Opioids

Avoid long-acting opioids in high-risk patients

This section covers use of opioids for analgesia and palliative care, with the exception of intrathecal opioids which are covered under Intrathecal Analgesia. Systemic harms of opioid medication are discussed separately under Opioid Harm Reduction Strategies.

Opioid medications are:

Management

Prescribing principles:

  • All conventional opioids can produce the same level of analgesia
  • Slow release opioids should not be used as sole agents in early acute pain
  • Immediate-release opioids should be used for breakthrough pain
    Breakthrough dosing is 1/6th to 1/12th of daily dose.

Considerations for PCA:

  • Require a competent patient
    • Can comprehend how and when to (appropriately) use the machine
    • Physically capable of pressing button
  • Improve analgesia
    Except where there are high nurse:patient ratios.
  • Improve patient satisfaction
  • ↑ Opioid consumption
  • Have equal efficacy SC or IV

Considerations for transdermal patches:

  • Should not be commenced in acute pain
  • Require regular doses of immediate release opioid for first 12 hours following application
  • If converting from a slow-release opioid, ensure a 12-hour crossover, e.g.
    • If 12-hour opioid, give the final dose of slow-release opioid when giving the patch
    • If 24-hour opioid, give the patch 12 hours after the final dose of opioid
  • If converting from a CSCI, then continue a:
    • Morphine infusion for 8-12 hours
    • Fentanyl infusion for 6 hours

Specific Agents

Comparison of Opioids
Agent Considerations Dosing
Tramadol
  • Mixed receptor activity
  • Relatively high NNT
  • Effective in neuropathic pain
  • Minimal improvement in pain score, but better subjective opinion of pain
Methadone
  • Old, synthetic, and cheap
  • Some NMDA affinity
  • High interindividual pharmacokinetic variability
  • Long half-life
    • Up to 60 hours
    • May lead to prolonged respiratory depression
  • High dose may ↑ QT interval
    TDP associated with chronic high dose, rather than single perioperative dosing.
  • Complex drug interactions via CYP3A4

Naive patient:

  • 0.2mg/kg IV, up to 20mg
  • 2.5mg PO BD
    Titrate weekly.

Opioid Rotation

Opioid conversion is an inexact science. Dosing considerations should include:

  • Duration of opioid therapy
  • Current pain severity
  • Use of PRN medication
  • Organ impairment

Steps for opioid conversion:

This in-exactness is supported by the fact that two peak bodies have published inconsistent guidelines. Most conversion studies are based on single-doses in opioid-näive patients.

  1. Calculate the current background 24-hour opioid requirement
  2. Convert this to an oral morphine
    This produces the 24-hour OME.
  3. Dose reduce by 25-50%, due to incomplete cross-tolerance
    ↑ Extent of dose reduction in groups at risk of opioid toxicity.
  4. Convert this OME to the new opioid, and round to a practically convenient dose.
  5. Dose breakthrough at 1/6th to 1/12th of the daily dose
Equianalgesic Opioid Conversion Table
Drug Route Ratio 30mg OME Considerations
Morphine PO 1:1 30mg
IV 3:1 10mg
SC 2-3:1 10-15mg
Oxycodone PO 1.5:1 20mg
IV 3:1 10mg
SC 3:1 10mg
  • 2:1 conversion from PO oxycodone
  • Identical to SC morphine
Fentanyl Top 100:1* 300μg
  • Given as 24-hourly doses
    e.g. 300μg = 12μg/hr patch.
  • Elimination half-life is 13-22 hours
SC 75:1* 450μg
Buprenorphine Top 75-100:1* 300μg
  • Given as 24-hourly doses
    e.g. 300μg = 12μg/hr patch.
  • Terminal half-life is ~24 hours
SL 40:1 750μg
  • Buprenorphine to oxycodone is ~20:1
    e.g. 200μg buprenorphine ≃ 5mg oxycodone.
  • Conversion ratio is identical for naloxone combination preparations
Hydromorphone PO 5:1 6mg
SC 5:1 6mg
  • Identical to PO hydromorphone
Tapentadol PO 1:3 90mg
Tramadol PO 1:5-10 150-300mg
Codeine PO 1:10 300mg
Methadone PO 4:1 (30-90mg OME) 7.5mg
  • Methadone conversion is complex and requires specific expertise
    • Recommended use TDS dosing initially
    • Complex conversions should occur in an inpatient setting
  • Use previous opioid for breakthrough
  • Round down
8:1 (90-300mg OME) ~4mg
12:1 (>300mg OME) 2.5mg
SC - -
  • 1-2:1 conversion from PO methadone
*Fentanyl and buprenorphine conversions include a unit change.

Adverse Effects

Management of Adverse Opioid Effects
Effect Considerations Management
OIVI
  • Sedation is a better predictor of ventilatory impairment than respiratory rate
  • ↑ Concern in high-risk groups
  • Monitoring
  • Naloxone 20-40μg
Pruritus
  • ↑ Risk with histamine-releasing agents
    e.g. Morphine.
  • Nalaxone
  • Naltrexone
  • Droperidol
Addiction
  • Short-term opioid therapy may lead to long term use
  • Many patients who retain unused opioid tablets are willing to share them with others
  • The most common source of prescription opioids for non-medical use is a friend or relative
  • Poorly managed acute pain may reduce retention in opioid-maintenance programs
  • Methadone and buprenorphine maintenance should be continued throughout acute pain episodes wherever possible
Falls

References

  1. Schug SA, Palmer GM, Scott DA, Alcock M, Halliwell R, Mott JF; APM:SE Working Group of the Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine (2020), Acute Pain Management: Scientific Evidence (5th edition), ANZCA & FPM, Melbourne.
  2. Safer Care Victoria. Opioid Conversion Ratios. 2021.
  3. Faculty of Pain Medicine. Opioid Dose Equivalence Calculation Table. ANZCA.
  4. Best Practice Advisory Centre. Methadone - Safe and Effective Use for Chronic Pain. 2008.