Choosing the opioid
For managing pain, first establish that the pain is of a type that responds to opioids1 (eg acute pain associated with surgery or labour, or chronic pain in cancer or palliative care). Opioid therapy is not suitable for some types of pain and alternative treatment should be chosen.
When selecting an opioid for relieving opioid-responsive pain, consider:
- severity of pain
- duration of action of the opioid formulation
- comorbidity (eg renal impairment)
- convenience of available formulation to the patient
- duration of likely use (eg short-acting opioid injection for a painful procedure versus sustained-release transdermal formulation for long-term use)
- likelihood of changes in pain severity (eg diminishing pain after surgery versus stable opioid requirement in palliative care) If the adverse effects of a particular opioid are especially troublesome, then it may be worth switching to another opioid or using a different route of administration. If the opioid has no effect on the pain, discontinue it and choose another type of analgesic (with further investigation of the cause if necessary).
Selecting the dose
Give an opioid at the lowest dose that gives maximal control of pain. Concerns about the development of tolerance2 or dependence3 should not, however, lead to withholding of effective doses of an opioid to control opioid-responsive pain.
Proportionately lower opioid doses may be appropriate for the very young and the elderly; both groups are more susceptible to the effects of opioids. Liver and kidney function can influence the dose; full doses of opioids can precipitate coma in marked liver impairment. Take great care calculating doses for neonates to avoid iatrogenic4 overdose.
Pain in an opioid-dependent individual may call for a higher dose than that needed for a non-dependent individual.
Rarely, because of genetic variability (genetic polymorphism5), an individual might be unexpectedly over- or under-responsive to the effects of an opioid.
Duration of treatment
For acute pain, the patient should receive only a small supply of opioid—ask the patient to return any unused medicine for disposal. The opioid should not be continued any longer than necessary.
Prolonged use of an opioid for non-cancer pain should be weighed carefully against the risk of long-term side-effects including addiction, hyperalgesia, cognitive impairment, and endocrine disorders.
Advise the patient that many adverse effects of opioids, such as nausea and sedation, diminish on continued use. However, constipation persists and may require specific treatment if opioid treatment is continued.
You should be alert to the possibility of abuse and diversion of opioids supplied for therapeutic purpose. Individuals with drug-seeking behaviour are more likely to:
- present to the clinic near closing time without an appointment
- visit health facilities frequently
- mention recently moving into the area from elsewhere
- request a specific drug and decline alternative suggestions (they may be well informed about drugs)
- complain about symptoms which are atypical or are inconsistent with physical examination Look out for signs of drug abuse (constricted pupils, nose and skin itchiness, dry mouth, inability to concentrate, puncture marks, signs of opioid withdrawal).
Sustained-release opioid formulations
Many opioids are available in long-acting or extended-release formulations. You should be familiar with how to initiate treatment with these products, modifying the dose and discontinuing their use. As these formulations often contain more opioid than immediate-release formulations, they may be associated with extra risks, including overdose, abuse, and misuse.
Advise the patient to take solid long-acting formulations, such as tablets or capsules, as specified in the patient information leaflet because any disruption of the formulation (eg by breaking, crushing or chewing the product) can release a large amount of opioid.
For transdermal patches6, the potential for opioid adverse effects is considerably enhanced if opioid absorption increases as a result of:
- temperature rise—either raised body temperature or exposure of the patch to external heat
- application of successive patches to the same area of skin
- failure to remove a patch when a new one is applied
- damage to the patch membrane that controls the rate of opioid release
- A substance that acts on the opioid receptor with similar effects to those of morphine. An opioid can be a substance that occurs naturally in the body (eg endorphins and enkephalins), or it can be derived from the opium poppy (ie an opiate), or it can be synthetic (eg methadone and pethidine)↩
- Tolerance follows repetitive exposure to a drug, leading to a reduction of the pharmacological effect of that drug↩
- Dependence is a state that develops as a result of repeated use of a certain chemical substance (eg alcohol, benzodiazepine, opioid, or even medicines for reducing blood pressure). It represents the resetting of homeostasis because of the persisting presence of the chemical substance↩
- An adverse effect which results from medical treatment↩
- The occurrence of two or more different forms of genetically determined entities (eg enzymes and receptors), due to variation in the genetic material between individuals↩
- An adhesive pad, containing a medicine, which, when affixed to the skin, releases the medicine at a controlled rate into the skin and thence into the bloodstream↩