The Australian and New Zealand College of Anaesthetists (ANZCA) has released a position statement recommending that slow-release opioids should not be used for the management of acute pain. For the purposes of this discussion, ANZCA includes transdermal opioid patches and the intrinsically long-acting methadone in its definition of ‘slow-release.’

ANZCA’s recommendations echo those of international guidelines as well as the indications approved by the Therapeutic Goods Administration (TGA). Slow-release opioids are considered inappropriate for acute pain as:

  • Individual variations make it difficult to predict an appropriate dose in opioid naïve patients;
  • Modified-release preparations cannot be divided which may complicate dose titration;
  • The use of slow-release opioids in this setting is associated with a significant risk of severe adverse events including respiratory depression and death;
  • Co-administration of slow-release opioids with immediate-release opioids increases the risk of adverse effects; and
  • Adverse effects are likely to be prolonged.

If opioids are required for the initial treatment of acute pain, it is recommended that an oral immediate-release opioid is administered on an as-needed basis. Temporary administration of a slow-release opioid may be appropriate in a previously opioid-naïve patient if a prolonged duration of pain is anticipated. However, preference should be given to agents with lower sedative potential to minimise respiratory depression.

The duration of opioid therapy must be carefully considered to prevent misuse. One large study demonstrates that 6.0% of patients who receive at least one day of opioid therapy will remain on opioid therapy one year later. However, this figure more than doubles for patients who receive at least eight days of opioid therapy. This highlights the importance of timely communication of the pain management plan to ensure that opioids are reduced and ceased as appropriate.

There is a wide range of opioid preparations available with significant clinical differences, as shown in Table 1. The intended formulation should be clearly specified on each opioid order to minimise medication errors.

Table 1. A comparison of immediate-release and ‘slow-release’ opioids

Medication Approximate duration of effect (hours) Comments
Immediate release ‘Slow-release’
Buprenorphine 6-8 (IM/SL) Norspan® patch
applied weekly
Partial agonist
Codeine 3-4 Contraindicated in
patients <12 years
Fentanyl 1-2 (IM) Durogesic®; patch
applied every 72 hours
Hepatic metabolism
to inactive metabolites –
preferred in renal impairment.
Caution with serotonergic drugs.
Hydromorphone 2-4 (Dilaudid®) 24 (Jurnista®)
Methadone 8-24 (chronic dosing) Long and variable duration
of effect with chronic use.
Caution with serotonergic drugs.
Morphine 2-3 (Sevredol®, Ordine®) 12 (MS Contin®)
24 (MS Mono®)
Oxycodone 3-4 (Endone®) 12 (OxyContin®) Hepatic metabolism to a
less active metabolite
plus minor conversion to
an active metabolite –
preferred in renal impairment
(adjust dose)
Pethidine 2-3 Associated with serotonin
syndrome – caution with
other serotonergic medications
Tapentadol 4-6 (Palexia® IR) 12 (Palexia® SR) Associated with serotonin
syndrome – caution with
other serotonergic medications
Tramadol 3-6 (Tramal®) 12 (Tramal® SR)
24 (Durotram® XR)
Associated with serotonin
syndrome – caution with
other serotonergic medications


  1. Australian and New Zealand College of Anaesthetists. Position statement on the use of slow-release opioid preparations in the treatment of acute pain. Melbourne: ANZCA; 2018.
  2. Rossi S (ed). Opioid analgesics. In: Australian Medicines Handbook. Adelaide: AMH; 2018.
  3. Shah A, Hayes CJ, Martin BC. Characteristics of initial prescription episodes and likelihood of long-term opioid use — United States, 2006–2015. MMWR Morb Mortal Wkly Rep. 2017; 66: 265–269.

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