What is a Poloxamer?
Poloxamers are also known as polyethylene- propylene glycol copolymer or polyoxvethylene-polyoxypropylene copolymer. They are a series of block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO).
All poloxamers are chemically similar in composition, differing only in the relative amounts of propylene and ethylene oxides added during manufacture. The presence of PEO and PPO blocks in a single polymer chain imparts to the molecule amphiphilic properties whose self-assembling properties display a wide range of phase behaviour.
Several different types of poloxamers are commercially available whose physical and surface-active properties vary over a wide range. Pharmacopoeial grades generally occur as white, waxy, granules or as solids. They are practically odourless and tasteless.
Poloxamers are listed in pharmacopoeia and generally regarded as nontoxic and non-irritant. Included in the FDA Inactive Ingredients Database (IV injections; inhalations, ophthalmic preparations; oral powders. solutions, suspensions, and syrups; topical preparations).
The general chemical structure of Poloxamers is shown below:
Generalised Chemical Structure of Poloxamer
| Chemical Name | Poloxamer |
| CAS Registration Number | [9003-11-6] |
| Empirical Formula | HO(C2H4O)a(C3H6O)b(C2H4O)aH |
| Molecular weight | 2090 – 14 600 (average) |
| Regulatory Status | PhEur; USP-NF; JPE |
| Poloxamer type | Ethylene oxide units (a) | Polypylene oxide units (b) | Content of oxyethylene (%) | Average molar mass |
| 124 | 10 – 15 | 18 – 23 | 44.8 – 48.6 | 2090 – 2360 |
| 188 | 75 – 85 | 25 – 30 | 79.9 – 83.7 | 7680 – 9510 |
| 237 | 60 – 68 | 35 – 40 | 70.5 – 74.3 | 8740 – 8830 |
| 338 | 137 – 146 | 42 – 47 | 81.4 – 84.9 | 12700 – 17400 |
| 407 | 95 to 105 | 54 to 60 | 71.5 to 74.9 | 9840 to 14 600 |
Key Physicochemical Properties of Poloxamers
| Acidity/aikalinity | pH = 5.0—7.4 for a 2.5% w/v aqueous solution |
| Cloud point | > 100C for a 1% w/s aqueous solution, and a 10% w/v aqueous solution of poloxamer 188 |
| HLB value | 0.5 – 30 |
| Melting Point | 16oC for poloxamer 124; 52 – 57oC for poloxamer 188; 49oC for poloxamer 237; 57oC for poloxamer 338 and 52-57 oC for poloxamer 407 |
| Solubilitiy | Solubility varies according to the poloxamer type |
| Surface tension | 19.8 mN/m for a 0.1% w/v aqueous poloxamer 188 solution at 25C; 24.0mN/m for a 0.01% w/w aqueous poloxamer 188 solution at 25C; 26.0 mN/m for a 0.001% w/v aqueous poloxamer solution at 25 C |
| Viscosity (dynamic) | 1000 mPas as a melt at 77C for poloxamer 188 |
How are Poloxamers Used in Formulations?
The main uses of poloxamers is as dispersing agents, emulsifying agents, solubilizing agents, tablet lubricants, wetting agents and foaming agents.
As nonionic polyoxyethylene-polyoxypropylene copolymers, poloxamers are used as emulsifying or solubilizing agents. They are used as emulsifying agents in intravenous fat emulsions and as solubilizing and stabilizing agents to maintain clarity of elixirs and syrups.
Poloxamers can also be used as wetting agents; in ointments, suppository bases, and gels; and in tablet binders and coatings. Poloxamer 188 has also been used as an emulsifying agent for fluorocarbons used as artificial blood substitutes, and in the preparation of solid-dispersion systems. More recently, poloxamers have found use in drug-delivery systems.
Therapeutically, poloxamer 188 is administered orally as a wetting agent and stool lubricant in the treatment of constipation; it is usually used in combination with a laxative such as dantron. Poloxamers may also be used therapeutically as wetting agents in eye-drop formulations, in the treatment of kidney stones, and as skin-wound cleansers.
Any Useful Tips?
Naming of poloxamers can be bewildering but typically, the nonproprietary name – poloxamer – is followed by a number: the first two digits of which, when multiplied by 100, correspond to the approximate average molecular weight of the polyoxypropylene portion of the copolymer and the third digit, when multiplied by 100, corresponds to the percentage by weight of the polyoxyethylene portion.
Similarly, with many of the trade names used for poloxamers e.g. Kolliphor 188, the first digit arbitrarily represents the molecular weight of the polyoxypropylene portion and the second digit represents the weight percent of the oxyethylene portion. The letters L, ‘P’, and ‘F’, stand for the physical form of the poloxamer: liquid, paste, or flakes.
Although the USP-NF contains specifications for five poloxamer grades, many more different poloxamers are commercially available that vary in their molecular weight and the proportion of oxyethylene present in the polymer.
Some poloxamers (e.g Poloxamer 188) are incompatible with parabens.
Poloxamers are used in the cosmetics field as oil-in-water emulsifiers, cleansers for mild facial products, and dispersing agents.
References
[1] R.G. Strickley, Solubilizing Excipients in Oral and Injectable Formulations, Pharmaceutical Research, 21 (2004) 201-230.
[2] G. Dumortier, J.L. Grossiord, F. Agnely, J.C. Chaumeil, A Review of Poloxamer 407 Pharmaceutical and Pharmacological Characteristics, Pharmaceutical Research, 23 (2006) 2709-2728.
[3] A.M. Bodratti, P. Alexandridis, Formulation of Poloxamers for Drug Delivery, Journal of Functional Biomaterials, 9 (2018).