DIFFERENTIAL EFFECTS OF MYONEURAL BLOCKING DRUGS ON NEUROMUSCULAR TRANSMISSION

Abstract

The relationship between the depression in the amplitude of the compound muscle action potennal and neuromuscular decrement (fade) was studied during the induction of non-depolarizing blockade, using a train of four supramaximal stimuli. Neuromuscular decrement (%) was defined as: {1 — (amplitude of fourth muscle action potential)/(amplitudc of first muscle action potential)} × 100. When the amplitude of the first action potential was reduced by M%, mean neuromuscular decrement increased in the order pancuronium ≪alcuronium ≪tubocurarine cfazadinium ≪gallamine. Similarly, the slope of the regression line relating the decrease in the amplitude of the action potential to decrement was least wth pancuronium and greatest with gallarmine. These results may reflects different affinities or intrinsic activities of the five drugs for prejunctional and postjunctional receptors. Thus, pancuronium may have a greater affinity for postsynaptic receptors, while tubocurarine and gallamine affect selectively the motor nerve terminal. It was confirmed that fazadinium had a more rapid onset of action than any of the other myoneural blocking drugs studied.