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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 Banan MuneerLaboum Wala’ Fayez Sabateen
Pharmacology Antihistamine with anti cholinergic properties Antitussive, anti emetic and local anesthetic properties
Antihistaminic (H1)propertyRelief itching and irritation caused by : Plant induced dermatitis Insect bites Animal serum antivenoms or anti toxin ( anaphylaxis)
Antichoilergic property controlling drug-induced extrapyramidal symptoms
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: 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
Relief of symptoms caused by excessive histamine effects: Scombroid – contaminated fish ingestion Niacin Rapid IV administration of acetylcysteine
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
Metoclopramide induced tardive dyskinesia: Blocks dopamine receptors in CTZ Sensitizes tissues to acetylcholine
Contraindications Prostatic hypertrophy with obstructive uropathy Angel- closure glaucoma Concurrent therapy with MAOI
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.
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.
Use in pregnancy: • FDA category B. • Fetal harm is extremely unlikely.
Drug or lab. interactions • Opioids, ethanol, and other sedatives • Additive sedative effect. • Other antimuscarinicdrugs • Additive anticholinergic effect.
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.
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.
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.
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).
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 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.
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).
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).
