What is the bioavailability of oxycodone (OxyContin) Immediate Release (IR) for all routes of administration (ROA)?

Bioavailability of Oxycodone IR Across Different Routes of Administration

Oral oxycodone IR has a high bioavailability of 60-87%, making it one of the most bioavailable oral opioids, while intranasal administration has a bioavailability of approximately 46%. Other routes of administration have varying bioavailability profiles that impact clinical efficacy and safety.

Bioavailability by Route of Administration

Oral Administration

• Bioavailability: 60-87% 1, 2, 3
• This high oral bioavailability compared to other oral opioids is due to lower presystemic and first-pass metabolism
• Reaches peak plasma concentration in approximately 1-1.8 hours 2
• Half-life of 3.5-4 hours 2, 3
• Food increases the extent of absorption (27% increase in AUC) but delays time to peak concentration (from 1.25 to 2.54 hours) 2

Intranasal Administration

• Bioavailability: 46% (with high interindividual variability) 4
• Peak plasma concentration reached in median time of 25 minutes
• Shows large interindividual differences in absorption rates
• May be an alternative route when oral administration is not possible

Intravenous Administration

• Bioavailability: 100% (reference standard)
• Plasma clearance of 0.83 L/min
• Volume of distribution at steady state: 2.02 L/kg
• Terminal elimination half-life: 157 minutes (approximately 2.6 hours) 4

Rectal Administration

• While specific bioavailability data for rectal oxycodone IR is not provided in the evidence, rectal administration is mentioned as a possible route 5

Clinical Implications of Bioavailability Differences

1. Dose Adjustments: When switching between routes, dosage adjustments are necessary to account for bioavailability differences

   • When converting from IV to oral, the oral dose should be higher to compensate for the incomplete bioavailability
   • Example: If IV dose is 10 mg, equivalent oral dose would be approximately 15-17 mg (assuming 60% bioavailability)

2. Patient-Specific Factors Affecting Bioavailability:

   • Hepatic Impairment: Oxycodone is extensively metabolized in the liver; clearance may decrease in hepatic impaired patients 2
   • Food Effects: High-fat meals enhance extent of absorption but delay onset of action 2

3. Metabolism Considerations:

   • Oxycodone is metabolized primarily by CYP3A4 (to noroxycodone) and CYP2D6 (to oxymorphone) 2
   • Oxymorphone is a potent analgesic metabolite that contributes to the clinical effect 3
   • Excretion is primarily via the kidney 2

Important Clinical Considerations

• Oxycodone has a more predictable metabolism than morphine, making dose titration easier 3
• For intranasal administration, dose titration should be individualized due to large interindividual differences in absorption 4
• When administered orally, controlled-release formulations have different pharmacokinetics but similar bioavailability to immediate-release formulations 6
• Oxycodone's high oral bioavailability makes it an effective option for oral pain management, with less need for route conversion than some other opioids

This bioavailability profile explains why oxycodone is effective as an oral analgesic and why it's considered comparable to morphine in terms of analgesic efficacy despite route differences.