Core pharmacology

Class Group

Opiate Analgesic

Legacy Cicm Level

Level 1

Introduction

semi-synthetic thebaine (opium alkaloid) derivative

Indications Uses

1. the treatment of moderate to severe pain in patients with cancer and
post-operative pain and
2. in the treatment of severe pain requiring a strong opioid.

Presentation

white tablets – immediate/sustained release. Paracet Combo in US

Main Action

primarily μ receptor activity but also has some weak κ and δ receptor activity

Mechanism of action

Binds primarily to inhibitory G-Protein Coupled μ-opioid receptors→ ↑adenylyl cyclase→ ↓cAMP→ hyperpolarization of cell→↓neurotransmitter release

Physiological effects

inhibitory action,
modulating the pain response to produce analgesia.

Mainly mu receptor actions

Adverse Effects Toxicity

weak K action may cause some of the
negative effects (dysphoria, psychomimetic)

Interindividual variability in metabolism. Other standard opioid side effects.

Absorption

PO. BA 60-87%

onset / duration 10-15 minutes / 3-6 hours

Distribution

LipId sol high-

crosses BBB

Protein binding

Prot bind ~45%

Volume of distribution

Vd 2.6L/kg

Metabolism

CYP3A family metabolism to noroxycodone and via CYP2D6 to oxymorphone (active), both subsequently conjugated

Excretion

excretion urine

Half-life

half life 2-4 hrs

Special Points

May precipitate encephalopathy in hepatic failure

Good reversal with naloxone

Route And Dose

20mg Oxy PO = 10mg Morphine IV

(Relative potency 0.5)