Analgesic drugs

Question 1

Give some examples of the following:

1. Strong opiods
2. Weak opiods
3. NSAID’s

Answer 1

1. Strong opioid (e.g. morphine, oxycodone, hydromorphone, heroin, fentanyl)
2. Weak opioid (e.g. codeine, tramadol, dextropropoxyphene)
3. NSAID (e.g. aspirin, diclofenac, ibuprofen, indometacin, naproxen), or paracetamol (which is not regarded as an NSAID)

Question 2

Describe the mechanism of action of opioids

Answer 2

Opioid action is mediated by G protein coupled opioid receptors, all of which couple, preferentially to produce:

1. Inhibition of opening of voltage-activated Ca2+ channels (suppresses excitatory neurotransmitter release from nociceptor terminals)
2. Opening of K+ channels

Question 3

What are the main classes of opioid receptors ?

Answer 3

1. μ-opioid receptors - responsible for most of the analgesic action of opioids
2. δ-opioid receptors - these receptors contribute to analgesia
3. κ-opioid receptors - these receptors also contribute to analgesia

Opioids are AGONISTS: as analgesics, act mainly through prolonged activation of μ-opioid receptors

Question 4

What is the mechanism of action of naloxone and what is it used for?

Answer 4

• It is a competitive antagonist at μ-receptors
• Used to reverse opioid toxicity (i.e. respiratory and/or neurological depression)

Question 5

What is the mechanism of action of naltrexone and what is it used in?

Answer 5

• Is similar to naloxone, but with the advantage of a much longer half-life, so mainly acts by competitive antagonism of μ-receptors
• It is used 1st line as the pharmacological management of relapse prevention for alcohol addiction

Question 6

What is the mechanism of action of NSAID’s?

Answer 6

Inhibiting the synthesis and accumulation of prostaglandins by cyclo-oxygenase (COX) enzymes COX-1 and COX-2

Question 7

List the main drugs used in the treatment of neuropathic pain

Answer 7

• Gabapentin and pregabalin (anti-epileptics)
• Amitriptyline (TCA)
• Carbamazepine

Question 8

What is the mechanism of action of gabapentin and pregabalin ?

Answer 8

They inhibit voltage-gated Ca2+ channels

Question 9

What is the mechanism of action of tricyclic antidepressants e.g. amitriptyline ?

Answer 9

They inhibit the reuptake of mainly noradrenaline, as well as serotonin (5HT)

Question 10

What is the mechanism of action of carbamazepine and what type of neuropathic pain is it first line in the treatment of ?

Answer 10

• Inhibits voltage-activated Na+ channels
• 1srt line treatment to control pain intensity and frequency of attacks in trigeminal neuralgia