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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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Scopolamine Hydrobromide 0.2% Nasal Spray
From International Journal of Pharmaceutical Compounding, 1/1/04

METHOD OF PREPARATION

Note: This preparation should be prepared in a laminar airflow hood in a cleanroom (or via isolation barrier technology) by a validated aseptic compounding pharmacist using strict aseptic technique.

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 scopolamine hydrobromide, citric acid, dibasic sodium phosphate and sodium chloride in approximately 95 mL of sterile water for injection.

4. Add the benzalkonium chloride 50% solution and mix well.

5. Adjust the pH if necessary, using either additional citric acid or sodium hydroxide 10% aqueous solution to a pH of 6.5.

6. Add sufficient sterile water for injection to volume and mix well.

7. Filter through an appropriate sicrilc 0.2-µm filter into a sterile container.

8. Package and label.

PACKAGING

Package in nasal-spray containers that are tight and light-resistant.1

LABELING

Keep out of reach of children. Use only as directed. For the nose.

STABILITY

A beyond-use date of up to 6 months can be used for this preparation.1

USE

Scopolamine hydrobromide 0.2% nasal spray has been used in the treatment of motion sickness.2

QUALITY CONTROL

Quality-control assessment can include final volume, pH, specific gravity, active-drug assay, color, clarity, physical observation, physical stability (discoloration, foreign materials, gas formation, mold growth), osmolality and sterility.3-5

DISCUSSION

Scopolamine hydrobromide is a naturally occurring tertiary amine antimuscarinic used for the prevention of nausea and vomiting induced by motion. An advantage to this nasal formulation is a rapid onset of action.

Scopolamine hydrobromide (C^sub 17^H^sub 21^NO^sub 4^.HBr.^sub 3^H2O, MW 438.31, hyoscine hydrobromide) occurs as colorless or white crystals or as a white, granular powder. It melts at about 197°C with decomposition. It is odorless and slightly efflorescent in dry air. It is freely soluble in water (l g in 1.5 mL) and soluble in alcohol (l g in 20 mL).1,6

The pH of the solution has been shown to affect the extent and rate of absorption. In a study using solutions prepared at pH levels of 4.0, 7.0 and 9.0, the higher the pH, the faster were the T^sub max^ values and the higher were the C^sub max^ values. The pH 7.0 formulation selected here provides relatively rapid onset of action and good absorption and is in the allowable pH range of the USP injection that goes up to pH 6.5.1,7

Citric acid, available in an anhydrous form (C^sub 6^H^sub 8^O^sub 7^, MW 192.12) or in a monohydrate form (C^sub 6^H^sub 8^O^sub 7^.H2O, MW 210.14), occurs as colorless or translucent crystals, or as a white crystalline. One gram is soluble in less than 1 mL of water and 1.5 mL of ethanol.8

Dibasic sodium phosphate (NaHPO^sub 4^.xH2O) is available in an anhydrous form (MW 141.96) and as a dihydrate (MW 177.99), heptahydrate (MW 268.07) and dodecahydrate (MW 358.14). It is used as a buffering agent and as a sequestering agent. It is very soluble in water but practically insoluble in ethanol.9

Benzalkonium chloride is a bactericidal antimicrobial. Benzalkonium Chloride Solution NF is a clear liquid, colorless or slightly yellow unless a color has been added. Benzalkonium chloride is composed of a mixture of straight-chain homologs.10

REFERENCES

1. US Pharmacopeial Convention, Inc. United States Pharmacopeia 26-National Formulary 21. Rockville, MD:US Pharmacopeial Convention, Inc.; 2003:1668,1939, 2197-2201, 2580.

2. Klocker N, Hanschke W, Toussaint S et al. Scopolamine nasal spray in mot!on sickness: A randomized, controlled, and crossover study for the comparison of two scopolamine nasal sprays with oral dimenhydrinate and placebo. Eur J Pharm Sci 2001;13:227-232.

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

4. Alien LV Jr. Standard operating procedure for particulate testing for sterile products. IJPC1998;2:78.

5. Alien LV Jr. Standard operating procedure: Quality assessment for injectable solutions. IJPC 1999;3:406-407.

6. McEvoy GK, ed. XlWFS Drug Information-2003. Bethesda, PVID:American Society of Health-System Pharmacists; 2003:1214-1218.

7. Ahmed S, Sileno AP, deMeireles JC et al. Effects of pH and dose on nasal absorption of scopolamine hydrobromide in human subjects. Pharm Res 2000;17:974-977.

8. Amidon GE. Citric acid monohydrate. In: Kibbe AH, ed. Handbook of Pharmaceutical Excipients. 3rd ed. Washington, DC:American Pharmaceutical Association; 2000:140-142.

9. Kearney AS. Sodium phosphate, dibasic. In: Kibbe AH, ed. Handbook of Pharmaceutical Excipients. 3rd ed. Washington, DC:American Pharmaceutical Association; 2000:493-495.

10. Kibbe AH. Benzalkonium chloride. In: Kibbe AH, ed. Handbook of Pharmaceutical Excipients. 3rd ed. Washington, DC:American Pharmaceutical Association; 2000:33-35.

Copyright International Journal of Pharmaceutical Compounding Jan/Feb 2004
Provided by ProQuest Information and Learning Company. All rights Reserved

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