Polyethylene Glycol

Chemical properties

Polyethylene glycol is a polymer which is hydrolyzed by ethylene oxide. It has no toxicity and irritation. It is widely used in various pharmaceutical preparations. The toxicity of low molecular weight polyethylene glycol is relatively large. In general, the toxicity of diols is very low. Topical application of polyethylene glycol, especially mucosal drug, can cause irritant pain. In topical lotion, this product can increase the flexibility of the skin, and has a similar moisturizing effect with glycerin. Diarrhoea can occur in large doses of oral administration. In injection, the maximum polyethylene glycol 300 concentration is about 30% (V/V). Hemolysis could occur when the concentration is more than 40% (V/V).

Application in biomedicine

Polyethylene glycol(25322-68-3) is also known as polyoxirane (PEO). It is a linear polyether obtained by ring opening polymerization of ethylene oxide. The main uses in the field of biomedicine are as follows:

1. Contact lens liquid. The viscosity of polyethylene glycol solution is sensitive to the shear rate and it is not easy for bacteria to grow on polyethylene glycol.
2. Synthetic lubricants. The condensation polymer of ethylene oxide and water. It is a cream matrix for preparing water-soluble drugs. It can also be used as a solvent for acetylsalicylic acid and caffeine, which is difficult to dissolve in water.
3. Drug sustained-release and immobilized enzyme carrier. The polyethylene glycol solution is applied to the outer layer of the pill to control the diffusion of drugs in the pill so as to improve the efficacy.
4. Surface modification of medical polymer materials. The biocompatibility of medical polymer materials in contact with blood can be improved by adsorption, interception and grafting of two amphiphilic copolymers containing polyethylene glycol on the surface of medical polymers.
5. It can make the membrane of the alkanol contraceptive pill.
6. It can make hydrophilic anticoagulant polyurethane.
7. Polyethylene glycol 4000 is an osmotic laxative. It can increase osmotic pressure and absorb moisture in the intestinal cavity, which makes the stool soften and increase in volume, resulting in bowel movement and defecation.
8. Denture fixing agent. Peg nontoxic and gelatinous nature can be used as a component of denture fixer.
9. PEG 4000 and PEG 6000 are commonly used to promote cell fusion or protoplast fusion and help organisms (such as yeasts) to take DNA in transformation. PEG absorbs water from the solution, so it is also used to concentrate the solution.

Description

Polyethylene glycols are a family of linear polymers formed by a base-catalyzed condensation reaction with repeating ethylene oxide units being added to ethylene. The molecular formula is (C2H4O)multH2O where mult denotes the average number of oxyethylene groups. The molecular weight can range from 200 to several million corresponding to the number of oxyethylene groups. The higher-molecular-weight materials (100 000 to 5 000 000) are also referred to as polyethylene oxides. The average molecular weight of any specific polyethylene glycol product falls within quite narrow limits (°5%). The number of ethylene oxide units or their approximate molecular weight (e.g., PEG-4 or PEG-200) commonly designates the nomenclature of specific polyethylene glycols. Polyethylene glycols with amolecular weight less than 600 are liquid, whereas those of molecular weight 1000 and above are solid. These materials are nonvolatile, water-soluble, tasteless, and odorless. They are miscible with water, alcohols, esters, ketones, aromatic solvents, and chlorinated hydrocarbons, but immiscible with alkanes, paraffins, waxes, and ethers.

Chemical Properties

The USP32–NF27 describes polyethylene glycol as being an addition polymer of ethylene oxide and water. Polyethylene glycol grades 200–600 are liquids; grades 1000 and above are solids at ambient temperatures.
Liquid grades (PEG 200–600) occur as clear, colorless or slightly yellow-colored, viscous liquids. They have a slight but characteristic odor and a bitter, slightly burning taste. PEG 600 can occur as a solid at ambient temperatures.
Solid grades (PEG>1000) are white or off-white in color, and range in consistency from pastes to waxy flakes. They have a faint, sweet odor. Grades of PEG 6000 and above are available as freeflowing milled powders.

Chemical Properties

White waxy crystalline flakes

Originator

MiraLax ,Braintree Laboratories

Uses

Used in conjunction with carbon black to form a conductive composite.1 Polymer nanospheres of poly(ethylene glycol) were used for drug delivery.2

Uses

polyethylene glycol (PEG) is a binder, solvent, plasticizing agent, and softener widely used for cosmetic cream bases and pharmaceutical ointments. Pegs are quite humectant up to a molecular weight of 500. Beyond this weight, their water uptake diminishes.

Uses

nonionic emulsifier

Uses

H2 histamine receptor antagonist, anti-ulcer agent

Uses

A polymer used to precipitate proteins, viruses, DNA and RNA

Uses

Polyethylene Glycol is a binder, coating agent, dispersing agent, flavoring adjuvant, and plasticizing agent that is a clear, colorless, viscous, hygroscopic liquid resembling paraffin (white, waxy, or flakes), with a ph of 4.0–7.5 in 1:20 concentration. it is soluble in water (mw 1,000) and many organic solvents.

Uses

Poly(ethylene Glycol) molecules of approximately 2000 monomers. Poly(ethylene Glycol) is used in various applications from industrial chemistry to biological chemistry. Recent research has shown PEG m aintains the ability to aid the spinal cord injury recovery process, helping the nerve impulse conduction process in animals. In rats, it has been shown to aid in the repair of severed sciatic axons, helping with nerve damage recovery. It is industrially produced as a lubricating substance for various surfaces to reduce friction. PEG is also used in the preparation of vesicle transport systems in with application towards diagnostic procedures or drug delivery methods.

Indications

Polyethylene glycol (Miralax) is another osmotic laxative that is colorless and tasteless once it is mixed.

Production Methods

Polyethylene glycol polymers are formed by the reaction of ethylene oxide and water under pressure in the presence of a catalyst.

Definition

Any of several condensa-tion polymers of ethylene glycol with thegeneral formula HOCH2(CH2OCH2)nCH2OH orH(OCH2CH2)nOH. Average molecular weightsrange from 200 to 6000. Properties vary with molec-ular weight.

Preparation

The ring-opening polymerization of ethylene oxide is readily effected by a variety of ionic reagents and several types of polymer have been prepared. For commercial purposes, poly(ethylene oxide)s of low molecular weight and of very high molecular weight are of interest.
(a) Low molecular weight polymers
Poly(ethylene oxide)s of low molecular weight, i.e. below about 3000, are generally prepared by passing ethylene oxide into ethylene glycol at 120-150??C and about 0.3 MPa (3 atmospheres) pressure, using an alkaline initiator such as sodium hydroxide. Anionic polymerization proceeds according to the following scheme:
20220127142458
The polymers produced by these methods are thus terminated mainly by hydroxy groups (a few unsaturated end-groups are also formed) and are often referred to as poly(ethylene glycol)s. Poly(ethylene glycol)s with molecular weights in the range 200-600 are viscous liquids which find use as surfactants in inks and paints and as humectants. At molecular weights above about 600, poly(ethylene glycol)s are low-melting waxy solids, uses of which include pharmaceutical and cosmetic bases, lubricants and mould release agents.
It may be noted that homogeneous cationic polymerization of ethylene oxide also generally leads to low molecular weight products; typical initiators include aluminium chloride, boron trifluoride and titanium tetrachloride. Systems of this type are not utilized on a commercial scale.
(b) High molecular weight polymers
Poly(ethylene oxide)s of molecular weight ranging from about 100000 to 5 x 106 and above are available. Details of the techniques used to manufacture these polymers have not been disclosed, but the essential feature is the use of (generally) heterogeneous initiator systems. Effective initiators are mainly of two types, namely alkaline earth compounds (e.g. carbonates and oxides of calcium, barium and strontium) and organometallic compounds (e.g. aluminium and zinc alkyls and alkoxides, commonly with added coinitiators).
The precise modes of action of these initiators have not, as yet, been fully resolved. However, it is now generally thought that polymerization occurs through a co-ordinated anionic mechanism, in which the ethylene oxide is coordinated to the initiator through an unshared electron pair on the oxirane oxygen atom:

Unlike the low molecular weight poly(ethylene oxide)s, the high molecular weight polymers are tough and extensible. They are highly crystalline, with a melting point of 66??C. Unlike most water-soluble polymers, the high molecular weight poly(ethylene oxide)s may be melt processed; they may be injection moulded, extruded and calendered without difficulty.
Poly(ethylene oxide)s are soluble in an unusually broad range of solvents, which includes water; chlorinated hydrocarbons such as carbon tetrachloride and methylene dichloride; aromatic hydrocarbons such as benzene and toluene; ketones such as acetone and methyl ethyl ketone; and alcohols such as methanol and isopropanol. There is an upper temperature limit of solubility in water for the high molecular weight poly(ethylene oxide)s; this varies with concentration and molecular weight but is usually between 90 and 100??C. Water-solubility is due to the ability of the polyether to form hydrogen bonds with water; these bonds are broken when the temperature is raised, restoring the anhydrous polymer which is precipated from the solution.
High molecular weight poly(ethylene oxide)s find use as water-soluble packaging films and capsules for such products as laundry powders, colour concentrates, tablets and seeds. In solution, the polymers are used as thickeners in pharmaceutical and cosmetic preparations, textile sizes and latex stabilizers.

Manufacturing Process

Polyethylene glycol 3350 was obtained by polymerization of ethylene oxide in an autoclave at 80-100°C using as a catalyst dipotassium alcogolate of polyethylene glycol 400.
Dipotassium alcogolate of polyethylene glycol 400 was synthesized by a heating of the dry mixture of polyethylene glycol 400 and potassium hydroxide. The molecular weight of polymer was regulated by the ratio of monomer:catalyst.

brand name

Atpeg 4000 (ICI Americas).

Therapeutic Function

Laxative

General Description

Clear colorless viscous liquid.

Air & Water Reactions

Water soluble.

Reactivity Profile

Poly(ethylene glycol) is heat-stable and inert to many chemical agents; Poly(ethylene glycol) will not hydrolyze or deteriorate under normal conditions. Poly(ethylene glycol) has a solvent action on some plastics.

Fire Hazard

Poly(ethylene glycol) is combustible.

Flammability and Explosibility

Not classified

Pharmaceutical Applications

Polyethylene glycols (PEGs) are widely used in a variety of pharmaceutical formulations, including parenteral, topical, ophthalmic, oral, and rectal preparations. Polyethylene glycol has been used experimentally in biodegradable polymeric matrices used in controlled-release systems.
Polyethylene glycols are stable, hydrophilic substances that are essentially nonirritant to the skin;They do not readily penetrate the skin, although the polyethylene glycols are water-soluble and are easily removed from the skin by washing, making them useful as ointment bases.Solid grades are generally employed in topical ointments, with the consistency of the base being adjusted by the addition of liquid grades of polyethylene glycol.
Mixtures of polyethylene glycols can be used as suppository bases,for which they have many advantages over fats. For example, the melting point of the suppository can be made higher to withstand exposure to warmer climates; release of the drug is not dependent upon melting point; the physical stability on storage is better; and suppositories are readily miscible with rectal fluids. Polyethylene glycols have the following disadvantages: they are chemically more reactive than fats; greater care is needed in processing to avoid inelegant contraction holes in the suppositories; the rate of release of water-soluble medications decreases with the increasing molecular weight of the polyethylene glycol; and polyethylene glycols tend to be more irritating to mucous membranes than fats.
Aqueous polyethylene glycol solutions can be used either as suspending agents or to adjust the viscosity and consistency of other suspending vehicles. When used in conjunction with other emulsifiers, polyethylene glycols can act as emulsion stabilizers. Liquid polyethylene glycols are used as water-miscible solvents for the contents of soft gelatin capsules. However, they may cause hardening of the capsule shell by preferential absorption of moisture from gelatin in the shell.
In concentrations up to approximately 30% v/v, PEG 300 and PEG 400 have been used as the vehicle for parenteral dosage forms. In solid-dosage formulations, higher-molecular-weight polyethylene glycols can enhance the effectiveness of tablet binders and impart plasticity to granules.However, they have only limited binding action when used alone, and can prolong disintegration if present in concentrations greater than 5% w/w. When used for thermoplastic granulations,a mixture of the powdered constituents with 10–15% w/w PEG 6000 is heated to 70–75°C. The mass becomes pastelike and forms granules if stirred while cooling. This technique is useful for the preparation of dosage forms such as lozenges when prolonged disintegration is required. Polyethylene glycols can also be used to enhance the aqueous solubility or dissolution characteristics of poorly soluble compounds by making solid dispersions with an appropriate polyethylene glycol.Animal studies have also been performed using polyethylene glycols as solvents for steroids in osmotic pumps. In film coatings, solid grades of polyethylene glycol can be used alone for the film-coating of tablets or can be useful as hydrophilic polishing materials. Solid grades are also widely used as plasticizers in conjunction with film-forming polymers.The presence of polyethylene glycols in film coats, especially of liquid grades, tends to increase their water permeability and may reduce protection against low pH in enteric-coating films. Polyethylene glycols are useful as plasticizers in microencapsulated products to avoid rupture of the coating film when the microcapsules are compressed into tablets.
Polyethylene glycol grades with molecular weights of 6000 and above can be used as lubricants, particularly for soluble tablets. The lubricant action is not as good as that of magnesium stearate, and stickiness may develop if the material becomes too warm during compression. An antiadherent effect is also exerted, again subject to the avoidance of overheating.
Polyethylene glycols have been used in the preparation of urethane hydrogels, which are used as controlled-release agents. Polyethylene glycol has also been used in insulin-loaded microparticles for the oral delivery of insulin;it has been used in inhalation preparations to improve aerosolization;polyethylene glycol nanoparticles have been used to improve the oral bioavailability of cyclosporine;it has been used in self-assembled polymeric nanoparticles as a drug carrier;and copolymer networks of polyethylene glycol grafted with poly(methacrylic acid) have been used as bioadhesive controlled drug delivery formulations.

Biochem/physiol Actions

Poly(ethylene glycol) (PEG) helps in the purification and crystal growth of proteins and nucleic acids. PEG also interacts with cell membrane, thereby allowing cell fusion.

Safety Profile

When heated to decomposition it emits acrid smoke and irritating fumes.

Safety

Polyethylene glycols are widely used in a variety of pharmaceutical formulations. Generally, they are regarded as nontoxic and nonirritant materials.
Adverse reactions to polyethylene glycols have been reported, the greatest toxicity being with glycols of low molecular weight. However, the toxicity of glycols is relatively low.
Polyethylene glycols administered topically may cause stinging, especially when applied to mucous membranes. Hypersensitivity reactions to polyethylene glycols applied topically have also been reported, including urticaria and delayed allergic reactions.
The most serious adverse effects associated with polyethylene glycols are hyperosmolarity, metabolic acidosis, and renal failure following the topical use of polyethylene glycols in burn patients. Topical preparations containing polyethylene glycols should therefore be used cautiously in patients with renal failure, extensive burns, or open wounds.
Oral administration of large quantities of polyethylene glycols can have a laxative effect. Therapeutically, up to 4 L of an aqueous mixture of electrolytes and high-molecular-weight polyethylene glycol is consumed by patients undergoing bowel cleansing.
Liquid polyethylene glycols may be absorbed when taken orally, but the higher-molecular-weight polyethylene glycols are not significantly absorbed from the gastrointestinal tract. Absorbed polyethylene glycol is excreted largely unchanged in the urine, although polyethylene glycols of low molecular weight may be partially metabolized.
The WHO has set an estimated acceptable daily intake of polyethylene glycols at up to 10 mg/kg body-weight.
In parenteral products, the maximum recommended concentration of PEG 300 is approximately 30% v/v as hemolytic effects have been observed at concentrations greater than about 40% v/v

Environmental Fate

Like other polymeric substances, polyethylene glycols are not readily biodegradable, with reported 5-day biochemical oxygen demand (BOD5) of 0–1%. However, owing to their hydrophilicity, they have a low potential to bioaccumulate.

Solubility in organics

Acetonitrile, benzene, chlorinated hydrocarbons, DMF, MEK, methanol, THF (hot), water

Solubility in organics

THF, water

storage

Polyethylene glycols are chemically stable in air and in solution, although grades with a molecular weight less than 2000 are hygroscopic. Polyethylene glycols do not support microbial growth, and they do not become rancid.
Polyethylene glycols and aqueous polyethylene glycol solutions can be sterilized by autoclaving, filtration, or gamma irradiation.
Sterilization of solid grades by dry heat at 150℃ for 1 hour may induce oxidation, darkening, and the formation of acidic degradation products. Ideally, sterilization should be carried out in an inert atmosphere. Oxidation of polyethylene glycols may also be inhibited by the inclusion of a suitable antioxidant.
If heated tanks are used to maintain normally solid polyethylene glycols in a molten state, care must be taken to avoid contamination with iron, which can lead to discoloration. The temperature must be kept to the minimum necessary to ensure fluidity; oxidation may occur if polyethylene glycols are exposed for long periods to temperatures exceeding 50℃. However, storage under nitrogen reduces the possibility of oxidation.
Polyethylene glycols should be stored in well-closed containers in a cool, dry place. Stainless steel, aluminum, glass, or lined steel containers are preferred for the storage of liquid grades.

Purification Methods

PEG is available commercially as a powder or as a solution in various degrees of polymerization depending on the average molecular weight, e.g. PEG 400 and PEG 800 have average molecular weights of 400 and 800, respectively. They may be contaminated with aldehydes and peroxides. Solutions deteriorate in the presence of air due to the formation of these contaminants. Methods available for purification are as follows: Procedure A: A 40% aqueous solution of PEG 400 (2L, average molecular weight 400) is de-aerated under vacuum and made 10mM in sodium thiosulfate. After standing for 1hour at 25o, the solution is passed through a column (2.5x20cm) of mixed-bed R-208 resin which has a 5cm layer of Dowex 50-H+ at the bottom of the column. The column was previously flushed with 30% aqueous MeOH, then thoroughly with H2O. A flow rate of 1mL/minute is maintained by adjusting the fluid head. The first 200mL are discarded, and the effluent is then collected at an increased flow rate. The concentration of PEG solution is checked by density measurement, and it is stored (preferably anaerobically) at 15o. Procedure B: A solution of PEG 800 (500g in 805mL H2O) is made 1mM in H2SO4 and stirred overnight at 25o with 10g of treated Dowex 50-H+ (8% crosslinked, 20-50 mesh). The resin, after settling, is filtered off on a sintered glass funnel. The filtrate is treated at 25o with 1.5g of NaBH4 (added over a period of 1minute) in a beaker with tight but removable lid through which a propeller-type mechanical stirrer is inserted and continuously flushed with N2. After 15minutes, 15g of fresh Dowex 50-H+ are added, and the rate of stirring is adjusted to maintain the resin suspended. The addition of an equal quantity of Dowex 50-H+ is repeated and the reaction times are 30 and 40minutes. The pH of a 1 to 10 dilution of the reaction mixture should remain above pH 8 throughout. If it does not, more NaBH4 is added or the addition of Dowex 50-H+ is curtailed. (Some samples of PEG can be sufficiently acidic, at least after the hydrolysis treatment, to produce a pH that is too low for efficient reduction when the above ratio of NaBH4 to Dowex 50-H+ is used.) About 30minutes after the last addition of NaBH4, small amounts of Dowex 50-H+ (~0.2g) are added at 15minute intervals until the pH of a 1 to 10 dilution of the solution is less than 8. After stirring for an additional 15minutes the resin is allowed to settle, and the solution is transferred to a vacuum flask for brief de-gassing under a vacuum. The de-gassed solution is passed through a column of mixed-bed resin as in procedure A. The final PEG concentration would be about 40% w/v. Assays for aldehydes by the purpural method and of peroxides are given in the reference below. Treatment of Dowex 50-H+ (8% crosslinked, 20-50 mesh): The Dowex (500g) is suspended in excess 2N NaOH, and 3mL of liquid Br2 is stirred into the solution. After the Br2 has dissolved, the treatment is repeated twice, and then the resin is washed with 1N NaOH on a sintered glass funnel until the filtrate is colourless. The resin is then converted to the acid form (with dilute HCl, H2SO4 or AcOH as required) and washed thoroughly with H2O and sucked dry on the funnel. The treated resin can be converted to the Na salt and stored. [Ray & Purathingal Anal Biochem 146 307 1985.]

Toxicity evaluation

Many years of human experience in the workplace and in the use of consumer products containing polyethylene glycols have not shown any adverse health effects, except in situations where very high doses are administered to hypersusceptible individuals or persons with underlying diseases.

Incompatibilities

The chemical reactivity of polyethylene glycols is mainly confined to the two terminal hydroxyl groups, which can be either esterified or etherified. However, all grades can exhibit some oxidizing activity owing to the presence of peroxide impurities and secondary products formed by autoxidation.
Liquid and solid polyethylene glycol grades may be incompatible with some coloring agents.
The antibacterial activity of certain antibiotics is reduced in polyethylene glycol bases, particularly that of penicillin and bacitracin. The preservative efficacy of the parabens may also be impaired owing to binding with polyethylene glycols.
Physical effects caused by polyethylene glycol bases include softening and liquefaction in mixtures with phenol, tannic acid, and salicylic acid. Discoloration of sulfonamides and dithranol can also occur, and sorbitol may be precipitated from mixtures. Plastics, such as polyethylene, phenolformaldehyde, polyvinyl chloride, and cellulose-ester membranes (in filters) may be softened or dissolved by polyethylene glycols. Migration of polyethylene glycol can occur from tablet film coatings, leading to interaction with core components.

Regulatory Status

Included in the FDA Inactive Ingredients Database (dental preparations; IM and IV injections; ophthalmic preparations; oral capsules, solutions, syrups, and tablets; rectal, topical, and vaginal preparations). Included in nonparenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.