DIPHENHYDRAMINE

brands

Class

• Antihistamine; anticholinergic agent

DIPHENHYDRAMINE commonly prescribed for

(Bold for FDA approved)

How DIPHENHYDRAMINE works

• For drug-induced parkinsonism: diminishes the excess acetylcholine activity caused by removal of dopamine inhibition when dopamine receptors are blocked</br>

• Also has potent histamine 1 antagonist properties

How long until DIPHENHYDRAMINE works

• For drug-induced parkinsonism, onset of action can be within minutes or hours

Notable Side Effects

• Sedation, dizziness

• Constipation, nausea

• Dry mouth, blurred vision

Life Threatening Side Effects

• Rare convulsions (at high doses)

• Urinary retention

• Tachycardia, cardiac arrhythmias

• Confusion

• Paralytic ileus/bowel obstruction

weight gain

problematic

sedation

common

What to do about DIPHENHYDRAMINE side effects

• For confusion or hallucinations, discontinue use

• For sedation, lower the dose and/or take the entire dose at night

• For dry mouth, chew gum or drink water

• For urinary retention, obtain a urological evaluation; may need to discontinue use

usual dosage range

• Oral: 50 mg/day

• Injection: 10–50 mg

Dosage Forms

• Injection 50 mg/mL

• Capsule 50 mg

• Elixir 12.5 mg/5 mL

• Also available in formulations in combination with other medications

long term use

• Safe

• Effectiveness may decrease over time, even after a few doses, but side effects such as cognitive impairment and sedation may persist

habit forming

• No

Renal Impairment

• No dose adjustment necessary

Hepatic Impairment

• No dose adjustment necessary

Cardiac Impairment

• Not systematically evaluated in patients with cardiac impairment

Elderly

• Some patients may tolerate lower doses better

• Diphenhydramine injection is preferred for parkinsonism in the elderly who are unable to tolerate more potent agents

Children and Adolescents

• Not recommended for children under age 12

• Injection: 5 mg/kg/24 hours or 150 mg/ m2 /24 hours; maximum daily dose 300 mg; divide into 4 doses; can be given intravenously at a rate not exceeding 25 mg/minute, or deep intramuscularly

• Contraindicated in neonates and premature infants

Pregnancy

• Controlled studies have not been conducted in pregnant women

• Animal studies have not shown adverse effects

Breast Feeding

• Contraindicated