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Carbamazepine/Selected Calcium Channel Blockers

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Moderate. These medicines may cause some risk when taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

Diltiazem and verapamil may slow down how quickly your liver processes carbamazepine.Carbamazepine may speed up how quickly your liver processes felodipine.

What might happen:

If you are taking diltiazem or verapamil, the amount of carbamazepine in your blood may increase and cause toxic side effects.If you are taking felodipine, the amount of felodipine in your blood may decrease and it may not work well.

What you should do about this interaction:

Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together. Your doctor may want to check the amount of your medicine in your blood. Your doctor may want you to check your blood pressure more often.If you experience changes in vision, restlessness, increased drowsiness, or if your blood pressure goes up , contact your doctor.Your healthcare professionals (e.g. doctor or pharmacist) may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.


1.Macphee GJ, McInnes GT, Thompson GG, Brodie MJ. Verapamil potentiates carbamazepine neurotoxicity: a clinically important inhibitory interaction. Lancet 1986 Mar 29;1(8483):700-3.

2.Brodie MJ, MacPhee GJ. Carbamazepine neurotoxicity precipitated by diltiazem. Br Med J (Clin Res Ed) 1986 May 3;292(6529):1170-1.

3.Eimer M, Carter BL. Elevated serum carbamazepine concentrations following diltiazem initiation. Drug Intell Clin Pharm 1987 Apr;21(4):340-2.

4.Price WA, DiMarzio LR. Verapamil-carbamazepine neurotoxicity. J Clin Psychiatry 1988 Feb;49(2):80.

5.Beattie B, Biller J, Mehlhaus B, Murray M. Verapamil-induced carbamazepine neurotoxicity. A report of two cases. Eur Neurol 1988;28(2):104-5.

6.Gadde K, Calabrese JR. Diltiazem effect on carbamazepine levels in manic depression. J Clin Psychopharmacol 1990 Oct;10(5):378-9.

7.Ahmad S. Diltiazem-carbamazepine interaction. Am Heart J 1990 Dec;120(6 Pt 1):1485-6.

8.Bahls FH, Ozuna J, Ritchie DE. Interactions between calcium channel blockers and the anticonvulsants carbamazepine and phenytoin. Neurology 1991 May;41(5):740-2.

9.Maoz E, Grossman E, Thaler M, Rosenthal T. Carbamazepine neurotoxic reaction after administration of diltiazem. Arch Intern Med 1992 Dec; 152(12):2503-4.

10.Cardizem LA (diltiazem hcl extended release tablets) US prescribing information. Abbott Pharmaceuticals, Inc. March, 2015.

11.Plendil (felodipine) US prescribing information. AstraZeneca Pharmaceuticals LP November, 2003.

12.Wijdicks EF, Arendt C, Bazzell MC. Postoperative ophthalmoplegia and ataxia due to carbamazepine toxicity facilitated by diltiazem. J Neuroophthalmol 2004 Mar;24(1):95.

13.Shaughnessy AF, Mosley MR. Elevated carbamazepine levels associated with diltiazem use. Neurology 1992 Apr;42(4):937-8.

Selected from data included with permission and copyrighted by First Databank, Inc. This copyrighted material has been downloaded from a licensed data provider and is not for distribution, expect as may be authorized by the applicable terms of use.

CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.

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