Pain and Analgesics

Question 1

What is nociceptive pain?

Answer 1

Cause by physical damage or response to inflammatory soup
Results in activation of free-nerve endings
Respond to mechanical, chemical, pressure and temperature changes
Physiological/acute pain - easily treatable
Responds to analgesics

Question 2

What is neuropathic pain?

Answer 2

Pain resulting from damage/changes in the pain neurons themselves
Often chronic and difficult to treat
Shooting/burning pain
Paraesthesias: Pins and needles
Tingling, Numbness, Burning and Throbbing

Question 3

If a patient has these symptoms, what type of pain do they have?
Low-back pain
Myofascial pain
Arthritis
Visceral pain:
Pancreatitis
Interstitial cystitis
Endometriosis

Answer 3

Nociceptive pain

Question 4

What is allodynia?

Answer 4

Allodynia refers to central pain sensitization (increased response of neurons) following normally non-painful, often repetitive, stimulation. Allodynia can lead to the triggering of a pain response from stimuli which do not normally provoke pain

Question 5

If a patient has these symptoms, what type of pain do they have?
Phantom limb
Trigeminal neuralgia
Post-stroke pain
Post-herpetic pain
Complex regional pain syndrome
Malignant pain

Answer 5

Neuropathic pain

Question 6

What can cause the worst ever headache?

Answer 6

Sub arachnoid haemorrhage

Question 7

What is the inflammatory soup?

Answer 7

The ‘inflammatory soup’ produced contains substances that activate free-nerve endings. It can cause problems with some of the local anaesthetics; as it changes the pH affecting their ability to cross the membrane into the nerve.

Question 8

What are rubefacients and capsaicins and how do they help with pain modulation in periphery?

Answer 8

They are creams, which trigger pain pathways and thus distract the brain by diluting the effects.

Question 9

How is Nociceptive pain sensed?

Answer 9

Nociceptive pain sensed by free ending on C- (groan) and Aδ- (ouch) fibres

Question 10

If you fall over and hurt yourself and then rub on your wound with you hand (mechanical stimulation), what will this do?

Answer 10

Mechanical stimulation activates inhibitory interneurons

Reduces pain transmission by inhibiting 2nd order cells

Question 11

Describe the biopsychosocial model of pain perception

Answer 11

Incorporates all aspects of pain and associated behaviours:
Illness behaviour
Psychological distress
Attitudes and beliefs

Question 12

Name the non-pharmacological options to treat pain.

Answer 12

Exercise, physiotherapy
Acupuncture
TENS (Transcutaneous electrical nerve stimulation)

Question 13

Name the invasive procedural options to treat pain.

Answer 13

Nerve blocks/injections (Trigger points and Joints)
Ablation
Implants (Pumps and Neuromodulators)
Placebos have similar effects

Question 14

Name the pharmacological options to treat pain.

Answer 14

Nociceptive Pain – NSAIDs and Opioids:
Ibuprofen
Co-codamol
Morphine

Neuropathic Pain* – Tricyclic antidepressants & antiepileptics:
Nortriptyline/Amitriptyline
Gabapentin ± Amitriptyline
Carbemazepine alone (never in combo)!

Question 15

Describe the general NSAID mechanism of action.

Answer 15

NSAIDs Block production of prostaglandins by inhibiting COX (cyclo-oxygenase) enzymes
Cyclooxygenases breakdown arachidonic acid to give prostaglandins

Question 16

What are the three forms of Cyclo-oxygenase and what are their functions?

Answer 16

COX 1 – Normal cell function (NSAID)
COX 2 – Inflammation (NSAID)
COX 3 – Fever? Does it exist? (Paracetamol)

Question 17

Describe the MoA of NSAIDs at a neuronal level.

Answer 17

Decreased production of prostaglandins by NSAIDs results in less activation of the prostanoid receptor and thus no depolarisation of the voltage gated Na+ channels

Question 18

Name some NSAIDs

Answer 18

Aspirin, Ibuprofen, Naproxen, Diclofenac, Indomethacin and COX-2 inhibitors: Celecoxib and Etoricoxib (lower GI effects)

Question 19

What are the side effects of NSAIDs?

Answer 19

GI problems: heartburn, nausea, vomiting, diarrhoea, bleeding/ulceration
CV incidents: thrombosis (esp. Cox-2)
Headache
Tinnitus

Question 20

What are side effects of NSAID intoxication?

Answer 20

Salicylism: Salicylate toxicity may occur with high dose acute or chronic ingestion of NSAIDs (1% mortalilty)

Question 21

Name two opioids.

Answer 21

Morphine (gold standard) and Heroin (diamorphine).

Act on opioid receptors (OP1-4)

Question 22

Name opioid agonists, partial agonists/mixed anatagonists and antagonists.

Answer 22

Agonists:
Strong - morphine, diamorphine,
Weak - codeine, dihydrocodeine

Partial agonists/mixed agonist-antagonist
buprenorphine (long half life)

Antagonists (stops highs of opioids)
naloxone, naltrexone

Question 23

What are the 4 ways opioids decrease neuronal transmission by?

Answer 23

Decreasing opening of voltage-dependent Ca2+ channels
Increasing K+ outflow via KATP and KIR channels
Decreasing Ca2+ release from intracellular stores
Decreasing exocytosis of transmitter vesicles
(reduction of neuronal transmission via hyperpolarisation)

Question 24

Name some symptoms of Opioid toxicity.

Answer 24

Respiratory depression
Conscious depression/mood alterations
Miosis

Question 25

What is Tramadol?

Answer 25

Synthetic opioid (agonist)
Also has atypical antidepressant effects (SNRI)
Great pain killer
Some very interesting side-effects (visual hallucinations)