BONUS: Mailbag - Do Patients Need to Separate Miralax From Other Medications?

They asked, "Is it true that polyethylene glycol, or PEG three fif- thirty-three fifty, needs to be separated from other meds? And if so, by how long?"

Hmm, that is an interesting question.

Mm-hmm.

So we know that intestinal transit time, so how fast an oral medication travels through the gut, can theoretically affect its absorption.

[lip smack] Right.

And the thought is that the faster a med moves through, the less time it has to be absorbed.

And that could lead to low blood levels.

So when I looked into this, Don, there are a handful of studies, but not many, that looked at laxatives and drug absorption.

And of those, very, very few looked at PEG.

Uh, one example I found is a 1999 study that showed daily PEG decreased digoxin absorption by up to 40%.

[lip smack] Okay.

So it could have effect on absorption then.

Yes, but what is interesting here is that none of the patients in that study saw any clinical effects despite those changes, and it's hard to really apply this study.

Uh, the patients were healthy volunteers given a single digoxin dose.

They weren't on chronic digoxin therapy for an actual heart condition.

Okay, so absorption can change, but that doesn't mean we'll always see changes in the actual effects.

But I could see how this would be important for meds with very narrow dosing windows, you know, where small changes can have big effects, you know, which we call the narrow therapeutic index, or NTI.

Uh, but not all meds are that finicky.

I agree.

Not all meds are alike.

And in fact, a 2025 study of using PEG with dabigatran, an anticoagulant, found no changes in absorption or blood levels with co-administration.

Still, some experts recommend prioritizing spacing any laxatives at least 30 minutes from specific meds, things like diuretics, corticosteroids, uh, and antiarrhythmics to just avoid this absorption issue, even if it is theoretical.

Right.

So it's not as cut and dry here.

May be ideal to separate PEG from certain medications, especially if they have a narrow therapeutic index or if the patient is taking multiple laxatives.