Ranitidine with Phenytoin Interaction Details
Brand Names Associated with Ranitidine
- Ranitidine
- Tritec®
- Zantac®
- Zantac® 75
- Zantac® EFFERdose®
- Zantac® Syrup
Brand Names Associated with Phenytoin
- Dilantin®
- Phenytek®
- Phenytoin
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 25, 2023
Interaction Effect
Increased phenytoin concentrations
Interaction Summary
Concomitant use of phenytoin and H2 receptor antagonists, such as ranitidine, may result in increased phenytoin plasma concentrations. Some patients may experience elevations in phenytoin serum levels when ranitidine therapy is initiated. Other reports have suggested a lack of an interaction . Monitoring phenytoin serum levels should be considered when fosphenytoin and ranitidine are coadministered.
Severity
Minor
Onset
Delayed
Evidence
Probable
How To Manage Interaction
Clinicians should be aware of the potential of increased phenytoin concentrations, though the significance of this interaction has not been established. No special monitoring appears necessary, though all patients should be followed for signs of phenytoin toxicity throughout their course of therapy.
Mechanism Of Interaction
Decreased phenytoin metabolism
Literature Reports
A) Combined therapy with oral ranitidine and phenytoin resulted in significant increases (40%) in steady-state phenytoin serum levels in one patient. Phenytoin was given orally as 400 mg/day and ranitidine was added as 150 mg twice a day. Withdrawal of the ranitidine resulted in reductions in phenytoin serum levels to the previous steady-state concentrations. This case report suggests that phenytoin serum levels should be monitored during the first month of combined ranitidine therapy; however, additional studies are required to more fully evaluate this interaction .
B) Concomitant phenytoin and ranitidine therapy produced no change in plasma phenytoin concentrations in 4 patients. This is contrary to cimetidine, which has been noted to produce significant increases in phenytoin concentrations and possible toxicity.
Ranitidine Overview
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Ranitidine is used to treat ulcers; gastroesophageal reflux disease (GERD), a condition in which backward flow of acid from the stomach causes heartburn and injury of the food pipe (esophagus); and conditions where the stomach produces too much acid, such as Zollinger-Ellison syndrome. Over-the-counter ranitidine is used to prevent and treat symptoms of heartburn associated with acid indigestion and sour stomach. Ranitidine is in a class of medications called H2 blockers. It decreases the amount of acid made in the stomach.
Phenytoin Overview
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Phenytoin is used to control certain type of seizures, and to treat and prevent seizures that may begin during or after surgery to the brain or nervous system. Phenytoin is in a class of medications called anticonvulsants. It works by decreasing abnormal electrical activity in the brain.
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Definitions
Severity Categories
Contraindicated
These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.
Major
This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.
Moderate
This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.
Minor
While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.
Onset
Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.
Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.
Evidence
Level of documentation of the interaction.
Established: The interaction is documented and substantiated in peer-reviewed medical literature.
Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.
How To Manage The Interaction
Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.
It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.
Mechanism Of Interaction
The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.
Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.
Where Does Our Information Come From?
Information for our drug interactions is compiled from several drug compendia, including:
The prescribing information for each drug, as published on DailyMED, is also used.
Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.
The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.