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What is trihexyphenidyl?

Trihexyphenidyl alters unusual nerve impulses and relaxes stiff muscles.

Trihexyphenidyl is used to treat the stiffness, tremors, spasms, and poor muscle control of Parkinson’s disease. It is also used to treat and prevent the same muscular conditions when they are caused by drugs such as chlorpromazine (Thorazine), fluphenazine (Prolixin), perphenazine (Trilafon), haloperidol (Haldol), thiothixene (Navane), and others.

Trihexyphenidyl may also be used for purposes other than those listed in this medication guide.

Precautions

Instructions

Side-effects

Interactions

Precautions

Do not use trihexyphenidyl without first talking to your doctor if you have

• ever had an allergic reaction to it;
• narrow-angle glaucoma;
• an obstruction in the bowel or a complication of bowel disease known as megacolon; or
• myasthenia gravis.

Before taking this medication, tell your doctor if you have

• enlargement of the prostate or difficulty urinating;
• epilepsy or another seizure disorder;
• heart disease or an irregular heartbeat;
• depression or any other psychiatric illness;
• kidney disease; or
• liver disease.

You may require a dosage adjustment or special monitoring during treatment if you have any of the conditions listed above.

It is not known whether trihexyphenidyl will be harmful to an unborn baby. Do not take this medication without first talking to your doctor if you are pregnant or could become pregnant during treatment.

It is not known whether trihexyphenidyl passes into breast milk. Do not take this medication without first talking to your doctor if you are breast-feeding a baby.

Use caution when driving, operating machinery, or performing other hazardous activities. Trihexyphenidyl may cause dizziness or blurred vision. If you experience dizziness or blurred vision, avoid these activities.

Use alcohol cautiously. Alcohol may increase drowsiness and dizziness while taking trihexyphenidyl.

Avoid becoming overheated. Trihexyphenidyl may cause decreased sweating. This could lead to heat stroke in hot weather or with vigorous exercise. Try to keep as cool as possible and watch for signs of heat stroke such as decreased sweating, nausea, and dizziness.

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Instructions

Seek emergency medical attention.

Symptoms of a trihexyphenidyl overdose include large pupils; warm, dry skin; flushed face; fever; dry mouth; fast or irregular heartbeat; anxiety; hallucinations; confusion; agitation; hyperactivity; loss of consciousness; and seizures.

Take the missed dose as soon as you remember. However, if it is almost time for the next dose, skip the missed dose and only take the next regularly scheduled dose. Do not take a double dose of this medication.

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Side-effects

If you experience any of the following serious side effects, stop taking trihexyphenidyl and seek emergency medical attention or contact your doctor immediately:

• an allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives);
• fever;
• fast or irregular heartbeats;
• anxiety, hallucinations, confusion, agitation, hyperactivity, or loss of consciousness;
• seizures;
• eye pain; or
• a rash.

Other, less serious side effects may be more likely to occur. Continue to take trihexyphenidyl and talk to your doctor if you experience

• dryness of the mouth;
• large pupils or blurred vision;
• drowsiness or dizziness;
• difficulty urinating or constipation;
• nervousness or anxiety;
• upset stomach; or
• decreased sweating.

Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

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Interactions

Before taking this medication, tell your doctor if you are taking any of the following medicines:

• a tricyclic antidepressant (used to treat depression, pain, or obsessive-compulsive disorder) such as amitriptyline (Elavil, Endep), doxepin (Sinequan), clomipramine (Anafranil), amoxapine (Asendin), desipramine (Norpramin), imipramine (Tofranil), nortriptyline (Pamelor), or protriptyline (Vivactil);
• a phenothiazine (used to treat mania, schizophrenia, other psychiatric conditions, and nausea and vomiting) such as chlorpromazine (Thorazine), fluphenazine (Prolixin), perphenazine (Trilafon), mesoridazine (Serentil), thioridazine (Mellaril), promazine (Sparine), trifluoperazine (Stelazine), and others;
• thiothixene (Navane) or chlorprothixene (Taractan);
• an antihistamine such as diphenhydramine (Benadryl, others), chlorpheniramine (Chlor-Trimeton, others), triprolidine (Actifed, others), brompheniramine (Dimetapp, others), clemastine (Tavist), and others (antihistamines are often found in prescription and over-the-counter cold, allergy, and sleep medicines);
• quinidine (Quinora, Quinaglute, Quinidex, Cardioquin);
• amantadine (Symmetrel);
• digoxin (Lanoxin, Lanoxicaps); or
• haloperidol (Haldol).

You may not be able to take trihexyphenidyl or you may require a dosage adjustment or special monitoring if you are taking any of the medicines listed above.

Drugs other than those listed here may also interact with trihexyphenidyl. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including herbal products.

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