Case 21 - NMBDs

Question 1

NMBDs MOA of skeletal muscle relaxation

Answer 1

• 1) competitive inhibition of AcH nicotinic receptors at NMJ
• 2) block prejunctional AcH receptors at NMJ thereby decreasing AcH release in response to motor nerve stimulation

Question 2

How do NMBDs differ

Answer 2

1) Structure - steroid (-onium) vs benzylisoquinone (-urium)
2) short vs intermediate vs long acting
3) routes of elimination, DOA, onset time, side effects, routes of elimination

• Atracurium = Hoffman elimination and ester hydrolysis, histamine release
• Mivacurium = plasma cholinesterase (along with Sux and ester local anesthetics)
• Panc = renal clerance, tachycardia
• Roc = Hepatic (and some renal)

Question 3

ED95

Answer 3

• mean effective dose producing 95% twitch height depression
  
  • Roc = - 0.3mg/kg
  • Vec = 0.05 mg/kg
  • Cis-Atra = 0.05 mg/kg

Question 4

Potentiates vs Resistence with NMBDs

Answer 4

Question 5

Inhaled anesthetics and NMBDs

Answer 5

• inhaled anesthetics potentiate NMBDs by direct action on CNS and inhibition of postsynaptic AcH nicotinic receptors.
• They also inhibit neuromuscular transmission at nicotinic receptors at NMJ.
• effect is dose dependent

Question 6

Local Anesthetics and Class IA antiarrhythmic drugs interaction with NMBDs

Answer 6

• these medications potentiate NMBDs becasue they block sodium channels.
• By blocking Na channels, they prevent influx of sodium into cell, decreaing muscle membrane ion conductance, thereby decreasing propagation of Action Potential.

Question 7

Aminoglycosides and NMBDs

Answer 7

• Aminoglycosides potentiate NMBds by decreasing release of AcH at motor nerve terminal and decreasing sensitiy of AcH receptor to AcH molecules.

Question 8

Metabolic derangments on NMBDs

Answer 8

• Acidosis (metabolic and respiratory) potentiate blockade
• Alkalosis causes resistance to blockade
• HYPO K+, hypo Ca+, hypermagnesima potentiate blockade

Question 9

Burns and NMBds

Answer 9

• Burn injury results in p**roliferation of extrajunctional nicotonic cholinergic receptors at NMJ. **
• As such, there are more receptors for NMBDsto block, thereby resulting in **resistance to blockade unless a larger than normal dose is given. **
• Sux is contraindicated from 24 hours after injury until burn has healed (due to increased risk of hyperkalemia)