Trihexyphenidyl

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Image:Trihexyphenidyl.png
Trihexyphenidyl
Systematic (IUPAC) name
1-cyclohexyl-1-phenyl-3- (1-piperidyl)propan-1-ol
Identifiers
CAS number	144-11-6
ATC code	N04 AA01
PubChem	5572
DrugBank	APRD00070
Chemical data
Formula	C₂₀H₃₁NO
Mol. weight	301.466 g/mol
Pharmacokinetic data
Bioavailability	?
Metabolism	?
Half life	3.3-4.1 hours
Excretion	?
Therapeutic considerations
Pregnancy cat.	C US
Legal status
Routes	Oral, as tablet or elixir

Trihexyphenidyl is an antiparkinson agent of the antimuscarinic class of agents and is chemically a tertiary amine. It has been in clinical usage for decades. The drug is available as hydrochloride.

1 Pharmacology
2 Pharmacokinetics
3 Established uses
4 Therapeutic prospects
5 Investigational uses
6 Contraindications and cautions
7 Pregnancy and lactation
8 Side-effects
9 Interactions
10 Dosage
11 Overdose
12 Brand names and dose forms
13 External links

[edit] Pharmacology

The exact mechanism of action in parkinsonian syndromes is not precisely understood, but it is known that Trihexyphenidyl blocks efferent impulses in parasympathetically innervated structeres like smooth muscles (spasmolytic activity), salvia glands and eyes (mydriasis). In higher doses direct central inhibition of cerebral motor centers may contribute. In very high doses central toxicity as seen in atropine overdose is noted.

[edit] Pharmacokinetics

Trihexyphenidyl is rapidly absorbed from the GI-Tract. The onset of action is within 1 hour after oral dosing. The peak activity is noted after 2 to 3 hours. The duration of action of one single dose is 6 to 12 hours in a dose dependent manner. It is excreted in the urine, probably as unchanged drug. More precise data in animals and humans have so far not been determined.

[edit] Established uses

Trihexyphenidyl is used for the symptomatic treatment of Morbus Parkinson in mono- and combination therapy. It is active in postencephalitic, arteriosclerotic, and idiopathic forms. The drug is also commonly used to treat extrapyramidal side effects occurring during antipsychotic treatment. It reduces the frequency and duration of oculogyric crises as well as of dyskinetic movements and spastic contractions. Excessive salivation may also respond. Trihexyphenidyl may improve psychotic depression and mental inertia frequently associated with Morbus Parkinson and symptomatic problems caused by antipsychotic treatment.

[edit] Therapeutic prospects

The drug is not able to cure Morbus Parkinson, but may provide substantial alleviation of symptoms. An estimated 50 to 75% of patients with M. Parkinson will react positively and experience a 20 to 30% symptomatic improvement. To increase therapeutic activity Trihexylphenidyl is often given concomitantly with levodopa, other antimuscarinic or antihistaminic (e.g. diphenhydramine) agents. Combination treatment with dopaminergic agonists such as cabergoline is also possible. This is often termed a 'multidimensional approach'.

[edit] Investigational uses

Equivocal preleminary results from small studies exist for:

Other Dyskinesias
Chorea Huntington
Spasmodic Torticollis

Trihexyphenidyl does not improve cerebral palsy and hemiplegia.

[edit] Contraindications and cautions

See Biperiden.

Patients under 18 yrs. of age should not be treated due to a lack of clinical experience.

[edit] Pregnancy and lactation

The safe use of Trihexyphenidyl during pregnancy and lactation has so far not been assured.

[edit] Side-effects

See Biperiden. Tolerance may develop during therapy which requires dose adjustments.

[edit] Interactions

See Biperiden.

[edit] Dosage

Morbus Parkinson : One mg is given on the first day. Increments are usually 2mg every 3 days until 6 to 10mg are reached. In postencephalitic cases up to 15 mg might be necessary, but then excessive dryness of mouth or nausea could be a problem. To increase tolerability Trihexyphenidyl may be given in 3 divided doses.

Extrapyramidal side effects : Usually, 5 to 15 mg daily are needed in 2 or 3 divided doses. Some patients, however, are successfully treated with as little as 1 mg daily.