opioid analgesics

Question 1

MOA of opioid analgesics

Answer 1

• inhibits propagation of pain signals

- alter emotional perception of pain

Question 2

which opioid receptor type is responsible for most clinical and adverse events?

Answer 2

mu (μ)

Question 3

which opioid receptor is responsible for dysphoria?

Answer 3

kappa (κ)

Question 4

list some of the dosing features of opioid analgesics

Answer 4

• elderly patients usually require a lower dose to achieve effective pain relief compared to younger patients
• neuropathic pain usually require higher opioid doses than nociceptive pain
• lower dose usually required for continuous maintenance of pain

Question 5

list some of the clinical uses of opioid analgesics

Answer 5

• analgesic: codeine, morphine, pethidine
• anesthetic adjuvant: fentanyl
• cough suppressant/antitussive: codeine
• anti-diarrheal: diphenoxylate

Question 6

what are some of the effects of pethidine?

Answer 6

• N-demethylation in liver can cause hallucinations & convulsant effects @ high doses
• restlessness > sedation
• antimuscarinic with no miosis and less muscle spasm

Question 7

10% of codeine users show reduced analgesic effect due to _________

Answer 7

lack of demethylating enzyme

Question 8

which drug interacts with tramadol’s analgesic effect?

Answer 8

ondansetron

Question 9

how does respiratory depression occur?

Answer 9

actions in nucleus tractus solitaries & nucleus ambiguus reduce responses to carbon dioxide and H+; suppresses voluntary breathing

Question 10

when can a normal dose cause respiratory depression?

Answer 10

• overdose, respiratory disease, hepatic dysfunction, combination with other CNS depressants, young children

Question 11

what are the adverse effects of opioids, and what are the causes?

Answer 11

• N/V: action on chemoreceptor trigger zone in area postrema of medulla (reduces with chronic use)
• drowsiness
• constipation due to reduced GI motility
• miosis due to action on oculomotor nucleus
• urinary retention due to increase bladder sphincter tone
• postural HoTN & bradycardia due to actions in cardioregulatory nuclei in medulla
• immunosuppressant with long term use
• morphine can trigger histamine release - results in itching, bronchoconstriction, HoTN (avoid in asthmatics)

Question 12

what are the opioid antagonists used to counteract opioid overdose?

Answer 12

• naloxone: short acting, usually IV
• naltrexone: long acting, oral administration
• nalmefene: long acting, IV