Opioid Agonist-antagonists Flashcards Preview

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Flashcards in Opioid Agonist-antagonists Deck (20)

How do competitive antagonists work?

Reversibly binds to receptor at same site as agonist but does not activate receptor

*prevents agonist from binding to and activating receptor

*clinical response depends on concentration of agonist that is competing for binding at receptor


How do non competitive antagonists work?

Irreversibly bind to receptor at a separate site from agonist
-exerts action from other biding site
-does not compete with agonist
-prevents conformational changes in receptor which are required for activation (disables)
-inhibits full agonist response
*no amount of agonist can completely overcome inhibition


How do partial agonists work?

Has a high affinity for the receptor but not so much intrinsic activity

-occupies receptor but produces decrease in response


What is a superagonist?

Has greater effects at the receptor than the defining receptor agonist
*fentanyl is 100x more potent at the Mu receptor than morphine


What are opioid agonists/antagonists?

-"mixed" agonist and antagonist
-synthetic or semi synthetic analgesics
-structurally related to morphine
-produce a degree of competitive antagonism to morphine and pure agonists


What are some benefits of agonist-antagonists use?

*opioid addiction (less addictive)
*acute and chronic pain
*beneficial when unable to tolerate pure opioid agonist
*maintain analgesic effect (k) while simultaneously reversing respiratory depression (Mu) or opioid od
*ceiling effect limits toxicity of drug (respiratory depression)
*no significant elevation of biliary pressure (useful with biliary colic; less constipation)


What are some disadvantages of agonist-antagonist use?

-subsequent dose of agonists after these may not provide adequate analgesia
-confusion, esp with elderly
*undesirable CV effects
*mu receptor antagonist can lead to withdrawal
-ceiling effect (weak ability to decrease anesthetic required)


What are the negatives of mu receptors that may be prevented with agonist-antagonists?

-slowed gastric emptying
-skeletal muscle rigidity
*decreased pulmonary compliance
-respiratory depression


Describe pentazocine (Talwin)

-weak antagonist of Mu receptors, partial kappa agonist

**does not antagonize respiratory depression
**can be antagonized by narcan
**antagonist effects cause withdrawal in patients chronically receiving opioids

*cause sedation, analgesia, mild respiratory depression


What are some indications of pentazocine use?

-Relief of moderate pain
*Chronic pain and increase risk of physical dependence


What are the side effects of pentazocine?

-sedation, dizziness
-"weird" feelings, hallucinations
*crosses placenta, potential fetal depression
**increased HR and cardiac workload (catecholamine release) increase SBP, pulm artery pressure, and myocardial O2 consumption
**caution with ischemic heart dx, CHF, MI


Describe butorphanol (Stadol)

-more potent than Talwin (agonist 20x and antagonizes 10-30x greater)
-analgesia more potent than morphine
-nasal spray available
*more kappa effect then Mu or delta
*withdrawal after dc'd

*effect: analgesia and respiratory depression (equal to 10 mg morphine or 80-100 mg Demerol)


What are some indications for butorphanol use?

-post op pain
*migraibe headaches
*post op shivering (if Demerol contraindicated)


What are the side effects of butorphanol?

-respiratory depression
-nausea, diaphoresis

**CV effects: increased CO and workload, increased SBP and PAP (caution with CHF and MI)
**dysphoria rare


Describe nalbuphine (Nubain)

-potency comparable to morphine
-Mu receptor antagonist, kappa agonist
*subsequent morphine dosing less effective

*can be antagonized by narcan

Withdrawal can occur after dc'd

**effects: adequate analgesia with less respiratory depression


What are some benefits of nalbuphine?

*useful in reversing lingering fentanyl-induced respiratory depressant effect while providing satisfactory analgesia

*antagonizes pruritus induced by epidural morphine caused by histamine release

*can give to patients with cardiac history


What are some side effects of nalbuphine?

Sedation (33%)
Respiratory depression (ceiling effect)

**no CV effects


Describe buprenorphine (Buprenex)

-Mu receptor affinity 50% > morphine
-prolonged duration of up to 8 hrs
-partial Mu agonist and antagonizes Mu

*withdrawal after dc'd
*resistant to narcan


What are some indications of buprenorphine?

-effective on moderate to severe cancer pain
-opioid dependence (d/t partial Mu agonist)
**antagonizes fentanyl-induced respiratory depression w/o antagonizing pain relief


What are some side effects of buprenorphine?