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Methylcellulose

Methylcellulose (or methyl cellulose) is a chemical compound derived from cellulose. It is a hydrophilic white powder in pure form and dissolves in cold (but not in hot) water, forming a clear viscous solution or gel. It is sold under a variety of trade names and is used as a thickener and emulsifier in various food and cosmetic products, and also as a treatment of constipation. Like cellulose, it is not digestible, not toxic, and not allergenic. more...

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Chemistry

Chemically, methylcellulose is a methyl ether of cellulose, arising from substituting the hydrogen atoms of some of cellulose's hydroxyl groups -OH with methyl groups -CH₃, forming -OCH₃ groups.

Different kinds of methylcellulose can be prepared depending on the number of hydroxyl groups so substituted. Cellulose is a polymer consisting of numerous linked glucose molecules, each of which exposes three hydroxyl groups. The Degree of Substitution (DS) of a given form of methylcellulose is defined as the average number of substituted hydroxyl groups per glucose. The theoretical maximum is thus a DS of 3.0, however more typical values are 1.3 - 2.6.

Different methylcellulose preparations can also differ in the average length of their polymer backbones.

Methylcellulose does not occur naturally and is synthetically produced by heating cellulose with caustic solution (e.g. a solution of sodium hydroxide) and treating it with methyl chloride.

The CAS number of methylcellulose is 9004-67-5.

Solubility and temperature

Methylcellulose dissolves in cold water. Higher DS-values result in lower solubility, because the polar hydroxyl groups are masked. The chemical is not soluble in hot water, which has the paradoxical effect that heating a saturated solution of methylcellulose will turn it solid, because methylcellulose will precipitate out. The temperature at which this occurs depends on DS-value, with higher DS-values giving lower precipitation temperatures.

Preparing a solution of methylcellulose with cold water is difficult however: as the powder comes into contact with water, a gluey layer forms around it, and the inside remains dry. A better way is to first mix the powder with hot water, so that the methylcellulose particles are well dispersed in the water, and cool down this dispersion while stirring, leading to the dissolution of those particles.

Uses

Thickener and emulsifier

Methylcellulose is often added to hair shampoos, tooth pastes and liquid soaps, to generate their characteristic thick consistency. This is also done for foods, for example ice cream or whipped cream. Methylcellulose is also an important emulsifier, preventing the separation of two mixed liquids.

The E number of methylcellulose as food additive is E461.

Treatment of constipation

When eaten, methylcellulose is not absorbed by the intestines but passes through the digestive tract undisturbed. It attracts large amounts of water into the colon, producing a softer and bulkier stool. It is used to treat constipation, diverticulosis, hemorrhoids and irritable bowel syndrome. It should be taken with sufficient amounts of fluid to prevent dehydration.

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Ursodiol 25-mg/mL Oral Liquid
From International Journal of Pharmaceutical Compounding, 11/1/05

METHOD OF PREPARATION

1. Calculate the required quantity of each ingredient for the total amount to be prepared.

2. Accurately weigh and/or measure each ingredient.

3. Empty the ursodiol capsules and pulverize the powder thoroughly.

4. Add the glycerin and mix until smooth.

5. Add the Ora-Plus and mix well.

6. Add the orange syrup, then the syrup to volume, and mix well.

7. Package and label.

PACKAGING

Package in tight, light-resistant containers.

LABELING

Keep out of reach of children. Use only as directed. Shake well before taking.

STABILITY

A beyond-use date of 60 days can be used for this preparation.1,2

USE

Ursodiol oral liquid is used as an anticholelithogenic agent.

QUALITY CONTROL

Quality-control assessment can include weight/volume, pH (3.2 to 4.0), specific gravity, active drug assay, color, rheological properties/ pourability, physical observation, and physical stability (discoloration, foreign materials, gas formation, mold growth).3

DISCUSSION

Ursodiol is a naturally occurring bile acid that is present in small quantities in human bile. It suppresses the synthesis and secretion of cholesterol by the liver and inhibits intestinal absorption of cholesterol. It has been used for the dissolution of cholesterol-rich gallstones and in the treatment of chronic liver disease.4

Ursodiol USP (C^sub 24^H^sub 40^O^sub 4^, MW 392.57, ursodeoxycholic acid, Actigall) occurs as a white or almost white, crystalline powder. It is practically insoluble in water, and freely soluble in alcohol and in glacial acetic acid.2 Ursodiol capsules (Actigall) also contain colloidal silicon dioxide, ferric oxide, gelatin, magnesium stearate, cornstarch, and titanium dioxide. Ursodiol tablets (URSO 250) also contain microcrystalline cellulose, povidone, sodium starch glycolate, magnesium stearate, ethylcellulose, dibutyl sebacate, carnauba wax, hydroxypropyl methylcellulose, polyethylene glycol 3350, polyethylene glycol 8000, cetyl alcohol, sodium lauryl sulfate, and hydrogen peroxide.5

Glycerin (C^sub 3^H^sub 8^O^sub 3^, MW 92.1, glycerol, 1,2,3-propane triol) occurs as a clear, colorless, odorless, viscous, hygroscopic liquid with a sweet taste about two thirds as sweet as sucrose. It has a specific gravity of about 1.25 and a melting point of 17.8°C. It is miscible with water and 95% ethanol. It is hygroscopic and should be stored in airtight containers in a cool place.6

Ora-Plus is an oral suspending vehicle with a pH of approximately 4.2 and an osmolality of about 230 mOsm/kg. It contains purified water, microcrystalline cellulose, sodium carboxymethylcellulose, xanthan gum, carrageenan, sodium phosphate and citric acid as buffering agents, simethicone as an antifoaming agent, and potassium sorbate and methylparaben as preservatives.7

Orange Syrup NF contains not less than 450 mg and not more than 550 mg of citric acid in each 100 mL. It is prepared from sweet orange peel tincture (50 mL), citric acid anhydrous (5 g), talc (15 g), sucrose (820 g), and sufficient purified water to make 1000 mL. It is prepared using the technique of clarification by filtration. It should be preserved in tight containers and stored in a cold place.2

Syrup NF (simple syrup) is a clear, sweet vehicle used as a sweetening agent and the base for many flavored and medicated syrups. It contains 85% w/v sucrose in water and has a specific gravity of not less than 1.30. It should be stored in tight containers, preferably in a cool place.2

References

1. Mallett MS, Hagan RL, Peters DA. Stability of ursodiol 25 mg/mL in an extemporaneously prepared oral liquid. Am J Health Syst Pharm 1337; 54(12):1401-1404.

2. US Pharmacopeial Convention, Inc. USP-Pharmacists' Pharmacopeia. Rockville, MD: US Pharmacopeial Convention, Inc.; 2005: 377, 388, 408-431, 716.

3. Allen LV Jr. Standard operating procedure for quality assessment of oral and topical liquids. IJPC 1999; 3(2): 146-147.

4. Sweetman SC. MARTINDALE: The Complete Drug Reference. 33rd ed. London: Pharmaceutical Press; 2002:1677-1678.

5. [No author listed.] Physicians' Desk Reference. 58th ed. Montvale, NJ: Thomson PDR; 2004; 802-803, 3298-3299.

6. Price JC. Glycerin. In: Rowe RC, Sheskey PJ, Weller PJ, eds. Handbook of Pharmaceutical Excipients. 4th ed. Washington, DC: American Pharmaceutical Association; 2003: 257-259.

7. Ora-Plus [product information]. Minneapolis, MN: Paddock Laboratories, Inc.

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