K4ii / 21A12 / 17A12: Oxycodone

21A12: Exam Report

Describe the pharmacology of oxycodone.

54% of candidates passed this question.

There were many exceptional answers which provided extensive detail on the drug. The best of these gave context for the drug characteristics, such as by referring to oxycodone relative to other opioid drugs that might be chosen, or to considerations for safe and effective administration. Some answers, however, provided generic information on opioid drugs, which could not gain all the available marks.

17A12: Exam Report

Describe the pharmacology of oxycodone.

53% of candidates passed this question.

Few candidates covered the pharmacokinetic aspect of the question sufficiently.
No marks were awarded for generic comments such as hepatic metabolism and renal excretion.

K4ii / 21A12 / 17A12: Describe the pharmacology of oxycodone

Oxycodone

Chemical

Semi-synthetic opium alkaloid derivative

Use

Analgesia

Presentation

PO → immediate & controlled release

      → 5/10/20mg capsules

IV → 10mg/mL

Dose

(IV) 2.5 – 5mg

(PO) 5 – 10mg

NB: PO oxycodone 10mg = PO morphine 20mg

       PO oxycodone 10mg = IV oxycodone 5mg

 ORAL bioavailability is high ~70% of IV dose

Recall: M OBA is 30% due to high 1st pass metabolism

∴ oral endone is more potent than oral morphine

Onset

Peak plasma

OFFSET

IR – 1.5hrs

IR – 3hrs

CR – 3hrs

CR – 4.5hrs

MoA

µOP

kPO

dOP

Agonist

PD

CNS – analgesia, miosis

CVS – ↓BP 2° histamine

GI – N&V, constipation

GU – ↑smooth m. tone → urinary retention

MSK – pruritus

PK

A

Good OBA 70%

pKa 8.5

= 10% UNIONISED

D

VD 2.6L/kg

Crosses placenta + breast milk

Low lipid solubility

M

Hepatic

  • CYP3A4 (79%) → noroxycodone
  • CYP2D6 (<3%) → oxymorphine

E

Renally excreted metabolites

20% unchanged

NB: oxymorphine is v potent

CYP2D6 has 2 phenotypes

  • Extensive metabolites → ↑dose
  • Poor metabolisers → ↓dose

Needs to be given with caution in hepatic & renal impairment

Although metabolites have less adverse effects cf. M

Adverse Effects

Resp D

Hypotension

N&V

Hallucinations

Dependence

Drug Interactions

Incompatible with prochlorperazine