Trihexylphenedyl

Absorption

Trihexyphenidyl is absorbed from the gastrointestinal tract. Trihexyphenidyl reaches a Cmax of 7.2 ng/mL, with a Tmax of 1.3 hours, and an AUC of 201 ng*h/mL.

Toxicity

Symptoms of overdose include mydriasis, dryness of mucous membranes, red face, atonic states of bowels and bladder, and hyperthermia in high doses. Trihexyphenidyl causes agitation, confusion, and hallucinations due to its effects on the central nervous system. Untreated overdose may result in death, especially in children. Respiratory depression and cardiac arrest may be seen as premortal signs.
Patients experiencing an overdose of trihexyphenidyl may experience dry mouth, anhidrosis, mydriasis, nausea, vomiting, tachycardia, hyperpyrexia, reduced gastrointestinal motility, urinary hesitancy or retention, rash, hyperthermia, confusion, restlessness, agitation, poor coordination, paranoia, psychosis, delirium, hallucinations, coma, respiratory failure, circulatory failure, and death. Patients should be treated with symptomatic and supportive care which may include airway maintenance and the use of physostigmine.

Originator

Artane,Lederle,US,1949

The Uses of Trihexylphenedyl

Anticholinergic; antiparkinsonian.

The Uses of Trihexylphenedyl

Trihexyphenidyl, an antiparkinsonian drug, possesses central and peripheral anticholinergic actions, as well as a direct relaxant effect on smooth muscle. It reduces muscle rigidity and general stiffness, and has a relatively minor effect on tremors. It is used in Parkinsonism in the form of monotherapy as well as in combination with levodopa.

Indications

Tihexyphenidyl is indicated as an adjunct in the treatment of parkinsonism, an adjuvant in the treatment of parkinsonism with levodopa, and in the control of extrapyramidal disorders caused by central nervous system drugs.

Background

Trihexyphenidyl is a centrally acting muscarinic antagonist used for treatment of parkinsonism and drug-induced extrapyramidal disorders. Its discovery was published in 1949 in a study looking for drugs with antispasmodic activity. Trihexyphenidyl is rarely used in the treatment of parkinsonism, and is not a first line treatment due to significant adverse effects. It has largely been replaced by drugs such as levodopa.
Trihexyphenidyl was granted FDA approval on 13 May 1949.

Definition

ChEBI: Trihexyphenidyl is an amine.

Manufacturing Process

Acetophenone, paraformaldehyde and piperidine are first reacted to give ω-(1- piperidyl)propiophenone. To an absolute ethyl ether solution of cyclohexylmagnesium bromide (prepared from 261 parts of cyclohexyl bromide, 38.8 parts magnesium turnings and 700 parts by volume absolute ethyl ether) a dry solution of 174 parts omega-(1-piperidyl)-propiophenonein 600 parts by volume of ether is added, with stirring, at such a rate that gentle reflux is maintained with no external cooling or heating. The reaction mixture is stirred for about 5 hours and then allowed to stand at room temperature until reaction appears complete. While being cooled the reaction mixture is then decomposed by the dropwise addition of 500 parts by volume of 2.5 N hydrochloric acid, and finally is made strongly acidic to Congo red by the addition of concentrated hydrochloric acid.
The resulting white solid is collected on a filter, air dried, redissolved in 2,500 parts water at 95°C and the resulting solution treated with decolorizing charcoal and clarified by filtration. The cooled filtrate is made alkaline with ammonia and the product, crude 3-(1-piperidyl)-1-cyclohexyl-1-phenyl-1- propanol is collected. The hydrochloride melts with decomposition in ten seconds in a bath held at 258.5°C. The alcohol melts at 114.3° to 115.0°C, according to US Patent 2,716,121.

brand name

Artane (Lederle); Tremin (Schering).

Therapeutic Function

Antiparkinsonian

Pharmacokinetics

Trihexyphenidyl is an antimuscarinic indicated as an adjunct in the treatment of parkinsonism or as a treatment for drug-induced extrapyramidal symptoms. It has a long duration of action as it does not need to be given every day. It has a wide therapeutic window, with acute toxicity being non fatal in doses as high as 300 mg. Patients should have their iridocorneal angle examined before and intraocular pressure monitored during therapy. Patients should be counselled regarding the risk of anhidrosis and hyperthermia.

Safety Profile

Poison by intraperitoneal, subcutaneous, and intravenous routes. When heated to decomposition it emits toxic fumes of NOx.

Synthesis

Trihexyphenidyl, 1-cyclohexyl-1-phenyl-3-piperidineopropan-1-ol (10.2.2), is synthesized by the reaction of 2-(1-piperidino)propiophenone (10.2.1) with cyclohexylmagnesiumbromide. The initial 2-(1-piperidino)propiophenone is synthesized in turn by the aminomethylation of benzophenone using paraformaldehyde and piperidine [24¨C27].

Metabolism

Data regarding the metabolism of trihexyphenidyl are not readily available. However, it is likely not heavily metabolized.