Benztropine
Benztropine
Definition
Benztropine is classified as an antiparkinsonian agent. It is sold in the United States under the brand name Cogentin and is also available under its generic name.
Purpose
Benztropine is used to treat a group of side effects (called parkinsonian side effects) that include tremors, difficulty walking, and slack muscle tone. These side effects may occur in patients who are taking antipsychotic medications used to treat mental disorders such as schizophrenia.
Description
Some medicines, called antipsychotic drugs, that are used to treat schizophrenia and other mental disorders can cause side effects that are similar to the symptoms of Parkinson’s disease. Patients do not have Parkinson’s disease, but they may experience shaking in muscles while at rest, difficulty with voluntary movements, and poor muscle tone. These symptoms are similar to the symptoms of Parkinson’s disease.
One way to eliminate these undesirable side effects is to stop taking the antipsychotic medicine. Unfortunately, the symptoms of the original mental disorder usually come back, so simply stopping the antipsychotic medication is not a reasonable option in most cases. Some drugs that control the symptoms of Parkinson’s disease, such as benztropine, also control the parkinsonian side effects of antipsychotic medicines.
Benztropine works by restoring the chemical balance between dopamine and acetylcholine, two neurotransmitter chemicals in the brain. Taking benztropine along with the antipsychotic medicine helps to control symptoms of the mental disorder, while reducing parkinsonian side effects. Benztropine is in the same family of drugs (commonly known as anticholinergic drugs) as biperiden and trihexyphenidyl.
Recommended dosage
Benztropine is available in 0.5-, 1.0-, and 2.0-mg tablets and in an injectable form containing 2 mg of drug in each 2 mL glass container. For the treatment of tremors, poor muscle tone, and similar side effects, benztropine should be started at a dose of 1 to 2 mg orally. In cases of severe side effects, benztropine can be given as an intramuscular injection two to three times daily or as needed. Parkinson-like side effects caused by antipsychotic drugs may come and go, so benztropine may not be needed on a regular basis. Benztropine may also be prescribed to prevent these side effects before they actually occur. This is called a prophylactic (preventative) therapy.
Precautions
Benztropine should never be used in children under age three. It should be used cautiously and with close physician supervision in older children and in the elderly. Like all anticholinergic drugs, benztropine decreases the body’s ability to sweat and cool itself. People who are unaccustomed to being outside in hot weather should take care to stay as cool as possible and drink extra fluids. People who are chronically ill, have a central nervous system disease, or who work outside during hot weather may need to avoid taking benztropine.
People who have the following medical problems may experience increased negative side effects when taking benztropine. Those who have these problems should discuss their conditions with their physician before starting the drug:
- glaucoma, especially closed-angle glaucoma
- intestinal obstruction
- prostate enlargement
- urinary bladder obstruction
Although rare, some patients experience euphoria while taking benztropine and may abuse it for this reason. Euphoria can occur at doses only two to four times the normal daily dose. Patients with a history of drug abuse should be observed carefully for benztropine abuse.
Side effects
Although benztropine helps to control the side effects of antipsychotic drugs, it can produce side effects of its own. A person taking benztropine may have some of the following reactions, which may vary in intensity:
- dry mouth
- dry skin
- blurred vision
- nausea or vomiting
- constipation
- disorientation
- drowsiness
- irritability
- increased heart rate
- urinary retention
KEY TERMS
Acetylcholine —A naturally occurring chemical in the body that transmits nerve impulses from cell to cell. Generally, it has opposite effects from dopamine and norepinephrine; it causes blood vessels to dilate, lowers blood pressure, and slows the heartbeat. Central nervous system well-being is dependent on a balance among acetylcholine, dopamine, serotonin, and norepinephrine.
Anticholinergic —Related to the ability of a drug to block the nervous system chemical acetylcholine. When acetylcholine is blocked, patients often experience dry mouth and skin, increased heart rate, blurred vision, and difficulty urinating. In severe cases, blocking acetylcholine may cloud thinking and cause delirium.
Catheterization —Placing a tube in the bladder so that it can be emptied of urine. Dopamine—A chemical in brain tissue that serves to transmit nerve impulses (is a neurotransmitter) and helps to regulate movement and emotions.
Neurotransmitter —A chemical in the brain that transmits messages between neurons, or nerve cells.
Parkinsonian —Related to symptoms associated with Parkinson’s disease, a nervous system disorder characterized by abnormal muscle movement of the tongue, face, and neck, inability to walk or move quickly, walking in a shuffling manner, restlessness, and/or tremors.
Dry mouth, if severe to the point of causing difficulty speaking or swallowing, may be managed by reducing or temporarily discontinuing benztropine. Chewing sugarless gum or sucking on sugarless candy may also help to increase the flow of saliva. Some artificial saliva products may give temporary relief.
Men with prostate enlargement may be especially prone to urinary retention. Symptoms of this problem include having difficulty starting a urine flow and more difficulty passing urine than usual. This side effect may be severe and require discontinuation of the drug. Urinary retention may require catheterization. People who think they may be experiencing any side effects from this or any other medication should tell their physicians.
Patients who take an overdose of benztropine are treated with forced vomiting, removal of stomach contents and stomach washing, activated charcoal, and respiratory support if needed. They are also given physostigmine, an antidote for anticholinergic drug poisoning.
Interactions
When drugs such as benztropine are taken with antidepressants such as amitriptyline, imipramine, trimipramine, desipramine, nortriptyline, protriptyline, amoxapine, and doxepin or with many antihistamines that also have anticholinergic properties, the effects and side effects of benztropine are usually intensified.
Drugs such as benztropine decrease the speed with which food moves through the stomach and intestines. Because of this, the absorption of other drugs being taken may be enhanced by benztropine. Patients receiving benztropine should be alerted to unusual responses to other drugs they might be taking and report any changes to their physicians.
Resources
BOOKS
American Society of Health-System Pharmacists. AHFS Drug Information 2002. Bethesda: American Society of Health-System Pharmacists, 2002.
Preston, John D., John H. O’Neal, and Mary C. Talaga. Handbook of Clinical Psychopharmacology for Therapists. 4th ed. Oakland, CA: New Harbinger Publications, 2004.
PERIODICALS
de Leon, Jose. “Benztropine Equivalents for Antimuscarinic Medication.” American Journal of Psychiatry 162.3 (March. 2005): 627.
Penetar, David M., and others. “Benztropine Pretreatment Does Not Affect Responses to Acute Cocaine Administration in Human Volunteers.” Human Psychopharmacology: Clinical and Experimental 21.8 (Dec. 2006): 549–59.
Jack Raber, Pharm.D.
Ruth A. Wienclaw, PhD