Analgesic Drugs Flashcards
What types of drug are available for analgesia?
NSAIDs
Paracetamol
Opioids
Local Anaesthetics
Alpha-2 agonists
Ketamine
How do NSAIDs work?
Non-steroidal anti-inflammatory drugs
1. When a cell is damaged, COX is activated
2. This stimulates the cell to produce prostaglandins which cause signs of inflammation (pain, redness, swelling)
3. NSAIDs target COX peripherally or centrally
NSAIDs also target descending pain pathways
Examples of SA licensed NSAIDs
Meloxicam
Carprofen
Robenacoxib
Fibrocoxib
Examples of Equine licensed NSAIDs
(DON’T USE IF HORSE IS GOING INTO FOOD CHAIN)
Phenylbutazone
Flunixin
Meloxicam
Examples of FA licensed NSAIDs
Meloxicam
Ketoprofen
Contraindications of NSAIDs in patients with…
- Renal or hepatic insufficiency
- Hypovolaemia
- Congestive heart failure & pulmonary disease
- Coagulopathies, active haemorrhage
- Spinal injuries
- Gastric ulceration
- Concurrent use of steroids
- Shock, trauma
- Pregnancy
Contraindications of NSAIDs in patients with…
- Renal or hepatic insufficiency
- Hypovolaemia
- Congestive heart failure & pulmonary disease
- Coagulopathies, active haemorrhage
- Spinal injuries
- Gastric ulceration
- Concurrent use of steroids
- Shock, trauma
- Pregnancy
When should NSAID use be limited?
Animals with co-morbidities
Long term use
Not in horses going into food chain
Side effects of NSAIDs
Vomiting
Diarrhoea
Renal Problems
Clotting disruption
What is grapiprant (Galliprant)?
New class of NSAID
More selective than other NSAIDs
Does NOT block COX
Works lower down inflammatory pathway
Blocs some activity of specific Prostaglandin
Targets oestoarthritis pain
Is paracetamol an NSAID?
Not anymore
How does paracetamol work?
Blocks peripheral and central COX
antipyretic action
What species can you use paracetamol in?
Off license - Horses
Off license - Dogs (unless with codeine)
NEVER CATS
How do opioids work?
Act on 4 key receptors:
Mu - most analgesic
Kappa
Delta
Orphanin
Should be used pre-emptively (pre surgery)
Examples of opioids
Morphine - not licensed
Methadone - SA
Butorphanol - SA, horses
Buprenorphine (partial Mu agonist) - SA
Pethidine - SA, horses
Fentanyl (50% stronger) - SA
What schedule are opioids?
Schedule 2
Except buprenorphine (3)
What are local anaesthetics?
Amides or esters
Very versatile
What is important to note about local anaesthetics?
Small therapeutic window
Easy to overdose
How do local anaesthetics work?
All clinically useful local anaesthetics are weak bases
Exist in equilibrium between the neutral, non‐ionized, lipid‐ soluble form (B) and the ionized, water‐soluble form (BH+)
Formulated as acidic solutions of hydrochloride salts (pH 4–7)
Which are more highly ionized and thus water soluble
The receptor for local anaesthetics is located within the pore of the Na+ channel close to the cytoplasm
Only the ionized, charged form of the local anaesthetic can interact with this receptor
Local anaesthetics used in horses
Mepivacaine
Lidocaine
Lignocaine
Procaine - not often used - can change colour of fur
Bupivacaine - not licensed
Local anaesthetics used in FA
Procaine (contraindicated for epidural or IV use)
Lignocaine - used off license
Local anaesthetics used in SA
Lidocaine
Procaine
Bupivacaine - used off license (longer lasting)
How do alpha-2 agonists work?
Bind to alpha-2 receptors on presynaptic terminal
Prevent release of noradrenaline and ACh
Short lived but potent analgesia
Can be antagonised with atipamezole
SA alpha-2 agonists
Medetomidine
Dexmedetomidine
FA alpha-2 agonists
Romifidine
Xylaxine
Equine alpha-2 agonists
Xylazine
What is ketamine?
NMDA antagonist
How does Ketamine work
Blocks NMDA receptor activity
this prevents signal transduction of NA and Ca ions going through channel
Blocks glutamate action
