Chronic administration of type A monoamine oxidase inhibitors increases duration of thiopentone anaesthesia in the rat.

Daily intraperitoneal administration for fifteen days of the mixed type A and type B monoamine oxidase inhibitors phenelzine, isocarboxazid, iproniazid and tranylcypromine caused a marked increase in the duration of thiopentone anaesthesia ('sleeping time') tested 48 hours after the last drug injection. This effect was not due to accumulation of drug or other carryover since it failed to occur after 5 days of daily administration. Similar prolongation of anaesthesia was seen after 15, but not 5 days of administration of the selective type A monoamine oxidase inhibitors clorgyline and LY 51641 but not with the type B inhibitors pargyline and deprenyl.