Oxycodone

 

Oxycodone is a convenient orally active opioid available as both immediate and controlled release preparations.  It is useful in renal and hepatic disease as avoids the potential accumulation of active or toxic metabolites that can occur with other opioids although a judicious dose reduction may be required.

 

Use

Pain!

 

Dose

Titrate according to requirements considering patients co-morbidities, age, pre-existing opioid tolerance and pain level expected, manufacturer recommends 5 – 15 mg q 4-6h.

 

Dose equivalents: 30 mg oral morphine 2 – 3 hourly equivalent to 15 – 20  mg oral oxycodone 2 – 3 hourly

 

Pharmaceutics

Available as immediately acting tablets, syrup or capsules, controlled release tablets (12 – 24 h analgesia, usually given as a BD dose), and as suppositories

 

Pharmacokinetics

Oxycodone is 70 – 80% as potent as morphine but has better oral bioavailability

Controlled release tablets have an onset of action of approximately 1 hour and a duration of action of around 12 hours, they should be commenced after a period of treatment with the immediate release formulation has been used to calculate the approximate total dose requirement for 24 hours (divide total dose by 2 and give 12 hourly controlled release doses).  In practice the controlled release formulation can be used to give some background analgesia with top up doses of immediate release preparation as required.

 

Pharmacodynamics

Mechanism of action

Central and peripheral opioid receptor agonist, preventing transmission of pain signals by acting pre and post synaptically in spinal cord and by modulating central descending inhibitory pathways.

 

Systemic effects of oxycodone are similar to those of other opioids, namely:

 

CNS

•           analgesia
•           sedation/euphoria/dysphoria
•           meiosis
•           decreased ACTH, prolactin, FSH and LH secretion; ­ increased ADH secretion (SIADH rare)
•           obtunds CNS response to hypercapnoea, hypoxia and interrupts rhythmicity of respiratory centre
•           itch
•           nausea and vomiting
•           EEG: increasing doses of opioid cause beta to alpha to theta to sleep spindles to delta waves with EP
•           drowsiness, dizziness, headache, confusion, hallucinations, delirium, agitation, mood changes, tremor, visual disturbances, seizures.

 

CVS 

• decreased sympathetic drive (thus indirectly decreased BP and HR)
•           histamine release with oxycodone does not occur
•           reduced baroreceptor sensitivity leading to postural hypotension
•           cardiac rhythm disturbances (bradycardia and tachycardia can occur)
•           hypertension can occasionally occur

 

RESP 

•           respiratory depression is the most significant potential side effect, take care in patients at risk of adverse effects of respiratory depression!
•           rate decreased, increased tidal volume
•           apnoeas
•           decreased airway protective reflexes, decreased cough, decreased respiratory epithelial cilial action
•           bronchospasm is usually related to histamine release so not significant

 

GIT 

•           decreased motility, nausea and vomiting and dyspepsia (possibly central components)
•           ­sphincter of Oddi tone and tone of other smooth muscle sphincters (eg ureteric)
•           constipation

Other 

•           urinary retention
•           dry mouth
•           muscle rigidity
•           myoclonus (high doses)
•           urticaria
•           allergy/anaphylaxis (uncommon!)
•           hypothermia

 

Precautions

Prolonged use can lead to physical (and less often psychological) dependence, abrupt opioid cessation can then precipitate a withdrawal syndrome with nausea, vomiting, diarrhoea, sweating and anxiety.

 

Monitoring for administration

•   watch for sedation/respiratory depression