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Overview of Pain Management |
What you need to know about opioids
Pharmacology of Opioids
Pharmacology General
- Act on opioid receptors in the brain and spinal cord
- Opioid receptor agonists - full or partial
- e.g. Morphine ...Opioid (µ) full agonist
- e.g. Oxycodone .... Opioid (?k µ and δ) agonist
Pharmacology specific drugs
This information can be found in the NZ formulary - see links for Individual Opioids (below)
- How quickly will they work?
- How long will they last?
- Contraindications?
Routes of Administration
When using a different route - different doses are required!
PO - oral
IV - intravenous
SC - subcutaneous
CSCI - continuous subcutaneous infusion - used commonly in palliative care using a syringe driver (Niki T pump)
Also:
Transdermal - (Fentanyl, Buprenorphine)
Epidural/spinal - (Fentanyl, morphine, pethidine)
Side Effects
- Toxicity
- Pinpoint pupils, sedation, respiratory rate (↓late sign), myoclonic jerks
- Constipation
- Confusion/delirium
- Nausea and vomiting
- Urinary retention
- Pruritis
Weak/Partial Opioids
Tramadol
Action: Partial opioid (µ) agonist & inhibitor of serotonin and noradrenaline reuptake (modulation)
Caution: Elderly (use smaller doses) / renal impairment/epilepsy/ Interaction with other medication, e.g. Tricyclic anti-depressants/ SSRIs - serotonin syndrome
Usual dose:
Acute pain: 50mg-100mg QID PO/IV (may be used with other opioids)
100mg SR BD PO
Chronic non-cancer pain: Sometimes used (seek advice)
Cancer pain: Often not used - use other opioids instead for severe pain
Advantages
- Less respiratory depression
- Not a controlled drug
- Can be effective for pain with a neuropathic element
Disadvantages
- Nausea and vomiting
- Confusion
- Has a 'ceiling dose' - not particularly useful in chronic, severe cancer pain
Codeine
Action: Weak opioid (µ) agonist - 'pro drug' of morphine
Caution: Renal failure/elderly/allergy to morphine
Usual dose: 30-60mg QID PO
Advantages
- Cheap, safe
- Good for mild-moderate acute nociceptive pain
- Best given regularly with paracetamol
Disadvantages
- Constipation
- Not good for chronic non-cancer pain
- Not always metabolised into active drug (morphine)
Full Opioids
Morphine
Action: Opioid (µ) agonist
Caution: Renal failure/opioid naive/severe liver impairment
Alternative IV opioid = Fentanyl. Alternative PO opioid = Oxycodone
Usual dose:
Check local protocols
Also see acute pain/cancer pain section
Start small doses if opioid naive
Oral dose is 2-3 times IV / SC dose because of the effect of first pass metabolism when given orally
Immediate release (short-acting) morphine - example = Sevredol
Sustained release (long-acting, controlled release) morphine - example = m-Eslon
Advantages
- Cheap, generally safe if used correctly
- Can be given orally, IV, SC
- Effective if given regularly
- Good for:
- Mod-severe acute nociceptive pain (e.g. post-op pain)
- Chronic cancer pain
Disadvantages
- Constipation and other side-effects
- Respiratory depression in high dose
- Misunderstandings about addiction
- Controlled drug
Oxycodone
Action: Opioid (?k µ and δ) agonist
Caution: Renal failure/opioid naive/severe liver impairment
Usual dose:
Start small doses if opioid naive
Check local guidelines - second line PO opioid after morphine
Also see acute pain/cancer pain section
Oxycodone is ≈ 1.5 to 2 times more potent than morphine i.e. 5mg oxycodone PO ≈ 10mg morphine PO
Oral dose is ≈2 times IV / SC dose because of the effect of first pass metabolism when given orally
Immediate release (short-acting) morphine - example = OxyNorm
Sustained release (long-acting, controlled release) morphine - example = OxyNorm Controlled Release (CR) or OxyContin
Advantages
- Cheap, generally safe
- Can be given orally, SC, IV
- Effective if given regularly
- Good for:
- Mod-severe acute nociceptive pain (e.g. post-op pain)
- Chronic cancer pain
Disadvantages
- Constipation and other side-effects
- Respiratory depression in high dose
- Misunderstandings about addiction
- Controlled drug
- Misunderstanding about effectiveness compared with morphine
See also: Useful information BPAC articles
Fentanyl
Action: Opioid (µ) agonist
Caution: Elderly/safer in renal impairment but still needs cautious use/ liver impairment
Usual dose:
Start small doses if opioid naive
Check local guidelines - second line IV opioid after morphine
Also see acute pain/cancer pain section
Can be given IV, SC and also Transdermal preparation - "Fentanyl Patches"
Advantages
- Can be given SC, IV
- Effective if given regularly
- Good for:
- Mod-severe acute nociceptive pain (e.g. post-op pain)
- Chronic cancer pain
Disadvantages
- Respiratory depression in high dose
- Only use Fentanyl patches if pain is at a stable level
- Tolerance develops rapidly
Controlled drug
Constipation and other side-effects
- Misunderstanding about effectiveness compared with morphine
- No oral preparation
- Buccal administration - can be unreliable
FENTANYL PATCHES - NZ FORMULARY
