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Dimenhydrinate

Dimenhydrinate, also known by the trade names Dramamine and Gravol, is an over-the-counter drug used to prevent motion-sickness (emesis). It is closely related to diphenhydramine HCl, or Benadryl. The differences relate to the weight-for-weight potency (50mg dimenhydrinate contains 30mg of the drug diphenhydramine), delay of action (dimenhydrinate must dissociate into diphenhydramine and its counterion in the body before it is active, therefore diphenhydramine produces effects sooner), and degree of sedation produced. more...

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Chemically, dimenhydrinate is a salt of two drugs: diphenhydramine(+) and 8-chlorotheophyllinate(-). Chlorotheophyllinate is a chlorinated form of the drug theophylline. The chlorination provides the necessary charge to associate with diphenhydramine as a solid. Theophylline is very closely related to caffeine and theobromine, mild central nervous system stimulants. It was thought that by combining the antiemetic effects of diphenhydramine with a stimulant, the extreme drowsiness induced by the former could be mitigated somewhat by the latter. In actuality, the sedation caused by diphenhydramine is substantially stronger than the stimulation caused by chlorotheophyllinate. Diphenhydramine, an ethanolamine-class antihistamine, is found in most OTC sleep aids and allergy preparations, such as Tylenol PM and Benadryl. It is primarily a H1-antagonist, but also possesses an antimuscarinic effect. It is used in Dramamine to produce and prevent nausea and emesis, however the development of the chemical meclizine has overtaken its usage (marketed as "Dramamine II") due to the fact that meclizine doesn't produce as much drowsiness.

Abuse

Recreational drug users sometimes take several times the recommended dose of dimenhydrinate in order to attain an intense and long-lasting state of anticholinergic delirium.

The mental effects are described by many as "dreaming while awake" involving visual and auditory hallucinations which, unlike those experienced with recreational drugs known as psychedelics, often cannot be readily distinguished from reality. Users often report a highly unpleasant side effect profile consistent with tropane glycoalkaloidal poisoning. This includes dry mouth and eyes, rapid heart beat (tachycardia), somnolence, insomnia, and extreme malaise. This is due to antagonism of muscarinic acetylcholine receptors in both the central and autonomic nervous system, inhibiting various signal transduction pathways.

In the CNS, diphenhydramine readily crosses the blood-brain barrier, exerting effects within the visual and auditory cortex, accounting for reported visual and auditory disturbances. Other CNS effects occur within the limbic system and hippocampus, causing confusion and temporary amnesia. Toxicology also manifests in the autonomic nervous system, primarily at the neuromuscular junction, resulting in ataxia and extrapyramidal side-effects, and at sympathetic post-ganglionic junctions, causing urinary retention, pupil dialation, tachycardia, and dry skin & mucous membranes. Considerable overdosage can lead to myocardial infarction, serious ventricular dysrhythmias, coma and death. Such a side-effect profile is thought to give ethanolamine-class antihistamines a relatively low abuse liability.

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Dimenhydrinate 5-mg/mL oral liquid
From International Journal of Pharmaceutical Compounding, 5/1/03

FORMULATIONS

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. Dissolve the dimenhydrinate and methylparaben in a mixture of the glycerin and ethanol.

4. Add the flavor and mix well.

5. Add the water and then sufficient syrup to volume and mix well.

6. Package and label.

PACKAGING

Package in tight, light-resistant containers.

LABELING

Protect from light. Keep out of reach of children.

STABILITY

A beyond-use date of up to 6 months can be used, dependent upon quality-control testing.1

USE

Dimenhydrinate is used in the prevention and treatment of nausea.

QUALITY CONTROL

Quality-control assessments can include weight/volume, pH, specific gravity, active drug assay, color, clarity, rheological properties, physical observation, and physical stability (discoloration, foreign materials, gas formation, and mold growth).2

DISCUSSION

Dimenhydrinate oral liquid was formerly available in three strengths: 12.5 mg/5 mL, 12.5 mg/4 mL, and 15.62 mg/5 mL; but all have been discontinued. The solid oral-dosage forms are still available.

Dimenhydrinate (C^sub 17^H^sub 21^ NO*C^sub 7^H^sub 7^C1N^sub 4^O^sub 2^, MW 469.96) occurs as a white, crystalline, odorless powder that is slightly soluble in water and freely soluble in alcohol.1 It is an ethanolaminederivative antihistamine that is used as an antiemetic. It is composed of 53% to 55.5% diphenhydrmaine and 44% to 45% of 8-chlorotheophylline. The injection has a pH in the range of 6.4 to 7.2. Dimenhydrinate is used in the prevention and treatment of nausea, vomiting and/or vertigo associated with motion sickness. It is most effective when administered prophylactically. It has also been used in the treatment of Meniere's disease and other vestibular disturbances.3

Glycerin (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 that of sucrose. It has a specific gravity of about 1.25. It is miscible with water, methanol, and 95% ethanol; practically insoluble in oils and chloroform; and slightly soluble in acetone. It is hygroscopic and should be stored in airtight containers in a cool place. When mixed with water, ethanol, and propylene glycol, the mixtures are chemically stable.4

Ethanol 95% (C^sub 2^H^sub 5^OH, MW 46.07, ethyl alcohol, ethanol, grain alcohol) is a clear, colorless, mobile, and volatile liquid with a slight, characteristic odor and a burning taste. Alcohol USP refers to 95% ethanol, and dehydrated alcohol refers to 99.5% alcohol. Its specific gravity is between 0.812 and 0.816, and its boiling point is 78.15 deg C. It is miscible with chloroform, glycerin, and water. It should be stored in a cool place.5

Methylparaben (C^sub 8^H^sub 8^O^sub 3^, MW 152.15, methyl hydroxybenzoate, methyl parahydroxybenzoate) is available as colorless crystals or as a white, crystalline powder that is odorless, or almost odorless, and has a slight burning taste. Methylparaben is most effective in solutions between pH 4 to 8, and its efficacy decreases at higher pH levels. One gram is soluble in 400 mL of water, 3 mL of 95% ethanol, 60 mL glycerin, 200 mL peanut oil, and 5 mL propylene glycol; and it is practically insoluble in mineral oil.6

Purified water is water that is obtained by distillation, ion exchange, reverse osmosis or some other suitable process. It is miscible with most polar solvents and is chemically stable in all physical states (ice, liquid, and steam).7

Syrup (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 is generally self-preserving, as long as the sucrose concentration is maintained sufficiently high.

References

1. United States Pharmacopeial Convention, Inc. United States Pharmacopeia 26/National Formulary2l. Rockville, Maryland:US Pharmacopeial Convention, Inc.; 2003:628-630, 2197-2201, 2375, 2558,

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

3. McEvoy GK, ed. AHFS Drug Information-2002. Bethesda, Maryland: American Society of Health-System Pharmacists; 2002:2803-2805.

4. Price JC. Glycerin. In: Kibbe AH, ed. Handbook of Pharmaceutical Excipients. 3rd ed. Washington, DC:American Pharmaceutical Association; 2000:220-222.

5. Weller PJ. Alcohol. In: Kibbe AH, ed. Handbook of Pharmaceutical Excipients. 3rd ed. Washington, DC:American Pharmaceutical Association; 2000:7-9.

6. Reiger MM. Methylparaben. In: Kibbe AH, ed. Handbook of Pharmaceutical Excipients. 3rd ed. Washington, DC:American Pharmaceutical Association; 2000:340-344.

7. Ellison A, Nash RA, Wilkin MJ. Water. In: Kibbe AH, ed. Handbook of Pharmaceutical Excipients. 3rd ed. Washington, DC:American Pharmaceutical Association; 2000:580-584.

Copyright International Journal of Pharmaceutical Compounding May/Jun 2003
Provided by ProQuest Information and Learning Company. All rights Reserved

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