Oxybutynin Clomipramine

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... 

An elderly woman had clomipramine and desmethylclomipramine blood levels of 405 and 50 nanograms/mL, respectively, after taking clomipramine 25 mg daily and fluvoxamine 100 mg daily for 18 days. Within one week of starting oxybutynin 5 mg daily, the levels of clomipramine and desmethylclomipramine had fallen to 133 and less than 25 nanograms/mL, respectively, and remained low during a further week of concurrent treatment. ... 

Clomipramine levels may be reduced because oxybutynin is an inducer of cytochrome P450 isoenzymes, which could increase the metabolism of clomipramine, and therefore reduce it levels. This appears to be the only report of an interaction, the mechanism of which is not fully clear. It is therefore of unknown general significance. However, note that both tricyclic antidepressants and oxybutynin have antimuscarinic effects, which... 

Grozinger M, Hartter S, Hiemke C, Roschke J. Oxybutynin enhances the metabolism of clomipramine and dextrorphan possibly by induction of a cytochrome P450 isoenz5fme. J Clin Psychopharmacol (1999) 19, 287-9. 

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