Chapter 31: Opioid Analgesics, Opioid Antagonists, and Nonopioid Centrally Acting Analgesics

Question 1

State the roles of the mu, kappa, and delta opioid receptors in causing analgesia, respiratory depression, and euphoria.

Answer 1

• Mu receptors cause analgesia, respiratory depression, euphoria, and sedation.
• Kappa receptors cause analgesia and sedation, and may cause psychotomimetic effects.
• Delta receptors are not significantly involved in opioid analgesia.

Question 2

Distinguish among pure opioid agonists, agonist-antagonists, and antagonists in terms of their mechanism of action; also, place various named drugs in the appropriate category.

Answer 2

• Pure opioid agonists (e.g., morphine, fentanyl) activate mu and kappa receptors.
• Agonist-antagonists (e.g., pentazocine, buprenorphine) generally block mu and activate kappa; buprenorphine is a partial mu agonist and kappa antagonist.
• Antagonists (e.g., naloxone, naltrexone) block both mu and kappa receptors and reverse opioid effects.

Question 3

Discuss the therapeutic uses for opioid agonists, agonist-antagonists, and antagonists.

Answer 3

• Pure agonists: treat moderate to severe pain and suppress cough (e.g., codeine, hydrocodone). Methadone is also used for opioid addiction.
• Agonist-antagonists: treat mild to moderate pain.
• Antagonists: naloxone reverses overdose; methylnaltrexone treats opioid-induced constipation; naltrexone helps manage opioid addiction.

Question 4

Discuss the adverse effects of opioids and both their pharmacologic and non-drug management.

Answer 4

• Respiratory depression: reversed with naloxone, monitor closely.
• Constipation: managed with fluids, fiber, laxatives, or methylnaltrexone.
• Orthostatic hypotension: manage with slow position changes.
• Sedation: adjust dosing, or use CNS stimulants.
• Urinary retention: monitor output; avoid anticholinergics.
• Nausea/emesis: may need antiemetics.
• Cough suppression: encourage coughing.
• Increased ICP: maintain normal respiration.
• Neurotoxicity: hydration, dose reduction, rotation.
• Others: miosis, biliary colic, hormonal and immune suppression with long-term use.

Question 5

Describe opioid drug-related factors that contribute to the development of physical and psychologic dependence

Answer 5

• Physical dependence increases with prolonged use, high doses, and pure agonists.
• Withdrawal severity depends on drug half-life and dependence level.
• Abrupt discontinuation or use of antagonists/agonist-antagonists in dependent users causes withdrawal.
• Psychologic dependence is linked to mu receptor-mediated euphoria.