Opioid analgesics
Many opiod analgesics are available to the prescriber. Examples include morphine, diamorphine, codeine, dihydrocodeine, tramadol, oxycodone, meptazinol, buprenorphine, pentazocine, alfentanil, pethidine, remifentanil, papeveretum (a mixture of morphine hydrochloride, papaverine hydrochloride, and codeine hydrochloride [253:23:20], a.k.a. Omnopon), hydromorphone, fentanyl, and dipipanone. Pholcodine is sold OTC in the UK as an antitussive, it has very little analgesic action.
Codeine and dihydrocodeine are available in fixed-dose formulations with paracetamol (co-codamol and co-dydramol respectively), as is tramadol. The paracetamol appears to potentiate the opioid effects.
Some opioids are combined with anti-emetic drugs, for example with cyclizine (as in dipipanone plus cyclizine) or buclizine (as in Migraleve, with codeine and paracetamol) or hyoscine (plus papeveretum, a premedication mixture).
Common side-effects include opioid-induced constipation (OIC), dizziness, drowsiness, respiratory depression (at larger doses) and often nausea and vomiting in initial stages of treatment. Drowsiness may affect driving and performance of skilled tasks, so patients should be advised not to drive at the start of opioid analgesic therapy, or following dose increases. Patients should also be warned that effects of alcohol are enhanced whilst taking these types of drugs. Repeated use of opioid analgesics is associated with the development of psychological and physical dependence. Although this is rarely a problem with therapeutic use, caution is advised if prescribing for patients with a history of drug dependence. Naloxone is a specific antidote for the reversal of opioid induced CNS and/or respiratory depression as experienced either postoperatively or as a result of opioid overdose.
All opioids are contra-indicated in patients with acute respiratory depression, in comatose patients, patients with head injury or raised intracranial pressure (because opioid analgesics interfere with pupillary responses vital for neurological assessment), and patients at risk of paralytic ileus.
In the control of pain in palliative care the cautions associated with opioid use should not necessarily be a deterrent to their use.
Morphine derivatives are common recreational drugs causing dependence. FIxed-dose formulations of opioids plus naloxone can be used as adjunct in the treatment of opioid dependence, in particular for patients for whom methadone is not suitable; for example buprenorphine plus naloxone (Suboxone).
Mechanisms of analgesia 2017_2018
This set of 17 slides introduces students (beginner to intermediate learners) to some of the basic physiological processes that are the targets of many analgesic drug classes. Specific areas covered include the regulation of nociceptive input to the spinal cord by processes within the superficial layers of the cord itself and also descending fibres from the brainstem.
This 12-slide slide set created with PowerPoint presents an introduction into the pharmacology of opioid analgesics in order to provide a basic background to facilitate later understanding of more detailed pharmacology of opioid analgesics. Topics covered include: opioid receptors, their signaling mechanisms and responses; and pharmacological effects of opioid receptor ligands. This introduction to the topic of opioid analgesics would be appropriate for intermediate level learners. Contributed by Christopher Fowler, Umeå University, Sweden.