Opioids : Definition, Classification, Example, Mechanism of Action, Uses, Side Effects, Contraindications, & Interactions
Introduction
Analgesics are divided into two groups, viz.
- Opioid / narcotic / morphine-like analgesics
- Nonopioid / non-narcotic/ aspirin-like / antipyretic or antiinflammatory analgesics
Opioid receptors
Opioids primarily exert their effects by three receptor families which are
- μ (mu),
- κ (kappa), and
- δ (delta).
Each receptor family exhibits a different specificity for the drug(s) it binds.
The analgesic properties of the opioids are primarily mediated by the μ receptors that modulate responses to thermal, mechanical, and chemical nociception. The κ receptors in the dorsal horn also contribute to analgesia by modulating the response to chemical and thermal nociception.
Classification
A. Opioid agonists
Analgesics
- Fentanyl
- Heroin / Diacetyl Morphine
- Hydrocodone
- Hydromorphone
- Meperidine
- Methadone
- Morphine
- Oxycodone
- Oxymorphone
- Codeine
- Pholcodeine
- Tapentadol
- Tramadol
- Pethidine / Meperidine
- Dextro propoxyphene
Nonanalgesics
- Noscapine
- Thebaine
- Papaverine
B. Partial Agonist : Partial agonists bind to the opioid receptor, but have less intrinsic activity than full agonists.
E.g.
- Buprenorphine
C. Opioid antagonists
E.g.
- Naloxone
- Naltrexone
- Nalmefene
D. Mixed Agonist-Antagonist : Mixed agonist–antagonists are drugs that stimulate one receptor but block another.
E.g.
- Butorphanol
- Nalbuphine
- Pentazocine
- Nalorphine
Endogenous Opioids
- Endorphins
- Enkephalins
- Dynorphins
Uses
A. Morphine and its congeners
- Analgesic
- Preanaesthetic medication
- Balanced anaesthesia and surgical analgesia
- Relief of anxiety and apprehension
- Acute left ventricular failure (cardiac asthma)
- Cough
- Diarrhoea
B. Opioid antagonists
- Opioid poisioning
- Alcohol intoxication & dependence
For detailed query about Uses, Side Effects, Contraindications, Interactions of opioid drugs, refer to individual drugs.
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