The inhibitory effect of glycopyrrolate on human plasma-cholinesterase

The in vitro inhibitory effect of glycopyrrolate and atropine on the hydrolysis of benzoylcholine at 50.0 microM concentration was determined in the plasma of 6 healthy volunteers at 37 degrees C and at 240 nm by the ultraviolet spectrophotometric method of Kalow. The 50 per cent inhibitory concentration (I50) of glycopyrrolate was found to be 1.0 mM and the I50 of atropine was 0.9 mM. This inhibitory effect of glycopyrrolate and atropine is moderate but its interaction with the in vivo hydrolysis of succinylcholine or that of ester-type of local anaesthetics in patients should be further studied. Although both glycopyrrolate and atropine inhibit PChE to the same extent, glycopyrrolate should be utilized in patients in whom inhibition of brain PChE or central effects ought to be avoided, since glycopyrrolate does not penetrate the blood-brain barrier.