Propoxyphene

[SH4:p116; NPS July 2003 PPR 22]

Usage

• Mild to moderate pain not adequately relieved by aspirin
  * The only clinical usage
  * Used in some popular pain-relievers such as di-gesic, capadex

Structure

• Structurally similar to methadone

Pharmacodynamics

Mechanism of action

• Binds to classic opioid receptors

Effects

• Does not have antipyretic or antiinflammatory effects
• No significant antitussive activity
• Analgesia
  * Oral doses 90-120mg produces analgesia and CNS effects like codeine 60mg + aspirin 650mg

Side-effects

• Most common side effects
  * Vertigo
  * Sedation
  * N&V
• Respiratory depression
  * 1/3 as potent as codeine in depressing ventilation
• Overdose
  --> Seizures and ventilation depression
• Mild withdrawal syndrome possible
• Similar abuse potential as codeine
• IV administration produce severe damage to veins
• Dependency possible

Pharmacokinetics

Absorption

• Completely absorbed from oral administration
  * But still poor bioavailability due to high first-pass hepatic metabolism

Metabolism

• High first-pass hepatic metabolism
• Propoxyphene is demethylated to norpropoxyphene

Elimination

• Elimination half-time = 14.5 hours

Clinical

Avoid paracetamol/dextropropoxyphene combinations (e.g. capadex, Di-Gesic, Paradex)
--> No more effective than paracetamol alone
* [NPS]