Stereoselectivity of cholinesterase inhibition by galanthamine and tolerance in humans.

The effect of galanthamine (GAL) and its 2 major metabolites on human cholinesterases has been explored. Epigalanthamine, a diastereomer of GAL, was 130-times less potent in vitro in its effect on acetylcholinesterase (AChE) in erythrocytes than the parent compound, and it did not differ significantly from the ketone galanthaminone. In vivo, the maximal 36-55% inhibition of AChE was approached 30 min after oral administration of 10 mg GAL. The duration of the catalytic inhibition corresponded to an elimination half-life of approximately 5-7 h. GAL was well tolerated in 8/8 healthy volunteers, and 3/4 Alzheimer patients tolerated the drug up to a daily dose of 40 mg.