Pain Management

Question 1

Features of selective COX2 inhibitors

Answer 1

Fewer GI side effects and toxicity
Higher CVS risk - MI and stroke
Addition of aspirin reverses GI benefits
Taken with meals

Question 2

Features of paracetamol

Answer 2

Inhibits central prostaglandin production
Well tolerated at therapeutic dose
OD- toxic metabolite NAPQI causes liver failure
Can cause nephropathy with chronic use
Use with caution in renal and liver impairment
Normal adult dose is 1g 4-6 hourly, max 4g/day

Question 3

Adverse effects of NSAIDs

Answer 3

Bronchoconstriction
Fluid retention
Nephropathy and ARF
Bleeding
Hypersensitivity
Dyspepsia and ulceration
Hepatotoxicity

Question 4

Features of NSAIDs

Answer 4

For mild to moderate pain
Inhibit COX - decrease prostaglandin - less inflammation
Take with meals

Question 5

Caution and contraindications of NSAIDs

Answer 5

Caution: renal or hepatic impairment, dyspepsia, cardiac failure, HPT, asthma, bleeding disorders
Contraindications: hypersensitivity, active PUD

Question 6

Features of chronic pain

Answer 6

Pain lasting beyond term of injury or painful stimulu s, over 4-6/52
Can be somatic, visceral or neuropathic
Manage s per cancer pain, using WHO analgesic ladder
A. Non-opioid with or without adjuvant
B. Weak opioid with or without non-opioid with or without adjuvant
C. Strong opioid with or without non-opioid with or without adjuvant

Question 7

Side effects of morphine

Answer 7

Nausea - resolves over few days, can give metoclopramide 10mg 8hourly
Sedation- resolves over a few days
Constipation - treat with stool softener and peristaltic stimulator eg senna solution

Question 8

Caution and complications of morphine

Answer 8

Caution in renal and hepatic impairment, elderly, pregnant close to term, lactation, neonates, reduced pulmonary reserve
Complications: respiratory depression - reduces responsiveness of BS respiratory center to CO2 and rhythmicity; can develop tolerance, dependence, addiction

Question 9

Features of morphine

Answer 9

Used for severe pain
Strong affinity for u-receptors
CNS effects: analgesia, euphoria, sedation
Causes histamine release: vasodilation, itching, bronchoconstriction
No ceiling dose- titrate upwards to effect, start 10mg 4 hourly for 24 hours increase 30-50%

Question 10

Features of codeine

Answer 10

Weak opioid used for mild and moderate pain
Prodrug metabolized by CYP2D6 - can get variants : slow metabolizer (poor analgesia but still constipation), fast metabolizer (resp depression, coma and death)
Adverse effects as with morphine
Adult dose: 30-60mg 4-6 hourly

Question 11

Features of tramadol

Answer 11

Used in conjunction with paracetamol
Weak opioid used for moderate to severe pain
Dual MOA: parent drug and active metabolite agonists of u-receptor, 5HT and NE reuptake inhibitors
Adverse effects similar to morphine but less abuse potential, resp depression and constipation
Interactions: risk of serotonin if used with SSRIs and MAOIs; metabolism induced by carbamazepine ; can drop seizure threshold
Dose: 50mg 4-6 hourly

Question 12

Adjuvant therapy options

Answer 12

TCAs

Anticonvulsants

Question 13

TCA used as adjuvant

Answer 13

Amitriptyline

Question 14

Features of amitriptyline

Answer 14

Has antidepressant, analgesic, anxiolytic and sedative effect
Useful if pain associated with sleep and anxiety disorders
Useful in neuropathic pain
Dose: 10-25mg nocte, upped to 75

Question 15

Anticonvulsants used as adjuvants and features of

Answer 15

Carbamazepine, valproate, lamotrigine, gabapentin
Useful for neuropathic pain
Start low, titrate up
Can be used alone or with TCAs

Question 16

Pathophysiology of pain

Answer 16

Nociceptive- normal pain processing pathway, free nerve endings stimulated by damage or inflammation
Neuropathic- abnormal pain pathway, processing of stimuli from PNS or CNS, no useful purpose
Peripheral pain pathways- noxious stimuli activate nociceptors, nociceptors induce inflammation by releasing inflammatory peptides