17. Narcotic Analgesics

Question 1

What are the two aspects of pain?

Answer 1

Physiological and psychological.

Question 2

Broadly, where do opioids act?

Answer 2

Centrally - psychoactive, peripherally - gate theory.

Question 3

What is the gate theory of pain?

Answer 3

Pain transmission goes to substantia gelatinosa, uses a neurotransmitter. Inhibitory descending pathways from higher centres in the brain.

Question 4

What is the pain pathway?

Answer 4

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.

Question 5

What are the three groups of endogenous opioid peptides?

Answer 5

Enkephalins, endorphins, dynorphins.

Question 6

What are the three types of opioid receptors?

Answer 6

Mu, delta, kappa.

Question 7

What is the mechanism of action of mu (u) binding in opioid receptors?

Answer 7

GPCR: increased efflux of K+ so less excitability and less pain felt.

Question 8

What is the mechanism of action of kappa (k) binding in opioid receptors?

Answer 8

GPCR: decreased influx of Ca2+ via channels.

Question 9

What is the mechanism of action of delta (d) binding in opioid receptors?

Answer 9

Decreased cAMP synthesis.

Question 10

What are the ADRs for opioids acting on mu (u) receptors?

Answer 10

Nausea, vomiting, constipation, drowsiness, miosis. DEPENDENCE TOLERANCE - key risk. Need to monitor for respiratory depression and hypotenison.

Question 11

What are the ADRs for opioids acting on kappa (k) receptors?

Answer 11

Dysphoria -> confusion. DEPENDENCE TOLERANCE.

Question 12

What is the half life of morphine?

Answer 12

1.3-6.7 hours.

Question 13

What is the half of diamorphine (heroine)?

Answer 13

0.08 hours.

Question 14

What is the half life of methadone (used to combat heroine addiction)?

Answer 14

15-30 hours.

Question 15

What are the clinical uses of opioid drugs?

Answer 15

Analgesic for moderate-sever pain, including of visceral origin.

Question 16

What are the clinical uses of morphine?

Answer 16

Analgesic in terminal illness, diarrhoea.

Question 17

What is the clinical use of diamorphine?

Answer 17

Analgesic in terminal illness, epidural analgesia (not licensed yet).

Question 18

What is the clinical use of methadone?

Answer 18

Maintenance in dependence.

Question 19

What is the clinical use of codeine?

Answer 19

Mild analgesic.

Question 20

What is the metabolism of codeine?

Answer 20

Metabolised by CYP2D6 to morphine.

Question 21

What is the use of fentanyl, alfentanil, remifentanil?

Answer 21

Anaesthetics.

Question 22

What is an ADR of fentanyl, alfentanil, remifentanil?

Answer 22

Can cause histamine release.

Question 23

What is the clinical use of pethidine?

Answer 23

Analgesia in labour.

Question 24

Why should pethidine not by used as frequent repeat doses?

Answer 24

It can cause convulsions.

Question 25

What receptor do naloxone and naltrexone act on?

Answer 25

Mu (u) receptor antagonists.

Question 26

What are the half lives of naloxone and naltrexone?

Answer 26

Naloxone 1-1.5 hours, naltrexone 4 hours.

Question 27

What are the uses of naloxone and naltrexone?

Answer 27

Opioid toxicity, reverse respiratory depression, treatment of dependence.

Question 28

What is meant by opioid analgesics being controlled drugs?

Answer 28

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.