The P-I-E-N-O Parkinsn's List Drug Database
trihexyphenidyl / ArtaneTM
ANTIPARKINSON:
Anticholinergic
Description: Trihexyphenidyl is an oral synthetic, tertiary antagonist of acetylcholine at muscarinic receptors. Its actions are similar to those of atropine. Because it is a tertiary compound, it will penetrate the CNS, making it useful in treating parkinsonism. Trihexyphenidyl was approved by the FDA in 1949.
Mechanism of Action: Trihexyphenidyl competes with acetylcholine and other cholinergic stimuli in the CNS and, to a lesser extent, in smooth muscle. It has a direct antispasmodic action on smooth muscle, and it has weak mydriatic, antisecretory, and positive chronotropic activities. In small doses, trihexyphenidyl has CNS-depressant effects, but, in larger doses, CNS-stimulatory effects similar to those seen with atropine toxicity can occur.
Trihexyphenidyl is used adjunctively to treat all types of parkinsonian syndromes including antipsychotic-induced extrapyramidal symptoms. This drug is frequently used in combination with other antiparkinsonian agents, and it is effective in 50-75% of patients. In general, anticholinergic agents can help control tremor but are less effective for treating bradykinesia or rigidity. Also, trihexyphenidyl can block dopamine reuptake, thus prolonging dopamine's effects. Tolerance to the effects of trihexyphenidyl can occur with prolonged use.
Pharmacokinetics: Trihexyphenidyl is administered orally and is rapidly absorbed from the GI tract. The drug crosses the blood-brain barrier. Onset of action is 1 hour, with peak effects lasting 2-3 hours, and the duration of action is 6-12 hours. The metabolic pathway is unknown, but unchanged drug is renally excreted.
CONTRAINDICATIONS/PRECAUTIONS: Trihexyphenidyl should be used with caution in patients with closed-angle glaucoma because the drug can induce cycloplegia and mydriasis, resulting in increased intraocular pressure.
Trihexyphenidyl is relatively contraindicated in patients with cardiac disease, such as ischemic heart disease, or with atherosclerosis and hypertension because of its positive chronotropic effect, which could cause tachycardia and/or coronary ischemia.
Trihexyphenidyl should be used cautiously in patients with renal disease, such as renal impairment, because the drug can accumulate, leading to toxicity.
Trihexyphenidyl is relatively contraindicated in patients with GI obstruction or urinary tract obstruction due to its antimuscarinic effects. Trihexyphenidyl can worsen GI obstructive symptoms or urinary retention. In patients with benign prostatic hypertrophy, trihexyphenidyl can cause urinary retention.
DRUG INTERACTIONS: Concomitant use of trihexyphenidyl with other drugs possessing anticholinergic activity can lead to additive toxicity. These drugs include amantadine, haloperidol, direct anticholinergics, antihistamines, tricyclic antidepressants, and phenothiazines.
Ethanol and other CNS depressants, such as anxiolytics, sedatives, and hypnotics, can increase the sedative effects of trihexyphenidyl.
The doses of trihexyphenidyl and levodopa/carbidopa must be adjusted when the drugs are given simultaneously. Trihexyphenidyl theoretically should increase the dopaminergic effects.
Antacids and antidiarrheals decrease the oral absorption of trihexyphenidyl. Administer trihexyphenidyl at least 1 hour before doses of these agents.
ADVERSE REACTIONS: Blockade of cholinergic receptors has many clinical manifestations. Anticholinergic effects are usually minor with the use of normal doses but can be serious in an acute overdose or in combination with other drugs that also possess anticholinergic effects. Minor adverse reactions can include xerostomia (dry mouth), constipation, blurred vision, cycloplegia, mydriasis, and urinary retention. Patients should take the drug after meals and should suck on hard candy, chew gum, or drink water to relieve xerostomia. Anxiety is experienced by 30-50% of all patients. More serious effects include tachycardia, increased intraocular pressure and/or exacerbation of narrow-angle glaucoma, and agitation or confusion. Amnesia, disorientation, restlessness, excitement, memory loss, giddiness, psychoses, paranoia, delirium, delusions, euphoria, parasthesia, hallucinations, headache, and depression have been reported.
PATIENT INFORMATION:
What do trihexyphenidyl tablets or extended-release capsules do?
Trihexyphenidyl (ArtaneTM ) can help to improve the stiffness and movement problems associated with Parkinson's disease. Trihexyphenidyl can also help to prevent or control movement-related side effects of other medicines. Generic trihexyphenidyl tablets are available, but not the sustained-release capsules.
What should my doctor, dentist, or pharmacist know before I take trihexyphenidyl?
They need to know if you have any of these conditions:
How should I take this medicine?
Take trihexyphenidyl tablets or capsules by mouth. Follow the directions on the prescription label. Swallow the tablets with a drink of water. If you are taking the extended-release capsules, swallow them whole, do not crush or chew. Take 30 to 60 minutes before meals, unless your doctor tells you otherwise. You can take trihexyphenidyl with food if it upsets your stomach. Take your doses at regular intervals. Do not take your medicine more often than directed. It may take several days to see the full effect of trihexyphenidyl; do not stop taking except on your doctor's advice.
Special precautions for use in children:
This medicine is not for children.
Elderly patients are more likely to get side effects and should be given smaller doses.
What if I miss a dose?
If you miss a dose, take it as soon as you can. If it is almost time for your next dose, take only that dose. Do not take double or extra doses. If you are taking the extended-release capsules, leave at least 6 to 8 hours between doses.
What other medicines can interact with trihexyphenidyl?
Tell your doctor or pharmacist: about all other medicines you are taking, including non-prescription medicines; if you are a frequent user of drinks with caffeine or alcohol; if you smoke; or if you use illegal drugs. These may affect the way your medicine works. Check before stopping or starting any of your medicines.
What side effects may I notice from taking trihexyphenidyl?
Serious side effects with trihexyphenidyl include:
Call your doctor as soon as you can if you get any of these side effects.
Minor side effects with trihexyphenidyl include:
Let your doctor know about these side effects if they do not go away or if they annoy you.
What do I need to watch for while I take trihexyphenidyl?
Visit your doctor for regular checks on your progress. Do not stop taking this medicine abruptly. Your doctor may want to gradually reduce the dose so that you do not get side effects or make your condition worse. Your doctor may want you to have an eye exam from time to time.
You may get dizzy or have blurred vision. Do not drive, use machinery, or do anything that needs mental alertness until you know how trihexyphenidyl affects you. To reduce the risk of dizzy or fainting spells, do not sit or stand up quickly, especially if you are an older patient. Alcohol can make you more drowsy, avoid alcoholic drinks.
Your mouth may get dry. Chewing sugarless gum or sucking hard candy, and drinking plenty of water will help.
Stay out of bright light and wear sunglasses if trihexyphenidyl makes your eyes more sensitive to light.
Antacid or diarrhea medicine can stop trihexyphenidyl working. If you want to take antacid or diarrhea medicine, leave an interval of at least 2 hours before or after you take trihexyphenidyl.
Where can I keep my medicine?
Keep out of the reach of children in a container that small children cannot open.
Store at room temperature between 15 and 30C (59 and 86F). Throw away any unused medicine after the expiration date.
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