Opioids Flashcards
What is the primary clinical use of opioid analgesics in dentistry?
To manage moderate to severe acute dental pain, especially post-surgical pain when NSAIDs alone are insufficient.
What are the three main classes of opioid receptors and their corresponding effects?
• Mu (μ): analgesia, respiratory depression, euphoria, miosis, physical dependence
• Kappa (κ): analgesia, sedation, dysphoria
• Delta (δ): analgesia, modulates mood and emotional responses
What is the mechanism of action of opioids at the cellular level?
Opioids bind to G protein-coupled receptors (Gi/o) → inhibit adenylyl cyclase → ↓ cAMP → open K⁺ channels (hyperpolarization) and close Ca²⁺ channels → reduced neuronal excitability and neurotransmitter release.
What are the primary sites of opioid action in the nervous system?
• Spinal cord: inhibit ascending pain transmission
• Brainstem: modulate pain perception and autonomic responses
• Limbic system: reduce emotional response to pain
What are endogenous opioids, and what are the three main types?
Naturally occurring opioid peptides in the body that bind opioid receptors:
• Endorphins (bind μ)
• Enkephalins (bind δ)
• Dynorphins (bind κ)
What are the hallmark signs of opioid toxicity or overdose?
Respiratory depression, miosis (pinpoint pupils), unconsciousness, and bradycardia—known as the classic “opioid overdose triad.”
What is the difference between opioid tolerance and dependence?
• Tolerance: a decreased response to the same dose over time
• Dependence: a physiologic adaptation where withdrawal symptoms occur if the drug is stopped abruptly
What are common adverse effects of therapeutic opioid use?
Constipation, nausea, sedation, respiratory depression, miosis, euphoria or dysphoria, and potential for addiction.
Which opioid antagonist is used to reverse overdose and how does it work?
Naloxone: a competitive antagonist at μ-opioid receptors, rapidly reverses respiratory depression and other effects of opioids.
Why is combining opioids with non-opioid analgesics (e.g., acetaminophen or ibuprofen) beneficial in dental pain management?
It provides synergistic pain relief with reduced opioid doses, minimizing side effects and potential for misuse.
What is the function of the periaqueductal gray (PAG) in opioid-mediated analgesia?
The PAG in the midbrain is a major site for opioid action in descending pain modulation. It activates inhibitory interneurons that suppress pain transmission in the spinal cord.
How do opioids alter pain perception?
They reduce the intensity, emotional response, and unpleasantness of pain rather than blocking nociceptive stimuli entirely.
What is the difference between full agonists, partial agonists, and antagonists at opioid receptors?
• Full agonist (e.g., morphine): strong receptor activation
• Partial agonist (e.g., buprenorphine): lower efficacy even at full receptor occupancy
• Antagonist (e.g., naloxone): blocks the receptor with no intrinsic activity
Why are partial opioid agonists like buprenorphine used in addiction treatment?
They have a ceiling effect on respiratory depression, reduce withdrawal and cravings, and block full agonist effects, lowering misuse risk.
What is a mixed agonist-antagonist opioid, and give an example?
A drug that stimulates one receptor type while blocking another.
Example: Pentazocine—agonist at κ, antagonist at μ.
What opioid receptor subtype is most responsible for reinforcing (addictive) effects?
Mu (μ) receptors, especially in the ventral tegmental area (VTA) and nucleus accumbens, contribute to reward and reinforcement.
Which opioid is considered the “gold standard” for analgesia in clinical pharmacology?
Morphine—a full μ-opioid receptor agonist with well-characterized pharmacokinetics and effects.
What is the role of codeine in dental pain, and how is it metabolized?
Codeine is a prodrug converted to morphine by CYP2D6. Its analgesic effect depends on metabolism; poor metabolizers may get no relief, and ultra-rapid metabolizers may have toxicity.
Why is tramadol unique among opioids?
Tramadol is a weak μ-opioid agonist and inhibits serotonin and norepinephrine reuptake, contributing to its analgesic effects.
What is the black box warning for codeine use in pediatric dental patients?
Risk of respiratory depression and death in ultra-rapid metabolizers, especially after tonsillectomy or adenoidectomy.
What is methadone used for, and what makes it pharmacologically distinct?
Methadone is used for opioid maintenance therapy and chronic pain. It is a long-acting μ-agonist and NMDA receptor antagonist, but has a long and variable half-life, increasing overdose risk.
How do opioids cause constipation?
They bind μ-receptors in the GI tract, decreasing peristalsis and intestinal secretions, leading to hard, dry stools and reduced motility.
What are signs of opioid withdrawal?
Yawning, lacrimation, rhinorrhea, sweating, anxiety, diarrhea, muscle aches, piloerection (“cold turkey”), and restlessness.
What is the pharmacologic difference between naloxone and naltrexone?
• Naloxone: short-acting μ-antagonist for emergency overdose reversal
• Naltrexone: long-acting μ-antagonist used for opioid and alcohol dependence maintenance
