Diphenhydramine
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Diphenhydramine. Banan Muneer Laboum Wala ’ Fayez Sabateen. Pharmacology. Antihistamine with anti cholinergic properties Antitussive, anti emetic and local anesthetic properties. Antihistaminic (H1)property Relief itching and irritation caused by :

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Diphenhydramine

Diphenhydramine

Banan MuneerLaboum

Wala’ Fayez Sabateen


Pharmacology

Pharmacology

Antihistamine with anti cholinergic properties

Antitussive, anti emetic and local anesthetic properties


Diphenhydramine

Antihistaminic (H1)propertyRelief itching and irritation caused by :

Plant induced dermatitis

Insect bites

Animal serum antivenoms or anti toxin

( anaphylaxis)


Diphenhydramine

Antichoilergic property controlling

drug-induced extrapyramidal symptoms


Pharmacokinetics

Pharmacokinetics

Maximal effects are at 1 hour after IV injection and lasts up to 7 hours

Serum half-life is 3-7 hours

Hepatic elimination


Indications

Indications:

Pruritus caused by poison oak , poison ivy or minor insect bites

Pretreatment before administration of animal serum antivenoms or antitoxins, esp. in patients with a history of hypersensitivity or with positive skin test


Diphenhydramine

Relief of symptoms caused by excessive histamine effects:

Scombroid – contaminated fish ingestion

Niacin

Rapid IV administration of

acetylcysteine


Diphenhydramine

Neuroleptic drug-induced extrapyramidal symptoms and priapism

Eg. of these drugs :

Haloperidol, Phenothiazines, Clozapine

Alteration in the normal balance between central acetylcholine and dopamine transmission


Diphenhydramine

Metoclopramide induced tardive dyskinesia:

Blocks dopamine receptors in CTZ

  Sensitizes tissues to acetylcholine


Contraindications

Contraindications

Prostatic hypertrophy with obstructive uropathy

Angel- closure glaucoma

Concurrent therapy with MAOI


Adverse effects

Adverse effects

  • Sedation, drowsiness, and ataxia may occur.

  • Paradoxicexcitation is possible in small children.

  • Excessive doses may cause:

  • Flushing, tachycardia, blurred vision, delirium, toxic psychosis, urinary retention, and respiratory depression.


Diphenhydramine

  • Some preparations may contain sulfite preservatives  allergic-type reactions in susceptible persons.

  • Extravasation from an IV admin. chronic regional pain syndrome.

  • Local necrosis from subcutaneous route.


Diphenhydramine

  • Use in pregnancy:

  • FDA category B.

  • Fetal harm is extremely unlikely.


Drug or lab interactions

Drug or lab. interactions

  • Opioids, ethanol, and other sedatives

  • Additive sedative effect.

  • Other antimuscarinicdrugs

  • Additive anticholinergic effect.


Dosage and method of administration

Dosage and method of administration

Pruritus:

  • Adult:

    -- 25-50 mg PO q. 4-6 hrs, max. daily dose is 300 mg.

  • Children, 5 mg/kg/day in divided doses:

  • Ages 2 to 6 years:

    -- 6.25 mg q. 4-6 hrs, max. daily dose is 37.5 mg

  • Ages 6-12 yrs:

    12.5 to 25 mg PO q. 4-6 hrs, max. daily dose 150mg.


Diphenhydramine

  • The drug may also be applied topically.

  • Systemic absorption and toxicity have been reported, especially when used on large areas with blistered or broken skin.


Diphenhydramine

Pretreatment before antivenom administration:

  • Adult : 50 mg IV

    Children: 0.5-1 mg/kg IV

  • If possible, it should be given at least 15-20 min. before antivenom use.

  • Rate of IV admin. should not exceed 25 mg/min.


Diphenhydramine

Drug-induced extrapyramidal symptoms:

  • Adult :50 mg

    Children, 0.5-1 mg/kg

  • IV at a rate not to exceed 25 mg/min, or deep IM

  • If there is no response within 30-60 min.

     Repeat dose to a maximum 100 mg (adults).


Diphenhydramine

  • Provide oral maintenance therapy to prevent recurrence:

  • Adult : 25-50 mg q. 4-6 hrs for 2-3 days

    Maxi. daily dose 400 mg.

  • Children (0.5-1 mg/kg):

  • If < 9 kg  6.25 to 12.5 mg q. 4-6 hrs for 2-3 days

  • If > 9 kg  12.5 to 25-mgq. 4-6 hrs for 2-3 days

  • Maxi. daily dose, 300 mg


Formulations

Formulations

Oral:

  • Diphenhydramine hydrochloride (Benadryl)

  • Tablets and capsules --- 25 mg and 50 mg.

  • Chewable tablets --- 12.5 mg.

  • Elixir, syrup, and oral solution --- 12.5 mg/5 mL.


Diphenhydramine

Parenteral:

  • Diphenhydramine hydrochloride (Benadryl)

  • 50 mg/mL in 1-mL cartridges, amps, steri-vials, and syringes

  • 50 mg/ml in 10-mL steri-vials (may contain benzethonium chloride).


Diphenhydramine

  • The suggested minimum stocking level to treat a 70-kg adult for the first 24 hours is:

  • One vial (50 mg/mL, 10 mL each)

  • Or eight vials (50 mg/mL, 1 mL each).


Thank you

Thank you 


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