Carbamazepine with Nelfinavir Interaction Details
Brand Names Associated with Carbamazepine
- Carbamazepine
- Carbatrol®
- Epitol®
- Equetro®
- Tegretol®
- Tegretol®-XR
- Teril®
Brand Names Associated with Nelfinavir
- Nelfinavir
- Viracept®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 25, 2023
Interaction Effect
Decreased nelfinavir plasma concentrations; increased serum carbamazepine levels and toxicity
Interaction Summary
The concurrent use of carbamazepine and nelfinavir may result in decreased nelfinavir plasma concentrations, potentially reducing the efficacy of nelfinavir. Carbamazepine toxicity has been reported in an HIV-positive patient upon concomitant treatment with nelfinavir, as part of a highly active antiretroviral regimen. This may be a result of inhibition of CYP3A4-mediated carbamazepine metabolism by nelfinavir. If used concurrently with nelfinavir, consider reducing the carbamazepine dose by 25 to 50%. Additionally, monitor patients for serum carbamazepine levels, 3 to 5 days after initiating nelfinavir .
Severity
Major
Onset
Delayed
Evidence
Theoretical
How To Manage Interaction
Monitor patients for signs of reduced efficacy of nelfinavir. Dosing adjustments of nelfinavir may be necessary. Additionally, coadministration of carbamazepine with a nelfinavir, as part of a highly active antiretroviral regimen, has resulted in increased serum carbamazepine levels and toxicity. If used concurrently with nelfinavir, consider reducing the carbamazepine dose by 25 to 50% and monitor patients for serum carbamazepine levels, 3 to 5 days after initiating nelfinavir.
Mechanism Of Interaction
Induction of cytochrome P450 3A-mediated metabolism of nelfinavir; inhibition of CYP3A4-mediated carbamazepine metabolism by nelfinavir
Literature Reports
A) Symptoms of carbamazepine toxicity developed in a 50-year-old HIV-positive male upon addition of lopinavir/ritonavir to his highly active antiretroviral therapy (HAART). The patient had been stabilized on carbamazepine 400 mg 3 times daily for 7 months, with a serum concentration within reference range (10.3 mg/L) 1 week prior to starting the HAART regimen of tenofovir 300 mg daily; lamivudine 150 mg twice daily; and lopinavir 133 mg/ritonavir 33 mg, 3 capsules twice daily. On day 9 of the new HAART regimen, the patient experienced excessive drowsiness, and the carbamazepine serum level had increased by 46% to 15 mg/L. Decreasing the carbamazepine dose to 400 mg twice daily improved drowsiness, and a repeat serum level on day 11 was 7.4 mg/L. On day 12, the patient developed fatigue, difficulty swallowing, and diffuse hemorrhagic lesions over the extremities. The HAART regimen was stopped and carbamazepine dose was increased to 400 mg 3 times daily. The patient was hospitalized 10 days later for evaluation of the rash. Blood tests also revealed bone marrow toxicity. Subsequently, a neurology consult resulted in tapering of carbamazepine (over 2 to 4 weeks) and initiating topiramate 25 mg twice daily and titrating to a target dose of 200 mg twice daily. On day 17 of hospitalization, the HAART regimen was re-initiated, replacing lopinavir/ritonavir with nelfinavir 1250 mg twice daily. On day 20, the patient began feeling tired and unsteady on his feet and the carbamazepine serum level had increased to 15 mg/L. Decreasing the carbamazepine dose as before prompted resolution of symptoms within 24 hours. This interaction between was identified as probable by the Naranjo probability scale and inhibition of CYP3A4-mediated carbamazepine metabolism by lopinavir/ritonavir or nelfinavir was postulated as the probable mechanism .
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.
Nelfinavir Overview
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Nelfinavir is used along with other medications to treat human immunodeficiency virus (HIV) infection. Nelfinavir is in a class of medications called protease inhibitors. It works by decreasing the amount of HIV in the blood. Although nelfinavir does not cure HIV, it may decrease your chance of developing acquired immunodeficiency syndrome (AIDS) and HIV-related illnesses such as serious infections or cancer. Taking these medications along with practicing safer sex and making other lifestyle changes may decrease the risk of transmitting the HIV virus to other people.
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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.