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Key points

  • Benztropine (Cogentin™) is an alternative to diphenhydramine in adults for the treatment of extrapyramidal reactions.
  • Extrapyramidal symptoms may recur in the 24 - 48 h following the initial reaction. Diphenhydramine can be administered once again to treat the relapse. Some authors suggest administering diphenhydramine by oral route for prophylaxis for 24 - 48 h to prevent such relapses.

+ Synonyms and other terms

  • Benadryl™
  • Diphenist™

+ Indications

  • Treatment of extrapyramidal reactions.
  • Relief of histamine-related symptoms (e.g., ingestion of spoiled fish of the family Scombridae, such as bonito, albacore, mackerel, tuna or during an anaphylactoid reaction).
  • Relief of secondary pruritus due to contact with stinging plants, such as poison ivy (Toxicodendron) or insect bites.

+ Dosage

+ Pediatric Dose

  • Treatment of extrapyramidal reactions:
    • ​1 mg/kg by direct IV (max. 50 mg)
    • Continue administering 1 mg/kg/dose (max 50 mg) PO every 4 to 6 h for 1 to 2 days.
  • Relief of pruritus or histamine-related symptoms:
    • 1 mg/kg/dose (max 50 mg) PO/NG tube/IV every 4 to 6 h.
    • Maximum: 5 mg/kg/day up to a maximum of 300 mg/day.

+ Adult Dose

  • Treatment of extrapyramidal reactions:
    • 50 mg by direct IV.
    • Continue administering 25 - 50 mg PO every 4 to 6 h for 1 to 2 days.
  • Relief of pruritus or histamine-related symptoms:
    • 25 - 50 mg PO/NG tube/IV every 4 to 6 h.
    • Maximum: 400 mg/day.

+ Renal Impairment

No data suggests that the dose should be modified for short-term use.

+ Hepatic Impairment

No data suggests that the dose should be modified for short-term use.

+ Hemodialysis Patient

No data suggests that the dose should be modified for short-term use.

+ Pregnancy

  • Safe.
  • No data suggests that the dose should be modified for short-term use.

+ Obese or Overweight Patient

No data suggests that the dose should be modified for short-term use.

+ Adverse effects

  • Drowsiness
  • Ataxia
  • Occasional paradoxical reaction in children.

+ Monitoring

  • Vital signs
  • State of consciousness
  • Excessive anticholinergic symptoms (e.g., dry mouth, tachycardia).

+ End of treatment

  • Discontinue administration when symptoms have ceased.

+ Special Notes on Administration

Intravenous Route (IV)

  • Direct IV
    • Administer undiluted by direct IV over 2 minutes or at a maximum rate of 25 mg/min.
    • It is possible to add a volume of up to 10 ml of NS to facilitate administration.

Subcutaneous Route (SC)

  • Not recommended (localized necrosis).

Intramuscular Route (IM)

  • Possible alternative to IV route.

Intraosseous Route (IO)

  • No available data.

Enteral Route (PO or NG Tube)

  • PO
  • NG tube
    • Syrup is preferred form.
    • If syrup is not available prepare extemporaneously
      • Finely grind tablets with a mortar and pestle.
      • Dissolve the resulting powder in 10 - 30 ml of SWFI and draw up the resulting liquid using an oral syringe.
    • Start by rinsing NG tube with 15 - 30 ml of SWFI.
    • Administer the antidote by NG tube.
    • Quickly rinse NG tube with 15 - 30 ml of SWFI.

Compatibility

Partial list only. Consult the pharmacist on duty at your health care facility.

  • Compatible solutions: ½NS, NS, D5W, D10W, LR.
  • Y-site compatibility:alfentanil, argatroban, atracurium, atropine, benztropine, calcium (chloride and gluconate), chlorpromazine, cisatracurium, digoxin, diltiazem, dobutamine, dopamine, enalapril, ephedrine, epinephrine, famotidine, fentanyl, folic acid, hydromorphone, isoproterenol, ketamine, labetalol, calcium leucovorin, lidocaine, lorazepam, magnesium (sulfate), mannitol, meperidine, metoclopramide, metoprolol, midazolam, morphine, MVI, naloxone, nicardipine, nitroglycerin, norepinephrine, octreotide, ondansetron, pancuronium, phentolamine, phenylephrine, phytonadione (vitamin K1), potassium (acetate and chloride), procainamide, prochlorperazine, promethazine, propofol, propranolol, protamine, pyridoxine, ranitidine, remifentanil, rocuronium, succinylcholine, sufentanil, thiamine, vasopressin, vecuronium, verapamil.
  • Y-site incompatibility: allopurinol, aminophylline, sodium bicarbonate, dantrolene, dexamethasone, diazepam, furosemide, regular insulin, methylprednisolone, milrinone, sodium nitroprusside, pantoprazole, pentobarbital, phenobarbital, phenytoin.

Stability

  • Store unopened vials at room temperature.

+ Available products

  • Diphenhydramine hydrochloride for injection, USP, 50 mg/ml, vial of 1 ml, Sandoz, DIN 00596612
  • Diphenist, 50 mg/ml, vial of 1 ml, Omega, DIN 02219336
  • Diphenhydramine (hydrochloride) for injection, USP, 50 mg/ml, vial of 1 ml, Fresenius Kabi Canada, DIN 02369567
  • PMS-diphenydramine hydrochloride injection, 50 mg/ml, vial of 1 ml, DIN 00878200
  • Partial list only.

+ Amount required to treat a person weighting 70kg during 24 hours

  • At least 400 mg of diphenhydramine for injection

© Centre antipoison du Québec, CIUSSS de la Capitale-Nationale, 2017. The information contained in this site may be cited, provided the source is acknowledged. Any use for commercial or advertising purposes is strictly prohibited.

Last updated : 2022-12-14