Tripar

Indications

Trihexyphenidyl is used to treat Parkinson's disease, especially tremor and stiffness, alone or together with Levodopa. It is also used to control movement side effects caused by some medicines, mainly antipsychotics, such as muscle stiffness, tremor and abnormal muscle spasms.

How It Works

In Parkinson's disease and with some medicines, the brain chemicals dopamine and acetylcholine get out of balance. Trihexyphenidyl is an anticholinergic: it blocks acetylcholine in the brain, helping restore the balance and reducing tremor and stiffness.

Dosage and Administration

• Adults: usually started at 1 mg a day and increased slowly by the doctor, by about 2 mg every few days.
• Parkinson's disease: usual maintenance dose is 6 to 10 mg a day, split into three or four doses with meals, as prescribed.
• Drug-induced movement problems: the dose is adjusted by the doctor, commonly 5 to 15 mg a day in divided doses.
• Older people usually need lower doses.
• Do not stop suddenly; the doctor will reduce the dose gradually.

Interactions

• Other medicines with anticholinergic effects, such as Amitriptyline, Chlorpromazine, Chlorphenamine and Oxybutynin, increase side effects such as dry mouth, constipation, urine retention and confusion.
• Alcohol and sedatives add to drowsiness.
• It may reduce the effect of Metoclopramide and Domperidone on the stomach.
• The Levodopa dose may need adjusting when used together.

Contraindications

• Allergy to trihexyphenidyl.
• Narrow-angle (closed-angle) glaucoma.
• Myasthenia gravis.
• Bowel blockage or paralysed bowel.
• Difficulty passing urine due to an enlarged prostate.
• Tardive dyskinesia (late-onset involuntary movements), which it can worsen.

Side Effects

Common: dry mouth, blurred vision, constipation, difficulty passing urine, dizziness, nausea, nervousness and a fast heartbeat.

Get urgent medical help for: confusion, hallucinations or agitation; being unable to pass urine; severe eye pain with blurred vision or halos around lights; a very fast or irregular heartbeat; high body temperature or feeling very hot in hot weather (it reduces sweating); or signs of an allergic reaction such as swelling of the face or difficulty breathing.

Pregnancy and Lactation

Safety in pregnancy is not well established; use only if the doctor decides it is needed. It may reduce milk supply and can pass into breast milk, so ask the doctor before using it while breastfeeding.

Precautions and Warnings

• Older people are more likely to get confusion, memory problems and constipation.
• Avoid overheating and heavy exercise in hot weather, and drink enough fluids.
• Use with care in heart disease, high blood pressure, liver or kidney disease and prostate problems; eye pressure may be checked.
• It can cause drowsiness or blurred vision; do not drive if affected.
• It can be misused for its mood effects; take only as prescribed.

Overdose

Overdose causes dry, hot, flushed skin, large pupils, a fast heartbeat, fever, agitation, confusion, hallucinations and sometimes fits. This is an emergency: get medical help immediately.

Therapeutic Class

Anticholinergic antiparkinsonian medicine.

Storage

Store below 30°C in a dry place, away from light and out of the reach of children.