Trihexyphenidyl (Tablets) Instructions for Use

ATC Code

N04AA01 (Trihexyphenidyl)

Active Substance

Trihexyphenidyl (Rec.INN registered by WHO)

Clinical-Pharmacological Group

Antiparkinsonian drug – inhibitor of cholinergic transmission in the CNS

Pharmacotherapeutic Group

Antiparkinsonian agents; anticholinergic agents; tertiary amines

Pharmacological Action

Antiparkinsonian agent. It has a strong central n-cholinoblocking action, as well as a peripheral m-cholinoblocking action. The central action helps to reduce or eliminate movement disorders associated with extrapyramidal disorders.

In parkinsonism, it reduces tremor, to a lesser extent affects rigidity and bradykinesia.

It has an antispasmodic effect, which is associated with anticholinergic activity and a direct myotropic action.

Pharmacokinetics

After oral administration, it is rapidly absorbed from the gastrointestinal tract.

The average T_1/2 is 6-10 hours. Trihexyphenidyl is excreted mainly unchanged. It does not accumulate.

It easily penetrates the blood-brain barrier.

Indications

Parkinsonism; prevention and control of drug-induced extrapyramidal symptoms (except for tardive dyskinesia).

ICD codes

Dosage Regimen

Administer orally. Initiate therapy at a low dose and titrate upward gradually based on individual tolerance and therapeutic response.

For Parkinsonism, the typical initial dose is 1 mg on the first day. Increase the dose by 2 mg increments at intervals of 3 to 5 days until a total daily dose of 6 to 10 mg is reached, administered in 3 or 4 divided doses.

For severe cases, the total daily dose may be increased to 12 to 15 mg. Do not exceed a maximum daily dose of 15 mg.

For drug-induced extrapyramidal symptoms, the usual dosage is 5 to 15 mg per day. Begin with a single 1 mg dose. If no significant relief is observed, increase the subsequent dose.

In some patients, 1 mg daily is sufficient. The majority of patients require 5 to 15 mg per day. For optimal control of acute dystonic reactions, administer the total daily dose in 3 or 4 divided doses.

For geriatric patients, initiate treatment with extreme caution. Use the lowest effective dose due to increased susceptibility to adverse effects, particularly confusion and hallucinations.

Monitor cognitive function and mental status closely in elderly patients during therapy. Adjust the dosing schedule and total daily dose based on patient response and tolerability.

When discontinuing treatment, taper the dose gradually. Do not stop therapy abruptly to avoid potential withdrawal symptoms or rapid worsening of the underlying condition.

Adverse Reactions

From the nervous system : increased nervous excitability, euphoria, psychomotor agitation, agitation, headache, dizziness, irritability, delirium, hallucinations, increased fatigue, decreased ability to concentrate, psychoses; with increased doses or increased sensitivity, anxiety, impaired consciousness, memory, insomnia, dyskinesias (especially in patients taking levodopa drugs), worsening of myasthenia gravis clinical indicators are possible.

Effects due to anticholinergic activity : dry mouth, accommodation paresis, increased intraocular pressure, mydriasis, visual impairment, decreased sweating, constipation, urinary retention, difficulty urinating, tachycardia, bradycardia.

From the digestive system: nausea, vomiting, abdominal pain.

Allergic reactions: skin rash, photophobia.

Other : purulent parotitis (due to xerostomia), skin hyperemia, decreased muscle tone, drug dependence.

Contraindications

Hypersensitivity to trihexyphenidyl; mechanical stenoses of the gastrointestinal tract, megacolon, angle-closure glaucoma, urinary retention, prostatic hyperplasia (with residual urine), tachyarrhythmias, acute alcohol poisoning, psychotropic drugs, including opioids, tardive dyskinesia (because Trihexyphenidyl may provoke or worsen the course of tardive dyskinesia); pregnancy, breastfeeding; children and adolescents under 18 years of age.

With caution

Tachycardia, arterial hypertension, prostatic hyperplasia, psychotic and manic disorders, dementia syndrome, acute myocardial infarction, myasthenia gravis, glaucoma, elderly patients, patients with heart disease, uncompensated kidney or liver disease, obstructive diseases of the gastrointestinal tract or genitourinary tract.

Use in Pregnancy and Lactation

Contraindicated for use during pregnancy and lactation (breastfeeding). If it is necessary to use during lactation, the issue of stopping breastfeeding should be decided.

Use in Hepatic Impairment

Use with caution in liver diseases.

Use in Renal Impairment

Use with caution in kidney diseases.

Pediatric Use

Contraindicated for use in children and adolescents under 18 years of age.

Geriatric Use

Should be used with caution in patients over 60 years of age.

Special Precautions

Treatment with trihexyphenidyl should not be stopped abruptly. At the end of treatment or when starting alternative treatment, the doses of trihexyphenidyl should be reduced gradually.

In patients over 60 years of age, the dose of trihexyphenidyl should be selected with caution due to the high likelihood of hypersensitivity reactions. Trihexyphenidyl is used in this category of patients under the control of cognitive functions and mental state.

During treatment, intraocular pressure should be regularly monitored.

With long-term treatment, the intensity of adverse reactions due to the anticholinergic activity of trihexyphenidyl usually decreases; drug dependence may develop.

With the simultaneous use of trihexyphenidyl with levodopa, adjustment of the dosage regimen is required.

Effect on the ability to drive vehicles and mechanisms

During the use of trihexyphenidyl, it is not recommended to engage in activities requiring high concentration of attention and speed of psychomotor reactions.

Drug Interactions

With simultaneous use of trihexyphenidyl and drugs that have a depressant effect on the central nervous system, this effect is enhanced.

With simultaneous use of anticholinergic agents and drugs with anticholinergic activity, MAO inhibitors with trihexyphenidyl, the anticholinergic effect of the latter is enhanced and gastrointestinal dysfunction, fever, hyperthermia, up to heat stroke are possible.

With simultaneous use, Trihexyphenidyl weakens the effect of metoclopramide and domperidone.

Simultaneous use of trihexyphenidyl with antihistamines may lead to manifestations of undesirable reactions associated with increased anticholinergic action.

With simultaneous use of quinidine and trihexyphenidyl, the anticholinergic effect on cardiac activity (inhibition of AV conduction) is enhanced.

With simultaneous use, Trihexyphenidyl reduces the effect of sublingually administered nitrates (due to dry mouth).

With simultaneous use of trihexyphenidyl with nefopam and antimuscarinic drugs, including those used by inhalation, the frequency and severity of anticholinergic side effects, such as dry mouth, constipation, drowsiness, may increase.

The effect of trihexyphenidyl may increase when used concomitantly with amantadine, H₁-histamine receptor blockers (diphenhydramine, promethazine, clemastine), phenothiazine derivatives (chlorpromazine, alimemazine), tricyclic antidepressants (imipramine, amitriptyline, trimipramine).

When used concomitantly with chlorpromazine, its metabolism increases, which may lead to a decrease in its plasma concentration.

With simultaneous use of trihexyphenidyl and reserpine, the antiparkinsonian effect of trihexyphenidyl decreases, which leads to an increase in parkinsonism syndrome.

When using trihexyphenidyl in combination with other antiparkinsonian drugs (for example, levodopa), dyskinesia may increase, especially at the beginning of treatment.

With simultaneous use of trihexyphenidyl and tranquilizers, dyskinesia is enhanced.

Trihexyphenidyl and parasympathomimetics (pilocarpine, carbachol, neostigmine) are antagonists; they should not be used together due to increased antimuscarinic side effects.

With simultaneous use of trihexyphenidyl and cannabinoids, barbiturates, opiates, alcohol, additive effects are possible.

Storage Conditions

Store at 2°C (36°F) to 25°C (77°F). Keep in original packaging, protected from light. Keep out of reach of children.

Dispensing Status

Rx Only

Important Safety Information

This information is for educational purposes only and does not replace professional medical advice. Always consult your doctor before use. Dosage and side effects may vary. Use only as prescribed.