– Pirlindole-d4 is intended for use as an internal standard for the quantification of pirlindole by GC- or LC-MS. Pirlindole is a selective and reversible monoamine oxidase A (MAO-A) inhibitor. It is selective for MAO-A over MAO-B. In rats, it reverses the depressive-like effects induced by chronic mild stress (CMS), increases proliferation of hippocampal neural progenitor cells, and reverses dendritic atrophy in granule neurons. Pirlindole is also an inhibitor of enterovirus-D68 and coxsackievirus B3 (CV-B3), inhibiting the genome replication phase of CV-B3 infection with an EC50 value of 7.7 µM independent of MAO-A activity.