PEG 3350 is Not Associated with Elevated Glycol Levels

Everyday parents ask me if Miralax (polyethylene glycol) is safe; this has been driven by social media claims of neurotoxicity and by articles in the NY Times (see prior blog references) indicating that more testing is needed.

A recent study (KC Williams et al. J Pediatr 2018; 195: 148-53) examines one of the areas of concern, whether miralax could result in toxic levels of glycols.  In this study with 9 treated children (ages 6-12 years) and 18 controls, careful study of potentially toxic agents, ethylene glycol (EG), diethylene glycol (DEG), and triethylene glycol (TEG), were measured every 30 minutes for 3 hours after receiving 17 g of PEG 3350.

Key findings:

  • Baseline blood levels of EG (390.51 ng/mmL) and TEG (2.21 ng/mL) did not differ between control and treated groups
  • Baseline DEG levels were lower in the PEG 3350 group (40.12 ng/mL vs 92.83 ng/mL, P=.008)
  • After PEG 3350 dose, EG and TEG levels remained well below toxic levels; DEG levels did not change.  The increases in EG and TEG, which peaked at 90 minutes, were not sustained at levels different from controls.
  • EG peaked at 1032.8 ng/mL. TEG peaked at 35.17 ng/mL
  • The highest levels of EG and DEG were actually identified in control patients. Thus, “all children are exposed routinely and have measureable amounts in the blood.”

With regard to TEG toxicity, in the discussion, the authors note that, based on animal studies, “very large doses of TEG are needed to cause side effects.” Even doses of 4000 mg/kg of TEG daily for 90 days did not result in local or systemic toxicity.  The authors note that TEG concentration in PEG 3350 is “approximately 22.1-30.6 mcg per 17 gram dose of PEG 3350.”

With regard to EG and DEG, “the average EG and DEG content of the PEG samples in this study were a 100 and 800 times less, respectively, than this required 0.2% cutoff” [FDA limit].  The agency of Toxic Substances and Disease Registry profile for EG, has indicated that “EG blood levels greater tan 0.2 mg/mL are needed for acute toxic poisoning.  The average level of EG at the 90-minute peak of 1100 +/- 350 ng/mL was 182 times lower than this level.”  For chronic exposure EG toxicity, the authors estimate that one would need to take “40 capfuls [17 gram each] of PEG 3350 per day for up to a year.”  The EPA also has advisories with regard to EG.  To achieve toxic levels for a 10-kg child, this would necessitate that the child “would have to drink 1 L of water with 50 capfuls (858 g) in 1 day or 15 capfuls (258 g) per day for 10 days.”

An important limitation of this study is that there may be other metabolites that are not measured that could cause neurotoxicity.

My take: This study shows that the theoretical risk of glycol toxicity is highly unlikely.  My advice for miralax usage: (borrowed from expert review): “Generally speaking, if your child has been prescribed PEG 3350 as part of his/her treatment plan, and you feel this medicine provides benefit, you should feel safe continuing PEG 3350. At this time, PEG 3350 appears to be safe based on current medical literature. We recommend discussing any concerns you have about the safety of PEG 3350 with your child’s health care provider. If you would prefer for your child to stop taking PEG 3350, discuss other treatments options with your child’s health care team before stopping PEG 3350 therapy. Although abruptly stopping PEG 3350 is not considered dangerous, it could lead to a relapse/worsening of constipation.”

Disclaimer: These blog posts are for educational purposes only. Specific dosing of medications/diets (along with potential adverse effects) should be confirmed by prescribing physician/nutritionist.  This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition.

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