Non Depolarizing Muscle Relaxants

Non Depolarizing Muscle Relaxants

Muscle relaxants resemble acetylcholine. The resemblance of muscle relaxants to Ach allows the muscle relaxant molecules to occupy the receptor site. By occupying the receptor site the muscle relaxant molecules prevent acetylcholine from attaching. Non depolarizing muscle relaxant (NDMR) do not cause fasciculation. This blocks the transmission of electrical impulses, producing muscle relaxation and paralysis of the muscles. The muscle relaxant is eventually metabolized and normal muscle function is regained. NDMRs usually need to be reversed with neostigmine to terminate its paralytic effects. If not reversed the patient may experience weakness due to residual neuromuscular blockade.

Pancuronium

Is a long acting nondepolarizing muscle relaxant. Onset of action is 3-5 minutes. Its duration of action is 60-90 minutes. Due to its vagal blockade effect, Pancuronium can cause an increase of 10-15% in a patient's heart rate and blood pressure. Sites of clearance are liver and kidneys.

Dose of pancuronium

  • Adults/children: 0.04-0.08 mg/kg IV
  • Maintenance dose is 0.01 mg/kg IV every 60 minutes as needed

Contraindication: Hypersensitivity for this drug

Vecuronium

It is a medium acting nondepolarizing muscle relaxant. Its onset of action is less than 3 minutes. Its peak effect occurs at 3-5 minutes. Duration of action is 25-30 minutes. Vecuronium is generally supplied as a powder that will need to be reconstituted with sterile water or normal saline. Once mixed it retains its potency for 24 hours. It may cause bradycardia when administered with fentanyl due to its vagotonic effects. If it is administered after succinylcholine has worn off, dosage requirements may be decreased by 30-40%. Always monitor the effects of Vecuronium with a peripheral nerve stimulator, if available. Sites of clearance are liver and kidneys.

Dose of Vecuronium

  • Intubation dose in adults and children: 0.08-0.1 mg/kg
  • Maintenance of blockade: 0.01-0.05 mg/kg

Contraindication: Hypersensitivity for vecuronium

Rocuronium

It is a medium acting nondepolarizing muscle relaxant. Its duration is the same to vecuronium. Onset of action occurs between 45-90 seconds. The peak effect occurs at 1-3 minutes. The duration of action is dose dependant and can last 15 minutes with small doses and up to 150 minutes with larger doses. Rocuronium may slightly increase heart rate. If administered after succinylcholine has worn off, dosage requirements may be decreased by 30- 40%. Site of clearance is liver and independent of renal excretion.

Dose of rocuronium

  • Intubation dose in adults: 0.6-1.2 mg/kg
  • Intubation dose in children: 0.4-1 mg/kg
  • Maintenance of blockade in adults and children: 0.06-0.6 mg/kg

Contraindication: Hypersensitivity for rocuronium

Atracurium

It is a nondepolarizing muscle relaxant with a moderate duration of action. The onset of action is approximately 3 minutes. The peak effect occurs at 3-5 minutes. Its duration of action ranges between 20-35 minutes. The main advantage of atracurium over other nondepolarizing muscle relaxants is its metabolism. Metabolism is independent of kidney, liver, and plasma cholinesterase function.

It is an excellent choice in patients with abnormal liver function, renal failure, and pseudocholinesterase abnormalities. Atracurium is metabolized by Hoffman elimination and ester hydrolysis. Hoffman elimination is temperature and pH dependent, metabolizing 1/3rd

of the dose of atracurium. Ester hydrolysis occurs with non-specific plasma esterases, metabolizing 2/3rds of the dose of atracurium. Laudanosine is the major metabolite of Hoffman elimination and ester hydrolysis. In high concentrations laudanosine may cause central nervous system excitement. This generally occurs only with long term continuous infusions.

Histamine release may be associated with an increase in heart rate and a decrease in blood pressure when higher than recommended doses or rapid injection occurs.

Dose of atracurium

  • Intubation in adults and children: 0.3-0.5 mg/kg
  • Maintenance of blockade in adults and children: 0.1-0.2 mg/kg

Contraindications: Use with caution in patients with asthma. If possible use a muscle relaxant that does not release histamine.

Last modified: Wednesday, 16 November 2016, 2:09 PM