Propylene glycol alginate is a propylene glycol ester of alginic acid. Alginic acid is a naturally-occurring anionic polysaccharide obtained from algae. It is composed of a mixture of mannuronic acid and guloronic acid residues.
Propylene glycol alginate is a whitish fibrous powder, that is practically odourless and tasteless. It exhibits both cold and hot water solubility. It is available in different grades, corresponding to difference in viscosity: standard grades and high esterification grades.
The general chemical structure of Propylene glycol alginate is shown below:
Current Regulatory Status
Propylene glycol alginate is listed in the USP-NF and approved for use in food in Europe (E405). A specification for propylene glycol alginate is contained in the Food Chemicals Codex (FCC) and the Japanese Pharmaceutical Excipients (JPE).
Propylene glycol alginate is included in the FDA Inactive Ingredients Database (oral preparations) and generally regarded as safe, nontoxic and non-irritant material, although excessive oral consumption may be harmful.
Applications in Pharmaceutical Formulations
Propylene glycol alginate is supplied in two types: standard and high esterification. Within each type are several grades having viscosities ranging from 50 to 600 mPa s.
The principal use of propylene glycol alginate is as a viscosity-increasing agent and thickener in topical and oral emulsions and suspensions. Higher viscosity grades are ideal for this application and are selected for the same reasons as sodium alginate but unlike sodium alginate propylene glycol alginate remains soluble at low pH and does not gel in the presence of polyvalent cations (e.g calcium).
Propylene glycol alginate exhibits surface active effects, enabling it to additionally function as an emulsion stabiliser, which distinguishes it from sodium alginate.
Propylene glycol alginate is also used as a binder and disintegrant in oral granules and tablets and can help enhance the rate of dissolution.
Owing to its mucoadhesive properties, propylene glycol alginate can be used to formulate lozenges, buccal, sublingual, nasal, ocular and other dosage forms that require extended residence times on mucosal surfaces.
Typical Uses of Propylene glycol alginate:
|Thickener in creams||1 – 5|
|Stabiliser for emulsions and suspensions||1 – 2|
|Suspending agent||1 – 5|
|Capsule and tablet binder||1 – 3|
|Capsule and tablet disintegrant||3 – 10|
Useful Tips and Comments
Propylene glycol alginate solutions are most stable at pH 3 – 6. In alkaline solutions, propylene glycol alginate is rapidly saponified. Please note that alginate solutions are susceptible to microbial spoilage and should be preserved with an antimicrobial preservative. Sterilization processes (e.g autoclaving) can adversely affect the viscosity of propylene glycol alginate solutions.
 W. Schmid, K.M. Picker-Freyer, Tableting and tablet properties of alginates: Characterisation and potential for Soft Tableting, European Journal of Pharmaceutics and Biopharmaceutics, 72 (2009) 165-172.
 Z. Shariatinia, Chapter 2 – Pharmaceutical applications of natural polysaccharides, in: M.S. Hasnain, A.K. Nayak (Eds.) Natural Polysaccharides in Drug Delivery and Biomedical Applications, Academic Press2019, pp. 15-57.
 J.N. BeMiller, 9 – Hydrocolloids, in: E.K. Arendt, F. Dal Bello (Eds.) Gluten-Free Cereal Products and Beverages, Academic Press, San Diego, 2008, pp. 203-215.