Muscle Relaxants and Ancillary Drugs Flashcards
What is an Ancillary Drug/ Medication?
An ‘additional’ drug added to improve the overall wellbeing and stability of the patient
What are the 4 classifications of Ancillary Drugs used in vet medicine?
1) Anticholinergics
2) Sympathomimetics
3) Bronchodilators
4) Doxapram
What part of the brain is the centre of the autonomic nervous system?
Hypothalamus
The sympathetic nervous system is made up of short _______ and long _______ fibres
- Preganglionic (myelinated)
- Postganglionic (unmyelinated)
All preganglionic fibres use ________ as the neurotransmitter, regardless of sympathetic or parasympathetic nerves
- Acetylcholine
note: which bind to Nicotinic receptors within the ganglion
What are the neurotransmitters and receptors involved in the Parasympathetic pathway to the Heart and vessels?
Preganglion ACh-Nicotinic receptor
Postganglion ACh-Muscarinic receptor
What are the neurotransmitters and receptors involved in the Sympathetic pathway to the Heart and vessels?
Preganglion ACh-Nicotinic receptor
Postganglion Norepinephrine- Beta + alpha adrenoreceptors
What are the neurotransmitters and receptors involved in the Sympathetic pathway to the Sweat Glands and Vessels?
Preganglion ACh-Nicotinic receptor
Postganglion ACh-Muscarinic receptor
What are the neurotransmitters and receptors involved in the Sympathetic pathway to the Renal vessels?
Preganglion ACh-Nicotinic receptor
Postganglion Dopamine-Dopaminergic receptor
What are the neurotransmitters and receptors involved in the Sympathetic pathway to the Adrenal medulla, and subsequent Heart and vessels?
Preganglion ACh-Nicotinic receptor
Epinephrine and Norepinephrine travel in the blood and bond to Beta + Alpha adrenoreceptors
What is the purpose of using Anticholinergics in a patient?
Anticholinergic medications are a class of drug that block the neurotransmitter acetylcholine in the central and peripheral nervous system. They are used to block a wide variety of conditions associated with activation of the parasympathetic nervous system.
Thus resulting in the following:
Heart: Increased HR and Contraction
Lungs: Bronchodilation
Pupils: Dilation
Salivary Glands: Decreased salivation
Arterioles: Vasoconstriction
Sweat Glands: Increased Sweating
Adrenal Glands: Release of adrenaline and noradrenaline
GI Tract: Decrease peristalsis- Caution with colic
Bladder: Relaxation
What are the 2 most commonly used Anticholinergics in vet medicine?
- Atropine
- Glycopyrrolate
What is Atropine used to treat?
- Bradycardia
- Integral part of CPR (cardiac-pulmonary resuscitation)
What routes can Atropine be administered?
- IV
- IM
- Down the trachea
Atropine is not considered helpful in rabbits, why?
And what drug should be used for rabbit bradycardia?
Rabbits possess Atropinase, and therefore rapidly metabolize atropine, rendering it ineffective
- Glycopyrrolate used be used instead
What are the main side effects associated with Atropine?
- 2nd degree AV block (P waves with no QRS wave)
- Paradoxical bradycardia due to activation of certain subtypes of Muscarinic receptors, leading to bradycardia
When is Atropine contraindicated?
- Patients with pre-existing tachycardia (e.g. shock or fever patients)
- Hyperthyroidism
- Phaeochromocytoma
What is the benefit of using Glycopyrrolate over Atropine?
- Slower onset of action, with a more controlled increase in HR
- Longer duration of action
- Does NOT cross the BBB
- Does NOT cause pupil dilation
What is a Sympathomimetic?
A type of drug that produces effects characteristic of the sympathetic nervous system by stimulating sympathetic nerves
What are the subclassifications of Sympathomimetics, and give examples?
- Mixed inotropes + vasopressors: Dopamine, Adrenaline, Noradrenaline and Ephedrine
- Positive inotropes: Dobutamine
- Vasopressors: Phenylephrine, Vasopressin
What Bronchodilators are used in vet medicine?
- Salbutamol
- Terbutaline
What receptors do sympathomimetics exert their effect on?
- Adrenoreceptors (alpha and beta)
- Dopamine receptors
What are the effects of Adrenaline and Noradrenaline binding to the alpha and beta adrenoreceptors?
Alpha adrenoreceptor = vasoconstriction
Beta adrenoreceptor = Smooth muscle relaxation, platelet aggregation, increased inotropy and chronotropy, and increased lipolysis
What are the effects of Dopamine binding to the Dopamine receptors?
Within the CNS: Reduces pituitary hormone output, and modulates extrapyramidal activity
Peripherally: Vasodilation of renal and mesenteric vasculature, and inhibits further noradrenaline release
When would you use Adrenaline in the patient?
- CPR
- Anaphylaxis
- Severe hypotension and bradycardia associated with sepsis
- Added to local anesthetics to cause vasoconstriction, reduced blood flow and prolonged effects of the anesthetic
What are the effects of Adrenaline administration on the CVS and Respiratory system?
CVS: increased chronotropy and inotropy, vasodilation of the heart, improvement of O2 delivery to the tissues
RS: Bronchodilation
When would you use Noradrenaline in the patient?
- Severe hypotension and bradycardia associated with sepsis
What are the effects of Ephedrine binding to alpha and beta adrenoreceptors?
- Increased blood pressure and + inotropic effect
- Bronchodilation
What type of drug is Dobutamine, and what is its use?
- Synthetic analog of Dopamine
- Positive inotrope and chronotrope
- Useful in severe congestive heart failure
- Rarely causes arrhythmias
How must Dobutamine be adminstered to the patient?
On a CRI (IV)
When is Phenylephrine (vasopressor) typically used in patients?
When the patient has adequate cardiac function and cardiac output, BUT the patient has hypotension (such as seen with an epidural, or sepsis)
- used as a spray for nasal edema in horses
- used to induce splenic contraction in horses
What is the caution associated to using Phenylephrine in patients?
- causes vasoconstriction, and can reduce tissue perfusion
What is the use of Vasopressin in the patient?
- Increases heart contractility
What are the effects of Salbutamol?
- Bronchodilation
- Tachycardia in high doses
- Relaxes the gravid uterus
- Can lead to muscle tremors
What are the effects and uses of Terbutaline?
- Bronchodilation
Commonly used prior to bronchoscopy and broncho-alveolar lavage
What kind of drug is Doxapram?
Central Nervous System Stimulant
What are the effects and uses of Doxapram?
- Stimulate respirations after anesthesia
- Increase respirations in neonates who have a low-frequency, gasping, erratic pattern of breathing after receiving oxygen
Note: This drug doesn’t seem to have any real purpose or use
How is muscular relaxation achieved in vet medicine, give examples
- Centrally acting agents: Benzodiazepines, Guaifenesin, Alpha2 agonists
- Peripherally acting agents: Neuromuscular blocking drugs (Depolarizing and Non-depolarizing)
When can Neuromuscular blocking drugs be used?
Only used if:
- appropriate hypnosis, unconsciousness and analgesia is provided
- the patient can be monitored regularly
- the patient is intubated and mechanical ventilation can be given
What are the risks associated with using Neuromuscular blocking drugs?
- Paralysis of the muscles, including respiratory muscles can occur
- They DONT provide hypnosis, unconsciousness or analgesia
Neuromuscular blocking agents block the action of ________ at the _______
- Acetylcholine
- Neuromuscular Junction
What is the difference between Depolarizing and Non-depolarizing Neuromuscular blocking agents?
- Depolarizing: are non-competitive at the Nicotinic-Acetylcholine receptor
- Non-depolarizing: are competitive at the Nicotinic-Acetylcholine receptor
What is the effect of Neostigmine?
ACh-esterase antagonist
What is the effect of Pralidoxime?
ACh-esterase agonist
What is the effect of Hemicholinium?
Disruption of ACh pathway by decreasing the recycling of ACh
What is the effect of Vesamicol?
Inhibition of ACh returning to the vesicle
What is the effect of Non-depolarizing NMBA (Neuro-muscular blocking agents)?
Post-synaptic AChR antagonist
What is the effect of ACh and Succinylcholine?
Post-synaptic AChR agonist
What is the effect of Iathratoxin (e.g. red back spider)?
ACh exocytosis agonist
What is the effect of botulism?
ACh exocytosis antagonist
What is the effect of Myasthenia gravis?
Destruction of motor endplates
What is the only depolarizing NMBA found in vet medicine?
Succinylcholine
What is the duration of action and recovery period of Succinylcholine?
- Duration of action = 3mins
- Recovery = 10 - 12 mins (but longer in dogs due to lower levels of plasma cholinesterases)
What are the side effects and contra-indications associated with Succinylcholine in the patient?
- CVS: bradycardia
- Increased K+ release: causing arrythmias and caution in renal disease and burn patients
- Increase IOP: NOT for use in patients with ocular problems
Contraindicated in:
- Eye injuries/ disease
- Myopathies
- Patients predisposed to Malignant Hyperthermia (e.g. certain pig breeds)
- GDV
- Burn Victims
- Birds
Between depolarizing and non-depolarizing NMBA’s, which are more commonly used in vet medicine, and why?
The Non-depolarizing agents are more commonly used
- Cause paralysis without muscle contraction
- Doesnt cross the BBB
What type of drug is Atracurium, Cis-atracurium, Mivacurium, Vecuronium and Rocuronium?
A Nondepolarizing Neuromuscular Blocker
What is the benefit and risks of using Atracurium?
Benefits:
- Minimal cardiovascular effects
- Valuable in critically ill patients who cannot receive standard inhalant anesthesia concentrations
- 3-5 mins onset of action
Risks:
- Possible histamine release, thus must be given slowly
- Many potential drug interactions
- One of its metabolites is Laudanosine- which can cause seizures
What is the benefit and risks of using Cis-Atracurium?
Benefits:
- 4x more potent than Atracurium
- Minimal cardiac effects
- No release of histamine
- Produces less Laudanosine, and thus less likely to cause seizures
Risks:
- Still produces small amounts of Laudanosine
What is the benefit and risks of using Mivacurium?
Benefits:
- Fast onset: 2mins
Risks:
- Short duration: 15 mins
- Histamine release, which can lead to hypotension
- caution must be used in dogs
What is the benefit and risks of using Vecuronium?
Benefits:
- Minimal cardiac effects
Risks:
- Not to be used in liver disease patients, due to metabolism
- Not to be used in renal disease patients, due to excretion
- Not to be used in biliary disease
- No analgesic or sedative actions
What is the benefit and risks of using Rocuronium?
Benefits:
- Faster onset compared to all other Nondepolarizing Neuromuscular Blockers
Risks:
- Intermediate duration
- High doses = vagolytic
- Anaphylactoid reactions reported in some patients
- No analgesia or sedation
How are Non-depolarizing Neuromuscular Blockers be reversed?
What caution must be known before giving the reversal agent ?
- Use Anticholinesterases
e. g. Neostigmine and edrophonium
They act by reducing ACh metabolism, therefore more is available at the junction for competition with the remaining blockers
caution: anticholinesterases also affect muscarinic receptors, thus can lead to bradycardia, salivation, bronchospasm and diarrhea
- -> To reduce this, administer an anticholinergic
What is the Anticholinesterase of choice when needed to reverse a NDNB?
Edrophonium + Atropine (atropine increases its onset)
What is the drug of choice when trying to diagnose Myasthenia gravis?
Edrophonium
What are the 2 Anticholinesterases used in vet medicine?
Edrophonium (+ atropine)
Neostigmine (+ glycopyrrolate)
What are the indications for Neuromuscular Blockades?
- Ocular surgery for eye position
- Deep abdomen/ chest cavity surgery
- Arrest ventilation e.g. for thoracic surgery
- Limb relaxation
- When immobility is paramount e.g. intracranial surgery
- When patients need to be ventilitated in the ICU
