PHARMACOLOGICAL CHARACTERISTICS OF NEUROMUSCULAR AGENTS

INTRODUCTION:
Neuromuscular drugs interact with acetylcholine (Ach) receptor either by depolarizing the endplate or by competing with Ach for binding sites. The former mechanism is characteristic of depolarizing drugs and the latter of non depolarizing agents. The only depolarizing agent still in use is SUCCINYLCHOLINE. All others are of the nondepolarizing type.
PHARMACOLOGICAL CHARACTERISTICS
1. POTENCY:
Potency of each drug is determined by constructing dose-response curves which describe the relationship between twitch depression and dose
2. ONSET TIME:
It is the time to the maximum blockade, can be shortened if the dose is increased.
3. DURATION OF ACTION:
It is the time from injection of neuromuscular blocking drug to the return of 25% of twitch height compared with control. The 25% twitch height is chosen because rapid reversal can normally be achieved at this level.
4. RECOVERY INDEX
It is the time interval between 25% and 75% twitch height. It provides information about the speed of recovery once return of twitch is manifest.
5. ASSESSMENT OF INTUBATING CONDITIONS:
The pharmacological characteristics of NMBA are completed by an assessment of intubating conditions. Intubating conditions depend on paralysis of centrally located muscles, but also on type and quantity of narcotic and hypnotic drug given for induction of anesthesia.Criteria to grade intubating conditions as EXCELLENT, GOOD, POOR, or IMPOSSIBLE in a scoring system is adopted