Muscle Relaxants - Neuromuscular Blocking Drugs

• Chemical Structure: 2 molecules of Acetyl Choline linked together with 2 quaternary amine groups.
• Physical Properties: It is available in 2 forms:
• Succinylcholine chloride - Aqueous - Temperate
• Succinylcholine bromide - Powder - Tropic
• Rapid onset, short duration: 3-5 minutes
• Indications: To facilitate endotracheal tube (ETT) placement
• Dose:
• Intubating dose in adults is 1mg/kg
• X-ray examinations, especially in infants, is 1.5-2.0mg/kg
• Rapidly hydrolyzed by plasma cholinesterase

SIDE-EFFECTS

• Cardiac arrhythmias:
• Sinus bradycardia
• Ventricular premature beats
• Hyperkalemia, especially in:
• Patients with massive burns
• Muscle trauma
• Upper motor neuron lesions (UMNL) and lower motor neuron lesions (LMNL)
• Renal disease
• Severe abdominal infections
• Raised Intraocular Pressure (IOP)
• Raised Intracranial Pressure (ICP)
• Raised Intragastric Pressure (IGP)
• Scoline pain, particularly in ambulant and muscular patients
• Anaphylactoid reaction
• Masseter spasm, which could herald Malignant Hyperthermia (MH)

CAUSES OF PROLONGATION OF ACTION IN PLASMACHOLINESTERASE DEFICIENCY

• Physiological
• Pregnancy
• Contraceptive pills
• Malnutrition
• Liver disease (cirrhosis)
• Hemodialysis
• Echothiopate (an eye drop)

• First NMB Agent Used in Anesthesia
• It Causes Muscle Paralysis Within 3 Minutes
• Duration = 30-40 Minutes (Long Acting)
• Causes Hypotension by Two Mechanisms:
• Sympathetic Ganglionic Blockage
• Histamine Release
• Metabolized in the Liver and Excreted by Kidney

• Is an Aminosteroid Muscle Relaxant Acting Within 2 Minutes
• Recommended Loading Dose Within 0.06-0.08 mg/kg
• Increment of 0.01-0.02 mg/kg
• Large Amount Bound to Plasma Protein
• Dependent on Renal Excretion (80%)
• Metabolized and Excreted by the Liver
• Does Not Release Histamine
• Cardiovascular System Effects:
• Increases Blood Pressure Due to Norepinephrine Release
• Sinus Tachycardia Due to Its Vagolysis Effect

• Solely Excreted by the Kidney, Hence Absolutely Contraindicated in Renal Disease
• Crosses the Placenta, Hence Contraindicated in Obstetrics
• Vagolytic, Causing Early, Severe Tachycardias

• Dose:
• 0.3-0.4 mg/kg or 30 mg increment 0.08-0.1 mg/kg
• Amps: 2.5 ml = 25 mg
• Cardiovascularly stable, but larger doses release histamine with mild hypotension
• Breakdown occurs spontaneously and is dependent on pH and Temperature (Hoffman degradation).
• Hepatic degradation also occurs resulting in the formation of Laudanosine.
• Laudanosine is a convulsant in high doses but clinically has not been a problem.
• It is safe in hepatic and renal failure.
• Non-cumulative, even after prolonged infusions.
• Similar duration of action to Vecuronium.
• Expensive

• Dose:
• 0.15 mg/kg or 10 mg
• Amps: 5 ml = 10 mg
• Features:
• Similar to Atracurium without the histamine release.

• Dose:
• 0.15 mg/kg or 10 mg
• Amps: 5 ml = 10 mg and 10 ml = 20 mg
• New on the market
• Much shorter acting than the previous 2 agents (approximately 10 minutes), with rapid recovery. It will not replace Suxamethonium.
• Degraded by plasma cholinesterase (competing with Suxamethonium) and thus contraindicated in patients with "Scoline Apnoea."
• May be used as an infusion
• Expensive

• Dose:
• 0.1 mg/kg or 6 mg
• Amps: 2 ml = 4 mg and 10 ml = 20 mg as a dry powder needing reconstituting with sterile water
• Cardiovascularly very stable, with occasional bradycardia
• No histamine release
• Shorter acting (approximately half the duration of the preceding drugs)
• Hepato-biliary excretion and can thus be used in renal failure
• Expensive

• Dose:
• 0.3 - 0.9 mg/kg or 20 - 50 mg
• Amps: 5 ml = 50 mg and 10 ml = 100 mg
• New on the market
• Low dose provides slow intubation and short duration (approximately 15 minutes). High dose provides very fast intubation (approximately 60 - 90 seconds) and long duration.
• Cardiovascularly stable with a mild increase in heart rate and blood pressure
• Very rapid onset (similar to, but not as predictable as Suxamethonium) but has an intermediate to long duration of action.
• Undergoes no metabolism and is primarily eliminated by the liver and slightly by the kidney
• Expensive

• Dose:
• 0.25 mg/kg or 15 mg
• Amps: 2 ml = 10 mg
• Cardiovascularly more stable, with occasional tachycardia
• Histamine release with possible mild hypotension

• Benzylisoquinoline compound closely related to mivacurium and atracurium
• Most potent currently
• Onset: 10 minutes
• Duration: 3 hours
• Eliminated unchanged by the kidney
• Slightly metabolized by plasma cholinesterase

• Bis-quaternary amine derivative of DTC
• Pharmacology similar to DTC

• Elimination depends on renal (70%) and secondarily biliary (20%).
• Principal advantage over pancuronium is its lack of cardiovascular side effects due to a decreased binding to cardiac muscarinic receptors.