Drug-Induced ParkinsonismThe optimal dose and dosing frequency of trihexyphenidyl required to control the extrapyramidal symptoms of commonly used CNS drugs, such as thioxanthenes and phenothiazines, is determined empirically by the clinician. The total daily dosage ranges from 5 to 15 mg for most patients, although there have been reported cases of symptoms being sufficiently controlled on as minimal as 1 mg daily. Therefore, the recommendations are to start treatment with a single dose of 1 mg. Failure of the extrapyramidal manifestations to resolve in a few hours could prompt an increase in dosage until achieving adequate control of symptoms. Adequate control of symptoms is sometimes possible in a shorter duration by briefly decreasing the CNS drug dosage when initiating trihexyphenidyl and gradually adjusting the dose of both drugs for the desired effects without the onset of extrapyramidal symptoms.