Principles of Analgesia in Patients with Opioid Dependence

Patients with an opioid dependency have 3 interlinked obstacles to effective pain management:

(1) Opioid-induced hyperalgesia (OIH), resulting in increased pain sensitivity;

(2) Opioid tolerance, leading to reduced effectiveness of opioids used to treat pain; and

(3) Opioid withdrawal, producing sympathetic stimulation and heightened stress responses if the usual opioids, such methadone or buprenorphine for opioid substitution therapy, are not given.

In patients with drug dependence it is essential to optimise non-opioid analgesia, ie simple analgesics and local anaesthetic blocks, to minimise the analgesic opioid needs.  

Pain transmission is complex with a multitude of receptors and transmitters.  With long-term opioid abuse, the endogenous opioid receptors become desensitised and tolerant, so that increasing amounts of opioid are needed to provide the same response.  By using drugs that act on the non-opioid parts of the pain pathway, we can optimise analgesia, and avoid or reduce the difficulty in using opioids for analgesia.

Acute moderate or severe pain will still require additional strong opioid analgesia (eg morphine or oxycodone) for which the doses will usually need to be higher than usual.  Opioid analgesic dosing should be regular where possible.  If the patient requests multiple additional “prn” doses, the regular doses should be increased.

There is evidence of additive effects and/or cross-tolerance with barbiturates, opioids, benzodiazepines and phenothiazines in cannabis users, so they may require higher than usual doses of opioids for analgesia.

For opioid-addicted patients, heroin and diamorphine are not the same.  The diamorphine content of heroin is typically very low and not predictable.

In all patients, initial opioid doses should be in the low range and the response assessed and titrated as appropriate.   

Even with opioid tolerance, the risk of opioid side effects is unpredictable so these patients need very careful monitoring.