benztropine mesylate
Cogentin

Available forms
Available by prescription only
Injection: 1 mg/ml in 2-ml ampule
Tablets: 0.5 mg, 1 mg, 2 mg

Indications and dosages
 Parkinsonism. Adults: 0.5 to 6 mg P.O. daily. Initially, 0.5 to 1 mg I.M. or P.O. increased 0.5 mg q 5 to 6 days. Adjust dosage to meet individual requirements. Maximum daily dose is 6 mg.
 Drug-induced extrapyramidal reactions.
Adults: 1 to 4 mg P.O. or I.M. daily or b.i.d. Adjust dosage to meet individual requirements. Maximum daily dose is 6 mg.
 Acute dystonic reaction. Adults: 1 to 2 mg I.V. or I.M. followed by 1 to 2 mg P.O. b.i.d. to prevent recurrence.

Pharmacodynamics
Antiparkinsonian action: Benztropine blocks central cholinergic receptors, helping to balance cholinergic activity in the basal ganglia. It also may prolong effects of dopamine by blocking dopamine reuptake and storage at central receptor sites.

Pharmacokinetics
Absorption: Absorbed from the GI tract.
Distribution: Largely unknown; however, drug crosses the blood-brain barrier and may cross the placental barrier.
Metabolism: Unknown.
Excretion: Like other muscarinics, benztropine is excreted in urine as unchanged drug and metabolites. After oral therapy, small amounts are probably excreted in feces as unabsorbed drug.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug or its components, in patients with acute angle-closure glaucoma, and in children younger than age 3. Use cautiously in hot weather, in patients with mental disorders, and in children older than age 3.

Interactions
Drug-drug. Amantadine: May amplify such adverse anticholinergic effects as confusion and hallucinations. Decrease benztropine dosage before giving amantadine.
Antacids, antidiarrheals: May decrease benztropine absorption. Administer benztropine at least 1 hour before administering these drugs.
CNS depressants: Increase sedative effects of benztropine. Use together cautiously.
Haloperidol, phenothiazines: Decreases effect of these drugs, possibly reflecting direct CNS antagonism. Monitor patient for clinical effect.
Phenothiazines: Increase risk of adverse anticholinergic effects. Use reduced phenothiazine dose.
Drug-lifestyle. Alcohol use: Increases sedative effects of benztropine. Discourage alcohol use.

Adverse reactions
CNS: disorientation, hallucinations, depression, toxic psychosis, confusion, memory impairment, nervousness.
CV: tachycardia.
EENT: dilated pupils, blurred vision.
GI: dry mouth, constipation, nausea, vomiting, paralytic ileus.
GU: urine retention, dysuria.

Effects on lab test results
None reported.

Overdose and treatment
Signs and symptoms of overdose include central stimulation followed by depression and psychotic symptoms such as disorientation, confusion, hallucinations, delusions, anxiety, agitation, and restlessness. Peripheral effects may include dilated, nonreactive pupils; blurred vision; hot, flushed, dry skin; dry mucous membranes; dysphagia; decreased or absent bowel sounds; urine retention; hyperthermia; tachycardia; hypertension; and increased respiration.
 Treatment is primarily symptomatic and supportive, as needed. Maintain a patent airway. If patient is alert, induce emesis (or use gastric lavage) and follow with a saline solution cathartic and activated charcoal to prevent further absorption. In severe cases, physostigmine may be administered to block the antimuscarinic effects of benztropine. Give fluids as needed to treat shock, diazepam to control psychotic symptoms, and pilocarpine (instilled into the eyes) to relieve mydriasis. If urine retention occurs, catheterization may be needed.

Special considerations
• To help prevent gastric irritation, administer drug after meals.
• Some patients may experience greatest relief by taking the entire dose at bedtime, as opposed to several doses throughout the day.
• Monitor patient for intermittent constipation and abdominal distention and pain, which may indicate paralytic ileus.
• Monitor patient periodically because effects are cumulative, especially if patient is prone to tachycardia and prostatic hypertrophy.
• Observe patients with mental disorders for worsening symptoms or toxic psychoses, especially at start of treatment and during dosage adjustment.
• Never discontinue drug abruptly.
• Store in well-sealed containers between 59° and 86° F (15° and 30° C). Avoid freezing injectable preparation.
• Some adverse reactions may result from atropine-like toxicity and are dose-related.
Pregnant patients
• Safe use during pregnancy hasn’t been established.
Breast-feeding patients
• Drug may appear in breast milk, possibly causing infant toxicity. Avoid use in breast-feeding women.
• Benztropine may decrease milk production.
Pediatric patients
• Drug isn’t recommended for children younger than age 3.

Patient education
• Explain to patient that the full effect of drug may not occur for 2 to 3 days.
• Caution patient not to stop drug suddenly; dosage should be reduced gradually.
• Tell patient that drug may increase sensitivity of eyes to light.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use