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What's new in analgesics |
Controlled release oxycodone (Oxycontin)
Oxycontin is now PBS listed for use in severe pain not responding to non-narcotic analgesics. This brief summary is limited to its use in palliative care.
What is it?
Oxycontin is controlled release oxycodone, a semisynthetic opioid which has similar therapeutic actions to other opioids (eg. morphine, codeine, fentanyl), namely analgesia. Oxycodone has long been used as an analgesic, but its use to date has been limited by the formulation. ie. 5mg tablets or 30mg suppositories. It is now available as a 10, 20, 40 or 80mg controlled release tablets taken 12 hourly (bd).
Oxycodone is well absorbed with an oral bioavailability of about 2/3, compared with 1/3 for morphine. By mouth therefore, oxycodone is more potent than morphine (published ratios vary between 2:1 and 1.5:1 ie. 30mg morphine = 15-20mg oxycodone).
It is metabolised by the liver and excreted primarily in the urine. It is metabolised to oxymorphone, noroxycodone and glucuronide conjugates but it is the parent compound that is responsible for the pharmacodynamic effects. Oxycodone has a short elimination half-life and neither the parent compound nor its metabolites have been shown to accumulate during repeated oral use.
Oxycodone has been incorporated into the “Acrocontin” system, which, without getting too technical, allows controlled delivery over 12 hours with onset of analgesia in one hour in most patients.
Advantages
The advantages of controlled release oxycodone can be divided up into: A) the advantages of oxycodone and B) the advantages of a controlled release formulation.
A). Advantages of oxycodone
1. Although it is an opioid, it is not morphine and therefore if patients refuse to take morphine (for many reasons including stigma), then oxycodone is a useful alternative.
2. If patients are experiencing unacceptable side effects from other opioids, e.g morphine, then oxycodone could be substituted with potential reduction of adverse effect but maintaining adequate analgesia.
This is thought to result from incomplete cross-tolerance to the analgesic and adverse effects of different opioids, which act at different opioid receptors in the central nervous system.
Other strategies for reducing adverse effects of opioids:
- Reduce the dose;
- Reduce the dose and add a co-analgesic;
- Symptomatic treatment of adverse effects;
- Change route of administration;
- Change the formulation;
- Change the opioid (as outlined above).
Eg. a patient experiences severe nausea on 60mg MS Contin bd but pain is controlled. Using the above strategies the nausea could be overcome by:
a) reducing the dose to 40mg bd;
b) reducing the dose and adding eg. paracetamol 1g qid;
c) adding metoclopramide 10mg qid, or haloperidol 1.5 - 5mg nocte;
d) changing the MS Contin to 5mg subcutaneous 4 hourly morphine (equivalent opioid dose);
e) changing to 10mg oral morphine 4 hourly, or Kapanol 60mg bd;
f) change to Oxycontin 80mg bd or Fentanyl patch 25mcg/hr (equivalent opioid dose).
B). Advantages of controlled release
Oxycontin has long been used in the palliation of pain. However its formulation as a 5mg tablet or 30mg suppository has limited its flexibility with dose titration especially when higher doses have been required.
The above example of 60mg MS Contin bd equates to 16 tablets a day of 5mg oxycodone but now would be substituted for 40mg bd Oxycontin (2 tablets / day). Thus controlled release oxycodone has become a realistic alternative opioid to morphine and fentanyl where decent doses are required.
Disadvantages
1. Controlled release oxycodone is still an opioid and therefore subject to the same side effect profile namely nausea, vomiting, constipation, sedation, respiratory depression, miosis, pruritis, etc.
2. Patients can only take oxycodone 5mg tablets for breakthrough doses, which may be a sizeable number of tablets with higher doses. This was overcome with oxycodone solution in the USA, but unfortunately is not available in Australia.
Cautionary notes
Taking broken, halved or crushed tablets can result in a rapid release of potentially toxic dose of oxycodone. This also applies to crushing MS Contin and Kapanol.
Initiation of dosing in patients with renal or hepatic impairment should be reduced to one-third to one-half of the usual dose with cautious dose titration. This also applies to very elderly or debilitated patients.
What's hot on the web?
There are many websites on palliative care related issues, some more useful than others. Below are listed some really useful, informative sites that are well worth a look.
http://www.jr2.ox.ac.uk/bandolier/
Not strictly speaking a palliative care site but an extremely useful evidence based medicine site voted NHS Best Web site 1999.
Recent update includes a review of Cox 2 inhibitors. Has a pain literature research facility.
http://www.growthhouse.org
Award winning site with useful links regarding issues in palliative care.
http://cherny.roxanelabs.net/
Site that has access to more than 20,000 palliative care related articles. Can also trial “EndNote” software, which is essential as a referencing tool.
http://www.multimed.com/oncology/oncopain/form.html
An interactive site that is aimed at problem solving, information sharing, anecdotal evidence and anything related to pain management especially related to cancer pain problems. You will need to subscribe and the “chat” comes across on your email. It's really quite interesting!
Joanne Doran is the area medical director for palliative care. She can be contacted at St Vincent’s Hospital jdoran@nor.com.au
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