Trihexyphenidyl interaction

Clinically important, potentially hazardous interactions with abacavir, clidinium, clomipramine, desipramine, dicyclomine, digoxin, doxepin, flavoxate, glycopyrrolate, hyoscyamine, imipramine, mepenzolate, methantheline, nortriptyline, oxybutynin, procydidine, propantheline, protriptyline, scopolamine, trihexyphenidyl, trimipramine... 

Interactions the sedative effects of antidepressants, anxiolytics and hypnotics are likely to be enhanced by antihistamines, as are the antimuscarinic actions and side-effects of drugs such as trihexyphenidyl, orphenadrine, tricyclic antidepressants and phenothiazines. 

A study in 6 healthy subjects and 6 patients with Parkinson s disease found that trihexyphenidyl 2 mg twice daily for 3 days lowered the peak plasma levels of a 500-mg dose of levodopa by 42% in the healthy subjects and 17% in the patients, although the interaction was present in only about half of the subjects. The AUC was reduced in both groups by less than 20%. ... 

Singh, M. M. and Kay, S. R. (1975) A longitudinal therapeutic comparison between two prototypic neuroleptics (haloperidol and chlor-promazine) in matched groups of schizophrenics. Non therapeutic interactions with trihexyphenidyl. Theoretical implications for potency differences. Psychopharmacologia (Berl.), 43,115. 

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