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

Can polyethylene glycol (PEG 3350, Miralax) affect the absorption of other medications?

In this BONUS mailbag episode of Rumor vs Truth, we answer a listener question about whether polyethylene glycol (PEG 3350) should be separated from other medications and, if so, by how long. Hosts Don Weinberger, PharmD and Steve Small, PharmD break down what the evidence actually shows about laxatives, intestinal transit time, and medication absorption.

Together, they discuss:

• Can PEG 3350 reduce the absorption of certain medications?
• Which medications might warrant extra caution when taken with PEG 3350?
• When spacing PEG 3350 doses may be reasonable...and when it may be unnecessary
• Practical counseling tips to balance adherence with potential interaction concerns

No CE credit is available for this bonus episode.
Want the full breakdown? CE credit is available for our full episode on laxatives.

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🎧 Related Episode (CE Available)

• Rumor vs Truth: Laxatives
  (Effective… or Hard Pass?)
  🎧Listen: https://rumorvstruth.buzzsprout.com/episodes/19520800
  ▶️ Watch: https://youtu.be/o3GlBngiaag 

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TRC Healthcare Editor Hosts

• Steve Small, PharmD, BCPS, BCPPS, BCCCP, CNSC
• Don Weinberger, PharmD, PMSP

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Clinical Resources:  

• FAQ: Management of Constipation

🏷️ Our listeners can get 10% off a new or upgraded subscription with code rvt1026 at checkout. 

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Email us: rumorvstruth@trchealthcare.com

The content of this podcast is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

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Transcript

This transcript is automatically generated. 

00:00:12 Don Weinberger

Welcome to Rumor vs Truth.

00:00:14 Don Weinberger

This is the bonus mailbag episode where we answer one listener question outside of our regular full episodes.

00:00:20 Steve Small

And we're dropping this as a separate bonus, so our main episodes stay focused and clean.

00:00:25 Steve Small

And keep in mind, there's no CE available for this episode.

00:00:29 Don Weinberger

So this one's about laxatives that came in from a pharmacist through our rumorvstruth@trchealthcare.com e-mail address.

00:00:37 Don Weinberger

They asked,

00:00:38 Don Weinberger

Is it true that polyethylene glycol or PEG 3350 needs to be separated from other meds?

00:00:45 Don Weinberger

And if so, by how long?

00:00:48 Steve Small

That is an interesting question.

00:00:50 Steve Small

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

00:00:59 Don Weinberger

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

00:01:05 Don Weinberger

That could lead to low blood levels.

00:01:08 Steve Small

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

00:01:14 Steve Small

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

00:01:18 Steve Small

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

00:01:27 Don Weinberger

Okay. So it could have an effect on absorption then?

00:01:33 Steve Small

Yes, but what is interesting here is that none of the patients in that study saw any clinical effects despite those changes.

00:01:41 Steve Small

And it's hard to really apply this study.

00:01:44 Steve Small

The patients were healthy volunteers given a single digoxin dose.

00:01:48 Steve Small

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

00:01:54 Don Weinberger

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

00:02:01 Don Weinberger

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

00:02:14 Don Weinberger

But not all meds are that finicky.

00:02:16 Steve Small

I agree. Not all meds are alike.

00:02:17 Steve Small

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

00:02:29 Steve Small

Still, some experts recommend prioritizing spacing any laxatives at least 30 minutes from specific meds, things like diuretics, corticosteroids, and antiarrhythmics.

00:02:39 Steve Small

So just avoid this absorption issue, even if it is theoretical.

00:02:43 Don Weinberger

Right. So it's not as cut and dry here.

00:02:46 Don Weinberger

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

00:02:54 Don Weinberger

I could see how this could be cumbersome for patients and affect adherence, which may not be worth it if clinical effects are rare.

00:03:02 Don Weinberger

An easy approach may be to recommend patients take their PEG dose at lunch, since most meds are taken in the morning or before bedtime.

00:03:11 Steve Small

Yeah, that is a creative option.

00:03:13 Steve Small

And something worth saying here is that laxatives are intended to get patients back to normal intestinal transit time, which most meds are designed for, right?

00:03:22 Steve Small

So my concerns for absorption issues would probably increase if PEG was giving a patient diarrhea or if the patient was cycling on and off PEG, making absorption of chronic meds erratic, right?

00:03:35 Don Weinberger

And adjusting the laxative regimen to the lowest doses needed

00:03:38 Don Weinberger

And monitoring the patient for clinical changes are good steps to take in that case.

00:03:43 Steve Small

And we're just talking about PEG here, folks.

00:03:45 Steve Small

Other laxatives have other interactions, such as magnesium-based laxatives binding to quinolone antibiotics, such as levofloxacin.

00:03:52 Steve Small

So explore our Management of Constipation chart for details on common interactions to watch for, along with dosing, warnings, and more.

00:04:00 Don Weinberger

Yeah, that is a great resource.

00:04:02 Don Weinberger

I'm glad we could squeeze out the facts on that question, Steve.

00:04:05 Don Weinberger

And thanks for listening to this bonus mailbag.

00:04:07 Don Weinberger

Keep sending questions through the link in the show notes or e-mail.

00:04:11 Steve Small

And we'll be back with our next full episode on opioids coming soon on August 18th, where we'll see which claims hold up and which ones are just a pain.

00:04:19 Steve Small

And we'll see you then.