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Trihexyphenidyl hydrochloride oral


Oral formulations of trihexyphenidyl hydrochloride

Drugs List

  • trihexyphenidyl 2mg tablets
  • trihexyphenidyl 5mg tablets
  • trihexyphenidyl 5mg/5ml oral solution
  • Therapeutic Indications


    Extrapyramidal symptoms - drug induced
    Parkinson's disease

    Unlicensed Uses

    Dystonias in children



    The dose should be administered empirically, usually by initiating therapy at a low dose and by subsequent graduated increments.

    Initial titration phase: 1mg on the first day, increased to 2mg on the second day. Then, increase in increments of 2mg per day at three to five day intervals until the optimal dose is reached.
    Maintenance dose: 5mg to 15mg daily, given in three or four divided doses.
    Maximum dose: 20mg daily.
    All dose adjustments (up or down) should be done in small increments over a period of days.

    When trihexyphenidyl is used concurrently with levodopa, the usual dose of each drug may need to be reduced and careful adjustment is necessary; 3 to 6 mg in divided doses is usually adequate.

    Drug-induced extrapyramidal disorder
    The size and frequency of the dose must be determined empirically.
    Usual total daily dose: 5mg to 15mg, although is some cases 1mg daily has been sufficient.
    Treatment should be of minimal duration and discontinued after symptoms have subsided for a reasonable period of time.


    Preferably at the lower end of the usual adult dose due to the increased susceptibility to the side effects of antimuscarinics in this age group.
    (See Dosage; Adults)


    Dystonia (unlicensed)
    Children aged 3 months to 18 years
    Initial dose: 1mg to 2 mg daily, given in one single or two divided doses.
    Increase every three to seven days by 1mg daily. Titrate to response and side effects.
    Maximum dose: 2mg/kg daily.


    Children under 3 months

    Precautions and Warnings

    Children aged 3 months to 18 years
    Patients over 65 years
    Predisposition to glaucoma
    Benign prostatic hyperplasia
    Cardiac impairment
    Gastrointestinal obstruction
    Glucose-galactose malabsorption syndrome
    Hepatic impairment
    Hereditary fructose intolerance
    Myasthenia gravis
    Psychiatric disorder
    Renal impairment
    Tardive dyskinesia
    Urinary obstruction

    May exacerbate myasthenia gravis
    Advise ability to drive/operate machinery may be affected by side effects
    Some formulations contain sucrose
    May precipitate glaucoma
    Potential for drug abuse
    Discontinue if psychiatric disturbances develop
    May exacerbate tardive dyskinesia
    Avoid abrupt withdrawal
    Not licensed for use in children under 18 years
    Reduce dose in elderly

    Pregnancy and Lactation


    Use trihexyphenidyl with caution in pregnancy.

    UK licensed product information advises that trihexyphenidyl should not be given in pregnancy unless it is clearly necessary.

    The use of trihexyphenidyl during pregnancy has only been studied in a limited number of human pregnancies. The outcome data show no increase in congenital anomalies or foetal toxicity, however the number of patients studied does not allow any assessment of the risk to mother and foetus.

    The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14 to 17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( ) or if this is unavailable at the backup site ( ).


    Use trihexyphenidyl with caution in breastfeeding.

    UK licensed product information advises that trihexyphenidyl should not be given to breastfeeding women.

    The same information further notes that infants may be very sensitive to the effects of antimuscarinic agents.

    At the time of writing, it is not known whether trihexyphenidyl is excreted into human breast milk.

    Limited information indicates that maternal doses of trihexyphenidyl up to 4 mg daily together with haloperidol did not produce any adverse effects in breastfed infants. Long term use of trihexyphenidyl may reduce milk production or milk letdown, but a single dose is not likely to interfere with breastfeeding. During long term use, observe for signs of decreased lactation e.g. insatiety, poor weight gain (LactMed).

    Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
    Specialist advice is available from the UK Drugs in Lactation Advisory Service at

    Side Effects

    Blurred vision
    Decreased bronchial secretions
    Difficulty in micturition
    Difficulty in swallowing
    Dilatation of pupils
    Disturbances in accommodation
    Dry mouth
    Dry skin
    Exacerbation of myasthenia gravis
    Gastro-intestinal disturbances
    Hypersensitivity reactions
    Increased intra-ocular pressure
    Memory disturbances
    Paranoid delusions
    Psychiatric disorders
    Tardive dyskinesia
    Urinary retention


    It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.

    The following number will direct the caller to the relevant local centre (0844) 892 0111

    Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Further Information

    Last Full Review Date: January 2015

    Reference Sources

    Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 9th edition (2011) ed. Briggs, G., Freeman, R. and Yaffe, S. Lippincott Williams & Wilkins, Philadelphia.

    Martindale: The Complete Drug Reference, 37th edition (2011) ed. Sweetman, S. Pharmaceutical Press, London.

    Summary of Product Characteristics: Trihexyphenidyl Hydrochloride Syrup 5 mg/5 ml. Rosemont Pharmaceuticals Ltd. Revised February 2013.

    Summary of Product Characteristics: Trihexyphenidyl Hydrochloride 2mg Tablets. Genus Pharmaceuticals. Revised May 2011.

    NICE Evidence Services Available at: Last accessed: 04 September 2017

    US National Library of Medicine. Toxicology Data Network. Drugs and Lactation Database (LactMed).
    Available at:
    Trihexyphenidyl Hydrochloride. Last revised: September 7, 2013.
    Last accessed: 14 January, 2015.

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