WHO proposes updated method for testing liquid drugs for DEG/EG
The World Health Organization (WHO) has released a proposed update to The International Pharmacopoeia (Ph. Int.) for public consultation, proposing an update to the testing methods for diethylene glycol (DEG) and ethylene glycol (EG) in liquid preparations intended for oral use. The guideline suggests replacing the current thin-layer chromatographic (TLC) procedure with a more advanced method known as high-performance thin-layer chromatography (HPTLC).In a related development, WHO has released a complementary guideline for public consultation proposing the inclusion of the updated testing method for HPLTC in the Ph. Int.
The proposal to update the testing method for DEG/EG was drafted in May 2025 and “based on information found in the scientific literature and on laboratory investigations.” The revision “aims to improve resolution, sensitivity, and reproducibility by replacing the current thin-layer chromatographic (TLC) procedure with a high-performance thin-layer chromatographic (HPTLC) method.”
If finalized, the proposal will be published in the supplementary section of pharmacopeia.
The revised draft was released due to reports of severe contamination incidents that resulted in hundreds of deaths, primarily among children, linked to toxic DEG and EG found in cough syrups and other liquid products. (RELATED: WHO, UN report uncover supply chain weaknesses that contributed to patient deaths, Regulatory Focus 8 August 2025)
The document describes HPTLC and a gas chromatographic (GC-FID) procedure as the two methods used to test pharmaceuticals for DEG and EG contamination.
The revised guideline said that "National Quality Control Laboratories should be ready to test oral liquids available in their markets for the presence of diethylene glycol (DEG) and ethylene glycol (EG) to protect patients from contaminated products. They should choose the analytical method they wish to use based on the availability of suitable equipment and the training and expertise of their staff."
The proposal states that in accordance with WHO best practices for pharmaceutical quality control laboratories, any detected contamination should be verified using a second method with different selectivity.
In this context, the HPTLC and GC procedures can serve as “complementary techniques,” providing mutual confirmation of the results.
WHO is accepting comments on the document through an online platform. The deadline for submitting comments is 9 September. Plans are to review the comment and release a working document for discussion at the 59th meeting of the Expert Committee on Specifications for Pharmaceutical Preparation October 2025.
The document will replace an earlier version on DEG/EG testing released in July 2024.
New HPTLC chapter proposed
WHO has also released a draft proposal for a new general chapter on HPTLC to be included the Ph. Int. This proposal is designated as Chapter 1.18 and covers the necessary equipment for performing this type of testing, guidelines for sample preparation, and methods for interpreting the test results.
WHO defines HPTLC as a “chromatographic technique in which variables are controlled within narrow ranges, using a standardized methodology and appropriate equipment, in order to achieve more reproducible results compared to traditional thin-layer chromatography (TLC).”
The agency is accepting comments on the document through an online platform. The deadline for submitting comments is 9 September.
After receiving the comment, WHO will present the revision at the 59th meeting of the Expert Committee on Specifications for Pharmaceutical Preparation in October 2025.
In other recent actions, WHO proposed a revision of the European Pharmacopoeia chapter on the micro-determination of water using the Karl Fischer method, which is a test to determine the water content in pharmaceuticals.
The proposal includes guidance on how to proceed when a monograph specifies the evaporation technique but does not provide an oven temperature.
The additional text specifies that “if an oven is used, the prescribed quantity of sample is introduced into the oven and heated at the temperature given in the monograph. If no temperature is given, a temperature gradient is run to determine a suitable temperature (temperature range 50 to 150 °C with a heating range of 2°C/min). The water released and the drift (µg of water/min) are recorded as a function of time). First surface water is released and subsequently water for crystallization. A temperature is chosen that is high enough for the water to be extracted completely without any decomposition of the sample.”
WHO is accepting comments on the document through an online platform. The deadline for submitting comments is 22 September.
WHO proposal on evaluating DEG and EG in pharmaceuticals; WHO proposal on HPTLC; WHO draft revision of Chapter 2.11 on micro determination of water
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