Pain management

  • Created by: MazzaW
  • Created on: 07-12-19 17:54


Acts within CNS to increase pain threshold by inhibiting central COX enzymes

Indications: mild-moderate pain, pyrexia

Cautions: reduce dose in liver failure/low body weight, 6hrly intervals in severe renal impairment

Adverse effects: S/E rare, may include flushing and hypotension

1 of 16


Inhibit COX enzymes to block prostaglandin synthesis

Indications: mild-moderate pain, pyrexia, inflammation

Contraindications: hypersensitivity (e.g. asthma), PUD, renal/liver impairment, pregnancy (3rd trimester), coagulopathy

Adverse effects: GI ulceration (COX1), AKI, hepatotoxicity, increased risk of MI/stroke (COX2)

COX1: routine physiological functions

COX2: induced by pain and inflammation

2 of 16

Opioids: mechanism and contraindications

Mechanism of action:

  • binds to opioid receptor
  • stimulates G protein: GTP -> GDP
  • inhibits intracellular cAMP production
  • blocks calcium efflux, increases potassium influx
  • ion imbalance: decreased neurotransmitter release and decreased transmission of pain


  • respiratory depression
  • comatose patients
  • head injury/raised intracranial pressure (interferes with neuro assessment- pupil responses)
  • risk of paralytic ileus
  • some specifics for each opioid
3 of 16

Opioids side effects

Side effects:

  • constipation (coprescribe senna +/- docusate)
  • N+V: usually settles in a few days, PRN haloperidol
  • sedation: decrease dose
  • dry mouth: oral hygiene, artificial saliva
  • respiratory depression
  • bradycardia, hypotension and arrhythmias
  • pruritus
  • tolerance + withdrawal
  • addiction- rare in severe pain

Opioid toxicity:

  • features: myoclonic jerks, pinpoint pupils, hallucinations, confusion, respiratory depression
  • mgmt: changing the opioid (reduce dose by 30-50%, contact specialist, consider alternative e.g. oxycodone), naloxone (if difficult to rouse/resp depression- RR<8/SaO2<90%, slow titration if opioid used for pain)
4 of 16


Metabolised via CYP450 enzymes to produce morphine, acts on opioid receptors

Used for mild-moderate pain

5 of 16


Mainly acts through its metabolite (opioid receptor agonist). Also inhibits noradrenaline and serotonin uptake

Indications: moderate-severe pain

May interact with SSRI/SNRI to cause serotonin syndrome

6 of 16


1st line for use (PO + SC)

Breakthrough doses should be 1/10 to 1/6 of regular daily dose

If breakthrough dose is >60mg this will be painful SC


  • Add together regular and breakthrough doses used in 24hrs to find total 24hr needs
  • Divide by 2 to get dose each 12hrs
  • Do not increase regular dose by more than 30-50%
  • Convert PO to SC (e.g. for a syringe driver) when no longer able to use oral route e.g. end of life, poor swallow, drowsiness
  • Convert to oxycodone if concerns about opioid toxicity
  • Convert to alfentanil if concerns about renal failure
7 of 16


Alternative to morphine in toxicity/intolerance

Beware dosage conversions

Naming differences: Oxynorm (PO, immediate release), Oxycontin (PO, modified release)

Better in renal failure (but use alfentanil if GFR <30)

8 of 16


Highly potent- don't use IV/SC

Practical choice for transdermal/transmucosal route in end-stage renal disease:

  • transmucosal: rapid onset, short duration
  • transdermal: slow onset

Don't stop patches for patients during their last few days

9 of 16


Highly potent

Short acting

If eGFR <30: SC opioid of choice

Seek specialist advice when prescribing this

10 of 16

Specialist pain services


  • nerve block
  • epidural
  • PCA pump
  • neurolytic block therapy
  • spinal stimulator
11 of 16


  • Corticosteroids: raised intracranial pressure, nerve compression, liver capsule pain, soft tissue pain
  • Antidepressants/anticonvulsants (e.g. amitriptyline, gabapentin, pregabalin): neuropathic pain
  • Muscle relaxants (e.g. baclofen, diazepam): muscle spasm
  • Bisphosphonates (e.g. pamidronate, zolendronic acid): bone pain
  • Antispasmodics (e.g. hyoscine butylbromide, hyoscine hydrobromide): bowel colic, bladder spasm- butylbromide in renal failure
12 of 16


Examples: amitriptyline

Used for neuropathic pain

Central and peripheral action on histamine, muscarinic, and serotonergic receptors

Need 2wks before full effects

Can be poorly tolerated. S/E: dry mouth, dizziness, blurred vision, confusion, constipation

13 of 16


Used for neuropathic pain

Less effective than TCAs

Decreased reuptake of serotonin/noradrenaline

Need 2-4wks of treatment before full effect.

S/E: GI upset, weight gain

Duloxetine is best tolerated and is licensed for diabetic neuropathic pain

14 of 16


Used for neuropathic pain

Acts on calcium channels

Benign S/E profile

Needs initial dose titration- 7 days for full effects

15 of 16


Used for neuropathic pain

Benign S/E profile

Quicker onset of action than gabapentin

Now a class C controlled drug

16 of 16


No comments have yet been made

Similar Medicine resources:

See all Medicine resources »See all Pharmacology resources »