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

Darifenacin is only a moderate inhibitor of CYP2D6 in vivo, and the inhibition is competitive and reversible. Thus no pharmacokinetic porphyrinogenic effects are suspected.

Selective muscarinic M3 receptor antagonist Lipophilic base; dihydrobenzofuranyl pyrrolidinium acetamide.

Darifenacin is an anticholinergic agent used in the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency and frequency. It is administered orally. The terminal half-life of darifenacin is 13-19 hours.

Darifenacin undergoes extensive metabolism by CYP2D6 and CYP3A4 in the liver, and CYP3A4 in the intestinal wall (SPC). Darifenacin is a moderate, reversible inhibitor of CYP2D6, which may be of clinical relevance (Skerjanec, 2006). When administered with the CYP2D6 substrate, desipramine, a 2.6-fold increase in the AUC of desipramine was observed (Skerjanec, 2006). In vitro studies also found darifenacin to be an inhibitor of CYP3A4, however this was not observed in vivo at clinical relevant doses (Skerjanec 2006). Darifenacin did not affect the metabolism of co-administered oral contraceptives.

Uneventful use reported in 1 patient with acute porphyria.