Metoclopramide decreases thiopental hypnotic requirements

We compared the effect of metoclopramide (MCA) with droperidol (DPD) on thiopental hypnotic requirements in 96 unpremedicated female patients. The study was randomized, double-blind, and placebo-controlled. The response to the verbal command was used as an end-point of anesthesia. Two methods of determination of thiopental hypnotic requirements were used: titration (infusion of thiopental at a rate of 0.5 mg.kg-1 x min-1) until the end-point was reached and construction of the dose-response curve based on bolus injections of predetermined doses of thiopental (with the use of probit analysis). The ED50 value of thiopental determined by probit analysis was reduced after the 0.2 mg/kg MCA administration by 44% (P < 0.0001). The thiopental hypnotic requirements obtained with the titration method were as follows: 5.3 +/- 0.3 mg/kg in control, 4.5 +/- 0.2 mg/kg (delta 14%, P < 0.03) with 0.1 mg/kg MCA, 3.2 +/- 0.2 mg/kg (delta 39%, P < 0.0001) with 0.2 mg/kg MCA, and 2.9 +/- 0.2 mg/kg (delta 45%, P < 0.0001) with 0.4 mg/kg MCA. DPD decreased thiopental hypnotic requirements almost to the same degree as MCA, with the ceiling effect observed at doses of 0.01 and 0.02 mg/kg (delta 44%, P < 0.0001). The results indicate that MCA causes a profound decrease in thiopental hypnotic requirements. The similarity between the thiopental sparing effects of MCA and DPD suggests that the blockade of D2 receptors is the main mechanism underlying this effect.