Phenelzine Carbamazepine

This case report (Figures 6-4Ato 6-4C) (McDermut et al. 1995) of selective response to dihydropyridine CCBs but not a phenylalkylamine CCB is of considerable interest in relationship to the patient s history of nonre-sponsivity to multiple tricyclic antidepressants, the selective serotonin reuptake inhibitors, lithium, carbamazepine (the patient developed drug-induced hepatitis on carbamazepine and was unable to be evaluated), alprazolam, trazodone, and phenelzine. This suggests that patients with refractory mood disorders may have differential responses to various CCBs and that nonresponse to one CCB does not preclude response to another CCB, particularly if the other CCB is from a different category (Table 6-3). 

Clinically important, potentially hazardous interactions with alcohol, alprazolam, carbamazepine, metoprolol, phenelzine, ritonavir, warfarin... 

Answer E. Lithium inhibits the dephosphorylation of IP2 (needed for the recycling of inositol), leading to depletion of membrane PIP2. Consequently, the activation of receptors by neurotransmitters such as ACh, NE, and 5HT fails to release the second messengers IP3 and DAG. Carbamazepine and the local anesthetic procaine block axonal Na channels ethosuximide may block Ca channels in thalamic neurons. Phenelzine is a non-selective inhibitor of MAO. 

Monoamine oxidase inhibitors (MAOIs) Phenelzine, tranylcypromine, and moclobemide have no clinically significant interactions with carbamazepine. 

Phenelzine, moclobemide and tranylcypromine appear not to interact adversely with carbamazepine. 

There appear to be no reports of adverse reactions during the concurrent use of MAOIs and carbamazepine. However, the manufacturers of carbamazepine say that concurrent use should be avoided because of the close structural similarity between carbamazepine and the tricyclic antidepressants (and therefore the theoretical risk of an adverse interaction). They suggest that MAOIs should be discontinued at least 2 weeks before carbamazepine is started. Several reports describe successful use of carbamazepine and MAOIs, namely tranylcypromine, phenelzine, and moclobemide. Bearing in mind that the MAOIs and the tricyclics can be given together under certain well controlled conditions (see MAOIs or RIMAs + Tricyclic and related antidepressants , p.ll49), the warning about the risks may possibly prove to be overcautious. Note that, rarely, the MAOIs have been seen to cause convulsions. 

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