Syrups contain non-ionic surfactants (polyethylene glycol, propylene glycol, glycerin/glycerol and sorbitol) which are prone to containing highly toxic impurities such as ethylene glycol (EG) and diethylene glycol (DEG).
Ethylene glycol & diethylene glycol (sweet in taste) are widely used in industries in cooling systems as anti-freezing agents, hydraulic brake fluids, stamp pad inks, ballpoint pens, solvents, synthetics, paints, plastics, films, and cosmetics, etc. These two notorious chemicals are highly toxic. On ingestion, these first affect the central nervous system, then the heart, and finally the kidneys.
Pharmacopoeia (standards for drugs products) of different countries (Indian Pharmacopoeia, British Pharmacopoeia, United States Pharmacopoeia or European Pharmacopoeia] have defined limits of ethylene glycol (EG) & diethylene glycol (DEG) in different surfactants (polyethylene glycol, propylene glycol, glycerin and sorbitol).
Indian Pharmacopoeia (IP) states clearly that these impurities should be absent in polyethylene glycol. Similarly, USP states that EG should not be more than 0.062% and the sum of EG & DEG should be less than 0.2% in polyethylene glycol. USP Grade propylene glycol, glycerin or glycerol and sorbitol should not contain both these impurities more than 0.1% each. British Pharmacopoeia doesn’t recommend DEG (classified as Impurity A) more than 0.1% and the sum of EG & DEG more than 0.5%.
In a nutshell, both impurities should not be present in any surfactant purported to be used in any orally taken drug product. These must never be used in any injectablesas they are highly lethal. Strict quality control and the use of highly sensitive techniques (such as the Capillary Column based Gas Chromatograph with FID or MS detector) can be used in case of dispute/doubt about the purity of the non-ionic surfactant being used.