Pharmacology: Drugs for Pain Flashcards
Example of a simple analgesic
Paracetamol
Example of a opiod analgesic
Morphein
What do we need to know about the meachanisms of paracetamol?
Don’t need to know the exact mechanism for exam as it’s still sort of unknown
Just need to know:
- It’s structure is similar to aspirin however it has no anti-inflamatory properties
- It acts on the central nervous system not the peripheral
Definition of an analgesic?
Something that reduces pain without completely knocking out the pain mechanism which would be an aneasthetic
Paracetamol dosage
0.5-1g every 4-6 hours
No more than 4g in 24h
Paracetamol half life in healthy patients?
2h
Why is paracetamol safe in low doses but causes hepatotoxicity in high doses?
In safe dose paracetamol is predominantly metabolises in phase II metabolism and excreted safely. A small amount is phase I metabolised and oxidised into a dangerous radical N-acetyl-p-benzoquinone imine (NAPQI). This is reduced into safe compounds by natural reducing agents in the liver.
In large doses the phase II metabolism become overwhelmed and a large amount is oxidised into NAPQI. There then isn’t enough natural reducing agents and NAPQI accumilates resulting in hepatotoxicity.
What is the name of the oxidising radical produced from paracatamol that causes hepatotoxicity?
NAPQI
Remember by it is the “key to napping” (the forever nap)
If discovered early how can you prevent hepatotoxicity from paracetamol overdose?
It can be prevented by administering supplementary reducing equivalents in the form of N-acetylcysteine (NAC).
Remember by NAC is knack to curing an overdose
What are the 4 main types of pain?
- Somatic
- Visceral(internal such as organs)
- Inflamatory
- Neuropathic
What is somatic pain?
What is visceral pain?
What is inflamatory pain?
What is neuropathic pain?
What is a nociceptor?
A pain receptor
On what parts of the nervous system do opioids act?
- Central nervous system
- Peripheral nervous system
Opioid presynaptic action?
Inhibits calcium channels on nociceptive nerves to inhibit the release of neurotransmitters such as substance P and glutamate
Opioid postsynaptic action?
Open inward potassium channels to hyperpolarise post synaptic cell membranes thus increasing the required action potential to generate nociceptive transmission
What receptors do opioids act on?
Specific G-coupled protien receptors:
- mu
- kappa
- delta
Morphine half-life
2-3 hours
