Nonionic emulsifiers

S.u. oil-in-water emulsifiers. Examples include esters and ethers of polyethylene glycols with higher fatty acids or fatty alcohols such as polysorbate types (e.g. Tween 20-80), polyoxyethylene glycerol monostearate (Tagat S2), polyethylene glycol stearates and polyethylene glycol fatty alcohol ethers.

An incompatibility is the interaction between the ether-oxygen of the PEG portion and the phenolic hydroxyl group of active ingredients or also auxiliary agents.

In many pharmaceutically used hydrophilic non-ionic emulsifiers, macrogol (polyethylene glycol) is part of the molecular structure. Since non-ionic emulsifiers (surfactants) do not have any dissociable functional groups, their hydrophilic part is usually hydroxyl groups or polyethylene glycol. The PEG chain is bound to the lipophilic part of the molecule via an ester or ether bond. With a constant lipophilic portion, the HLB value increases with increasing length of the PEG block, i.e. the surfactant behaves increasingly hydrophilic. Non-ionic emulsifiers with polyethylene glycol in the molecule are also used in many semi-solid emulsion preparations.

Although this is a weak electrostatic interaction, in certain concentration ranges it can be sufficient to significantly disturb the function of the emulsifier and thus lead to the breaking of the emulsion.