AGITANE, 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 6-10 mg per day although some patients chiefly in the post-encephalitic group may require an average total dose of 12- 15 mg daily.

It should be given orally either three or four times a day at mealtimes. Normal dosage for drug-induced Parkinsonism is usually between 5 mg and 15 mg per day, although some cases have been controlled by 1 mg 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 three to five-day intervals until the optimum dose is reached. If patients are already being treated with other parasympathetic inhibitors, trihexyphenidyl should be substituted as part of the therapy.

When trihexyphenidyl is used concomitantly with levodopa the usual dose of each may need to be reduced. Careful adjustment is necessary, depending on side effects and the degree of symptom control. Trihexyphenidyl dosage of 3-6 mg daily in divided doses, is usually adequate.

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.

Treatment of drug-induced extrapyramidal disorder:

The size and frequency of dose of trihexyphenidyl needed to control extrapyramidal reactions to commonly employed transquillisers, notably the phenothiazines, thioxanthenes, and butyrophenones must be determined empirically. The total daily dosage usually ranges between 5 and 15 mg, although in some cases, these reactions have been controlled by as little as 1 mg daily.

Satisfactory control may sometimes be more rapidly achieved by temporarily reducing the dosage of both drugs until the desired ataractic effect is retrained without concomitant extrapyramidal reactions. It is sometimes possible to maintain the patient on reduced trihexyphenidyl dosage after the reactions have remained under control for several days.

Minor side effects such as dryness of mouth, constipation, blurring of vision, dizziness and 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 disturbances 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-indications, 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.

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