Pre-medication Drugs Flashcards by Eloise Newsom

Opioid Examples

Methadone - Mu agonist
Fentanyl - Mu agonist
Pethidine - Mu agonist
Morphine - Mu agonist
○ Not licensed in veterinary
Buprenorphine - Partial Mu agonist (kappa antagonist)
Butorphanol - Mu antagonist, Kappa agonist

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Opioid Licensing

Morphine - Not licensed
Methadone - Licensed in dogs/cats
Pethidine - Licensed in dogs. cats, horses

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What schedule are Opioids?

Schedule 2
Except Buprenorphine (schedule 3)

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What do opioids do?

Sedation
Analgesia
Used in sicker animals
Used for painful surgeries

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Pharmacodynamics of Opioids

Act peripherally and in CNS on 4 main receptor types:
○ Mu - most profound analgesic effects
○ Kappa
○ Delta
○ Nociceptin

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Mu Agonist Examples

Methadone
Fentanyl
Pethidine
Morphine
Buprenorphine - Partial Mu agonist (lesser effects)

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What is important to remember about Butorphanol

Mu antagonist and Kappa agonist
Good sedation but poor short-lived analgesia
Might use for non-painful procedures
Birds have high proportion of kappa receptors so could be good analgesic in birds

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Effects of opioids on Cardiovascular system

Generally considered to cause minimal cardiovascular depression
○ Some vagally mediated bradycardia can be seen at high doses

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Effects of opioids on Respiratory system

Respiratory depression usually minimal at clinical doses
○ Might be seen with fentanyl or high doses of methadone given IV
○ Sometimes if given intraoperatively you might see apnoea

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Effects of opioids on Gastrointestinal system

Opioids reduce gastrointestinal motility and decrease gastric emptying
○ Morphine may also induce emesis, but not very commonly used (other than in a CRI)
Methadone is licenced and doesn’t seem to cause nausea and sickness

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Can you antagonise opioids?

Yes
Reversed by naloxone

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Alpha-2 Agonist Examples

Medetomidine (faster acting and more effective)
Dexmedetomidine
Xylazine
Detomidine
Romifadine

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Alpha-2 agonist Licensing

Medetomidine - small animals (most common)
Dexmedetomidine - small animals
Xylazine - Small animals, cows and horses
Detomidine - Horses and cows
Romifadine - Horses

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What are alpha-2 agonists used for?

Sedation
Often used in combination with opioid
Short lived analgesia
Useful in lively/aggressive patients

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How do Alpha-2 agonists affect balanced anaesthesia

Selective alpha-2 agonists reduce the amount of anaesthetic drug required to induce and maintain anaesthesia
Reduce MAC - less isoflurane needed

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How do Alpha-2 agonists work?

Bind to presynaptic Alpha-2 receptors
Sympathetic nervous system activity decreases
This reduces the release of noradrenaline and ACh
Therefore HR and BP drop

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Effects of Alpha-2 agonists on Cardiovascular system

Can cause significant cardiovascular depression
DO NOT USE IN PATIENTS WITH CARDIOVASCULAR DISEASE
Not used in sick patients
Effects are biphasic
Initially peripheral vasoconstriction results in an increase in blood pressure
In response there is a reflex bradycardia and reduction in cardiac output
After something like 15-20 minutes blood pressure and heart rate return to normal

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Effects of Alpha-2 agonists on Respiratory system

Minimal respiratory depression
Can cause upper respiratory tract obstruction in brachycephalic

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Effects of Alpha-2 agonists on Gastrointestinal system

Can cause emesis in cats if used alone
Reduce endogenous insulin production
DON’T USE IN UNSTABLE DIABETIC
Increases urine production as a result of reduced renin and vasopressor secretion
DON’T USE IN BLOCKED ANIMALS

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Can you reverse Alpha-2 agonists?

Yes
Atipamezole
Antagonises sedative, drug sparring and analgesic properties

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Properties of Alpha-2 agonists

Marked sedative, muscle relaxant and analgesic properties
Associated with marked bradycardia/hypotension
Rapid onset
Short duration

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Examples of Phenothiazines

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Acepromazine (ACP) - only one licensed for veterinary use
Common component in premedication
Often combined with Alpha-2 agonist

Acepromazine Licensing

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Cats
Dogs
Horses

What are phenothiazines agonists used for?

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Contributes to sedation or tranquillisation (mild-moderate)
Provides anxiolysis
No analgesia
Relatively slow to take effect (30-40 minutes)
Long acting (6-8hrs)
Not suitable for:
Sepsis
Hypovolaemia
Cardiovascular compromise
Dogs with MDR1 mutations can be more sensitive

What are the pharmacokinetics of ACP?

1. Oral absorption can be erratic and unpredictable Hence IM or IV preferable 2. Rapid distribution and will cross BBB and placenta 3. Absorbed in fat and released slowly 4. High plasma protein binding Not active when bound 5. Slow elimination with half-life of 24-28 hours Longer duration of action

How do phenothiazines work?

Centrally acting by antagonising: ○ D1 and D2 receptors ○ Alpha-1 receptors ○ Muscarinic receptors ○ H1 receptors

Effects of Phenothiazines on Cardiovascular System

Causes vasodilation - can result in hypotension and hypothermia Giant breeds are more susceptible to these effects Considered antiarrhythmic

Effects of Phenothiazines on Respiratory System

Minimal depression in healthy patients

What is Neuroleptanalgesia?

Combination of an opioid and a tranquilizer/sedative Reduces amount of each required Results in improved sedation E.g. Opioid + ACP

Examples of Benzodiazepines

Diazepam (IV only) Midazolam (IV and IM but stings)

Licensing of Benzodiazepines

Diazepam - dogs/cats Midazolam - horses

What are Benzodiazepines used for?

Not analgesic Anxiolysis Sedation - often poor and can result in disinhibition Hyponosis NOT normally used in healthy patients Used in 'Quad' for cats IM Midazolam lowers dose of propofol needed Sometimes used in sick patients as co-induction agent Contributes to muscle relaxation USE IN SEIZURING ANIMAL - anticonvulsant

How do Benzodiazepines work?

Centrally acting via GABA-A receptor Binds to alpha subunit (GABA binds to beta) Enhances effect of GABA binding More CL- ions released post-synaptically preventing AP

Pharmacokinetics of Benzodiazepines

High lipid solubility - aids oral and IM absorption Widely distributed in body Metabolised by liver

Effects of Benzodiazepines on Cardiovascular System

Minimal cardiovascular depression - useful in sick patients with opioid or ketamine

Effects of Benzodiazepines on Respiratory System

Minimal cardiovascular depression - useful in sick patients with opioid or ketamine

Can Benzodiazepines be reversed?

Yes Flumazenil - compete for receptor without producing effects Short lived and doses may need repeating Expensive

Examples of NMDA Receptor Agonists

Ketamine

Licensing of Ketamine

Dogs Cats Horses Cows

What is ketamine used for?

Dissociative anaesthetic at high doses *Depresses thalamocortical system and activates limbic system * Profoundly reduces the amount of induction agent and inhalation anaesthetics you might otherwise need Sedation at lower Doses Only analgesic induction drug Analgesia at even lower doses - Infusion Short acting When used alone it’s a poor muscle relaxant ○ Often used in combination with something that causes good muscle relaxation E.g. midazolam or alpha-2. Common combination would be ketamine and midazolam in a sick cat

How does Ketamine work?

Blocks NMDA receptor activity Blocks signal transduction of Na and Ca ions going through channel Blocks glutamate action (excitatory neurotransmitter) Not totally selective ○ Weak Mu opioid agonist ○ Weak GABA-A agonist ○ Anti-cholinergic effects

How does Ketamine effect the Cardiovascular System?

Good cardiovascular stability Transient increase in Cardiac output and BP In some sick patients administration has caused a reduction in blood pressure probably due to myocardial depression in the presence of altered sympathetic tone

How does ketamine effect Respiratory System?

Dose dependent respiratory suppression More concern at pre-med doses

Examples of Anticholinergic Drugs

Atropine Glycopyrrolate (AKA parasympatholytic/vagolytic drugs)

Licensing of Atropine

Dogs Cats Horses

How does Atropine effect the Cardiovascular System?

Reduces bradycardia Often used intraoperatively to combat bradycardia DON'T use in presence of Alpha-2s

How does Atropine effect the Gastrointestinal System?

Anti-emetic

When is atropine used?

To combat bradycardia during anaesthesia Not routinely used in pre-med: ○ Mydriasis ○ Reduced gut motility ○ Bronchodilation

How does Atropine affect respiratory system?

Bronchodilation - improve ventilation

What is alfaxalone?

Neuroactive steroid

What is alfaxalone used for?

Induction agent via IV General anaesthetic agent Can be used to sedate sick patients Occasionally given if robust pre-med didn't provide enough sedation

Alfaxalone effects on Cardiovascular system

Few adverse effects Mild vasodilation following IV Cardiac output and tissue perfusion maintained

Alfaxalone effects on Respiratory system

Apnoea reported when IV

Pre-medication Drugs Flashcards

(53 cards)