Common adverse reactions of fesoterodine that can be confused with an acute porphyric attack are nausea, diarrhoea, constipation and abdominal pains. These side effects may potentially be porphyrinogenic if leading to a decrease in carbohydrate intake.

Fesoterodine is not suspected to be an inducer or a mechanism-based inhibitor of CYP enzymes, and is not observed to alter the metabolism of other CYP metabolized drugs.

Muscarinic receptor antagonist

Fesoteridine is an antimuscarinic prodrug used in the treatment of overactive bladder syndrome. It is administered orally.

Fesoterodine is rapidly metabolized to its active metabolite (5-hydroxymethyl tolterodine) by plasma esterases, and is further metabolized by CYP3A4 and CYP2D6 (Malhotra 2008). In vitro data demonstrates that fesoterodine does not inhibit or induce CYP1A2, 2B6, 2C9, 2C19 or 3A4 at clinically relevant concentrations (SPC). In vivo studies have also been conducted and they confirm the results from in vitro studies. Fesoterodine does not affect the pharmacokinetic of ethinyl estradiol and levonorgestrel (Malhotra 2009), and neither does it affect the pharmacokinetic of warfarin (Malhotra 2011). Thus fesoterodine does not inhibit or induce the major CYP enzymes 3A4 and 2C9. No drug-drug interaction with fesoterodine as a perpetrator has been reported in the literature.