daily. the total daily dose will depend upon what is found to be the optimal level. many patients derive maximum benefit from this daily total of 6 to 10 mg, but some patients, chiefly those in the postencephalitic group, may require a total daily dose of 12 to 15 mg. trihexyphenidyl hcl in drug-induced parkinsonism the size and frequency of dose of trihexyphenidyl hcl needed to control extrapyramidal reactions to commonly employed tranquilizers, 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 satisfactorily controlled on as little as 1 mg daily. it may be advisable to commence therapy with a single 1 mg dose. if the extrapyramidal manifestations are not controlled in a few hours, the subsequent doses may be progressively increased until satisfactory control is achieved. satisfactory control may sometimes be more rapidly achieved by temporarily reducing the dosage of the tranquilizer on instituting trihexyphenidyl hcl therapy and then adjusting dosage of both drugs until the desired ataractic effect is retained without onset of extrapyramidal reactions. it is sometimes possible to maintain the patient on a reduced trihexyphenidyl hcl dosage after the reactions have remained under control for several days. instances have been reported in which these reactions have remained in remission for long periods after trihexyphenidyl hcl therapy was discontinued. concomitant use of trihexyphenidyl hcl with levodopa when trihexyphenidyl hcl is used concomitantly with levodopa, the usual dose of each may need to be reduced. careful adjustment is necessary, depending on side effects and degree of symptom control. trihexyphenidyl hcl dosage of 3 to 6 mg daily, in divided doses, is usually adequate. concomitant use of trihexyphenidyl hcl with other parasympathetic inhibitors trihexyphenidyl hcl may be substituted, in whole or in part, for other parasympathetic inhibitors. the usual technique is partial substitution initially, with progressive reduction in the other medication as the dose of trihexyphenidyl hcl is increased. trihexyphenidyl hydrochloride tablets - the total daily intake of trihexyphenidyl hcl tablets is tolerated best if divided into 3 doses and taken at mealtimes. high doses (> 10 mg daily) may be divided into 4 parts, with 3 doses administered at meal times and the fourth at bedtime.

patients with arteriosclerosis or with a history of idiosyncrasy to other drugs may exhibit reactions of mental confusion, agitation, disturbed behavior, or nausea and vomiting. such patients should be allowed to develop a tolerance through the initial administration of a small dose and gradual increase in dose until an effective level is reached. if a severe reaction should occur, administration of the drug should be discontinued for a few days and then resumed at a lower dosage. psychiatric disturbances can result from indiscriminate use (leading to overdosage) to sustain continued euphoria. potential side effects associated with the use of any atropine-like drugs include constipation, drowsiness, urinary hesitancy or retention, tachycardia, dilation of the pupil, increased intraocular tension, weakness, vomiting, and headache. the occurrence of angle-closure glaucoma due to long-term treatment with trihexyphenidyl hydrochloride has been reported. to report suspected adverse events, contact actavis at 1-800-272-5525 or fda at 1-800-fda-1088 or http://www.fda.gov/ for voluntary reporting of adverse reactions.