Venlafaxine (Effexor), a bicyclic compound that is structurally different from other antidepressants, was released in 1994 for the treatment of depression. In contrast to the SSRIs, venlafaxine is a nonselective inhibitor of serotonin, norepinephrine, and dopamine reuptake. 16 Whether this nonselectivity offers any advantage over SSRIs, bupropion, trazodone, nefazodone, or mirtazapine is currently unknown. Venlafaxine has no significant direct effect on presynaptic or postsynaptic neurotransmitter receptors and does not inhibit MAO activity. It is available in 25-mg, 37.5-mg, 50-mg, 75-mg, and 100-mg tablets. The recommended starting dose is 75 mg/day, which can be gradually increased up to a maximum daily dose of 375 mg. It has a category C rating in pregnancy.

Peak levels occur 2 h after ingestion. It is poorly protein bound (27 percent), and it has volume of distribution of 6 to 7 L/kg and a half-life of approximately 5 h. The majority of venlafaxine undergoes hepatic P-450 oxidation, but it is a weak inhibitor of P-450 enzyme activity. To date, no significant pharmacokinetic drug interactions have been reported. It has one active metabolite, O-desmethylvenlafaxine, which is pharmacologically similar to its parent drug, except for a longer half-life of 11 h. The adverse effect profile for venlafaxine is similar to the aforementioned one for SSRIs. The only notable exception is the occurrence of mild to moderate hypertension when doses exceed 225 mg/day, which is probably secondary to inhibition of norepinephrine reuptake. Venlafaxine has the same potential as other serotonin agonists to produce serotonin syndrome. Therefore, it should not be combined with MAOIs or other serotonin agonists. Because of its shorter half-life, venlafaxine requires only a 1-week abstinence period before initiating MAOI therapy. However, a 2-week abstinence period is still required after MAOI discontinuation before starting venlafaxine therapy.

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