CPT1: muscle relaxants Flashcards
What do muscle relaxants do?
Cause skeletal muscle relaxation
What classes of muscle relaxants are there?
- Centerally acting: acting on the CNS
- Peripherally acting: act on muscle or neuromuscular junction
What can centerally acting drugs be used for?
To treat chronic severe muscle spasms from a variety of causes: (PITA)
- pain
- inflammation
- anxiety
- trauma
most commonly used for MS
What are the pharmacokinetics of centerally acting muscle relaxants
Drug absorebd rapidly from GI tract; distributed widely’ metabolised minimly by liver; excreted in urine
What are examples of centerally acting muscle relaxants?
Baclofen
tizanidine
diazepam
What is the mechanism of action of baclofen
Baclofen is a GABA agonist. It binds to the GABA receptor and activates it. This causes Cl- influx which leads to membrane polarisation, loss of excitbility and less NT being released. THere is therefore less NT to act on skeletal muscle and cause contraction
How does Diazepam work?
Positive allosteric modulator. BInds to BZ binding site on the GABA receptor and facilitates GABA binding. This allows Cl- infulx, membrane hyperpolarisaiton, decrease in excitability and less NT released to act on skelteal muscle
How does Tizanidine work?
a2 agonist. Therefore limits NT release which reduces excitability of motor neurone and therefore reducing stimulation of skeletal muscle
What drug interactions occur with centerally acting muscle relaxants?
- CNS depression when taken with other CNS depressants
What are side effects of Centerally acting muscle relaxants?
- Dependance
- drowsiness
What i the drug of choice to treat spacicty?
Dantrolene sodium
What is an example of a peripherally acting drug which acts on the muscle directly?
Dantrolene sodium
What is the pharmacokinetics of muscle peripheral drugs?
- absorbed poorly from GI tract; highly protein bound; metabolised by liver; excreteed in urine
what are mucle peripheral drugs mechanism of action?
Acts on muscle reducing contractility by interfering with the ability of the sarcoplasmic recticulm to release Ca2+ ions via ryanondine receptors
What are peripharal muscle drugs used for?
- MS
- cerebral palsy
- spinal cord injury
- stroke
What are drug interactions with peripheral muscle muscle relaxants?
When taken with CNS depressants can result in sedation, lack of cooridination and resipraotry depression
What classes of neuromuscular blocking drugs is there?
- Non depolarising
- depolarising
What classes of non-depolarising muscular blocking drugs is there? what drugs are in these?
Aminosteriod
- pancuronium
- Rocuronium
- Vecuronium
Benzylisoquinolinium
- Atracurium
- Cisatracurium
- gallamine
- micacurium
What are depolarising neuromuscular blocking drugs?
suxamethonium
How do non-depolarising neuromuscular blocking drugs work?
They are competivie antagonists of Ach and compete with Ach for the nicotinic acetylcholine receptor and bind to it preventing Ach from binding. There is no conformational change in the receptor leading to influx of Na+ ions in the skeltal muscle so no activation of dihydropyrindine or ryanidine receptors therfore no contraction
How do depolarising neuromuscular blocking drugs work?
They bind to the NCR receptors and generate an action potential (increase permebability to Na and K). However, because they are not metabolized by acetylcholinesterase, the binding of this drug to the receptor is prolonged resulting in an extended depolarization of the muscle end-plate. As the muscle relaxant continues to bind to the ACh receptor, the end plate cannot repolarize, resulting in a phase I block.
Muslce fibres become insensitive to stimulation
What are the major indications for neuromuscular blocking drugs?
- Relax skeletal mucle during surgery
- reduce intensity of muscle spasms
- manage patinets fighting the use of a ventilator to help breathing
Clinical uses of neuromuscular blocking drugs
- endotracheal intubation
- dislocated joint
- in adjunction to anaesthesia
- eyeball imbolisation prior to eye surgey
- convulsion control
What are cholinesterases in the CNS and periphry called?
where are these found?
- CNS - acetylcholinesterases
- Peripheral - butyrylcholinesterases
- AchE - soluble near nerve terminals and around CSF
- BchE - soluble in plasma
