Attenuation of erythrocytic acetyl cholinesterase by paracetamol and chloroquine: evidence in an in vitro study.

The present study deals with the erythrocytic acetylcholinesterase inhibitory activity of paracetamol and chloroquine in an in vitro protocol using Michaelis Menten parameters (Apparent Michaelis Constant (aKm) and Apparent Maximum Velocity (aVm). Paracetamol showed marked inhibition of the erythrocytic acetylcholinesterase. The inhibitory values for aKm and aVm were 65.6% 51.36% respectively, which reduced with respect to control and therefore, proposed an un-competitive type of antagonism. When chloroquine was tested, it showed 45.14% inhibition for aKm which increased while 69.21% for aVm decreased with respect to control; proposed a mixed type of antagonism. In conclusion, the cholinergic intervention by paracetamol in this study suggested a new mechanism for its analgesic activity as acetylcholinesterase inhibitors have already shown both peripheral and central analgesic activity, while the cholinergic activation by chloroquine provided explanation for some of its side effects.