Calcium Channel Blockers

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Calcium Channel Blockers - Interactions and Warnings

Findings suggest that Ginkgo biloba extract reduces the therapeutic potency of the Ca2+ channel blocker, nicardipine.
- Life Sci 2002 Apr 26;70(23):2783-92 -- Feeding of Ginkgo biloba extract (GBE) enhances gene expression of hepatic cytochrome P-450 and attenuates the hypotensive effect of nicardipine in rats. -- Shinozuka K, Umegaki K, Kubota Y, Tanaka N, Mizuno H, Yamauchi J, Nakamura K, Kunitomo M.

Both phenytoin and isradipine have been shown to bind to calcium channels and to inhibit calcium entry into the cells. Binding of isradipine to the brain has been described in humans and animals, and calcium-channel blockers have been shown to cause potentiation of anticonvulsant action of phenytoin. Acute pharmacokinetic and pharmacodynamic interactions between phenytoin and isradipine were probably responsible for the lethargy, dysarthria, ataxia, and weakness the patient developed. The combination of phenytoin and calcium-channel blockers should be used with caution.
- Ann Pharmacother 2002 Sep;36(9):1399-402 -- Phenytoin/Isradipine interaction causing severe neurologic toxicity. -- Cachat F, Tufro A.

Concomitant administration of diltiazem with morphine prevented the development of tolerance to the latter. However, combination of diltiazem with morphine, like morphine alone was found to be ineffective in morphine tolerant animals. Results, thus, show that Calcium channel blockers produced an analgesic effect of their own in formalin-induced tonic pain and potentiated the analgesic activity of morphine. They also modulated opioid-induced tolerance.
- Indian J Exp Biol 2001 Jul;39(7):636-42 -- Potentiation of analgesia and reversal of tolerance to morphine by calcium channel blockers. -- Verma V, Mediratta PK, Sharma KK.

Calcium pretreatment may reduce drug-induced hypotension without preventing the antiarrhythmic effect.
- Ann Intern Med 1987 Nov;107(5):623-8 -- Intravenous verapamil for treatment of multifocal atrial tachycardia with and without calcium pretreatment. -- Salerno DM, Anderson B, Sharkey PJ, Iber C.

Grapefruit juice can markedly augment oral drug bioavailability. Based on an unexpected observation from an interaction study between the dihydropyridine calcium channel antagonist, felodipine, and ethanol in which grapefruit juice was used to mask the taste of the ethanol. Subsequent investigations showed that grapefruit juice acted by reducing presystemic felodipine metabolism.
- Br J Clin Pharmacol 1998 Aug;46(2):101-10 -- Grapefruit juice-drug interactions. -- Bailey DG, Malcolm J, Arnold O, Spence JD.

Consult with your physician before using herbs and herbal products.

last update: November 2008

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