Cimetidine 400mg Tablets
It is used to treat or prevent GI (gastrointestinal) ulcers.It is used to treat gastroesophageal reflux disease (GERD; acid reflux). It is used to treat heartburn and sour stomach.It is used to treat syndromes caused by lots of stomach acid.It may be given to you for other reasons. Talk with the doctor.
Drug Class
Histamine H2-receptor antagonist
Pharmacologic Class
H2-receptor antagonist
Pregnancy Category
Category B
FDA Approved
Aug 1977
DEA Schedule
Not Controlled
Overview
What is this medicine?
Cimetidine is a medication that helps reduce the amount of acid your stomach makes. It's used to treat conditions like heartburn, stomach ulcers, and acid reflux (GERD). It works by blocking a natural chemical in your body called histamine, which tells your stomach to produce acid.
How to Use This Medicine
Taking Your Medication
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take this medication with meals and at bedtime, or as directed by your doctor. It's essential to take this medication with food to help prevent stomach upset. However, do not take antacids at the same time as this medication, as they may interfere with its absorption. If you have any questions or concerns, discuss them with your doctor.
To help prevent heartburn, take this medication 30 minutes before consuming foods or drinks that trigger heartburn.
Storing and Disposing of Your Medication
Store this medication at room temperature in a dry place, away from the bathroom. Keep all medications in a safe and secure location, out of the reach of children and pets. When disposing of unused or expired medications, do not flush them down the toilet or pour them down the drain unless instructed to do so by your pharmacist. Instead, check with your pharmacist for guidance on the best disposal method or participate in a drug take-back program in your area.
Missing a Dose
If you take this medication on a regular schedule, take a missed dose as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses. If you take this medication as needed, do not take it more frequently than directed by your doctor.
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take this medication with meals and at bedtime, or as directed by your doctor. It's essential to take this medication with food to help prevent stomach upset. However, do not take antacids at the same time as this medication, as they may interfere with its absorption. If you have any questions or concerns, discuss them with your doctor.
To help prevent heartburn, take this medication 30 minutes before consuming foods or drinks that trigger heartburn.
Storing and Disposing of Your Medication
Store this medication at room temperature in a dry place, away from the bathroom. Keep all medications in a safe and secure location, out of the reach of children and pets. When disposing of unused or expired medications, do not flush them down the toilet or pour them down the drain unless instructed to do so by your pharmacist. Instead, check with your pharmacist for guidance on the best disposal method or participate in a drug take-back program in your area.
Missing a Dose
If you take this medication on a regular schedule, take a missed dose as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses. If you take this medication as needed, do not take it more frequently than directed by your doctor.
Lifestyle & Tips
- Avoid foods and drinks that trigger your symptoms (e.g., spicy foods, caffeine, alcohol, fatty foods).
- Avoid smoking, as it can worsen acid reflux and delay ulcer healing.
- Eat smaller, more frequent meals.
- Do not lie down for at least 2-3 hours after eating.
- Elevate the head of your bed if you experience nighttime heartburn.
- Manage stress, as it can contribute to digestive issues.
Available Forms & Alternatives
Dosing & Administration
Adult Dosing
Standard Dose:
For Duodenal Ulcer: 800 mg once daily at bedtime or 400 mg twice daily. For GERD: 800 mg twice daily or 400 mg four times daily.
Dose Range:
400 - 2400 mg
Condition-Specific Dosing:
Duodenal Ulcer (active):
800 mg once daily at bedtime or 400 mg twice daily or 300 mg four times daily for 4-8 weeks.
Duodenal Ulcer (maintenance):
400 mg once daily at bedtime.
Gastric Ulcer (active):
800 mg once daily at bedtime or 300 mg four times daily for 6-8 weeks.
GERD:
800 mg twice daily or 400 mg four times daily for 6-12 weeks.
Pathological Hypersecretory Conditions (e.g., Zollinger-Ellison Syndrome):
300 mg four times daily, may increase up to 2400 mg/day.
Pediatric Dosing
Neonatal:
Not established (limited data, often off-label: 5-10 mg/kg/day divided every 8-12 hours)
Infant:
Not established (limited data, often off-label: 10-20 mg/kg/day divided every 6-12 hours)
Child:
Not established (limited data, often off-label: 20-40 mg/kg/day divided every 6-8 hours, max 1600 mg/day)
Adolescent:
Similar to adult dosing for specific indications, but generally not preferred over newer agents.
Dose Adjustments
Renal Impairment:
Mild:
No adjustment needed (CrCl > 50 mL/min)
Moderate:
Reduce dose by 50% (e.g., 400 mg once daily or 300 mg twice daily for CrCl 30-50 mL/min)
Severe:
Reduce dose significantly (e.g., 300 mg once daily or 200 mg twice daily for CrCl < 30 mL/min)
Dialysis:
Administer after dialysis. Supplemental dose may be needed. Max 300 mg every 12 hours.
Hepatic Impairment:
Mild:
No specific adjustment needed.
Moderate:
No specific adjustment needed, but use with caution and monitor for CNS effects.
Severe:
No specific adjustment needed, but use with caution and monitor for CNS effects due to potential accumulation.
Pharmacology
Mechanism of Action
Cimetidine is a histamine H2-receptor antagonist. It competitively inhibits the binding of histamine to H2 receptors on the gastric parietal cells, leading to a reduction in gastric acid secretion (both basal and stimulated by food, histamine, or gastrin). This reduces the volume and acidity of gastric acid.
Pharmacokinetics
Absorption:
Bioavailability:
60-70%
Tmax:
1-2 hours
FoodEffect:
Food may slightly delay absorption but does not significantly affect the extent of absorption.
Distribution:
Vd:
0.8 L/kg
ProteinBinding:
13-25%
CnssPenetration:
Limited, but can cross the blood-brain barrier, especially with high doses or in patients with renal impairment, leading to CNS side effects.
Elimination:
HalfLife:
Approximately 2 hours (in patients with normal renal function)
Clearance:
Approximately 300-400 mL/min
ExcretionRoute:
Primarily renal (glomerular filtration and tubular secretion)
Unchanged:
50-80%
Pharmacodynamics
OnsetOfAction:
Within 30 minutes
PeakEffect:
1-2 hours
DurationOfAction:
4-6 hours (single dose), up to 12 hours (with repeated dosing)
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience any of the following symptoms, contact your doctor or seek medical attention immediately:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Confusion
Agitation
Mood changes
Hallucinations (seeing or hearing things that are not there)
Enlarged breasts
* Liver problems, which can be rare but potentially deadly. Warning signs may include:
+ Dark urine
+ Tiredness
+ Decreased appetite
+ Upset stomach or stomach pain
+ Light-colored stools
+ Vomiting
+ Yellow skin or eyes
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to contact your doctor or seek medical help if you have any symptoms that bother you or persist. This is not an exhaustive list of possible side effects. If you have questions or concerns, consult your doctor.
Reporting Side Effects
If you experience any side effects, you can report them to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch. Your doctor can also provide guidance on managing side effects and offer medical advice.
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience any of the following symptoms, contact your doctor or seek medical attention immediately:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Confusion
Agitation
Mood changes
Hallucinations (seeing or hearing things that are not there)
Enlarged breasts
* Liver problems, which can be rare but potentially deadly. Warning signs may include:
+ Dark urine
+ Tiredness
+ Decreased appetite
+ Upset stomach or stomach pain
+ Light-colored stools
+ Vomiting
+ Yellow skin or eyes
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to contact your doctor or seek medical help if you have any symptoms that bother you or persist. This is not an exhaustive list of possible side effects. If you have questions or concerns, consult your doctor.
Reporting Side Effects
If you experience any side effects, you can report them to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch. Your doctor can also provide guidance on managing side effects and offer medical advice.
Seek Immediate Medical Attention If You Experience:
- Severe or persistent headache or dizziness.
- Unusual tiredness or weakness.
- Confusion, agitation, or hallucinations (especially in older adults or those with kidney problems).
- Unexplained breast enlargement or tenderness (gynecomastia).
- Difficulty urinating or changes in urine output.
- Yellowing of the skin or eyes (jaundice).
- Dark urine or pale stools.
- Any signs of allergic reaction (rash, itching, swelling, severe dizziness, trouble breathing).
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances. Be sure to describe the allergic reaction and its symptoms.
If you are currently taking dofetilide, as this may interact with the medication.
If you are breast-feeding, as you should not breast-feed while taking this medication.
Additionally, to ensure safe treatment, provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
Your existing health problems
This will help your doctor and pharmacist assess potential interactions and determine the safety of taking this medication with your other treatments and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances. Be sure to describe the allergic reaction and its symptoms.
If you are currently taking dofetilide, as this may interact with the medication.
If you are breast-feeding, as you should not breast-feed while taking this medication.
Additionally, to ensure safe treatment, provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
Your existing health problems
This will help your doctor and pharmacist assess potential interactions and determine the safety of taking this medication with your other treatments and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. If you experience any of the following symptoms, contact your doctor immediately: throat pain, chest pain, severe abdominal pain, difficulty swallowing, or signs of a bleeding ulcer, such as black, tarry, or bloody stools, vomiting blood, or vomit that resembles coffee grounds, as these may indicate a more serious health issue.
When taking this medication, it is crucial to coordinate with other medications you are using, as they may need to be taken at a different time. Consult with your doctor or pharmacist to determine the best schedule for taking your medications.
If you are 50 years or older, exercise caution when using this drug, and discuss any concerns with your doctor. Additionally, if you are pregnant or planning to become pregnant, inform your doctor, as you will need to discuss the potential benefits and risks of using this medication during pregnancy.
When taking this medication, it is crucial to coordinate with other medications you are using, as they may need to be taken at a different time. Consult with your doctor or pharmacist to determine the best schedule for taking your medications.
If you are 50 years or older, exercise caution when using this drug, and discuss any concerns with your doctor. Additionally, if you are pregnant or planning to become pregnant, inform your doctor, as you will need to discuss the potential benefits and risks of using this medication during pregnancy.
Overdose Information
Overdose Symptoms:
- Respiratory depression
- Tachycardia
- Arrhythmias
- CNS depression (sedation, confusion, disorientation)
- Slurred speech
- Dilated pupils
- Muscle twitching
- Seizures
What to Do:
Seek immediate medical attention or call Poison Control at 1-800-222-1222. Treatment is supportive and symptomatic. Gastric lavage and activated charcoal may be considered if ingestion is recent. Hemodialysis can remove cimetidine from the blood.
Drug Interactions
Major Interactions
- Warfarin (increased anticoagulant effect, increased bleeding risk)
- Phenytoin (increased phenytoin levels, toxicity)
- Theophylline (increased theophylline levels, toxicity)
- Lidocaine (increased lidocaine levels, toxicity)
- Procainamide (increased procainamide levels, toxicity)
- Metformin (increased metformin levels, increased risk of lactic acidosis due to OCT2 inhibition)
- Calcium channel blockers (e.g., nifedipine, diltiazem, verapamil - increased levels, hypotension)
- Tricyclic antidepressants (e.g., imipramine, amitriptyline - increased levels, toxicity)
- Benzodiazepines (e.g., diazepam, chlordiazepoxide - increased levels, enhanced sedation)
- Ketoconazole, Itraconazole (decreased absorption due to increased gastric pH)
Moderate Interactions
- Amiodarone (increased amiodarone levels)
- Carbamazepine (increased carbamazepine levels)
- Flecainide (increased flecainide levels)
- Quinidine (increased quinidine levels)
- Sulfonylureas (e.g., glipizide, glyburide - increased hypoglycemic effect)
- Iron salts (decreased absorption due to increased gastric pH)
- Delavirdine (decreased absorption due to increased gastric pH)
- Atazanavir (decreased absorption due to increased gastric pH)
Minor Interactions
- Alcohol (may increase blood alcohol levels slightly)
- Sucralfate (may decrease cimetidine absorption if given concurrently; separate by 2 hours)
Monitoring
Baseline Monitoring
Renal function (BUN, Creatinine)
Rationale: Cimetidine is primarily renally eliminated; dose adjustment is necessary in renal impairment.
Timing: Prior to initiation, especially in elderly or patients with known renal issues.
Liver function tests (ALT, AST, Bilirubin)
Rationale: Although hepatic metabolism is minor, liver dysfunction could theoretically affect clearance or predispose to adverse effects.
Timing: Prior to initiation in patients with known hepatic impairment.
Routine Monitoring
Symptom resolution (e.g., heartburn, dyspepsia)
Frequency: Daily/Weekly
Target: Significant reduction or absence of symptoms
Action Threshold: Lack of improvement after 2-4 weeks may indicate need for dose adjustment, alternative therapy, or further diagnostic workup.
Adverse effects (e.g., headache, dizziness, diarrhea, CNS effects)
Frequency: Regularly, especially during initial therapy
Target: Absence or mild, tolerable effects
Action Threshold: Persistent or severe adverse effects warrant dose reduction or discontinuation.
Drug-drug interactions (e.g., INR for warfarin, drug levels for phenytoin, theophylline)
Frequency: As clinically indicated, especially when co-administering interacting drugs
Target: Therapeutic range for co-administered drugs
Action Threshold: Levels outside therapeutic range or signs of toxicity/inefficacy require dose adjustment of interacting drug or cimetidine.
Renal function (BUN, Creatinine)
Frequency: Periodically in patients with renal impairment or prolonged therapy
Target: Stable renal function
Action Threshold: Worsening renal function may necessitate further dose reduction.
Symptom Monitoring
- Abdominal pain
- Heartburn
- Dyspepsia
- Nausea
- Diarrhea
- Headache
- Dizziness
- Confusion (especially in elderly or renally impaired)
- Hallucinations
- Gynecomastia (rare, with prolonged high-dose use)
- Impotence (rare)
Special Patient Groups
Pregnancy
Cimetidine is Pregnancy Category B. Animal studies have not shown harm to the fetus, and there are no adequate and well-controlled studies in pregnant women. It is generally considered safe for use during pregnancy when clearly needed, but other H2 blockers (e.g., ranitidine, famotidine) or PPIs may be preferred due to more extensive human data.
Trimester-Specific Risks:
First Trimester:
Low risk based on available data.
Second Trimester:
Low risk based on available data.
Third Trimester:
Low risk based on available data.
Lactation
Cimetidine is excreted into breast milk. The American Academy of Pediatrics considers it compatible with breastfeeding. LactMed rates it as L3 (Moderately Safe). While generally considered safe, other H2 blockers with lower milk concentrations or shorter half-lives may be preferred, especially in neonates or preterm infants. Monitor infant for potential side effects like CNS depression or GI upset.
Infant Risk:
Low to moderate. Potential for mild GI upset or CNS effects in the infant, though unlikely with typical doses. Monitor for drowsiness or changes in feeding.
Pediatric Use
Use in pediatric patients is generally off-label and not as well-established as in adults. Dosing is weight-based. Due to potential for CNS side effects and drug interactions, newer H2 blockers or PPIs are often preferred. Close monitoring is required.
Geriatric Use
Elderly patients are more susceptible to CNS side effects (e.g., confusion, disorientation, hallucinations) due to reduced renal clearance and potential for higher plasma concentrations. Dose adjustments are often necessary based on renal function. Use with caution and start with lower doses.
Clinical Information
Clinical Pearls
- Cimetidine is a potent inhibitor of several CYP450 enzymes (especially CYP1A2, 2C9, 2D6) and OCT2, leading to numerous significant drug interactions. Always review patient's medication list for potential interactions.
- CNS side effects (confusion, disorientation) are more common in elderly patients or those with renal impairment. Monitor closely.
- Gynecomastia and impotence are rare but recognized side effects, particularly with high doses or prolonged use.
- Administering cimetidine with meals or at bedtime can help optimize its effect on gastric acid secretion.
- For patients requiring an acidic environment for drug absorption (e.g., ketoconazole, iron), separate administration times by at least 2 hours or consider an alternative acid-reducing agent.
Alternative Therapies
- Other H2-receptor antagonists (e.g., Famotidine, Ranitidine (if available), Nizatidine)
- Proton Pump Inhibitors (PPIs) (e.g., Omeprazole, Esomeprazole, Lansoprazole, Pantoprazole, Rabeprazole)
- Antacids (e.g., Aluminum hydroxide/Magnesium hydroxide, Calcium carbonate)
- Sucralfate (for ulcer treatment)
- Prokinetics (e.g., Metoclopramide, for GERD with motility issues)
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets (400mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 or Tier 2 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it's essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so be sure to check with your pharmacist for more information. If you have any questions or concerns about this medication, don't hesitate to reach out to your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek medical attention. When seeking help, be prepared to provide details about the medication, including the amount taken and the time it happened, to facilitate prompt and effective treatment.