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Benadryl

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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BAD (Benadryl, Ativan and Decadron) Intravenous Drip
From International Journal of Pharmaceutical Compounding, 11/1/04

METHOD OF PREPARATION

Note: This preparation should be done 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. With continued mixing, add the Benadryl and Decadron injection to the calculated quantity of 5% dextrose injection.

4. With continued mixing, slowly add the Ativan injection and mix well.

5. Package and label.

PACKAGING

Package in tight, light-resistant containers.1

LABELING

Keep out of reach of children. Use only as directed.

STABILITY

A beyond-use date of 48 hours at room temperature, 14 days at refrigerated temperature or 45 days at

USE

This combination has been used in the treatment of nausea and vomiting.

QUALITY CONTROL

Quality-control assessment can include weight/volume, physical observation, pH, specific gravity, osmolality, assay, color, clarity, paniculate matter, sterility and pyrogenicity.2,3

DISCUSSION

A number of combinations of an antihistamine, corticostcroid, sedative, etc., are used for the treatment of nausea in patients. Different antihistamines, corticosteroids, sedatives, etc. in various combinations have been used over the years. This formulation is relatively simple and easy to prepare.

Benadryl injection is available containing diphenhydramine hydrochloride 50 mg/mL and also containing 0.1 mg/mL of benzethonium chloride with pH adjusted to the range of 5-6. Diphenhydramine HCl (C^sub 17^H^sub 21^NO.HCl, MW 291.82) occurs as a white, odorless, crystalline powder. It slowly darkens on exposure to light. Its solutions are practically neutral. It is freely soluble in water and in alcohol. It is an H^sub 1^-receptor antagonist used for the relief of hypersensitivity reactions. It is also used in the treatment of nausea, vomiting and vertigo.1,4

Ativan injection (lorazepam) is available in 2- and 4-mg/mL concentrations. Each milliliter also contains 0.18 mL of polyethylene glycol 400 and 2% benzyl alcohol in propylene glycol.

Lorazepam (C^sub 15^H^sub 10^C^sub 12^N^sub 2^O^sub 2^) should be preserved in single-dose or multiple-dose containers, preferably of type I glass, and protected from light.1

Decadron injection (dexamethasone) is an anti-inflammatory and immunosuppressant agent with only minimal mineralocorticoid properties. It is used in the treatment of shock, cerebral edema, allergic conditions, inflammatory diseases, bacterial meningitis, tuberculosis, and meningitis, and in the prevention of hyaline membrane disease in premature infants and the prevention of cancer chemotherapy-induced nausea and vomiting. Dexamethasone sodium phosphate injection is available in 4- and 24-mg/mL strengths. Both strengths contain, per mL, creatinine (8 mg), sodium citrate (10 mg), sodium bisulfite (1 mg), methylparaben (1.5 mg), propylparaben (0.2 mg) and sodium hydroxide to adjust pH and water for injection. The 24-mg/mL also contains disodium edetate (0.5 mg). The pH of the solutions is in the range of 7 to 8.5. The injection contains not more than 31.3 USP endotoxin units per mg of dexamethasone phosphate.1 Dexamethasone sodium phosphate (C^sub 22^H^sub 28^FNa^sub 2^O^sub 8^P, MW 516.40) occurs as a white or slightly yellow crystalline powder. It is odorless or has a slight odor of alcohol and is very hygroscopic. It is freely soluble in water and slightly soluble in alcohol.1

5% Dextrose injection is a sterile solution of dextrose in water for injection. It contains not less than 95.0% and not more than 105.0% of the labeled amount of C^sub 6^H^sub 12^O^sub 6^.H2O. Dextrose injection contains no antimicrobial agents. It contains not more than 0.5 USP endotoxin units per mL for injections containing less than 5% of dextrose and not more than 10.0 USP endotoxin units per g for injections containing between 5% and 70% of dextrose. The pH of the solution is between 3.2 and 6.5.1

REFERENCES

1. US Pharmacopeial Convention, Inc. United States Pharmacopeia 27-National Formulary 22. Rockville, MD: US Pharmacopeial Convention, Inc.; 2004: 562-564, 582, 1107-1108, 2345-2349, 2758, 2760.

2. Allen LV Jr. Standard operating procedure for paniculate testing for sterile products. IJPC 1998; 2: 78.

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

4. Trissel LA. Handbook on Injectable Drugs. 12th ed. Bethesda, MD: American Society of Health-System Pharmacists; 2003: 444-453.

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