Figure 4.

Enzyme inhibition kinetic analysis of duloxetine against human acetylcholinesterase. (A) Nonlinear regression analyses estimated an inhibition constant (K_i) of 65.5 μM for duloxetine against human AChE. Duloxetine behaved as a mixed-competitive inhibitor of AChE. Similar analyses on (B) citalopram and (C) its S-enantiomer, escitalopram, estimated K_i values of 58.9 and 32.8 μM, respectively. The analyses in addition indicated that citalopram behaves like a noncompetitive inhibitor, while escitalopram is a mixed-competitive inhibitor like duloxetine. Thus, escitalopram appears twice as potent an AChE inhibitor as duloxetine and citalopram. Nonetheless, the K_i values suggest that all three drugs have moderate potency toward human AChE. Data are given as mean ± SD. The nonlinear regression analyses were done with GraphPad Prism 9.