UI - 000099

AU - Bovill JG

TI - Which potent opioid? Important criteria for selection

AB - Opioids remain the drugs of choice for the treatment of severe pain. In recent years several new potent

opioids have become available for clinical use. These newer drugs are generally safer than the older

morphine-like compounds and their differing pharmacological and pharmacokinetic properties allow the

physician to choose an appropriate drug according to the clinical situation and need of an individual patient.

These drugs are classified according to their activity at the opioid receptors. The opioid agonists produce

their pharmacological effect by an almost exclusive action at mu-receptors. The agonist-antagonist group are

kappa-receptor agonists and either competitive antagonists at the mu-receptor or weak mu-agonists. The use

of the potent opioid agonists, because of their potential for causing respiratory depression, is restricted to

hospitals. Fentanyl, the oldest drug of this class, is extensively used as a supplement to general anaesthesia,

or in high doses as a 'complete' anaesthetic for patients undergoing cardiac surgery. Alfentanil and sufentanil

are newer fentanyl derivatives. Alfentanil is unique in having a very short elimination half-life. This is a

particular advantage during short operations and for day-case surgery. For longer operations alfentanil can

be given as a continuous infusion to supplement nitrous oxide anaesthesia. Sufentanil is about 10 times more

potent than fentanyl and is more rapidly eliminated. Initial reports suggest that it may be more effective than

fentanyl as an anaesthetic supplement and that recovery may be more rapid. Both sufentanil and alfentanil

are also used in cardiac anaesthesia. The newer agonist-antagonist opioids, butorphanol, nalbuphine and

buprenorphine, have largely replaced pentazocine in clinical practice. Unlike pentazocine, they cause a low

incidence of dysphoric side effects. Like the pure agonists, they cause respiratory depression; however, in

contrast to the pure agonists this is not dose related, reaching a 'ceiling' as dose increases. The risk of

dependence is also less, so that these drugs are safer for the treatment of chronic pain. Additionally, it is

particularly worth noting that buprenorphine and nalbuphine cause minimal cardiovascular changes, and are

safe and effective drugs for treatment of pain associated with myocardial infarction. Buprenorphine, which is

effective parenterally, orally and sublingually, has a prolonged duration of action (up to 12 hours after a

single dose)

SO - Drugs 1987;33:520-530