Fentanyl is a strong opioid. The transdermal patch is a long-acting formulation with a delayed onset of effect initially and a prolonged duration of action; plasma concentrations are halved about 17 hours after removal.2 It is unsuitable for acute pain. Each patch lasts 72 hours. Fentanyl accumulates to form a ‘depot’ in the skin below the patch, from where it gradually enters the circulation. A matrix ‘drug-in-adhesive’* formulation has replaced the previous gel-reservoir patches, which had problems with leaking † and potential for extraction for illicit use.4
Oral morphine is generally the first choice when an opioid is required for severe chronic pain, because of its familiarity, availability and range of strengths and formulations that allow greater flexibility in dose titration. Use immediate-release preparations to find the dose that provides effective analgesia with the most acceptable side effects, then switch to a sustained-release preparation to ensure stable, ‘round-the-clock’ analgesia. 5
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Reserve fentanyl patches for patients with chronic pain and established opioid needs who are unable to take oral morphine. Fentanyl patches can be useful when morphine cannot be used in severe renal impairment or when the oral route cannot be used because of vomiting or difficulty swallowing.6,7 Individual response to opioids varies and some patients might experience uncontrollable adverse effects or poor analgesic response to morphine; in such cases fentanyl is one of several alternative opioids that might be considered.6,7 (See Evidence for fentanyl compared with other opioids and Adverse effects).
* Matrix patches were introduced in Australia in 2006 and are expected to replace supplies of reservoir patches by August 2006, when the reservoir patches will be discontinued and withdrawn from the market.
†Two batches of 50 microgram-per-hour patches were recalled in Australia in October 2005 because of reports of leaking.3
Risks in opioid-naïve patients
Opioid-naïve patients are vulnerable to potentially fatal opioid effects such as respiratory depression. Do not use fentanyl patches in opioid-naïve patients with non-cancer pain.2,8 The prolonged duration of action of the fentanyl patch means that adverse opioid effects will be difficult to control; its use in opioid-naïve patients is rarely justified. Oral morphine is preferred because of the relative ease of dose adjustments. Although the approved indication and the PBS listing allow use of the fentanyl patch in opioid-naïve patients with cancer pain, it is still best practice to use oral morphine initially to assess how well patients tolerate the opioid and to find the dose that provides stable analgesia. For some opioid-naïve cancer patients the potential harms with the fentanyl patch may be considered acceptable when balanced with expected benefits — if so, start with the lowest-dose patch (12 micrograms per hour) and monitor closely. Wean other analgesics gradually (see Dosing issues).
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For opioid-tolerant patients, see Dosing issues below for equi-analgesic doses of other opioids.
Always use a stepwise approach to analgesia and pain management
Fentanyl should be prescribed within a stepwise approach to analgesia (as for all opioids5):
- use non-drug measures as appropriate, such as exercise, physiotherapy and psychological strategies for pain management
- always start with non-opioids: consider starting opioids when regular dosing of non-opioids (paracetamol, NSAIDs) or weak opioids (codeine, tramadol) is ineffective
- titrate to maximum doses before moving to the next drug
- encourage regular (rather than as-needed) use of analgesics.
Diagnose the type of pain as nociceptive (tissue damage) or neuropathic (nerve damage), as this affects treatment choice9 (see Therapeutic Guidelines: Analgesic6).
Discuss and agree on the specific goals of therapy with the patient and document these before embarking on opioid therapy; in non-cancer pain these would include pain relief, functional improvement and quality of life. If goals are not achieved after a reasonable trial, consider stopping the medication.10,11
(See NSW Therapeutic Advisory Group guidelines for further details5).
Ideally, refer patients with chronic non-cancer pain to a multidisciplinary pain management clinic, especially when6,7:
- the diagnosis is uncertain
- there is significant disability, mood change or medication difficulties
- there are multiple issues beyond pain alone
- the patient has a history of substance abuse.
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Although waiting lists are often prohibitively long, the change in PBS restrictions means that patients can more easily start opioid treatment while awaiting a pain clinic appointment.
Assess ongoing need for opioids through regular review. PBS authority requirements mean that recent review by a second medical practitioner is needed before opioids can be prescribed for more than 12 months. Although this review does not have to be conducted by a pain specialist, early referral to a pain clinic can ensure appropriate review and also fulfill the PBS requirement.
Evidence for fentanyl compared with other opioids
There is little good-quality published trial evidence comparing fentanyl with other analgesics in chronic non-cancer pain, and no blinded trials. Most guidelines are based on clinical experience and consensus.7,11,12
The available evidence suggests no efficacy advantage over standard opioids. A large, randomised open-label trial (n = 680) in patients with chronic lower back pain found similar effects on pain measured with a visual analogue scale (VAS) when transdermal fentanyl was compared with oral sustained-release morphine. 13 A smaller open-label trial in which patient preference was the primary outcome found small differences in mean VAS ratings, but these were unlikely to be of clinical significance.14 Some studies have shown that patients prefer fentanyl patches for pain relief over oral morphine, but the lack of blinding means factors other than efficacy cannot be ruled out (e.g. novelty of the delivery mechanism). 14,15
Consider the patient’s drug and alcohol history
Patients with a history of substance abuse should not be denied effective analgesia for genuine pain. Management is more complex in these patients because:
- previous users of opioids can have high opioid tolerance and may need higher doses for effective analgesia6
- concurrent use of alcohol and other central nervous system depressants can have additive effects and place the patient at risk8
- there may be a greater risk of dependence in such patients.
Involve pain management or drug and alcohol specialists when possible.
Renal impairment
Fentanyl can be used in severe renal impairment when other opioids are inappropriate. It is metabolised in the liver and does not have active metabolites.2
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