Muscle relaxants

Question 1

drugs used to reduce tone of skeletal muscle

Answer 1

1. central acting (CNS)
2. Neuromuscular junction (peripheral)
3. Muscle (peripheral)

Question 2

Central acting muscle relaxants

Answer 2

1. Diazepam
2. Baclofen (spascisity in MS/spinal cord lesions)

Question 3

Diazepam

PKPD,P-therapeutics,interactions,adverse reactions

Answer 3

• absorbed rapidly from the GI tract, wide vd, minimal metabolism in liver, excreted by kidneys.
• binds to a site on the GABA-A receptor different from GABA binding site and increases the binding affinity for GABA also increasing the frquency of the chloride channel open
• Used in MS/trauma for spinal cord lesions
• increased CNS depression when taken with other CNS depressants
• Dependance, drowsiness

Question 4

Baclofen

PKPD,P-therapeutics,interactions,adverse reactions

Answer 4

• Baclofen binds to GABA-B receptors which are coupled to preysnaptic and postsynaptic Ca2+ and K+ channels, Inhibitng spinal reflexes.
• lessons neuron activity, decreasing the number and severity of mscle spasms, reducing pain
• CNS depression risk increased when taken with another CNS depressant
• Dependence, drowsiness

Question 5

Dantrolene (Dantrium)

Answer 5

• 1st line to treat malignant hyperthermia
• main effect on muscle, but can cause adverse cns effects
• high protein binding, poor absorption in GI tract, metabolized by liver, excreted in urine
• acts on muscle by interfering with calcium ion release from the sarcoplasmic reticulum weakening force of contractions
• manages all types of spacisity: cerebral palsy, ms, spinal cord injury, stroke, malignant hyperthermia
• can result in sedation when taken with cns depressants, lack of coordination, respiratory depression
• no alcohol

Question 6

counselling peripheral + cns acting muscle relaxants

Answer 6

• drowsiness
• no alcohol
• driving/heavy machinery

Question 7

2 categories of neuromuscular blocking drugs

Answer 7

1. Non-depolarising
   subdivided into two groups
   * aminosteroid
   * Benzylisoquinolinium
2. depolarising
   * suxamethonium

Question 8

Non-depolarising blocking drug

PKPD,P-therapeutics, contraididications, side affects

Answer 8

• Parental administration - rapid absorption, mostly excreted in the urine
• compete with Ach at the cholinergic receptor sites of the skeletel muscle membrane, preventing muscle contraction. patient remains concious and feels pain therefore analgesic/anti-anxiety required.
• used for moderate/prolonged muscle relazation in many situations: realignment of fractures and dislocated joints
• interacts with aminoglycoside antibiotics, anaesthetics
• adverse reactions: apnea, hypotension, bronchospasm

Question 9

depolarising blocking drug

PKPD,P-therapeutics, contraididications, side affects

Answer 9

• suxamethonium
• IV or IM, hydrolyzed in liver and plasma by pseudocholinesterase, renal excretion
• Remains attached to receptor sites on the skeletal muscle for a longer period of time preventing repolarization of the motor end plate
• The drug of choice for short-term muscle relaxation (during intubation and ECT).
• Potentiated by a number of anesthetics and antibiotics.
• apnea and hypotension, tachycardia (1st dose), bradycardia (repeated doses).