The characteristics of the inhibition of serum cholinesterase by metoclopramide.

The inhibition of serum cholinesterase by metoclopramide has been previously characterised in vitro at high dilution of the enzyme. We examined the effect of varying enzyme dilution over a range of 1000 fold dilution, and assay temperature at 25 degrees C and 37 degrees C on the fractional inhibition of enzyme activity by metoclopramide. Neither enzyme concentration nor reaction temperature affected this fractional inhibition. Concentrations of metoclopramide producing 50% inhibition of enzyme activity were in the range 1.0-1.9 x 10(-6) M. Lineweaver-Burk analysis of the enzyme reaction suggests that the pattern of this inhibition is competitive.