Diphenhydramine

Drug #250

Diphenhydramine is H1 antihistiminic agent. Diphenhydramine is used to relief the symptoms of allergic reactions such as rash, hives, watery eyes, runny nose, itchy eyes and sneezing. Diphenhydramine is also used to treat motion sickness, anxiety, tension, sleeplessness or involuntary movements due to the side effects of psychiatric drugs.

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Primary Characteristics

Diphenhydramine is also known as Diphenhydramine Hcl.

It is of Synthetic origin and belongs to Benzoalkylamine.

It belongs to H1-antagonist pharmacological group on the basis of mechanism of action and also classified in sedative pharmacological group.

Molecular Weight: 291.8 · pK_a: 9.0 · Solubility in Water: Very soluble · Solubility in Alcohol: Freely soluble · Non-proprietary name: Diphenhydramine · pH: 5.5 · Isotonic value: 5.7.

Pharmacokinetics

Absorption: Diphenhydramine has an oral bioavailability is 92.5% (±2.5%), pre-systemic (first-pass) metabolism accounts for 50%.

Distribution: Diphenhydramine has a volume of distribution is 3.28 l/kg. plasma protein binding is 85-98%.

Elimination: it is metabolised via extensive by liver, plasma half-life is 3.3 hr, renal excretion is 65%.

Indications

Diphenhydramine is primarily indicated in conditions like Anaphylactic reactions, Angioneurotic edema, Antiemetic poisoning, Conjuctivitis, Cough, Menieres disease, Motion sickness, Parkinsonism, Perennial rhinitis, Pruritus, Seasonal rhinitis, Urticaria, Vasomotor rhinitis.

Diphenhydramine is also indicated for secondary conditions like Extrapyramidal disorders, Nausea and vomiting, Vertigo.

Contraindications

Diphenhydramine is contraindicated in conditions like Glucoma, Urinary retention.

Dosage

Diphenhydramine's dosage details are as follows:

Dose	Single Dose	Frequency	Route
Adult Dosage
20 – 50 mg	—	Every 3h	PO,IV,IM
Paediatric Dosage (20kg)
1.875 mg/kg	1.875 mg/kg	Every 8h	Oral
Neonatal Dosage (3kg)
No data.

Drug Interactions

Unknown3 interactions

8 interactions

Moderate1 interaction

Always consult your physician for the change of dose regimen or an alternative drug of choice that may strictly be required.

Side Effects

The signs and symptoms that are produced after acute overdosage of Diphenhydramine are Flushing, Nausea, Tachycardia , Convulsions , Coma, Drowsiness, Drowsiness, Cardiorespiratory depression, Dry mouth, Urinary retention, Hallucinations , Fever, Dilated pupils, Ataxia, Headache, Cardiorespiratory depression.

Diphenhydramine is known to cause more or less tolerable side effects which are usually transient. These include Ataxia, Blurred vision, Dermatitis, Diplopia, Dizziness, Epigastric pain, Euphoria, Fatigue, Nausea and vomiting, Nervousness, Sedation , Tinnitus, Tiredness , Tremors.

Warnings / Precautions

Diphenhydramine should be used with caution in bone marrow depression. Patients should observe caution while driving or performing other task requiring alertness because it may cause drowsiness. It should be used with caution in patients with urinary retention, history of bronchial asthma, hyperthyroidism, cardiovascular or liver disease. It should be used with caution in person with acute or chronic respiratory impairment, especially in children. Do not administer subcutaneously because irritation or lesion may occur. Care should be given in pregnancy.

Interference in Pathology

Diphenhydramine may interfere in the diagnosis of Wheal formation in Skin Sensitizing Test. , Determination of plasma theophylline levels by radioimmunoassay. .

Available Brands

Click on a strength to view available brands.

Single Ingredient

Syrup

13.5 mg/5ml 5 mg/5ml

Multi-Ingredient Combinations

Caps

50 mg

Dry Susp

8 mg/5ml

Lotion

1 %w/v

Syrup

1.665 mg/5ml 10 mg/5ml 12.5 mg/5ml 13.5 mg/5ml 14 mg 30 mg/5ml 4 mg/5ml 45 mg/5ml 5 mg 5 mg/5ml 8 mg/5ml

Syrup

14 mg/5ml 31.5 mg/5ml

Storage Conditions

Diphenhydramine should be stored Elixir. Tab, Caps, Cream.

Drug Classification

1.3 — Anti-allergics (Antihistamines) and drugs used in anaphylaxis
2.25.2.3 — Cough sedatives