Phenadryl10 mg/5 ml

Diphenhydramine hydrochloride is a first-generation sedating antihistamine used for a broad range of conditions, available as oral tablets/capsules/syrup and as an injection, with the specific route depending on the product and clinical need:

Allergic Conditions

• Symptomatic relief of allergic conditions, including urticaria (hives), angioedema, allergic rhinitis, and allergic conjunctivitis
• Amelioration of allergic reactions to blood or plasma transfusion, and as an adjunct to epinephrine in anaphylaxis, after the acute, life-threatening symptoms have been controlled by other emergency measures
• Pruritic (itchy) skin conditions

Sleep and Motion-Related Uses

• Short-term management of occasional insomnia
• Prevention and treatment of motion sickness
• Treatment of vertigo

Movement Disorders

• Control of drug-induced extrapyramidal symptoms (movement side effects caused by certain psychiatric medicines), due to its antimuscarinic properties
• Adjunctive treatment in parkinsonism

Diphenhydramine does not treat the underlying cause of allergies or insomnia and provides only symptomatic relief; for insomnia persisting beyond 2 weeks, medical evaluation is recommended rather than continued self-treatment.

Contains Phenadryl 10 mg/5 ml as the active ingredient, marketed in several forms: oral tablets and capsules (commonly 25 mg and 50 mg), chewable tablets (commonly 12.5 mg), oral syrup (commonly 12.5 mg per 5 mL), and injection (commonly 50 mg/mL). Confirm the specific formulation and strength on the product dispensed, since dosing and route are not interchangeable.

Diphenhydramine hydrochloride is one of the most widely used first-generation antihistamines, valued for its broad range of uses spanning allergy relief, short-term insomnia management, motion sickness prevention, and control of certain drug-induced movement symptoms. Unlike newer, non-sedating antihistamines, diphenhydramine crosses readily into the brain, which is responsible for both its sedative effect (useful for sleep) and its more pronounced drowsiness and anticholinergic side effects compared to modern allergy medicines. It has a long track record of safe use, though caution is needed in the elderly, given increased sensitivity to its sedative and anticholinergic effects.

Therapeutic Class: Antihistamine (Sedating, First-generation)

Diphenhydramine has a rapid onset of action, particularly when given by injection, and is widely distributed throughout the body, including into the central nervous system, which accounts for its sedative effect and greater central side-effect burden compared to non-sedating, second-generation antihistamines. It is metabolized mainly in the liver, with a portion excreted unchanged in the urine.

• Oral tablets/capsules may be taken with or without food; taking with food may reduce mild stomach upset
• For insomnia, take about 30 minutes before bedtime
• Chewable tablets should be chewed thoroughly before swallowing
• Injection is given only by a healthcare professional, by deep intramuscular injection or slow intravenous injection (not exceeding 25 mg per minute), when oral administration is not practical
• Do not drive or operate machinery until you know how this medicine affects you, given its sedative effect

The following should be assessed by a healthcare professional before combining with diphenhydramine:

• Other central nervous system depressants (alcohol, opioids, sedatives, other antihistamines): additive sedation and risk of respiratory depression when combined.
• Monoamine oxidase inhibitors (MAOIs): may intensify and prolong the anticholinergic effects of diphenhydramine.
• Other anticholinergic medicines (such as certain antidepressants, antipsychotics, or antispasmodics): additive anticholinergic effects (dry mouth, urinary retention, confusion, constipation) when combined.
• Medicines affecting cardiac conduction: use with caution, given diphenhydramine's own potential, particularly at high doses, to affect cardiac rhythm.

Common side effects

• Drowsiness or sedation (can be pronounced)
• Dry mouth, nose, or throat
• Dizziness
• Constipation
• Blurred vision
• Thickened respiratory secretions

Less common but notable effects

• Paradoxical excitation, particularly in children: restlessness, nervousness, or irritability instead of sedation
• Urinary retention or difficulty urinating

Serious side effects (seek medical attention)

• Signs of a severe allergic reaction: rash, swelling of the face or throat, difficulty breathing
• In the elderly, particularly with regular or higher-dose use: confusion, memory problems, increased fall risk
• Rapid or irregular heartbeat, particularly with excessive doses
• Injection-site reactions or, rarely, tissue injury with the injectable form if not administered correctly

Pregnancy

Diphenhydramine has been used in pregnancy for various indications, including nausea, with a long history of use, but should be used only when a doctor determines it is necessary, particularly close to delivery, given the potential for sedative effects in the newborn.

Breastfeeding

Diphenhydramine passes into breast milk in small amounts; because it can cause drowsiness and, in infants, has been associated with excitability or sedation, use during breastfeeding should be discussed with a healthcare professional, and non-sedating antihistamines are often preferred if breastfeeding.

• Elderly patients: more sensitive to sedative and anticholinergic effects, including confusion, dry mouth, constipation, and urinary retention, and at increased risk of falls; non-sedating antihistamines are often preferred where appropriate in this population, and diphenhydramine, if used, should be at the lowest effective dose.
• Driving and hazardous activities: avoid until you know how this medicine affects you, given its sedative effect, which can persist into the next day, particularly at higher doses.
• Avoid alcohol while taking diphenhydramine, given additive sedation.
• Not recommended for use as a sleep aid for more than about 2 weeks continuously; consult a doctor if insomnia persists beyond this.
• Use with caution in patients with asthma, chronic obstructive pulmonary disease, glaucoma, or urinary retention, given anticholinergic and secretion-thickening effects.

Diphenhydramine overdose can cause a range of effects from sedation and confusion to paradoxical central nervous system stimulation (particularly in children), including hallucinations, agitation, and seizures, along with anticholinergic effects such as dry, flushed skin, dilated pupils, rapid heartbeat, and urinary retention; severe overdose can cause dangerous cardiac arrhythmias, coma, and respiratory depression. Suspected significant overdose is a medical emergency requiring immediate care; treatment is generally supportive, provided in a medical facility, with cardiac monitoring for severe cases.

Store oral tablets, capsules, and syrup at room temperature, protected from light and moisture. Store injectable ampoules/vials as directed on the product label, generally at room temperature, protected from light.

• Elderly: Increased sensitivity to sedative and anticholinergic effects, with increased fall and confusion risk; use the lowest effective dose, and consider alternatives where appropriate.
• Children: Dosing is weight- or age-based; paradoxical excitation (rather than sedation) can occur in this age group. The injectable form is not used in premature infants or neonates.
• Hepatic impairment: Use with caution, given hepatic metabolism of the drug.

For allergy symptoms or motion sickness, diphenhydramine is generally used on an as-needed basis. For insomnia, use is generally limited to short-term, occasional use (not more than about 2 weeks continuously) without medical evaluation, since chronic insomnia may need a different underlying diagnosis and treatment approach.

Drug Class: Ethanolamine-derivative H1-antihistamine with anticholinergic and sedative properties

Diphenhydramine works primarily by blocking histamine H1 receptors, which relieves allergy symptoms such as itching, sneezing, hives, and watery eyes triggered by histamine release. Because it also readily crosses into the brain and has anticholinergic activity, it produces sedation (useful for short-term insomnia) and, at the same doses, can reduce certain drug-induced movement symptoms by blocking excess acetylcholine activity associated with dopamine-blocking medicines.

Diphenhydramine is used in children 1 month and older for allergy symptoms and certain other indications, with weight-based or age-based dosing as shown in the dosage table. Paradoxical excitation (restlessness or irritability instead of drowsiness) can occur in children more often than in adults. The injectable form is not used in premature infants or neonates.