Oxybutynin extended-release: a review of its use in the management of overactive bladder

The OROS-based oxybutynin extended-release (ER) formulation (Lyrinel XL; Ditropan XL) represents a new form of oral delivery for oxybutynin, a muscarinic receptor antagonist used in the treatment of overactive bladder (OAB). The release of oxybutynin from oxybutynin ER occurs in a sustained manner, resulting in a smoother plasma concentration-time profile and a lower maximum plasma concentration than those seen with oxybutynin immediate-release (IR). The ER formulation has been developed with the aim of improving the tolerability of oxybutynin therapy and facilitating once-daily administration. Moreover, oxybutynin ER offers greater flexibility in dosage (5-30 mg/day) than the other available treatment options. At dosages of 5-30 mg once daily, oxybutynin ER produced significant decreases from baseline in weekly urinary urge incontinence in patients with OAB. In addition, there were significant decreases in weekly total incontinence episodes and micturition frequency. In two randomised, double-blind studies in patients with OAB, the improvement in all the symptoms with once-daily oxybutynin ER 5-30 mg/day was similar to that produced by oxybutynin IR 5-20 mg/day given one to four times daily. Once-daily oxybutynin ER 10 mg was superior to tolterodine IR 4 mg/day given as two daily doses and as effective as once-daily tolterodine ER 4 mg/day in decreasing urinary incontinence; the decreases in micturition frequency with oxybutynin ER were significantly greater than those seen with either of tolterodine formulations. Oxybutynin ER was well tolerated in all the trials, with adverse events usually being mild to moderate and transient. In direct comparisons, the overall tolerability profile of oxybutynin ER was better than that of oxybutynin IR. Oxybutynin ER was similar to tolterodine (IR and ER) with respect to the incidence of clinically important dry mouth. A large 12-month tolerability study demonstrated no significant risks associated with the long-term use of oxybutynin ER. A few noncomparative studies have shown promising results with oxybutynin ER in the treatment of adult and paediatric patients with neurogenic bladder dysfunction secondary to neuronal injury. Long- and short-term studies have reported significant improvements in health-related quality of life with oxybutynin ER therapy. In addition, pharmacoeconomic studies have suggested that oxybutynin ER is more cost effective than oxybutynin IR and at least as cost effective as tolterodine IR. In conclusion, oxybutynin ER shows excellent efficacy in the treatment of symptoms associated with OAB in adults and the elderly with a good tolerability profile over a prolonged period of use (12 months). The ER formulation of oxybutynin provides a smooth plasma concentration profile over the 24-hour dosage interval, facilitating once-daily administration. Hence, given its overall efficacy/tolerability profile and dosage flexibility, oxybutynin ER provides an excellent treatment option in the first-line pharmacotherapy of OAB.