17. Narcotic Analgesics Flashcards
What are the two aspects of pain?
Physiological and psychological.
Broadly, where do opioids act?
Centrally - psychoactive, peripherally - gate theory.
What is the gate theory of pain?
Pain transmission goes to substantia gelatinosa, uses a neurotransmitter. Inhibitory descending pathways from higher centres in the brain.
What is the pain pathway?
Nociceptor detects pressure/heat/chemical, type A (myelinated) and C (non-myelinated) fibres carry information to dorsal root of spinal cord. Interneurones in substantia gelatinosa have inhibitory effects on signals. Reaches thalamus and primary sensory cortex.
What are the three groups of endogenous opioid peptides?
Enkephalins, endorphins, dynorphins.
What are the three types of opioid receptors?
Mu, delta, kappa.
What is the mechanism of action of mu (u) binding in opioid receptors?
GPCR: increased efflux of K+ so less excitability and less pain felt.
What is the mechanism of action of kappa (k) binding in opioid receptors?
GPCR: decreased influx of Ca2+ via channels.
What is the mechanism of action of delta (d) binding in opioid receptors?
Decreased cAMP synthesis.
What are the ADRs for opioids acting on mu (u) receptors?
Nausea, vomiting, constipation, drowsiness, miosis. DEPENDENCE TOLERANCE - key risk. Need to monitor for respiratory depression and hypotenison.
What are the ADRs for opioids acting on kappa (k) receptors?
Dysphoria -> confusion. DEPENDENCE TOLERANCE.
What is the half life of morphine?
1.3-6.7 hours.
What is the half of diamorphine (heroine)?
0.08 hours.
What is the half life of methadone (used to combat heroine addiction)?
15-30 hours.
What are the clinical uses of opioid drugs?
Analgesic for moderate-sever pain, including of visceral origin.
What are the clinical uses of morphine?
Analgesic in terminal illness, diarrhoea.
What is the clinical use of diamorphine?
Analgesic in terminal illness, epidural analgesia (not licensed yet).
What is the clinical use of methadone?
Maintenance in dependence.
What is the clinical use of codeine?
Mild analgesic.
What is the metabolism of codeine?
Metabolised by CYP2D6 to morphine.
What is the use of fentanyl, alfentanil, remifentanil?
Anaesthetics.
What is an ADR of fentanyl, alfentanil, remifentanil?
Can cause histamine release.
What is the clinical use of pethidine?
Analgesia in labour.
Why should pethidine not by used as frequent repeat doses?
It can cause convulsions.
What receptor do naloxone and naltrexone act on?
Mu (u) receptor antagonists.
What are the half lives of naloxone and naltrexone?
Naloxone 1-1.5 hours, naltrexone 4 hours.
What are the uses of naloxone and naltrexone?
Opioid toxicity, reverse respiratory depression, treatment of dependence.
What is meant by opioid analgesics being controlled drugs?
Prescriptions are only valid for 28 days, they must have thorough information including name and form of drug, strength and dose, total quantity or number of doses in words and figures.
