TRIHEXYPHENIDYL

Posology:

Adults Only: Optimal dosage should always be determined empirically, usually by initiating therapy at a relatively low level and by subsequent graduated increments. The usual dosage for Parkinsonism is 6-10mg per day although some patients chiefly in the post-encephalitic group may require an average total dose of 12-15mg daily.

It should be given orally either three or four times a day at mealtimes. Normal dosage for drug-induced Parkinsonism is usually between 5mg and 15mg per day, although some cases have been controlled by 1mg daily. In all cases, trihexyphenidyl dosage should be increased or decreased only be by small increments over a period of several days.

In initial therapy the dose should be 1mg the first day, 2mg the second day with further increase of 2mg per day at 3-5 day intervals until the optimum dose is reached. Trihexyphenidyl may be taken before or after meals according to the way the patient reacts.

If trihexyphenidyl tend to dry the mouth excessively, it may be better to take it before meals, unless it causes nausea. If taken after meals, induced thirst can be allayed by peppermint, chewing gum or water.

Paediatric Population:

Trihexyphenidyl is not recommended for children.

The Elderly:

Patients over 60 years of age tend to be relatively more sensitive and require smaller amounts of trihexyphenidyl.

Method of administration:

Trihexyphenidyl tablets are to be taken by mouth.

Minor side effects such as dryness of mouth, constipation, blurring of vision, dizziness, mild nausea or nervousness will be experienced by 30-50% of all patients. These reactions tend to become less pronounced as treatment continues.

Patients should be allowed to develop a tolerance using the smaller initial dose until the effective level is reached.

Immune System disorder:

Hypersensitivity.

Psychiatric disorders:

Nervousness, restlessness, confusional states, agitation, delusions, hallucinations, insomnia, especially in the elderly and patients with arteriosclerosis. The development of psychiatric disturbance may necessitate discontinuation of treatment.

Euphoria may occur. There have been reports of abuse of trihexyphenidyl due to its euphoric and hallucinogenic properties.

Nervous system disorders:

Dizziness. Impairment of immediate and short-term memory function has been reported. 4). 4).

Cardiac disorders:

Tachycardia.

Respiratory, thoracic and mediastinal disorders:

Decreased bronchial secretions.

Gastrointestinal disorders:

Dry mouth with difficulty swallowing, constipation, nausea, vomiting.

Skin and subcutaneous tissue disorders:

Flushing and dryness of skin, skin rashes.

Renal and urinary disorders:

Precautions:

Since the use of trihexyphenidyl may, in some cases, continue indefinitely, the patient should be under careful observation over the long term. It should be administered with care to avoid allergic or other untoward reactions. Except in the case of vital complications, abrupt discontinuation of the drug should be avoided.

Incipient glaucoma may be precipitated by para-sympatholytic drugs such as trihexyphenidyl. Hypertension, cardiac, liver or kidney disorders are not contra-indicated, but such patients should be followed closely. As trihexyphenidyl may provoke or exacerbate tardive dyskinesia, it is not recommended for use in patients with this condition.

Trihexyphenidyl should be used with caution in patients with glaucoma, obstructive disease of the gastro-intestinal or genito-urinary tracts, and in elderly males with possible prostatic hypertrophy. Since trihexyphenidyl has been associated with the clinical worsening of myasthenia gravis, the drug should be avoided or used with great caution in patients with this condition.

Since certain psychiatric manifestations such as confusion, delusions and hallucinations, all of which may occur with any of the atropine-like drugs, have been reported rarely with trihexyphenidyl, it should be used with extreme caution in elderly patients (see Dosage and Administration).

Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.

Warnings:

Trihexyphenidyl may be the subject of abuse (on the basis of hallucinogenic or euphoriant properties, common to all anti-cholinergic drug) if given in sufficient amounts.

1.