Trihexyphenidyl pharmacokinetics

AChs are an effective treatment (see Table 71-4). Benztropine has a half-life that allows once- to twice-daily dosing. Dose increases above 6 mg/day must be slow because of nonlinear pharmacokinetics. Trihexyphenidyl, diphenhydramine, and biperiden usually require three-times-daily dosing. Diphenhydramine produces more sedation, but all of the AChs have been abused for euphoriant effects. 

Example Trihexyphenidyl HC1 (Artane) Route PO Pregnancy category C Pharmacokinetic PB UK Well absorbed excreted in urine. ... 

Estrogens (HRT) and tobacco smoking may reduce the clearance of ropinirole. Amantadine and trihexyphenidyl appear not to alter the pharmacokinetics of ropinirole. 

The manufacturer notes that population analysis revealed that trihexyphenidyl did not have any relevant effects on ropinirole pharmacokinetics. ... 

An important pharmacokinetic study correlated CPZ plasma levels with therapeutic response and found that plasma levels in the range of 150-300 ng/ml usually corresponded to clinical improvement.Significantly, concomitant administration of an antiparkinson agent (trihexyphenidyl) tended to lower plasma levels of CPZ, an effect ascribed to reduced gastric motility and decreased absorption of CPZ. 

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