Carbamazepine with Felbamate Interaction Details
Brand Names Associated with Carbamazepine
- Carbamazepine
- Carbatrol®
- Epitol®
- Equetro®
- Tegretol®
- Tegretol®-XR
- Teril®
Brand Names Associated with Felbamate
- Felbamate
- Felbatol®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 25, 2023
Interaction Effect
Decreased carbamazepine or felbamate effectiveness
Interaction Summary
Felbamate reduces carbamazepine levels, and carbamazepine decreases felbamate levels .
Severity
Moderate
Onset
Delayed
Evidence
Probable
How To Manage Interaction
Consider monitoring carbamazepine levels following the addition of felbamate therapy. Although carbamazepine concentrations may be reduced, there is an increase in the active metabolite (carbamazepine-epoxide) concentration, such that the overall effectiveness of carbamazepine may not change.
Mechanism Of Interaction
Increased carbamazepine or felbamate metabolism
Literature Reports
A) The manufacturer reports that a 50% increase in felbamate clearance and a 40% decrease in felbamate's steady-state trough concentration occurs when carbamazepine is added to felbamate therapy. Additionally, felbamate causes a decrease in the steady-state plasma concentrations of carbamazepine and an increase in the steady-state carbamazepine epoxide plasma concentration .
B) Four patients who were receiving carbamazepine, phenytoin, and felbamate have been described. Following discontinuation of phenytoin, felbamate clearance decreased 21%. Carbamazepine dosage was reduced, resulting in an additional felbamate clearance of 16.5% .
C) Felbamate has been reported to increase carbamazepine metabolism. The effect of felbamate 3000 mg daily on carbamazepine levels in four patients on monotherapy was studied. Carbamazepine levels had previously been maintained at 4 to 12 mcg/mL with dosages of 800 to 1800 mg carbamazepine daily. Carbamazepine levels were reduced an average of 25% with concurrent use; this effect was evident within one week of initiation of felbamate and plateaued in two to four weeks. Felbamate appeared to reduce carbamazepine concentrations and increase carbamazepine-epoxide concentrations without affecting free fraction . Similar results were reported in another study .
D) If phenytoin or carbamazepine (or any prodrugs) is used in pregnant women, there is a substantially increased risk of teratogenicity with many combinations of other anticonvulsants. The teratogenicity of these drugs is largely or wholly related to the levels of the reactive epoxide metabolites . The epoxide/parent drug ratio is generally increased when phenytoin or carbamazepine is combined with each other, any other drugs that induce cytochrome P450 enzymes (3A4, 2C9, 2C19), or drugs which inhibit epoxide hydrolase, such as valproic acid, progabide, and lamotrigine . Such combinations increase the risk of major birth defects 3- to 4-fold over monotherapy and about 10-fold over background rates.
Carbamazepine Overview
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Carbamazepine is used alone or in combination with other medications to control certain types of seizures in people with epilepsy. It is also used to treat trigeminal neuralgia (a condition that causes facial nerve pain). Carbamazepine extended-release capsules (Equetro brand only) are also used to treat episodes of mania (frenzied, abnormally excited or irritated mood) or mixed episodes (symptoms of mania and depression that happen at the same time) in patients with bipolar I disorder (manic-depressive disorder; a disease that causes episodes of depression, episodes of mania, and other abnormal moods). Carbamazepine is in a class of medications called anticonvulsants. It works by reducing abnormal electrical activity in the brain.
Felbamate Overview
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Felbamate is used to treat certain seizures in adults and children with epilepsy whose seizures have not improved with other treatments. It is used alone or in combination with other medications to treat partial seizures in adults. It is used in combination with other medications to treat partial and generalized seizures in children with Lennox-Gastaut syndrome (a disorder that causes seizures and developmental delays). Felbamate is in a class of medications called anticonvulsants. It works by decreasing abnormal 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.