Abstract
Preclinical studies with nisoxetine (Compound 94939) (3-[o-Methoxyphenoxy]-N-methyl-3-phenylpropylamine HCl) had shown it to have antidepressant properties and to be almost devoid of anticholinergic activity and depressant effects on cardiac conduction (in contrast to the commonly used tricyclic antidepressants from which nisoxetine significantly differs in structure). Placebo and nisoxetine (10-20 mg b.d. for 7 days) were administered to normal volunteers in a single-bind crossover study. Adverse side effects were minimal. There were no significant changes in heart rate or blood pressure seen when no other drugs were given. The effect of nisoxetine on uptake of biogenic amines was utilized to study its mechanism of action. The transient rise in blood pressure seen after an intravenous bolus of tyramine decreased by one-half to two-thirds while the rise in blood pressure upon continuous noradrenaline infusion was enhanced some two-to eight-fold. Both effects occurred after on dose and were greater with larger doses and chronic administration. In vitro, nisoxetine inhibits 5-HT uptake into platelets. However, platelets harvested from subjects receiving chronic nisoxetine administration did accumulate 5-HT. Plasma concentration of nisoxetine in these individuals was shown to be lower than that needed to block 5-HT uptake. We concluded that nisoxetine, in safe doses, specifically increased the sensitivity of noradrenaline and decreased tyramine responsiveness, presumably by blocking uptake at the axonal membrane. In contrast, in these clinical doses it had virtually no effect on 5-HT uptake into platelets.