Analgesia 1 Flashcards
What are the 4 areas of the conduction of pain that analgesics can act at?
- Sit of injury e.g. NSAIDs (decrease the inflammation)
- Alter nerve conduction (Local anaesthetics)
- Modify transmission in the dorsal horn (opioids and some antedepressants)
- Central competent and emotional aspects of pain e.g. opioids and antidepressants.
What is appropriate pain?
Pain that lasts whilst the injury is still present
What is chronic pain?
Pain that remains past the time of the injury.
With pre-emptive analgesia, what does not occur at the time of injury?
Pain or hypersensitivity.
What are the 4 opioid receptors?
- mu
- delta
- kappa
- nociception
Name 4 things that affects the success of opioids?
Route, species, dose and stimulus.
name 10 clinical side-effects associated with the use of opioids?
- mania
- respiratory depression
- CVS effects
- Pancreatic duct
- Ileus
- Nausea and vomiting
- urinary retention
- pruritus
- miosis
- mydriasis
What is the name of our own endogenous opioids?
Endorphins
Which is the most efficacious opioid at relieving pain?
Morphine
What is morphine?
A full agonist at mu, delta and kappa receptors.
What is the duration of morphine?
4 hours
What is the oral availability of morphine and how much will an increased dose extend its action by via this route?
25% bioavailability - can be extended to 8 hours duration.
Is morphine licensed and what class of drug is it?
Not licensed. class II drug.
What is methadone?
It is a full mu agonist with affinity for the NDMA receptor.
What does it inhibit?
Inhibits epinephrine and serotonin reuptake.
What is the duration of action of methadone and how can it be extended?
about 4 hours, can be extended with SC administration.
What is the bioavailability of methadone and what class drug is it?
Poor oral bioavailability - class II drug.
Is methadone licensed?
Licensed for dogs and cats.
What is an advantage of methadone over morphine?
Morphine sometimes causes sickness, methadone can, but very rare.
What is the NDMA receptor involved in?
Chronic pain.
What is Pethidine (Meperidine)?
Short acting agonist of the mu receptor and shown to block sodium channels.
Agonist at alpha 2 B sub types.
What impact does pethidine have on the heart?
Negative inotrope, however increases heart rate therefore cardiac output is maintained.
Why should you not give pethidine IV?
Can induce histamine release.
Which drug should pethidine not be administered with and why?
Selegiline in dogs - combination of a monoamine oxidase inhibitor and pethidine should be avoided to prevent a serotonin like syndrome from occurring.
Is pethidine licensed and what category drug is it?
Licensed for dogs, cats and horses (spasmodic colic).
Category II drug.
What is fentanyl?
It is a short acting mu agonist.
What drug class is fentanyl
Class II.
When is the peak fentanyl effect following bolus administration?
3-5 mins later
Can be used for what?
Induction with BZD in compromised patients.
What kind of transfermal administration can be used for fentanyl?
Transdermal patches - never send an animal home with these on in case they eat them and overdose.
What is a negative impact of fentanyl and why dangerous?
Fentanyl causes significant bradycardia and if there is an overdose, the animal can stop breathing for 2/3 mins.
What kind of solubility is fentanyl?
it is really lipid soluble - only lasts about 20-30 mins.
Name another opioid which has been used in dogs for mild-moderate pain?
Codeine
Name another opioid which is used post-operatively in dogs?
oxycodone
What is the reversal agent/ antagonist of pure opioids?
Naloxone.
What is tramadol?
It is a pro-drug that is metabolised in only about 5-10% dogs. It is a low potency mu selective partial agonist.
What does tramadol increase and what is the result of this?
increases serotonin and therefore looks like analgesic effects.
Why should tramadol not be used as a sole drug analgesic?
Because they might still be in pain, despite showing signs that they are not.