This is the second of two episodes about opioid medications. In this episode I cover the pharmacokinetics and pharmacodynamics of opioids, some of the common uses for these medications, mixed agonist-antagonist compounds, opioid antagonists, and opioid interaction with other medications.
Slides to go along with this episode are here: Opioids part 2
6 thoughts on “Episode 14: Opioids part 2”
Great talk! I’m familiar with naloxone infusions for for spinal cord protection for TAA procedures, I haven’t heard of it being used for AAAs?
Hi Stephen, you’re absolutely right. The data, such as it is, is for thoracic and thoracoabdominal aortic aneurysms, not for isolated AAAs. Thanks!
Great talk! I’m trying to get a better understanding of the competing effects of acid/base status on on the amount of biologically active opioid (unbound and unionized). In my understanding an acidic environment decreases protein-binding, hence increases the potency or duration of action. However, I also thought than an acidic environment increased the fraction of the ionized form of the opioid, thereby increasing the amount of biologically active compound. Is one’s effect greater than the other?
Also, do you think pKa is something to know for each opioid? If so, what would the take away be on the importance of the pKa on opioid activity?
Thanks so much for the great podcasts!
Good questions. Unfortunately there isn’t a great answer because these medications behave differently clinically than they do in vitro. The key to keep in mind for testing is that the duration of action is related to protein binding and the potency is related to lipid solubility. The degree of ionization is related to speed of onset of action.
I definitely do not think you need to know the pka of each opioid. I don’t think you’ll be tested on it and I don’t think it will be relevant clinically, though there may be some out there who would disagree.
do you have any articles on this?
Epidural fentanyl: infusion is no different than IV, bolus does have some neuraxial action
Thank you very much!
I am a regular listener from Lisbon, Portugal
This study showed it: http://anesthesiology.pubs.asahq.org/article.aspx?articleid=1950737 and references 5-10 also support it. Hope that’s helpful!