Cimetidine

Cimetidine
Cimetidine

Table of Contents

Cimetidine

Overview

Cimetidine is an H2 receptor antagonist. It’s a competitive, reversible inhibitor of the action of histamine at the histamine H2-receptors, including receptors on the gastric cells. Cimetidine does not lower serum Ca++ in hypercalcemic states. Also, it is not an anticholinergic agent.

Cimetidine when given as an intravenous bolus, stimulates the secretion of Prolactin, but other pituitary hormones are not affected. This increase in Prolactin levels is due to high serum drug level that is achieved with an IV bolus. A similar effect is also observed in Ranitidine but not in nizatidine. When Cimetidine is taken orally, no effect on Prolactin levels is observed. This is because relatively low drug concentrations are achieved in the serum with an oral dose.

Uses

  • Gastric Ulcer
    • Treatment (Short Term) of active benign gastric ulcer.
  • Duodenal Ulcer
    • Treatment (Short Term) of active duodenal ulcers.
    • Maintenance of healing and reduction in recurrence of duodenal ulcers.
  • GERD
    • Short term treatment of erosive esophagitis in patients with Gastro Esophageal Reflux Disease.
    • Treatment of the symptoms of GERD
  • Upper GI bleeding
    • Prevention of upper GI bleeding resulting from stress-related mucosal damage in critically ill patients.
    • Treatment of Gastro-Intestinal bleeding secondary to esophagitis, hepatic failure, duodenal or gastric ulcer when hemorrhage is not caused by major blood vessel erosion.
  • Short term self-medication for heartburn (pyrosis), Acid indigestion (hyperchlorhydria) or sour stomach.
  • Allergic conditions and urticarias.

Pharmacological Classification

H2 Blocker

Brand names

  • Tagamet (USA)
  • Cimetiget (India)
  • Tymidin (India)

Dosage Forms

Tablets and Injectables

Mechanism of action

Cimetidine blocks the histamine effects by binding to an H2 receptor located on the basolateral membrane of the gastric parietal cell. This competitive inhibition results in reduced gastric acid secretion and a reduction in gastric volume and acidity.

Dosage & Administration

  • Though the patient may take an antacid to treat pain, simultaneous use of antacids is not recommended as antacids may interfere with the absorption of cimetidine.

Adult Dose

Duodenal Ulcers

  • For short term treatment of active duodenal ulcers: 800 to 1600 mg orally once a day at bedtime for up to 6 weeks
  • No safety data available for the treatment of uncomplicated duodenal ulcer beyond 8 weeks
  • Treatment should be continued for 4 to 6 weeks unless healing has been demonstrated by endoscopic examination.

For prophylaxis of Duodenal Ulcers

  • Maintenance therapy for patients with duodenal ulcers at reduced dosage after healing of active ulcers: 400 mg orally once a day at bedtime for up to 5 years.

Gastric Ulcer

  • Short term treatment of active benign gastric ulcer:
    • 800 mg orally once a day at bedtime or
    • 300 mg orally 4 times a day (with meals and at bedtime)
  • No safety data available for the treatment of uncomplicated duodenal ulcer beyond 8 weeks
  • Due to a lower potential for drug interactions and patient convenience, once a day regimen is preferred
  • In order to assure rapid progress of complete healing, the patient should be monitored during the treatment

Pathological hypersecretory conditions like Zollinger-Ellison syndrome

  • 300 mg orally 4 times a day with meals and at bedtime; not exceeding the maximum dose of 2400mg/day
  • No safety data available for the treatment of uncomplicated duodenal ulcer beyond 8 weeks

Erosive esophagitis

  • 800 mg orally twice a day or 400 mg orally 4 times a day
  • Treatment is indicated to control symptoms and heal lesions
  • Data for treatment beyond 12 weeks is not available

Gastroesophageal Reflux Disease

  • 800 mg orally twice a day or 400 mg orally 4 times a day
  • Treatment is indicated to control symptoms and heal lesions
  • Data for treatment beyond 12 weeks is not available

Dyspepsia

  • For symptomatic relief: 200 mg orally with a glass of water
  • For prevention of symptoms: 200 mg orally with a glass of water (30 minutes before having any food that causes heartburn)
  • Maximum dose fo 2 tablets/day for up to 14 days

Pediatric Dose

Pediatric dose for the treatment of Duodenal Ulcer

  • Use of cimetidine in pediatric patients is not recommended unless the anticipated benefits outweigh the potential risk.
  • The manufacturer states “In very limited experience, doses of 20 to 40 mg/kg per day have been used.”

Pediatric dose for the prophylaxis of duodenal ulcer

  • Use of cimetidine in pediatric patients is not recommended unless the anticipated benefits outweigh the potential risk.
  • The manufacturer states “In very limited experience, doses of 20 to 40 mg/kg per day have been used.”

Pediatric dose for erosive esophagitis

  • Use of cimetidine in pediatric patients is not recommended unless the anticipated benefits outweigh the potential risk.
  • The manufacturer states “In very limited experience, doses of 20 to 40 mg/kg per day have been used.”

Pediatric dose for Gastric Ulcer

  • Use of cimetidine in pediatric patients is not recommended unless the anticipated benefits outweigh the potential risk.
  • The manufacturer states “In very limited experience, doses of 20 to 40 mg/kg per day have been used.”

Pediatric dose for Gastroesophageal reflux disease

  • Use of cimetidine in pediatric patients is not recommended unless the anticipated benefits outweigh the potential risk.
  • In infants, children, and adolescents (1 to 15 years):
    • The manufacturer states “In very limited experience, doses of 20 to 40 mg/kg per day have been used.”
  • In premature and term neonates:
    • 10 mg/kg per day orally in divided dose every 6 to 12 hours.

Pediatric dose for Stress Ulcer Prophylaxis

  • Use of cimetidine in pediatric patients is not recommended unless the anticipated benefits outweigh the potential risk.
  • In infants, children, and adolescents (1 to 15 years):
    • The manufacturer states “In very limited experience, doses of 20 to 40 mg/kg per day have been used.”
  • In premature and term neonates:
    • 10 mg/kg per day orally in divided dose every 6 to 12 hours.

Pediatric dose for Zollinger Ellison Syndrome

  • Use of cimetidine in pediatric patients is not recommended unless the anticipated benefits outweigh the potential risk.
  • The manufacturer states “In very limited experience, doses of 20 to 40 mg/kg per day have been used.”

Pediatric dose for Dyspepsia

  • For symptomatic relief: 200 mg orally with a glass of water
  • For prevention of symptoms: 200 mg orally with a glass of water (30 minutes before having any food that causes heartburn)
  • Maximum dose fo 2 tablets/day for up to 14 days

Hepatic Dose Adjustment

  • Dose adjustments may be required in patients with impaired hepatic function.
  • No specific guidelines are available.
  • Caution should be exercised while administering or prescribing cimetidine to a patient with impaired hepatic function.

Renal Dose Adjustment

  • For patients with severe renal dysfunction(CrCl less than 30mL/min): 300 mg orally every 12 hours.
    • If the condition of the patient requires, the frequency of dosing can be increased to every 8 hours or even further.
  • For patients with severe renal failure: Lowest frequency of dosing required for an adequate patient response should be used.
  • For patients on hemodialysis: Dose should be given at the end of the hemodialysis session.
  • Data are not available for dosing in patients on peritoneal dialysis.

Other Dose Adjustment

  • In patients who are heavy smokers and ulcers larger than 1 cm are confirmed by an endoscopy: 1600 mg orally once a day at bedtime for 4 weeks or 800 mg orally once a day for 8 weeks.

Overdose

  • Cimetidine is removed to some extent by hemodialysis.
  • Side effects observed or experienced in an event of overdose are similar to the ones experienced under normal dosage conditions.
  • When overdosage occurs, the usual measures to remove unabsorbed material from the gastrointestinal tract, clinical monitoring, and supportive therapy should be employed.

Side Effects

Body as a whole

  • Headache
  • Fever (Rare Occurrence)
  • Anaphylaxis (Rare Occurrence)

Gastrointestinal side effects

  • Diarrhoea
  • Constipation
  • Vomitting
  • Nausea
  • Flatulance
  • Hepatitis (Rare Occurrence)

Nervous system side effects

  • Dizziness
  • Drowsiness
  • Tiredness
  • Depression (Uncommon Occurrence)

Dermatological side effects

  • Rash

Musculoskeletal side effects

  • Musculoskeletal pain

Urogenital side effects

  • Interstitial nephritis (Rare Occurrence)

Metabolic/Nutritional side effects

  • Pancreatitis (Rare Occurrence)

Cardiovascular side effects

  • Hypersensitivity vasculitis (Rare Occurrence)
  • Sinus bradycardia (Rare Occurrence)
  • Tachycardia (Rare Occurrence)
  • Heart block (Rare Occurrence)

Haematologic/Lymphatic side effects

  • Leucopenia (Rare Occurrence)
  • Thrombocytopenia (Rare Occurrence)
  • Pancytopenia (Rare Occurrence)
  • Aplastic anemia (Rare Occurrence)
  • A benefit/risk assessment should be made when concomitant use of cimetidine with drugs known to cause bone marrow depression is contemplated.

Endocrine side effects

  • Gynaecomastia (Uncommon Occurrence)

Immunologic side effects

  • Strongyloidiasis Infection (Very rare occurrence)

Respiratory side effects

  • Pneumonia (Frequency not reported)
    • In a large epidemiological study, it was indicated that patients taking H2 receptor antagonists were at an increased risk of developing pneumonia in comparison to patients who stopped the treatment. However, a causal relationship between the H2 receptor antagonist and pneumonia has not been established.

Fertility

  • Cimetidine can increase the amount of Prolactin hormone, thereby decreasing the levels of the testosterone hormone.
  • This can result in decreased libido, decreased sexual functioning and lowered sperm count, which all leads to male infertility.

Warnings & Precautions

  • Safety and efficacy of cimetidine is not established in children younger than 12 years of age.
  • Tablets should be swallowed with water.
  • In patients with gastric ulceration, malignancy should be excluded by endoscopy and biopsy prior to treatment in such patients.
  • Cimetidine may cause drowsiness or dizziness. Hence after taking cimetidine, driving a vehicle or operating heavy machinery should be avoided.
  • Patient taking cimetidine should be advised that the symptomatic response to treatment does not prelude the presence of gastric malignancy.
  • Patient on a low salt diet should be aware that each tablet of Tagamet (800 mg effervescent tablet) contains 433 mg of sodium.
  • The Tagamet 800 mg effervescent tablets should be used with caution in patients with phenylketonuria. Tagamet 800 mg effervescent tablets contain 25 mg aspartame per tablet.
  • Tobacco smoking
    • Tobacco smoking is one of the risk factors for the development of Peptic Ulcer Disease. This may also impair ulcer healing and increase the risk of ulcer recurrence. Patients should avoid smoking while taking cimetidine.
  • Neonates
    • Cimetidine oral solution contains 2.8% alcohol, which should be considered in the dosing of infants and young children. Multidose vials of cimetidine injection contain benzyl alcohol as a preservative and it should be avoided in neonates. There have been reports of fatal ‘gasping syndrome’ in neonates of less than 1 month of age after the administration of parenteral solutions containing the preservative benzyl alcohol at dosages of more than 99 mg/kg/day. The minimum amount of benzyl alcohol to cause toxicity is unknown. Therefore, use preservative-free cimetidine injection formulations in neonates.

Contraindications

  • Hypersensitivity to cimetidine or any of the ingredient of the formulation.

Pregnancy

Category B, which means that Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.

Nursing Mothers

  • Cimetidine is secreted in mother’s milk.
  • Caution should be exercised when Cimetidine is administered to a nursing mother.

Interactions

Drug-drug interactions

  • Duloxetine: Cimetidine may increase the blood levels and effects of Duloxetine.
  • Hydrocodone: Cimetidine may increase the blood levels of hydrocodone. This may lead to an increase in side effects such as drowsiness, dizziness, lightheadedness, difficulty in concentrating and impairment in thinking and judgment.
  • Atorvastatin: Concomitant use of cimetidine with atorvastatin may increase the blood levels of atorvastatin. This increases the risk of liver damage and a rare but serious condition called rhabdomyolysis in which there is a breakdown of skeletal muscle tissue.
  • Loperamide: Cimetidine may significantly increase the blood levels of loperamide. This can lead to complications like irregular heart rhythm and cardiac arrest which are serious and potentially fatal.
  • Methadone: Cimetidine increases the blood levels and effects of methadone. Dose adjustment in 1 or both of these drugs may be required.
  • Oxycodone: Cimetidine may increase the blood levels of Oxycodone. This may lead to an increase in side effects such as drowsiness, dizziness, lightheadedness, difficulty in concentrating and impairment in thinking and judgment.
  • Theophylline: Concomitant use of theophylline and cimetidine may increase the blood levels and effects of theophylline. Consult your doctor or pharmacist if you experience insomnia, tremors, nausea, vomiting, restlessness, seizures, and uneven heartbeat.
  • Tramadol: Cimetidine increases the blood levels and effects of tramadol. Dose adjustment in 1 or both of these drugs may be required.
  • Warfarin: Concomitant use of cimetidine with warfarin may cause you to bleed more easily. If you are taking these 2 medications together, you may need dose adjustment in addition to the determination of prothrombin time or international normalized ratio.
  • Acalabrutinib: Since cimetidine reduces the level of acidity in the stomach, it may interfere with the absorption of Acalabrutinib and reduce its effectiveness.
  • Acebutolol: Concomitant use of acebutolol and cimetidine can increase the effects of acebutolol. This can lower blood pressure and slows the heart rate.
  • Benzhydrocodone: Concomitant use of cimetidine with Benzhydrocodone may lead to increased concentrations of Benzhydrocodone and hence prolonged or increased adverse effect and may cause potentially fatal respiratory depression.
  • Dextromethorphan: Cimetidine increases the blood levels and effects of Dextromethorphan. Dose adjustment in 1 or both of these drugs may be required.
  • Codeine: Cimetidine may reduce the effectiveness of codeine. Dose adjustment in 1 or both of these drugs may be required.
    • Codeine is metabolized by CYP2D6 hepatic isoenzyme.
  • Dihydrocodeine: Cimetidine may increase the blood levels of dihydrocodeine. If you are taking these medicines together, you may need dose adjustment in 1 or both of these drugs.
    • This is because dihydrocodeine is metabolized primarily by CYP2D6 and CYP3A4. Inhibitors of CYP3A4 may increase dihydrocodeine related adverse effects while inhibitors of CYP2D6 may reduce efficacy. Cimetidine is a weak inhibitor of CYP3A4 and CYP2D6.
  • Pentazocine: Cimetidine may increase the blood levels and effects of Pentazocine. Dose adjustment of 1 or both the drugs may be required.
  • Propoxyphene: Cimetidine may increase the blood levels and effects of Propoxyphene. Dose adjustment of 1 or both the drugs may be required.
  • Acetohexamide: Concomitant use of acetohexamide and cimetidine can increase the effects of cimetidine, which may cause your blood sugar to get too low.
    • This may be due to an increase in absorption or decreased clearance of acetohexamide. This is also applicable to other sulfonylureas.
  • Adefovir: Coadministration of Adefovir and Cimetidine may increase the side effect of either or both these drugs.
    • Adefovir is eliminated by a combination of glomerular filtration and active tubular secretion. Cimetidine competes with Adefovir for active tubular secretion, thereby decreasing the elimination of Adefovir and hence increased concentrations of cimetidine or Adefovir.
  • Alfentanil: Cimetidine may increase the blood levels of alfentanil, leading to an increased risk and/or severity of side effects such as excessive sedation, respiratory depression, low blood pressure, and irregular heart rhythm.
  • Alogliptin: Cimetidine may increase the effect of Alogliptin.  Increased Alogliptin exposure due to the use of cimetidine may lead to gastrointestinal complaints, altered glycemic control, and a potential for an increased risk for lactic acidosis. 
    • This is because Cimetidine inhibits renal elimination of Alogliptin.
  • Metformin: Cimetidine may increase the effect of Metformin. Increased Metformin exposure due to the use of cimetidine may lead to gastrointestinal complaints, altered glycemic control, and a potential for an increased risk for lactic acidosis. 
    • This is because Cimetidine inhibits renal elimination of Metformin.
  • Alosetron: Cimetidine may increase the blood levels of alosetron, leading to an increased risk of potentially serious gastrointestinal side effects.
  • Alprazolam: Cimetidine may increase the effects or duration of activity of alprazolam.
    • Contact your doctor if you experience difficulty in concentrating, drowsiness, confusion and dizziness.
  • Altretamine: Cimetidine may increase the effects of altretamine. Contact your doctor if you experience:
    • Allergic reactions: Swelling of the lips, tongue, face or hives, difficulty in breathing, the closing of the throat.
    • Decreased bone marrow function and increased blood problems: easy bruising or bleeding, extreme fatigue, black, bloody or tarry stools, fever or chills.
    • Neurologic problems: Mood disorders, altered consciousness, weakness, dizziness, vertigo.
  • Aminophylline: Cimetidine may increase the effects of aminophylline.
    • Nausea, vomiting, tremors, insomnia, restlessness, uneven heartbeats and seizures are the side effects observed.
  • Amiodarone: Cimetidine increases the effects of amiodarone.
    • Weakness, slow heart rate, feeling light-headed and fainting are the side effects observed.
  • Amitryptiline: Cimetidine increases the effects of amitryptiline.
    • Dry mouth, blurry vision, irregular or fast heartbeat, constipation, urinary retention, or extreme drowsiness are some of the side effects.
    • This can also cause dizziness or feeling like you might pass out, especially when getting up from a sitting or lying position.
  • Amoxapine: Cimetidine increases the effects of amoxapine.
    • Dry mouth, blurry vision, irregular or fast heartbeat, constipation, urinary retention, or extreme drowsiness are some of the side effects.
    • This can also cause dizziness or feeling like you might pass out, especially when getting up from a sitting or lying position.
  • Anagrelide: Cimetidine increases the blood levels and hence the effects of anagrelide.
    • Nausea, vomiting, diarrhea, bleeding, swelling, shortness of breath, low blood pressure, palpitations, congestive heart failure, and irregular heart rhythm are the side effects observed.
  • Anisindione: Concomitant use of cimetidine with anisindione may cause you to bleed more easily. If you are taking these 2 medications together, you may need dose adjustment in addition to the determination of prothrombin time or international normalized ratio.
  • Aprepitant: Concomitant use of cimetidine may increase the blood levels and effects of aprepitant.
    • Nausea, constipation, diarrhea, or loss of appetite are some of the side effects observed.
  • Aripiprazole: Cimetidine may increase the blood levels of aripiprazole.
    • Drowsiness, seizure, Parkinson-like symptoms, abnormal muscle movements, and low blood pressure are some of the side effects observed.
  • Asenapine: Cimetidine may increase the blood levels of asenapine.
  • Astemizole: This drug is withdrawn from most of the markets. It has a rare but fatal side effect QTc interval prolongation and related arrhythmias due to hERG channel blockade. If you are taking astemizole, stop taking it.
  • Atazanavir: cimetidine may reduce the effectiveness of atazanavir.
  • Atenolol: Cimetidine may increase the effects of atenolol. This can slow the heart rate and lower blood pressure.
  • Bacampicillin: Cimetidine decreases the acid in the stomach, which can decrease the absorption and blood levels of bacampicillin, making it less effective when taken with cimetidine.
  • Bendamustine: The blood levels of bendamustine may be increased in some patients when it is taken along with cimetidine. This can affect bone marrow functioning resulting in a lower number of different types of blood cells.
  • Betaxolol: Cimetidine increases the blood concentrations and hence the effects of betaxolol resulting in low blood pressure and slow heart rate. This can cause headache, dizziness or a feeling that you may pass out.
  • Bisoprolol: Cimetidine increases the blood concentrations and hence the effects of Bisoprolol resulting in low blood pressure and slow heart rate. This can cause headache, dizziness or a feeling that you may pass out.
  • Bosentan: Cimetidine may increase the blood levels of bosentan which can increase the risk and/or severity of the side effects such as fatigue, nausea, headache, vomiting, fluid retention, low blood pressure, anemia and liver problems.
  • Bosutinib: Cimetidine decreases the acid in the stomach, which can decrease the absorption and blood levels of bosutinib, making it less effective when taken with cimetidine.
  • Brexpiprazole: Cimetidine can increase the blood concentrations of Brexpiprazole, which can increase the side effects such as drowsiness, seizures, Parkinson’s – like syndrome, abnormal muscle movements, and low blood pressure. Dose adjustment of one or both the drugs may be required.
  • Brigatinib: Cimetidine and Brigatinib may have an additive effect in the lowering of the heart rate. The common symptoms of this are may experience headache, dizziness, lightheadedness, fainting, and/or changes in pulse or heartbeat.
  • Buprenorphine: Cimetidine can increase the blood levels of Buprenorphine leading to increased side effects such as drowsiness, dizziness, lightheadedness, difficulty concentrating, and impairment in thinking and judgment. In severe cases, low blood pressure, respiratory distress, fainting, coma, or even death may occur. Dose adjustment of one or both the drugs may be required.
  • Butorphanol: Cimetidine increases the blood levels of Butorphanol leading to dizziness, fainting, confusion, excessive drowsiness, slow heart rate, shallow or difficulty in breathing, and/or shortness of breath. Contact your doctor if you experience any of the side effects mentioned above. Dose adjustment of one or both the medicines may be necessary.
  • Carbamazepine:
  • Cariprazine: Concomitant use of cimetidine and carbamazepine may increase the effects of carbamazepine. Shallow breathing, fast heartbeat, nausea, vomiting, urinating less or not at all, muscle twitches, restlessness, tremors, slurred speech, staggering walk, and feeling light-headed or fainting are some of the side effects observed. Contact your doctor if you experience any of the above-mentioned side effects since this may require an adjustment in the dose of one or both the medicines.
  • Cariprazine: Concomitant use of cimetidine and cariprazine may increase the blood levels of cariprazine. This may increase the risk of side effects such as drowsiness, Parkinson-like symptoms, abnormal muscle movements, seizures, high blood sugar, diabetes, high cholesterol, weight gain, low white blood cell count, difficulty swallowing, and heat-related disorders such as heat intolerance or heat stroke. A person taking these two medicines together is more likely to experience side effects associated with low blood pressure such as dizziness, lightheadedness, headache, flushing, fainting, and heart palpitations.
  • Carmustine: Concomitant use of carmustine and cimetidine may increase the suppressive effect of carmustine on the bone marrow function, resulting in low numbers of different types of blood cells.
  • Carteolol: Cimetidine increases the blood concentrations and hence the effects of Carteolol resulting in low blood pressure and slow heart rate. This can cause headache, dizziness or a feeling that you may pass out.
  • Carvedilol: Cimetidine increases the blood concentrations and hence the effects of carvedilol resulting in low blood pressure and slow heart rate. This can cause headache, dizziness or a feeling that you may pass out.
  • Cefditoren: Cimetidine decreases the acid in the stomach, which can decrease the absorption and blood levels of cefditoren, making it less effective when taken with cimetidine.
  • Cefpodoxime: Cimetidine decreases the acid in the stomach, which can decrease the absorption and blood levels of Cefpodoxime, making it less effective when taken with cimetidine.
  • Cefuroxime: Cimetidine decreases the acid in the stomach, which can decrease the absorption and blood levels of cefuroxime, making it less effective when taken with cimetidine.
  • Celecoxib: Concomitant use of cimetidine and celecoxib can increase the effects of celecoxib. This can cause nausea, vomiting, abdominal pain, tarry stools, lethargy or drowsiness.
  • Ceritinib: Cimetidine decreases the acid in the stomach, which can decrease the absorption and blood levels of Ceritinib, making it less effective when taken with cimetidine.
  • Cerivastatin: Concomitant use of cimetidine with Cerivastatin may increase the blood levels of Cerivastatin. This increases the risk of liver damage and a rare but serious condition called rhabdomyolysis in which there is a breakdown of skeletal muscle tissue. In some cases, this may lead to kidney damage and even death.
  • Cevimeline: Concomitant use of cimetidine and cevimeline may increase the blood levels of cevimeline. The occurrence of side effects such as nausea, vomiting, diarrhea, sweating, drooling, increased urination, blurred vision, confusion, tremor, heart palpitations, and irregular heartbeat is increased.
  • Chlordiazepoxide: Cimetidine can increase or prolong the effects of Chlordiazepoxide. Dizziness, drowsiness, confusion, and difficulty concentrating are some of the side effects observed.
  • Chloroquine: Cimetidine may increase the blood levels of chloroquine leading to an increased risk of side effects such as headache, nausea, vomiting, diarrhea, abdominal cramps, loss of appetite, vision impairment, ringing in the ears, hearing loss, anxiety, confusion, depression, and seizures.
  • Chlorpropamide: Concomitant use of cimetidine with chlorpropamide may increase the effects of chlorpropamide, which may cause your blood sugar to get too low.
  • Cilostazol: Cimetidine may increase the blood levels of Cilostazol. The side effects observed are Dizziness, lightheadedness, fainting, nausea, diarrhea. Bleeding, heart palpitations, or irregular heartbeat. Dose adjustment of one or both the drugs may be necessary.
  • Cisapride: This is no longer available in the market in the US. DO NOT TAKE Cisapride. Cisapride increases the risk of cardiac arrhythmias.
  • Citalopram: Cimetidine may increase the blood levels of Citalopram which may increase the risk of certain side effects such as an irregular heart rhythm that may be serious or life-threatening.
  • Clobazam: Concomitant use of Cimetidine and clobazam may lead to increased blood concentrations and hence increased effects of Clobazam. This may increase the risk and/or severity of side effects such as drowsiness, tiredness, drooling, constipation, and breathing difficulties. 
  • Clomipramine: Concomitant use of Cimetidine and Clomipramine increases the blood levels of Clomipramine. Side effects such as blurred vision, irregular or fast heartbeat, dry mouth, constipation, urinary retention, and extreme drowsiness may be observed.
  • Clonazepam: Concomitant use of Cimetidine and Clonazepam may increase or prolong the effects of Clonazepam. Drowsiness, dizziness, confusion, and difficulty in breathing are the side effects observed.
  • Clopidogrel: Concomitant use of Cimetidine and Clopidogrel may decrease the effects of Clopidogrel. This may make Clopidogrel less effective in preventing heart attacks and stroke.
  • Clorazepate: Concomitant use of Cimetidine and Clorazepate increases or prolongs the effects of Clorazepate. Dizziness, drowsiness, confusion, and difficulty in concentrating are some of the side effects observed.
  • Clozapine: Cimetidine can increase blood levels or add to the side effects of Clozapine. Shallow breathing, shortness of breath, weak pulse, muscle weakness, headache, excessive drowsiness, and slurred speech are some of the side effects observed.
  • Cobimetinib: Cimetidine increases the blood levels of Cobimetinib. This can lead to increased side effects such as nausea, vomiting, mouth sores, heart problems, bleeding, eye problems, rash, photosensitivity, liver injury and muscle damage.
  • Codeine: Cimetidine may reduce the effectiveness of codeine. Contact your doctor if you experience inadequate relief of the symptoms.
  • Colchicine: The effects of Colchicine may be increased when taken along with Cimetidine. Nausea, vomiting, diarrhea, fever, abdominal pain, seizures, muscle aches or weakness are some of the side effects.
  • Dabigatran: Dabigatran, when taken with Cimetidine, may worsen the stomach ulcers and increases the risk of bleeding.
    • Red or black stools, vomiting blood or blood clots, dizziness, lightheadedness, and abdominal pain are the signs and symptoms of bleeding. Consult your doctor if you experience any of these symptoms.
  • Dabrafenib: Cimetidine may decrease the absorption and hence the effects of Dabrafenib by reducing the secretion of acid in the stomach.
  • Dacomitinib: Cimetidine may decrease the absorption and hence the effects of Dacomitinib by reducing the secretion of acid in the stomach.
  • Dalfampridine: Cimetidine may increase the blood levels and effects of Dalfampridine. Dizziness, insomnia, weakness, nausea, headache, confusion and seizures. Contact your doctor if you experience these side effects.
  • Darifenacin: The blood levels of Darifenacin may be increased by cimetidine. Dry mouth, nausea, abdominal pain, constipation, and heartburn are some of the side effects observed.
  • Dasatinib: Concomitant use of Cimetidine and Dasatinib is not recommended. Cimetidine may reduce the absorption of Dasatinib making it less effective.
  • Delavirdine: Cimetidine may decrease the absorption and hence the effects of Delavirdine.
  • Desipramine: Cimetidine may increase the blood levels and hence the effects of Desipramine. Blurry vision, constipation, urinary retention, irregular or fast heartbeat, and extreme drowsiness are some of the side effects observed. Consult your doctor if you experience any of these side effects.
  • Dezocine: The blood levels and effects of Dezocine may be increased when taken along with Cimetidine. Fainting, dizziness, confusion, slow heart rate, excessive drowsiness, shallow or difficulty in breathing and slow heart rate are some of the symptoms. Consult your doctor if you experience these symptoms.
  • Diazepam: The effects of Diazepam may be increased or prolonged when taken along with cimetidine. The side effects observed are drowsiness, dizziness, confusion, and difficulty in concentrating.
  • Dicumarol: Concomitant use of cimetidine with Dicumarol may cause you to bleed more easily. If you are taking these 2 medications together, you may need dose adjustment in addition to the determination of prothrombin time or international normalized ratio.
  • Dihydroergotamine: The blood levels and effects of Dihydroergotamine may be increased when taken along with Cimetidine. In some individuals, this may lead to excessive narrowing of the blood vessels in the body leading to reduced blood flow to the vital organs and increases the risk of rare but serious side effects such as stroke, high blood pressure, heart attack, and gangrene.
  • Diltiazem: