Effects of echothiophate on enzymatic hydrolysis of dipivefrin

Dipivefrin is an antiglaucoma prodrug that is hydrolyzed to the active drug, epinephrine, by esterases in the cornea. Since cholinergic antiglaucoma agents are frequently used in combination with adrenergic agents, it was of interest to determine the effects of a commonly used irreversible cholinesterase inhibitor, echothiophate (Phospholine) iodide, on the dipivefrin esterases. In vitro studies showed that echothiophate is a competitive, reversible inhibitor of the soluble corneal dipivefrin esterases. In vivo studies substantiated the reversible nature of echothiopate inhibition, since no inhibition of dipivefrin hydrolysis could be detected 1 3/4 hours after echothiophate treatment and as early as 15 minutes after dipivefrin application.