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Diphenhydramine

Diphenhydramine hydrochloride (trade name Benadryl^®, or Dimedrol outside the US) is an over-the-counter (OTC) antihistamine and sedative. It is also given in conjunction with typical antipsychotics to prevent akathisia. It is a member of the ethanolamine class of antihistaminergic agents. more...

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Diphenhydramine is widely used in nonprescription sleep aids (Nytol, Sominex, Unisom, Compoz, Excedrin PM, etc.) with a 50mg recommended dose mandated by the FDA. In the United Kingdom, Australia, New Zealand, South Africa, and other countries, a 50 to 100mg recommended dose is permitted. In spite of its use and effectiveness as a sleep-inducing agent, when this drug is sold as an antihistamine, warning of the potential loss of alertness is never prominently displayed on packaging, leading to unknown numbers of traffic fatalities.

Unlike true antihistamines, which prevent the release of histamine, diphenhydramine works by blocking the effect of histamine at H1 receptor sites. This results in effects such as the reduction of smooth muscle contraction, making diphenhydramine a popular choice for treatment of the symptoms of allergic rhinitis, hives, motion sickness, and insect bites and stings.

Diphenhydramine is a first generation antihistamine drug. Despite being one of the oldest antihistamines on the market, it is by and large the most effective antihistamine available, either by prescription or over-the-counter, and has been shown to exceed the effectiveness of even the latest prescription drugs. Consequently, it is frequently used when an allergic reaction requires fast, effective reversal of the (often dangerous) effects of a massive histamine release. However, it is not always the drug of choice for treating allergies. Like many other first generation antihistamines, is also a potent anticholinergic agent. This leads to profound drowsiness as a very common side-effect, along with the possibilities of motor impairment (ataxia), dry mouth and throat, flushed skin, rapid or irregular heartbeat (tachycardia), blurred vision at nearpoint due to lack of accommodation (cycloplegia), abnormal sensitivity to bright light (photophobia), pupil dilatation, urinary retention, constipation, difficulty concentrating, short-term memory loss, visual disturbances, hallucinations, confusion, and delirium.

In the 1960s it was found that diphenhydramine inhibits reuptake of the neurotransmitter serotonin. This discovery led to a search for viable antidepressants with similar structures and fewer side effects, culminating in the invention of fluoxetine (Prozac), a selective serotonin reuptake inhibitor (SSRI). A similar search had previously led to the synthesis of the first SSRI zimelidine from chlorpheniramine, also an antihistamine.

Recreational drug users sometimes take several times the recommended dose of diphenhydramine in order to attain an intense hallucinogenic (more accurately, delirious) state. Abusers often call diphenhyramine "The Pink Panther", in reference to the pink colored pills and syrups or they will say they are "drillin" or "Benatrippin" because of the common name brand, Benadryl^®. The mental effects are described by many as "dreaming while awake" involving visual and auditory hallucinations which, unlike those experienced with most psychedelics, often cannot be readily distinguished from reality. Many users report a side effect profile consistent with tropane glycoalkaloidal poisoning. 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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Diphenhydramine Hydrochloride 0.1%, Lidocaine Hydrochloride 1%, Misoprostol 0.0024% and Triamcinolone Acetonide 0.12% Oral Rinse
From International Journal of Pharmaceutical Compounding, 7/1/04

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. Mix the misoprostol and the triamcinolone acetonide with the glycerin to form a smooth paste.

4. Dissolve the diphenhydramine hydrochloride, lidocaine hydrochloride and potassium sorbate in about 60 mL of purified water.

5. Add the sorbitol 70% solution to the misoprostol-triamcinolone-glycerin mixture and mix until uniform.

6. Add the aqueous solution of the water soluble drugs and the flavor and mix well.

7. Adjust the pH with the citric acid solution to the range of 5.5 to 6.0.

8. Add sufficient purified water to volume and mix well.

9. Package and label.

PACKAGING

Package in tight, light-resistant containers.1

LABELING

Keep out of reach of children. Use only as directed. Shake well before using. Keep in refrigerator.

STABILITY

A beyond-use date of 14 days would be appropriate for this preparation when stored in a refrigerator.1

USE

This preparation has been used in the treatment of oral mucositis.

QUALITY CONTROL

Quality-control assessment can include weight/volume, pH, active drug assay, color, physical observation and physical stability.2

DISCUSSION

There are numerous combinations of misoprostol and lidocaine with different corticosteroids and antihistamines that are commonly used for the treatment of oral mucositis or for the prevention of radiation-induced oral mucositis.

Diphenhydramine hydrochloride (C^sub 17^H^sub 21^NO.HCl, MW 291.82) occurs as a white, odorless, crystalline powder. It is freely soluble in water and in alcohol. It is a Hi-receptor antagonist used for the relief of hypersensitivity reactions, nausea, vomiting and vertigo.1

Lidocaine hydrochloride (C^sub 14^H^sub 22^N^sub 2^O-HCl.H^sub 2^O, MW 288.81) occurs as a white, odorless, crystalline powder with a slightly bitter taste. It is an amide-type local anesthetic with a rapid onset and intermediate duration of action. It is very soluble in water (1:0.7) and in alcohol (1:1.5).1,3

Misoprostol (C^sub 22^H^sub 38^O^sub 5^, MW 382.53, Cytotec) is a synthetic analog of prostaglandin EI (alprostadil) and occurs as a watersoluble, viscous liquid. It is a gastric antisecretory agent with protective effects on the gastroduodenal mucosa. Cytotec tablets contain either 100 µg or 200 µg of misoprostol. The tablets also contain hydrogenated castor oil, hydroxypropyl methylcellulose, microcrystalline cellulose and sodium starch glycolate.4

Triamcinolone acetonide (C^sub 24^H^sub 31^FO^sub 6^, MW 434.51) occurs as a white-to-cream colored, crystalline powder with not more than a slight odor. It is practically insoluble in water and sparingly soluble in dehydrated alcohol.1

Glycerin (C^sub 3^H^sub 8^O^sub 3^, MW 92.10, 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 is miscible with water, methanol and 95% ethanol, practically insoluble in oils and slightly soluble in acetone.5

Sorbitol (C^sub 6^H^sub 14^O^sub 6^, MW 182.17, D-glucitol) is a hexahydric alcohol related to mamiose and is isomeric with mannitol. It occurs as an odorless, white or almost colorless, crystalline, hygroscopic powder. It has a pleasant, cooling, sweet taste.1

Potassium sorbate (C^sub 6^H^sub 7^KO^sub 2^, MW 150.22) occurs as white crystals or powder with a characteristic odor. It is freely soluble in water and soluble in alcohol. It is an antimicrobial preservative.1

Citric acid (C^sub 6^H^sub 8^O^sub 7^.H^sub 2^O, MW 210.14, citric acid monohydrate) occurs as colorless or translucent crystals or as a white crystalline, efflorescent powder that is odorless and has a strong tart, acidic taste. One gram is soluble in less than 1 mL of water and 1.5 mL of ethanol.7

REFERENCES

1. US Pharmacopeial Convention, Inc. United States Pharmacopeia 27National Formulary22. Rockville, MD: US Pharmacopeial Convention, Inc.; 2004: 1087-1088, 1875-1876, 2267, 2345-2349, 2768, 2778, 2921.

2. Alien LV Jr. Standard operating procedure for performing physical quality assessment of oral and topical liquids. IJPC1999; 3(2): 146-147.

3. McEvoy GK. AHFS Drug Information-2004. Bethesda, MD: American Society of Health-System Pharmacists; 2004: 2807-2812, 3089-3090.

4. [No author listed.] Physicians' Desk Reference. 58th ed. Montvale, NJ: Thomson PDR; 2004: 3109-3111.

5. 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.

6. Nash RA. Sorbitol. In: Rowe RC, Sheskey PJ, Weller PJ, eds. Handbook of Pharmaceutical Excipients. 4th ed. Washington, DC: American Pharmaceutical Association; 2003: 596-599.

7. Amidon GE. Citric acid monohydrate. In: Rowe RC, Sheskey PJ, Weller PJ, eds. Handbook of Pharmaceutical Excipients. 4th ed. Washington, DC: American Pharmaceutical Association; 2003: 158-160.

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