Cimetidine 800mg 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
Antiulcer agent
Pharmacologic Class
Histamine H2-receptor antagonist
Pregnancy Category
Category B
FDA Approved
Aug 1977
DEA Schedule
Not Controlled
Overview
What is this medicine?
Cimetidine is a medicine that reduces the amount of acid your stomach makes. It's used to treat conditions like heartburn, 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 Correctly
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. Take your medication with meals and at bedtime, or as instructed by your doctor.
It's essential to avoid taking antacids at the same time as this medication. If you have any questions or concerns, discuss them with your doctor. To help prevent heartburn, take your medication 30 minutes before consuming foods or drinks that trigger heartburn.
Storing and Disposing of Your Medication
Store your medication at room temperature in a dry location, avoiding the bathroom. Keep all medications in a safe place, out of the reach of children and pets. Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so by your doctor or pharmacist. If you're unsure about the best way to dispose of your medication, consult with your pharmacist. You may also want to check if there are any drug take-back programs available in your area.
What to Do If You Miss a Dose
If you take your medication on a regular schedule, take the 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 your medication as needed, do not take it more frequently than directed by your doctor.
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. Take your medication with meals and at bedtime, or as instructed by your doctor.
It's essential to avoid taking antacids at the same time as this medication. If you have any questions or concerns, discuss them with your doctor. To help prevent heartburn, take your medication 30 minutes before consuming foods or drinks that trigger heartburn.
Storing and Disposing of Your Medication
Store your medication at room temperature in a dry location, avoiding the bathroom. Keep all medications in a safe place, out of the reach of children and pets. Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so by your doctor or pharmacist. If you're unsure about the best way to dispose of your medication, consult with your pharmacist. You may also want to check if there are any drug take-back programs available in your area.
What to Do If You Miss a Dose
If you take your medication on a regular schedule, take the 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 your medication as needed, do not take it more frequently than directed by your doctor.
Lifestyle & Tips
- Take cimetidine exactly as prescribed by your doctor. Do not take more or less than directed.
- If taking once daily, it's often taken at bedtime.
- Avoid or limit alcohol consumption, as it can worsen stomach irritation and may interact with cimetidine.
- Avoid foods and drinks that trigger your symptoms (e.g., spicy foods, caffeine, fatty foods, acidic juices).
- Elevate the head of your bed if you experience nighttime heartburn.
- Do not take antacids within 1 hour of taking cimetidine, as they can interfere with absorption.
Available Forms & Alternatives
Dosing & Administration
Adult Dosing
Standard Dose:
Duodenal Ulcer (active): 800 mg once daily at bedtime or 400 mg twice daily or 300 mg four times daily. GERD: 800 mg twice daily or 400 mg four times daily. Zollinger-Ellison Syndrome: 300 mg four times daily, may increase up to 2400 mg/day.
Dose Range:
300 - 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 4-6 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.
Gastroesophageal Reflux Disease (GERD):
800 mg twice daily or 400 mg four times daily for 12 weeks.
Zollinger-Ellison Syndrome:
300 mg four times daily, may increase up to 2400 mg/day in divided doses.
Pediatric Dosing
Neonatal:
Not established (limited data, consult specialist).
Infant:
Not established (limited data, consult specialist).
Child:
20-40 mg/kg/day in 4 divided doses (max 2400 mg/day) for peptic ulcer disease/GERD. (Off-label use, consult specialist).
Adolescent:
Similar to adult dosing for specific indications, generally 20-40 mg/kg/day in divided doses (max 2400 mg/day).
Dose Adjustments
Renal Impairment:
Mild:
CrCl 50-80 mL/min: No adjustment typically needed.
Moderate:
CrCl 10-50 mL/min: Reduce dose by 50% (e.g., 400 mg once daily or 300 mg twice daily).
Severe:
CrCl <10 mL/min: Reduce dose by 75% (e.g., 300 mg once daily or 200 mg twice daily).
Dialysis:
Administer after dialysis. Supplemental dose may be needed. Hemodialysis removes cimetidine.
Hepatic Impairment:
Mild:
No specific adjustment needed.
Moderate:
No specific adjustment needed, but monitor for CNS effects.
Severe:
No specific adjustment needed, but monitor for CNS effects due to potential accumulation and increased sensitivity.
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). This reduces the volume of gastric acid and its hydrogen ion concentration.
Pharmacokinetics
Absorption:
Bioavailability:
60-70% (oral)
Tmax:
1-2 hours
FoodEffect:
Food may slightly delay absorption but does not significantly affect the extent of absorption.
Distribution:
Vd:
0.8-1.2 L/kg
ProteinBinding:
Approximately 20%
CnssPenetration:
Limited (can cross blood-brain barrier, especially with high doses or renal impairment, leading to CNS effects)
Elimination:
HalfLife:
2 hours (normal renal function), prolonged in renal impairment (up to 3.5-12 hours)
Clearance:
Approximately 500-600 mL/min
ExcretionRoute:
Primarily renal (glomerular filtration and tubular secretion)
Unchanged:
Approximately 48% (oral dose) to 70% (IV dose) excreted unchanged in urine.
Pharmacodynamics
OnsetOfAction:
Within 30 minutes
PeakEffect:
1-2 hours
DurationOfAction:
4-6 hours (single dose), up to 10-12 hours (bedtime dose for acid suppression)
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Attention Immediately
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 help right away:
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. Be aware of signs such as:
+ 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 potential 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 is also available to provide medical advice and guidance on managing side effects.
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 help right away:
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. Be aware of signs such as:
+ 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 potential 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 is also available to provide medical advice and guidance on managing side effects.
Seek Immediate Medical Attention If You Experience:
- Severe or persistent stomach pain
- Black, tarry stools or vomit that looks like coffee grounds (signs of bleeding)
- Yellowing of the skin or eyes (jaundice)
- Unusual tiredness or weakness
- Easy bruising or bleeding
- Fever, chills, or sore throat (signs of infection)
- Confusion, disorientation, or hallucinations (especially in older adults or those with kidney problems)
- Rash or hives
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, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
If you are currently taking dofetilide, as this may interact with the medication.
If you are breastfeeding, as you should not breastfeed while taking this medication.
Additionally, to ensure your safety, it is crucial to 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 information will help your doctor and pharmacist determine whether it is safe for you to take this medication in combination with your other medications and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor to confirm that it is safe to do so.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
If you are currently taking dofetilide, as this may interact with the medication.
If you are breastfeeding, as you should not breastfeed while taking this medication.
Additionally, to ensure your safety, it is crucial to 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 information will help your doctor and pharmacist determine whether it is safe for you to take this medication in combination with your other medications and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor to confirm that it is safe to do so.
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)
- Seizures
- Vomiting
What to Do:
Seek immediate medical attention. Call 911 or your local emergency number. For poison control, call 1-800-222-1222. Treatment is supportive and symptomatic. Gastric lavage and activated charcoal may be considered if ingestion is recent.
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)
- Tricyclic Antidepressants (e.g., imipramine, desipramine; increased TCA levels, toxicity)
- Benzodiazepines (e.g., diazepam, chlordiazepoxide; prolonged sedation)
- Calcium Channel Blockers (e.g., nifedipine, diltiazem; increased levels)
- Metformin (increased metformin levels, increased risk of lactic acidosis)
- Dofetilide (increased dofetilide levels, increased risk of QT prolongation and Torsades de Pointes)
Moderate Interactions
- Ketoconazole, Itraconazole (decreased absorption due to increased gastric pH)
- Iron salts (decreased absorption due to increased gastric pH)
- Sucralfate (decreased absorption of cimetidine if given concurrently)
- Alcohol (increased blood alcohol levels)
- Opioids (increased respiratory depression)
- Fluoroquinolones (e.g., ciprofloxacin; altered absorption)
- Cyclosporine (increased cyclosporine levels)
- Tacrolimus (increased tacrolimus levels)
Minor Interactions
- Antacids (may decrease cimetidine absorption if given too close)
Monitoring
Baseline Monitoring
Renal function (BUN, serum creatinine)
Rationale: Cimetidine is primarily renally eliminated; dose adjustment is required in renal impairment.
Timing: Prior to initiation of therapy.
Liver function tests (ALT, AST, bilirubin)
Rationale: Although rare, hepatic dysfunction has been reported.
Timing: Prior to initiation of therapy.
Complete Blood Count (CBC)
Rationale: Rare reports of blood dyscrasias (e.g., agranulocytosis, thrombocytopenia).
Timing: Prior to initiation of therapy, especially in patients with pre-existing hematologic abnormalities.
Routine Monitoring
Renal function (BUN, serum creatinine)
Frequency: Periodically, especially in elderly or patients with pre-existing renal impairment.
Target: Within normal limits or stable for patient's baseline.
Action Threshold: Significant increase in creatinine or BUN; consider dose adjustment.
Mental status/CNS effects
Frequency: Regularly, especially in elderly or renally impaired patients.
Target: No new or worsening confusion, disorientation, or hallucinations.
Action Threshold: Onset of new CNS symptoms; consider dose reduction or discontinuation.
Drug interaction monitoring (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 drug.
Action Threshold: Subtherapeutic or toxic levels of co-administered drug; adjust dose of interacting drug or cimetidine.
Symptom Monitoring
- Abdominal pain relief
- Heartburn relief
- Dyspepsia improvement
- Signs of bleeding (black, tarry stools; coffee-ground vomit)
- Signs of CNS effects (confusion, disorientation, hallucinations, dizziness)
- Signs of liver dysfunction (yellowing of skin/eyes, dark urine, persistent nausea/vomiting)
- Signs of blood dyscrasias (unusual bruising/bleeding, fever, sore throat)
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 use should be weighed against potential benefits.
Trimester-Specific Risks:
First Trimester:
No increased risk of congenital malformations observed in human studies.
Second Trimester:
No specific risks identified.
Third Trimester:
No specific risks identified.
Lactation
Cimetidine is excreted into breast milk. The American Academy of Pediatrics considers it compatible with breastfeeding. However, due to potential for CNS effects in the infant (though rare) and theoretical risk of altering gastric pH, caution is advised. Monitor infant for side effects.
Infant Risk:
Low risk. Potential for minor gastrointestinal effects (e.g., diarrhea) or CNS effects (e.g., drowsiness) in the infant, though rarely reported.
Pediatric Use
Use in pediatric patients is generally off-label and should be done under the guidance of a specialist. Dosing is weight-based. Safety and efficacy have not been fully established in all pediatric age groups, especially neonates and infants. Monitor for CNS effects.
Geriatric Use
Elderly patients are more susceptible to adverse effects, particularly CNS effects (e.g., confusion, disorientation, hallucinations), due to age-related decline in renal function and increased sensitivity. Lower doses and careful monitoring are recommended, especially in those with renal impairment. Dose adjustments based on creatinine clearance are crucial.
Clinical Information
Clinical Pearls
- Cimetidine is a potent inhibitor of several CYP450 enzymes (especially CYP1A2, CYP2C9, CYP2D6, CYP3A4), leading to numerous significant drug interactions. Always review patient's medication list for potential interactions.
- CNS side effects (confusion, disorientation, hallucinations) are more common in elderly patients, those with renal or hepatic impairment, or those receiving high doses. Monitor closely.
- Unlike other H2RAs, cimetidine has antiandrogenic effects at high doses, which can lead to gynecomastia and impotence in men, and galactorrhea in women. These effects are usually reversible upon discontinuation.
- Tolerance to the acid-suppressing effects of H2RAs can develop with prolonged use.
- Administer cimetidine at least 1 hour apart from antacids to avoid reduced absorption.
Alternative Therapies
- Other H2-receptor antagonists (e.g., Famotidine, Ranitidine (withdrawn in some regions due to NDMA concerns, but still available in others), Nizatidine)
- Proton Pump Inhibitors (PPIs) (e.g., Omeprazole, Lansoprazole, Esomeprazole, Pantoprazole, Rabeprazole) - generally more potent acid suppressants.
- Antacids (for symptomatic relief)
- Sucralfate (for ulcer treatment, forms a protective barrier)
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets (generic 800mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic) or Tier 2 (Preferred Brand) on most formularies.
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure safe and effective treatment, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it's a good idea to check with your pharmacist for more information. If you have any questions or concerns about this medication, don't hesitate to discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide details about the medication taken, the amount, and the time it happened.