Neuromuscular Blocking Drug (NMBD)

Agents	Structure of NMBD [1]	Potency [1]	Duration of action	Elimination	Others
Suxamethonium	Contains 2 quaternary ammonium compound (bisquaternary amines)	More potent	Ultra short [3]	Kidney for <2 % [3]	Stimulates autonomic ganglia, cardiac muscles and slight histamine release.
Atracurium			Intermediate duration of action) [1]	Hoffman elimination [3]	Metabolite has CNS stimulant properties with long half life dependent on liver & kidney for elimination. Metabolite also has CV effects. Causes histamine release. [2]
Pancuronium			Long duration of action especially in renal failure [1]	60 % excreted unchanged by kidney [1]	Direct vagolytic & sympathomimetic [1]
Rocuronium	Contains 1 permanent quaternary cation and 1 tertiary amine (monoquaternary amines	Less potent than bisquaternary compounds but  in acidotic conditions, tertiary amine gets protonated and becomes positively charged making it more potent than bisquaternary compounds	Rapid onset & immediate duration of action [1]	10 % excreted in urine [1]	No direct sympathomimetic effect but in high doses has vagolytic properties. More likely to cause anaphylactoid reaction than Pancuronium and Vecuronium. [1]
Vecuronium			Intermediate duration of action) [1]	Unstable as solution, supplied as lyophilized powder. Has metabolite as potent as drug. [1]	In renal failure, active metabolite drug can accumulate and contribute to neuromuscular block during prolonged infusions. No direct CV effect and do not release histamine. [1]

• Atracurium is a muscle relaxant of intermediate duration.  It is preferred in patients with hepatic or renal impairment as its metabolism is substantially non-enzymatic and is therefore not dependent on hepatic or renal function.  It has little effect on cardiovascular function or intra-cranial pressure.  Histamine release may occur and large doses may cause hypotension.
• Pancuronium is a long-acting muscle relaxant.  It may cause tachycardia and hypertension.  It does not cause histamine release.  It is metabolised hepatically and excreted renally which may result in delayed clearance in patients with impaired hepatic and/or renal function.
• Vecuronium is a derivative of pancuronium but is shorter acting.  It has minimal effect on cardiovascular function.  Recovery is usually rapid.  It is predominantly excreted in the bile.
• Rocuronium has a similar profile to vecuronium but has a quicker onset of action which may be clinically useful.  It has few cardiovascular side-effects.

Clinical Use:

• Succinylcholine is the most common depolarizing NMBA. Its onset of action is rapid (less than one minute) and its duration of effect is brief (seven to eight minutes).
• Succinylcholine is generally used to facilitate intubation or treat laryngospasm
• In general, the nondepolarizing NMBAs have an onset of action of one to five minutes and a half-life ranging from 5 to 300 minutes
• For patients who require paralysis for more than one hour:
• Pancuronium is appropriate for patients with normal hepatic and renal function.
• Cisatracurium or atracurium is appropriate for patients with hepatic or renal insufficiency.
• For patients who are hemodynamically unstable or have cardiovascular disease, vecuronium, pipecuronium, or rocuronium may be used.

References:

1. http://ceaccp.oxfordjournals.org/content/4/1/2.full#T1
2. http://www.nhsgrampian.org/nhsgrampian/
3. Faculty.washington.edu/ramaiahr/3BChapter_13.pdf
4. http://ceaccp.oxfordjournals.org/content/4/1/2/T1.expansion.html
5. http://www.globalrph.com/neuromuscular.htm
6. www.uptodate.com