3. Old stuff
          3.1. Old pharm stuff (pre 2009)
              3.1.3. Pharmacology
                  3.1.3.5. Opioids
                      3.1.3.5.3. Opioid agonists
                          3.1.3.5.3.9. Other opioid agonists
 3.1.3.5.3.9.2. Oxycodone 

Oxycodone

[SH4:p116; PI on MIMS]

Usage

Moderate to severe pain

Structure

  • Semisynthetic narcotic analgesic
  • Derived from opium alkaloid thebaine
  • Chemical name is 14-hydroxydihydrocodeinone

Pharmacodynamics

Potency

1 mg of oxycodone PO
= Morphine 2mg PO, or 1/3 mg IV
= Pethidine 10mg PO, or 2.5mg IV
= Codeine 7mg PO (approx)
* [PI: OxyContin]

Mechanism of action

  • Agonist at MOP receptors
  • Weak agonist at DOP and KOP receptors

Effects

Similar to other opioid agonists

Side effects

  • High abuse potential
  • Risk of tempering
    * Crushing and powdering for IV or intranasal use

Overdose

Symptoms and signs

  • Respiratory depression
  • Somnolence
  • Eventually coma and skeletal muscle flaccidity
  • Rhabdomyolysis leading to renal failure has been reported
  • Pulmonary oedema

 

Pharmacokinetics

Absorption

  • High oral bioavailability = up to 87% after PO
    * Morphine PO bioavailability is about 30%
  • Absorption of OxyContin is biphasic
    * Initial absorption of about 40% within first hour
    * than more controlled absorption

Metabolism

  • Extensively metabolised to noroxycodone
    * By CYP3A isoenzymes
  • Also some metabolised to oxymorphone
    * By CYP2D6

Elimination

Both metabolites eventually undergo glucuronidation

Action profile

Endone

  • Analgesic effect occurs within 10-15 minutes
  • Peak action in 30-60 minutes
  • Persists for 3-6 hours
    * May be shorter if tolerance
  • Elimination half-life = 2-4 hours

OxyContin

Maximal plasma concentration in about 3 hours

Half-life = 6.5 hours

Pharmaceutics

Formulation

  • Active
    * Oxycodone hydrochloride
  • Inactive
    * Stearic acid
    * Microcrystalline cellulose
    * Anhydrous lactose

Clinical

Interactions

Can potentiate anticoagulant activity of coumarin derivatives (e.g. warfarin)

Effects of oxycodone is
* Increased by alkalising agents
* Decreased by acidifying agents

Special considerations

  • Reduce doses in elderly, hepatic or renal impairments
  • Females have 25% higher plasma oxycodone concentration
    * Reasons unknown
  • Not recommended for children under 12 y.o.