An 86-year-old man who lives in a skilled nursing ...
diphenhydramine and other Gen 1 antihistamines are good choices for chronic cough in allergy and patients with posterior draining and post viral chronic cough (careful with the elderly). That being said, apparently it also causes constipation, so dextro is still the correct answer.
According to Sketchy and Amboss: dextromethorphan is a weak opioid receptor AGONIST and NMDA receptor ANTAGONIST (it's not an agonist).
Tiotropium would cause constipation bc it’s an anticholinergic. Don’t have any insight into why dextromethorphan is the right answer though, other than process of elimination and diphenhydramine wouldn’t treat his symptoms.
I thought it was dextromethorphan because it would bind NMDA receptors and have weaker opioid effect = less constipation? Idk though :/
I agree. I mainly went by way of elimination but even DXM made me think of opiod-induced constipation. Though, all the other answer choices had obvious anticholinergic effects. At least, that was my reasoning for picking dxm.
No, not so. Dextro *is* the correct answer here. From the choices given, dextro is the least likely to cause constipation since its main mechanism of action is NMDA antagonism w/ *some* opioid activity -- it can cause constipation but the other choices are MUCH MORE likely to. As for diphenhydramine = it is not appropriate for elderly patients and it isn’t an antitussive.
Agreed with @rockediny. Dextro would be the best to prescribe because it has the least amount of constipation out of the drugs that you could prescribe + Anti-cholinergics in the elderly have much more morbidity and risk of mortality.
The only way to wrap your head around this is to conclude that Dextro is the "least wrong". I thought a lot about this, and I can't think of any drugs that can suppress cough without also causing constipation, so it makes sense that Dextro is the answer because it is the "least likely" to cause significant constipation. This is probably just a clinical correlate that will be learned during rotations/years in practice.