Opioids Flashcards
3 major opioid receptors
How do they work?
Which one is clinically useful. What are the effects?
Delta, kappa, mu (clinically useful)
All are G protein-coupled receptors
Mu –> analgesia, euphoria, respiratory depression, miosis, and constipation.
Analgesic effects of opioids
No ceiling effect for full agonists. Do not alter pain threshold of nerves nor conductance, but rather changes the perception of pain and emotional response to pain.
Adverse effects of opioids
Respiratory depression, sedation, constipation, nausea / vomiting, bradycardia (cholinergic effect), puririts / orthostatic hypotension (histamine effect), decreased renal blood flow, decreased libido / erection / amenorrhea / infertility (due to decreased LH / testosterone)
Smooth muscle effects of opioids (4)
- Contraction of biliary tract smooth muscle
- Increased ureteral and bladder sphincter tone
- Decreased uterine tone
- Miosis is characteristic of all opioids except meperidine, which has muscarinic blocking action. Pinpoint pupils is a red flag for opioid overdose
Withdrawal sxs of opioids
How long do they last?
How do you prevent withdrawal?
What treats the autonomic effects of withdrawal?
- Flu-like sxs: Nausea, diarrhea, coughing, lacrimation, yawning, sneezing, rhinorrhea, diaphoresis, twitching muscles, abdominal and muscle pain / cramps, hot and cold flashes, and piloerection
- Usually resolve after 5-14 days w/o treatment
- Taper dose by 10-20% every 1-2 days to avoid withdrawal sxs
- Clonidine (a2 agonist; decreases NE release) can be used to treat autonomic hyperactivity sxs
Morphine Use Mechanism Dosing Adverse rxns
- Use – analgesic used for moderate / severe pain, preop sedation, and supplement to anesthesia. DOC for MI and cancer pain. Analgesic during labor. Some cough suppression. Reduces pulmonary edema in LVHF by decreasing preload (decreased venous tone) and afterload (decreased TPR)
- Mechanism – Full agonist at mu receptors. Weak agonist at delta and kappa receptors.
- Dosing – no predictable relationship b/w serum concentrations and analgesic response. Must ask px what their pain is like.
- Adverse rxns – see above
Codeine Use Mechanism Pharmacokinetics Adverse rxns
- Use – Antitussive agent. May be used in combo w/ acetaminophen for mild / moderate pain.
- Mechanism – weak agonist at mu and delta receptors.
- Pharmacokinetics – O-demethylation of codeine into morphine by CYP2D6 is essential for analgesic activity to work. CYP2D6 has high genetic variability, so some pxs may need higher / lower doses
- Adverse rxns – Less analgesic, respiratory depressive, and other side effects compared to morphine.
Buprenorphine Brand name Use Mechanism Adverse rxns
- Suboxone
- Use – IV form is 30x more potent than morphine for moderate / severe pain. Sublingual form is used for treatment of opioid dependence (combined w/ naloxone so IV route does not produce high)
- Mechanism – mixed. Partial agonist at mu, antagonist at kappa. Ceiling effect is present, reducing risk of overdose, abuse, and toxicity
- Adverse rxns
- Normal rxns seen above
- Antagonism of kappa receptor → anxiety, insomnia, confusion, disorientation, and depersonalization
Naloxone Brand name Use Mechanism Pharmacokinetics
- Narcan
- Use – DOC for opioid overdose. Also treats opioid-induced constipation and respiratory depression.
- Mechanism – competitive antagonist at all opioid receptors. No effect in people who have not received opioids.
- Pharmacokinetics – IV form only. Short acting (45 min), so pxs may need multiple doses.
Meperidine
Use
Mechanism
- Use – 2nd line for acute (not chronic) pain
* Mechanism – Mu and kappa agonist
Tramadol
Use
Mechanism
- Analgesic effects
* Mechanism – Synthetic analog of codeine. Weak mu receptor agonist.
Hydrocodone use
Antitussive and analgesic
Mechanism of methadone
Full mu receptor agonist w/ long half-life
Dextromethorphan use
Antitussive
Loperamide
Brand name
Use
Imodium
Antidiarrheal effects
