Opioids Flashcards
What is an opiate?
A drug derived from opium - naturally occurring
What is an opioid?
All exogenous substances, natural and synthetic, that bind specfically to any of the opioid receptors and produce at least some agonist effects
What are the 2 distinct classes of opium alkaloids?
Phenanthrenes - morphine
Benzylisoquinolines - Papaverine
Describe the structure of a phenanthrene
Phenanthrene nucleus has 3 rings containing 14 Carbon atoms
A fourth piperidine ring includes a tertiary amine nitrogen
At pH 7.4 the tertiary amine nitrogen is highly ionised, making it water soluble
Describe the mechanism of action of opioids
Bind at presynaptic and post-synaptic sites in CNS and periphery
Mimic the action of endogenous peptides resulting in activation of anti-nociceptive systems
Binding to the receptor causes a decrease in neurotransmission via presynaptic inhibition of release of ACh, dopamine, noradrenaline and substance P
The inhibition occurs by increased K conductance, Ca channel inactivation or both
Delayed effects may relate to inhibition of cAMP
What are the three main types of opioid receptors?
Mu, Kappa, Delta
What are the effects of Mu receptor activation?
Mu-1 Analgesia - supraspinal, spinal Euphoria Miosis Bradycardia Hypothermia Urinary retention Mu-2 Analgesia - spinal Vent depression Dependence Constipation
What are the effects of Kappa receptor activation?
Analgesia -supraspinal and spinal Dysphoria Sedation Miosis Diuresis
What are the effects of Delta receptor activation?
Analgesia - supraspinal and spinal Vent depression Dependence Minimal constipation Urinary retention
How are opioids classified?
Agonists - Morphine, Fentanyl, Codeine, Hydromorphone, Oxycodone etc
Agonist-antagonists - Buprenorphine, Pentazocine, Butorphanol
Antagonists - Naloxone, Naltrexone, Nalmefene
Are opioids acids or bases?
Bases
