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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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Calculations
From International Journal of Pharmaceutical Compounding, 11/1/05 by Prince, Shelly J

1 You need to prepare 60 mL of a sildenafil citrate suspension with a concentration of 15 mg per teaspoonful, and you have in the pharmacy Viagra 50-mg tablets.

A. How many of these tablets will you need to prepare the suspension?

15mg/5mL × 60ml = 180 mg

180 mg × 1 tab/50 mg = 3.6 tablets = 4 tablets needed (you will use three whole tablets and part of a fourth)

B. In order to obtain the correct amount of drug, you weigh all four tablets and find that they weigh 1.24 g total. How much powder will you need to weigh after the tablets are crushed to obtain the needed amount of drug?

4 tablets × 50 mg/tablet = 200 mg drug in 4 tablets

180 mg drug × 1.24 g powder/200 mg drug = 1.12 g powder

C. If Viagra 50-mg tablets cost $223.03 for a bottle of 30 tablets, how much money is wasted if the remaining powder from part B is discarded?

Amount of drug discarded: 200 mg 180 mg = 20 mg

$223.03/30 tablets × 1 tablet/50 mg × 20 mg = $2.97

D. You use 10 mL of a 4% w/v methylcellulose gel as a suspending agent in preparing this mixture. What is the percent strength of methylcellulose in the final product?

4 g/100 mL × 10 mL = 0.4 g methylcellulose

0.4g/60 mL × 100 = 0.67% w/v methylcellulose in the final product

A formula reported to aid in killing lice is as follows:1

Rx Geranium oil 8 drops

Rosemary oil 7 drops

Jojoba oil 15 mL

This entire formula is to be massaged vigorously into the hair and scalp at bedtime, then shampooed out the next morning. The manager from a nearby church camp calls and asks you to prepare enough of this formula to treat 26 children for two applications each.

A. Ratherthan tediously counting drops, you decide to use an estimated drop factor of 50 µL/drop to determine the amount of geranium oil and rosemary oil needed. How much of each of these and the jojoba oil will be necessary to prepare the needed amount of the formula?

Amount of formula needed: 26 children × 2 doses/child = 52 doses

Geranium oil: 8 drops/dose × 52 doses × 50 µL/drop × 1 mL/1000 µL = 20.8 mL

Rosemary oil: 7 drops/dose ×52 doses × 50 µL/drop × 1 mL/1000 µL = 18.2 mL

Jojoba oil: 15 mL/dose × 52 doses = 780 mL

B. Assuming that volumes are additive, what would be the ratio strength of the geranium oil and rosemary oil in the mixture?

Total volume =. 20.8 mL + 18.2 mL + 780 mL = 819 mL

Geranium oil: 819 mL mixture/20.8 mL oil = 39.375

Ratio strength = 1:39 v/v

Rosemary oil: 819 mL mixture/18.2 mL oil = 45 Ratio strength = 1:45 v/v

C. What would be the volume of mixture prepared expressed as fluid ounces?

819 mL × 1 fl.oz/29.57 mL = 27.7 fl. oz.

3 A 5-year-old child who is 3 feet 4 inches tall weighs 45.4 pounds.

A. What is the ideal body weight for this child?

The ideal body weight for a child can be calculated by using the following equation:2

IBW (kg) = [(height in cm)^sup 2^ × 1.651/1000

3 feet 4 inches = 40 inches × 2.54 cm/inch = 101.6 cm

IBW = [(101.6 cm)^sup 2^ × 1.651/1000 = 17.03 kg

B. What percentage of his ideal body weight is the actual body weight of this child?

45.4 lbs × 1 kg/2.2 lbs = 20.64 kg

20.64 kg/17.03 kg × 100 = 121.16%

The child's actual body weight is 121.16% of his ideal body weight; therefore, he is slightly overweight.2

C. The expected growth velocity in a 5-year-old child is 5 to 6 g/day and 0.5 to 0.6 cm/month.^sup 2^ If this child weighed 39.1 lbs and was 3 feet 1 inch tall exactly 1 year ago, is he within the normal growth velocity range?

45.4 lbs 39.1 lbs = 6.3 lbs × 454 g/lb = 2860.2 g

2860.2 g/365 days = 7.84 g/day

3 feet 4 inches 3 feet 1 inch = 3 inches × 2.54 cm/inch = 7.62 cm

7.62 cm/12 months = 0.64 cm/month

This child is slightly above the normal growth velocity range for both height and weight.

References

1. Allen LV Jr. Natural head lice repellant spray. IJPC2001; 5(1): 48.

2. Dipiro JT, Talbert RL, Yee GC et al, eds. Pharmacotherapy: A Pathophysiologic Approach. 6th ed. New York, NY: McGraw-Hill Companies, Inc.; 2005: 2561-2562.

Shelly J. Prince, PhD, RPh

Southwestern Oklahoma State University

College of Pharmacy

Weatherford, Oklahoma

Address correspondence to Shelly J. Prince, PhD, RPh, College of Pharmacy, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, OK 13096.

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