without effect on H1 receptors or, indeed on receptors for other autacoids or drugs. The most prominent of the effects of histamine that are mediated by H2 receptors is stimulation of gastric acid secretion and they interfere remarkably little with physiological functions other than gastric secretion.

Cimetidine inhibits gastric acid secretion elicited by histamine or other H2 agonists in a dose-dependent, competitive manner; the degree of inhibition parallels the plasma concentration of the drug over a wide range. In addition, the H2 blockers inhibit gastric secretion elicited by muscarinic agonists or by gastrin, although this effect is not always complete.

This breadth of inhibitory effect is not due to non-specific actions at the receptors for these other secretagogues. Rather, this effect, which is non-competitive and indirect, appears to indicate either that these two classes of secretagogues utilise histamine as the final common mediator or, more probably, that ongoing histaminergic stimulation of the parietal cell is important for amplification of the stimuli provided by ACh or gastrin when they act on their own discrete receptors. Receptors for all three secretagogues are present on the parietal cell. The ability of H2 blockers to suppress responses to all three physiological secretagogues makes them potent inhibitors of all phases of gastric acid secretion. Thus these drugs will inhibit basal (fasting) secretion and nocturnal secretion and also that stimulated by food, sham feeding, fundic distension, insulin, or caffeine. The H2 blockers reduce both the volume of gastric juice secreted and its hydrogen ion concentration. Output of pepsin, which is secreted by the chief cells of the gastric glands (mainly under cholinergic control), generally falls in parallel with the reduction in volume of the gastric juice. Secretion of intrinsic factor is also reduced, but it is normally secreted in great excess, and absorption of vitamin B12 is usually adequate even during long-term therapy with H2 blockers.

Concentrations of gastrin in plasma are not significantly altered under fasting conditions; however, the normal prandial elevation of gastrin concentration may be augmented, apparently as a consequence of a reduction in the negative feedback that is normally provided by acid.

Pharmacotherapeutic Group: H2-receptor Antagonists, ATC code: A02BA01

Citidine is a histamine H2-receptor antagonist which rapidly inhibits both basal and stimulated gastric secretion of acid and reduces pepsin output. It is a reversible, competitive antagonist, and is used as an anti-ulcer drug. It is highly selective in its action, is virtually without effect on H1 receptors, or indeed on receptors for other autocoids or drugs. Despite the widespread distribution of H2-receptors in the body, Citidine interferes remarkably little with physiological functions other than gastric secretion, implying that the extragastric H2-receptors are of minor physiological importance.

However, H2 blockers like Citidine do inhibit those effects on the cardiovascular and other systems that are elicited through the corresponding receptors by exogenous or endogenous histamine.

Citidine inhibits gastric acid secretion elicited by histamine or other H2 agonists in a dose-dependent, competitive manner; the degree of inhibition parallels the plasma concentration of the drug over a wide range. In addition, the H2 blockers inhibit gastric secretion elicited by muscarinic agonists or by gastrin, although this effect is not always complete.

This breadth of inhibitory effect is not due to non-specific actions at the receptors for these other secretagogues. Rather, this effect, which is non-competitive and indirect, appears to indicate either that these two classes of secretagogues utilise histamine as the final common mediator or, more probably, that ongoing histaminergic stimulation of the parietal cell is important for amplification of the stimuli provided by ACh or gastrin when they act on their own discrete receptors. Receptors for all three secretagogues are present on the parietal cell. The ability of H2 blockers to suppress responses to all three physiological secretagogues makes them potent inhibitors of all phases of gastric acid secretion. Thus these drugs will inhibit basal (fasting) secretion and nocturnal secretion and also that stimulated by food, sham feeding, fundic distension, insulin, or caffeine. The H2 blockers reduce both the volume of gastric juice secreted and its hydrogen ion concentration. Output of pepsin, which is secreted by the chief cells of the gastric glands (mainly under cholinergic control), generally falls in parallel with the reduction in volume of the gastric juice. Secretion of intrinsic factor is also reduced, but it is normally secreted in great excess, and absorption of vitamin B12 is usually adequate even during long-term therapy with H2 blockers.

Concentrations of gastrin in plasma are not significantly altered under fasting conditions; however, the normal prandial elevation of gastrin concentration may be augmented, apparently as a consequence of a reduction in the negative feedback that is normally provided by acid.

Cimetidine is a histamine H₂-receptor antagonist; it is highly selective in its action and is virtually without effect on H₁ receptors or, indeed on receptors for other autacoids or drugs. The most prominent of the effects of histamine that are mediated by H₂ receptors is stimulation of gastric acid secretion and they interfere remarkably little with physiological functions other than gastric secretion.

Cimetidine inhibits gastric acid secretion elicited by histamine or other H₂ agonists in a dose-dependent, competitive manner; the degree of inhibition parallels the plasma concentration of the drug over a wide range. In addition, the H₂ blockers inhibit gastric secretion elicited by muscarinic agonists or by gastrin, although this effect is not always complete.

This breadth of inhibitory effect is not due to the non-specific actions at the receptors for these other secretagogues. Rather, this effect, which is non-competitive and indirect, appears to indicate either that these two classes of secretagogues utilise histamine as the final common mediator or, more probably, that ongoing histaminergic stimulation of the parietal cell is important for amplification of the stimuli provided by ACh or gastrin when they act on their own discrete receptors. Receptors for all three secretagogues are present on the parietal cell. The ability of H₂ blockers to suppress responses to all three physiological secretagogues makes them potent inhibitors of all phases of gastric acid secretion. Thus these drugs will inhibit basal (fasting) secretion and nocturnal secretion and also that stimulated by food, sham feeding, fundic distension, insulin or caffeine. The H₂ blockers reduce both the volume of gastric juice secreted and its hydrogen ion concentration. Output of pepsin, which is secreted by the chief cells of the gastric glands (mainly under cholinergic control), generally falls in parallel with the reduction in volume of the gastric juice. Secretion of intrinsic factor is also reduced, but it is normally secreted in great excess, and absorption of vitamin B12 is usually adequate even during long-term therapy with H₂ blockers.

Concentrations of gastrin in plasma are not significantly altered under fasting conditions; however, the normal prandial elevation of gastric concentration may be augmented, apparently as a consequence of a reduction in the negative feedback that is normally provided by acid

Cimetidine is rapidly and virtually completely absorbed. Absorption is little impaired by food or by antacids. Peak concentrations in plasma are attained in about 1 to 2 hours. Hepatic first-pass metabolism results in bioavailabilities of about 60% for cimetidine. The elimination half-life is about 2 to 3 hours. Cimetidine is eliminated primarily by the kidneys, and 60% or more may appear in the urine unchanged; much of the rest is oxidation products. Small amounts are recovered in the stool.

Citidine is rapidly and virtually completely absorbed from the gastro-intestinal tract. Absorption is little impaired by food or by antacids. Peak plasma concentrations are obtained about an hour after administration on an empty stomach, and about 2 hours after administration with food. The duration of action is reported to be prolonged by administration with food. Peak concentrations in plasma are attained in about 1 to 2 hours. Hepatic first-pass metabolism results in bioavailabilities of about 60% for Citidine. The elimination half-life is about 2-3 hours. Citidine is eliminated primarily by the kidneys, and 60% or more may appear in the urine unchanged; much of the rest is oxidation products. Small amounts are recovered in the stools.

Citidine crosses the placental barrier and is excreted in milk. It does not readily cross the blood-brain barrier.

Cimetidine is rapidly and virtually completely absorbed. Absorption is little impaired by food or by antacids. Peak concentrations in plasma are attained in about 1 to 2 hours. Hepatic first-pass metabolism results in bioavailabilities of about 60% for cimetidine. The elimination half -life is about 2 -3 hours. The effects on acid secretion are of longer duration. Cimetidine is eliminated primarily by the kidneys, and 60% or more may appear in the urine unchanged; much of the rest is oxidation products. Small amounts are recovered in the stool.

Not available.

There are no preclinical data of relevance to the prescriber which are additional to that already included in other sections of the SPC.

Relevant information for the prescriber is provided elsewhere in the Summary of Product Characteristics.

Not applicable.

Nothing stated.

Not applicable