CHAPTER 3-11: BENZTROPINE

INTRODUCTION

1. Pharmacology. Benztropine is an antimuscarinic agent with pharmacologic activity similar to that of atropine. The drug also exhibits antihistaminic properties. Benztropine is used for the treatment of parkinsonism and the control of extrapyramidal side effects associated with neuroleptic drug use.

2. Indications. Benztropine is an alternative in adults to diphenhydramine (the drug of choice for children) for the treatment of acute dystonic reactions associated with neuroleptic drugs or metoclopramide. It has a longer duration of action than does diphenhydramine and is administered twice daily. Note: It is not effective for tardive dyskinesia, nor neuroleptic malignant syndrome.

3. Contraindications

   1. Angle-closure glaucoma.

   2. Obstructive uropathy (prostatic hypertrophy).

   3. Myasthenia gravis.

   4. Not recommended for children younger than 3 years by the manufacturer; alternatively, use diphenhydramine or consider benztropine if the patient is unresponsive or hypersensitive to diphenhydramine and is experiencing a severe or life-threatening situation (eg, dystonic laryngeal or pharyngeal spasms).

   5. Tardive dyskinesia.

   6. Known hypersensitivity.

4. Adverse effects

   1. Adverse effects include sedation, confusion, blurred vision, tachycardia, urinary hesitancy or retention, intestinal ileus, flushing, dry mouth, and hyperpyrexia. Adverse effects are minimal after single doses.

   2. Use in pregnancy. Not categorized by FDA. Safe use not established. However, this does not preclude its acute, short-term use for a seriously symptomatic patient (Introduction).

5. Drug or laboratory interactions

   1. Benztropine has additive effects with other drugs that exhibit antimuscarinic properties (eg, antihistamines, phenothiazines, cyclic antidepressants, and disopyramide).

   2. Slowing of GI motility may delay or inhibit absorption of certain drugs.

6. Dosage and method of administration

   1. Parenteral. Give 1–2 mg IV or IM (children 3 years of age: 0.02 mg/kg and 1 mg maximum). May repeat dose in 15 minutes if the patient is unresponsive.

   2. Oral. Give 1–2 mg PO every 12 hours (children 3 years old: 0.02 mg/kg and 1 mg maximum) for 2–3 days to prevent recurrence of symptoms. Maximum recommended dose for adults is 6 mg/d.

7. Formulations

   1. Parenteral. Benztropine mesylate (Cogentin, generic), 1-mg/mL, 2-mL ampules and vials.

   2. Oral. Benztropine mesylate (Generic), 0.5-, 1-, and 2-mg tablets.

   3. Suggested minimum stocking levels to treat a 100-kg adult for the first 8 hours and 24 hours: benztropine, first 8 hours: 4 mg or two ampules of benztropine (1 mg/mL, 2 mL each); first 24 hours: 6 mg or three ampules of benztropine (1 mg/mL, 2 mL each).