Venlafaxine occupation at the noradrenaline reuptake site: in-vivo determination in healthy volunteers

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Abstract
Venlafaxine, a serotonin and noradrenaline reuptake inhibitor, is an effective antidepressant at doses of 75 mg p.o. daily and above. Preclinical and healthy volunteer studies have demonstrated that venlafaxine is more potent at the serotonin than at the noradrenaline reuptake site, with noradrenergic blocking effects being observed at doses >75 mg p.o. in man. We used the Multiple Organs Coincidences Counter and [11C] meta hydroxy ephedrine (MHED) to test whether significant occupation of cardiac sympathetic neurones was achieved in man in vivo after the acute administration of venlafaxine 75 mg p.o. in nine healthy volunteers. MHED is a tracer which binds at the noradrenaline reuptake site. This study demonstrates that the [11C]MHED signal is significantly reduced after the administration of venlafaxine 75 mg p.o. thus showing that noradrenaline reuptake blockade is observable at this dose. This effect is predominantly seen in volunteers who received > 1 mg/kg venlafaxine.