Methylparaben and propylparaben do not alter cerebral blood flow in humans

In vitro studies suggest that the preservatives methylparaben and propylparaben included in some multidose vials of succinylcholine are the cerebral vasodilators responsible for the increases in intracranial pressure (ICP) documented after succinylcholine administration. To test this hypothesis, we measured cerebral blood flow (CBF) and cerebral blood flow velocity (CBFV) with inhaled 133Xenon and transcranial Doppler respectively in healthy humans before and after the intravenous administration of methylparaben and propylparaben. We found no change in either CBF or CBFV after the paraben injections and therefore conclude that it is unlikely that the rise in ICP seen with succinylcholine is caused by cerebral arterial vasodilatation from the preservatives methylparaben and propylparaben.