Physostigmine half-life

Heptylphysostigmine (eptastigmine) (17) has been shown to be as active as physostigmine in AChE inhibition, but superior to physostigmine in terms of oral bioavadabihty and half-life (118—120). However, further clinical evaluation of this compound has been halted because of dmg-related hematological toxicity. 

ACh is metabolised extraneuronally by the enzyme acetylcholinesterase, to reform precursor choline and acetate. Blocking its activity with various anticholinesterases has been widely investigated and some improvement in memory noted. Such studies have invariably used reversible inhibition because of the toxicity associated with long-term irreversible inhibition of the enzyme. Physostigmine was the pilot drug. It is known to improve memory in animals and some small effects have been seen in humans (reduces number of mistakes in word-recall tests rather than number of words recalled), but it really needs to be given intravenously and has a very short half-life (30 min). 

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