A comparison of the effects on saliva output of oxybutynin chloride and tolterodine tartrate

Treating Lower Urinary Tract Symptoms in Older Adults: Intravesical Options

This article provides an overview of the diagnosis and the treatment of lower urinary tract symptoms in older adults complicated by the neurodegenerative changes in the micturition reflex and further confounded by age-related decline in hepatic and renal clearance raising the propensity of adverse drug reactions. The first-line drug treatment for lower urinary tract symptoms, orally administered antimuscarinics, fails to reach the equilibrium dissociation constant of muscarinic receptors even at their maximum plasma concentration and tends to evoke a half-maximal response at a muscarinic receptor occupancy of just 0.206% in the bladder with a minimal difference from exocrine glands, which raises the adverse drug reaction risk. On the contrary, intravesical antimuscarinics are instilled at concentrations 1000-fold higher than the oral maximum plasma concentration and the equilibrium dissociation constant erects a downhill concentration gradient that drives passive diffusion and achieves a mucosal concentration around ten-fold lower than the instilled concentration for a long-lasting occupation of muscarinic receptors in mucosa and sensory nerves. A high local concentration of antimuscarinics in the bladder triggers alternative mechanisms of action and is supposed to engage retrograde transport to nerve cell bodies for neuroplastic changes that underlie a long-lasting therapeutic effect, while an intrinsically lower systemic uptake of the intravesical route lowers the muscarinic receptor occupancy of exocrine glands to lower the adverse drug reaction relative to the oral route. Thus, the traditional pharmacokinetics and pharmacodynamics of oral treatment are upended by intravesical antimuscarinics to generate a dramatic improvement (~ 76%) noted in a meta-analysis of studies enrolling children with neurogenic lower urinary tract symptoms on the primary endpoint of maximum cystometric bladder capacity as well as the secondary endpoints of filling compliance and uninhibited detrusor contractions. The therapeutic success of intravesical multidose oxybutynin solution or oxybutynin entrapped in the polymer for sustained release in the pediatric population bodes well for patients with lower urinary tract symptoms at the other extreme of the age spectrum. Though generally used to predict oral drug absorption, Lipinski's rule of five can also explain the ten-fold lower systemic uptake from the bladder of positively charged trospium over oxybutynin, a tertiary amine. Chemodenervation by an intradetrusor injection of onabotulinumtoxinA is merited for patients with idiopathic overactive bladder discontinuing oral treatment because of a lack of efficacy. However, age-related peripheral neurodegeneration potentiates the adverse drug reaction risk of urinary retention that motivates the quest of liquid instillation, delivering larger fraction of onabotulinumtoxinA to the mucosa as opposed to muscle by an intradetrusor injection can also probe the neurogenic and myogenic predominance of idiopathic overactive bladder. Overall, the treatment paradigm of lower urinary tract symptoms in older adults should be tailored to individual's overall health status and the risk tolerance for adverse drug reactions.

Urinary incontinence: pharmacotherapy options

The impact of incontinence is felt by millions of people worldwide, with tremendous decrement in quality of life and enormous cost reaching billions of dollars. Urinary incontinence is defined as 'involuntary leakage of urine' and is categorized into two main types: urgency urinary incontinence (UUI) and stress urinary incontinence (SUI). Behavioral modifications and pharmacologic therapies, primarily antimuscarinic agents, are the mainstay of treatment for UUI. These drugs are moderately efficacious but have troublesome side-effects, the combination resulting in poor compliance and persistence with therapy. There are several agents on the market today, each with some variation in pharmacologic properties. Whether these translate into meaningful differences in clinical efficacy and tolerability remains a matter of debate. Treatment of SUI has seen little success with pharmacologic therapy. In Europe, duloxetine is approved for treatment of SUI with marginal success rates; this drug, although available in the United States for treatment of depression, is not approved for SUI. The search for newer and better pharmacologic options and novel therapies is on-going, fueled primarily by the high prevalence of bothersome incontinence and the tremendous number of health care dollars spent on current therapy. This review addresses pharmacologic options for treatment of urinary incontinence.

Oxybutynin extended release for the management of overactive bladder: a clinical review

Overactive bladder (OAB) is a common condition which negatively impacts the quality of life of afflicted patients. This can result in alterations in social interactions at home, in the workplace and in the community, often leading to depression and poor self esteem as well as loss of productivity. Traditional mainstays of treatment include both behavioral therapy and pharmacotherapy. Oxybutynin immediate release (IR) represents the first such medication approved by the FDA specifically for treatment of OAB in 1975. Nevertheless, bothersome side effects in addition to thrice daily dosing often led to treatment cessation which raised the question that patients may actually prefer to live with their OAB symptoms rather than incur side effects or complex dosing schemes. Pharmacological advances ultimately led to development of a long-acting formulation of oxybutynin in the form of oxybutynin extended release (ER) with the hope that this drug would maintain efficacy while decreasing bothersome side effects and improve compliance with the convenience of once daily dosing regimen. This paper will review the major clinical studies involving oxybutynin ER as well as its role in different patient populations and potential concerns with its use.

Patient perspectives in the management of overactive bladder, focus on transdermal oxybutynin

Overactive bladder syndrome (OAB) is a constellation of distressing symptoms that significantly impair quality of life, sexual function, and work productivity, and imposes a significant economic burden to society. Pharmacological treatment with antimuscarinic agents, behavioral modification, bladder retraining, and/or pelvic floor exercises are often used alone or in combination as the mainstay treatment in the management of OAB. Oxybutynin has been used in the treatment of OAB for over 20 years with proven efficacy and is often the comparator in drug treatment trials. Oral formulations of oxybutynin have proven efficacy, but not without significant antimuscarinic effects, which reduce patient persistence with medical treatment. Low levels of patient persistence with oral formulations of oxybutynin provided an impetus for the development of a transdermal oxybutynin delivery system. The oxybutynin transdermal formulation has been found to have side effects similar to that of a placebo in randomized controlled trials while providing excellent efficacy. Patient persistence with therapy, improved quality of life, sexual function and interpersonal relationships have been observed with use of the transdermal oxybutynin delivery system. Its twice weekly dosing, low side effect profile, and high efficacy have made it a good choice for initial treatment of overactive bladder syndrome.

M2 mediated contractions of human bladder from organ donors is associated with an increase in urothelial muscarinic receptors

AIMS

Previous studies have shown increased density of M2 receptors in hypertrophied rat bladders that possess an M2 contractile phenotype. The aim of the current study is to determine whether human bladders with an M2 contractile phenotype also have a greater density of bladder M2 receptors.

MATERIALS AND METHODS

Human bladders were obtained from 24 different organ transplant donors. Darifenacin and methoctramine affinity was determined by the rightward shift of cumulative carbachol concentration contractile response curves for each bladder. Radioligand binding and immunoprecipitation was used to quantify M2 and M3 subtypes in isolated detrusor muscle and urothelium. In addition, pig bladder muscle and urothelial receptors were quantified for comparison.

RESULTS

In the human urothelium total, M2 and M3 muscarinic receptor density is significantly negatively correlated with the affinity of darifenacin for inhibition of contraction of the detrusor muscle. In the detrusor muscle there is no correlation between receptor density and darifenacin affinity for inhibition of contraction. Muscarinic receptor density is greater in the muscle than in the urothelium in human bladders whereas in the pig bladder the density is greater in the urothelium than in the muscle.

CONCLUSIONS

The greater density of urothelial muscarinic receptors in human bladders with lower darifenacin affinity, indicative of a greater contribution of M2 receptors to the contractile response, points towards a possible role of the urothelium in controlling M2 mediated contractile phenotype. In comparison between human and pig bladders, the distribution of muscarinic receptor subtypes in the muscle and urothelium are quite different.

Symptomatic treatment of multiple sclerosis. Multiple Sclerosis Therapy Consensus Group (MSTCG) of the German Multiple Sclerosis Society

Besides immunomodulation and immunosuppression, the specific treatment of symptoms is an essential component of the overall management of multiple sclerosis (MS). Symptomatic treatment is aimed at the elimination or reduction of symptoms impairing the functional abilities and quality of life of the affected patients. Moreover, with symptomatic treatment the development of a secondary physical impairment due to an existing one may be avoided. Many therapeutic techniques as well as different drugs are used for the treatment of MS symptoms, but only a few of them have been investigated, especially in MS patients, and are approved by the national health authorities. Despite an overwhelming number of publications, only a few evidence-based studies exist and consensus reports are very rare, too. Therefore, it seemed necessary to develop a consensus statement on symptomatic treatment of MS comprising existing evidence-based literature as well as therapeutic experience of neurologists who have dealt with these problems over a long time. This consensus paper contains proposals for the treatment of the most common MS symptoms: disorders of motor function and coordination, of cranial nerve function, of autonomic, cognitive, and psychological functions as well as MS-related pain syndromes and epileptic seizures.

Pharmacotherapy for Neurogenic Detrusor Overactivity

Chancellor MB, Anderson RU, Boone TB: Pharmacotherapy for neurogenic detrusor overactivity. Am J Phys Med Rehabil 2006;85:536-545. Patients with neurogenic detrusor overactivity are a heterogeneous group with voiding dysfunction secondary to neurologic injury or disease. The neurogenic detrusor overactivity syndrome, which may include urinary frequency, urgency, and incontinence, frequently contributes to a loss of independence, or even institutionalization. Urodynamic assessment provides the best method of quantifying and classifying neurogenic detrusor overactivity dysfunction in patients with primary diagnoses as diverse as Parkinson's disease, cerebral palsy, multiple sclerosis, spinal cord injury, and spina bifida. For many patients, management of urinary symptoms includes pharmacotherapy with an anticholinergic agent. Several novel approaches to managing neurogenic detrusor overactivity, including intravesical instillation of anticholinergic agents, vanilloids, and neurotoxins, are being investigated. For most patients, however, flexible dosing with an anticholinergic agent, with clean intermittent catheterization when indicated, has been shown to reduce the risks of urologic complications, improve levels of continence, and enhance patient quality of life in both children and adults.

Comparison of dry mouth in women treated with extended-release formulations of oxybutynin or tolterodine for overactive bladder

The incidence, severity and tolerability of dry mouth was compared in 790 women with overactive bladder who were treated with extended-release oxybutynin chloride 10 mg/day or extended-release tolterodine tartrate 4 mg/day for 12 weeks in a multicenter, double-blind, parallel-group study. Dry mouth was the most common adverse event associated with treatment, with an incidence rate of 28.1% in the oxybutynin group and 21.6% in the tolterodine group (P = 0.039). The majority of dry mouth events were mild in both treatment groups. Severe dry mouth occurred in 1.5% and 0.5% of patients in the oxybutynin and tolterodine groups, respectively (P = 0.173). Seven patients on extended-release oxybutynin and 4 patients on extended-release tolterodine discontinued treatment due to dry mouth (P = 0.380). The results of this analysis showed that dry mouth was common with both treatments, but most events were mild; there was no difference in the rate of severe dry mouth or in the rate of withdrawal due to dry mouth.

Extended-release formulations of oxybutynin and tolterodine exhibit similar central nervous system tolerability profiles: a subanalysis of data from the OPERA trial

OBJECTIVE

This study was undertaken to compare the central nervous system (CNS) tolerability profiles of the extended-release formulations of oxybutynin chloride and tolterodine tartrate in the treatment of women with overactive bladder (OAB), as observed in the OPERA (Overactive bladder: Performance of Extended Release Agents) trial.

STUDY DESIGN

The OPERA trial was a randomized, double-blind, active-control comparison of the efficacy and safety of extended-release oxybutynin (10 mg/d) and extended-release tolterodine (4 mg/d) given to 790 women with OAB for 12 weeks. The incidence of reported CNS events was compared between the treatment groups by using the Fisher exact test.

RESULTS

The incidence of CNS adverse events was 9% and 8% for the oxybutynin and tolterodine treatment groups, respectively. The difference between groups was not statistically significant. All reported CNS adverse events were rated as mild or moderate in severity. There were no serious treatment-related adverse events in either group, and discontinuation because of a CNS adverse event was infrequent.

CONCLUSION

The extended-release formulations of oxybutynin and tolterodine were observed to be associated with a similar low incidence of CNS adverse events, which were mostly mild or moderate in severity.

Benefit-Risk Assessment of Tolterodine in the Treatment of Overactive Bladder in Adults

Overactive bladder is associated with symptoms of urgency, with or without urge incontinence, usually with daytime frequency and nocturia in the absence of local pathological factors. Muscarinic receptor antagonists (antimuscarinics) are the first-line pharmacotherapy. Tolterodine, a competitive, nonselective antimuscarinic specifically developed for the treatment of overactive bladder, demonstrated tissue selectivity for the bladder over the parotid gland in an animal model. As of March 5, 2003, the immediate-release (IR) formulation had been approved in 72 countries and the extended-release (ER) formulation had been approved in 28 countries, and tolterodine had been administered to 5 million patients. This review evaluates the benefit-risk profile of tolterodine in the treatment of adults with overactive bladder, summarising clinical trial and postmarketing surveillance data. Tolterodine has been found to significantly reduce micturition frequency, urgency perception and the number of episodes of urge incontinence and increase the volume voided per micturition. Dry mouth, an antimuscarinic class effect, is the most commonly reported adverse effect but is mostly mild to moderate in severity. Serious adverse effects are reported infrequently. Based on summary and review of postmarketing surveillance and clinical trial safety data received by the market authorization holder and contained in the Periodic Safety Update Reports for tolterodine, several monitored serious events of the gastrointestinal tract (e.g. ileus or haemorrhage), nervous system (e.g. syncope, convulsions and memory disorders) and cardiovascular system (e.g. ventricular arrhythmia, atrial fibrillation, palpitations, bradycardia, transient ischaemic attacks and hypertension) were not considered related to tolterodine. QT or corrected QT (QTc) prolongation was not observed in any of the five cases of verified ventricular arrhythmia in patients administered tolterodine; there is insufficient evidence to indicate that tolterodine causes ventricular arrhythmia or extrasystoles or any specific type of cardiac rhythm abnormality. The safety profile of tolterodine is similar in patients aged > or =65 years and in younger adults. Clinically relevant drug interactions are limited to cytochrome P450 3A4 inhibitors, such as ketoconazole, and co-administration with such agents warrants a tolterodine dosage decrease. In addition, tolterodine IR 2mg twice daily is similar in efficacy to oxybutynin IR 5mg three times daily, and tolterodine ER 4 mg once daily is similar in efficacy to oxybutynin ER 10mg once daily. Dry mouth occurred less frequently with tolterodine than oxybutynin, and moderate to severe dry mouth occurred more than three times less frequently. Based on the low frequency of adverse events, the absence of unexpected adverse events and the very low frequency of serious adverse events, we conclude that tolterodine is a well tolerated treatment for overactive bladder in adults, in whom it should be considered as first-line therapy.

Oxybutynin Extended-Release

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.

Clinical pharmacology of old age syndromes

Several syndromes occur in old age. They are often associated with increased mortality and in all there is a paucity of basic and clinical research. The recent developments in the clinical pharmacology of three common syndromes of old age (delirium, urinary incontinence, and falls) are discussed along with directions for future research.

Pharmacokinetics, metabolism, and saliva output during transdermal and extended-release oral oxybutynin administration in healthy subjects

OBJECTIVE

To compare the pharmacokinetics and adverse effect dynamics of 2 modified-release oxybutynin treatments.

SUBJECTS AND METHODS

Between October 15 and November 6, 2001, 13 healthy subjects (7 men and 6 women) participated in a randomized, 2-way crossover study of transdermal (Oxytrol, 3.9 mg/d) and extended-release oral (Ditropan XL, 10 mg) oxybutynin. Multiple blood and saliva samples were collected. Pharmacokinetic parameters and total salivary output were assessed. Statistical analyses included 95% confidence intervals, paired t test, analysis of variance, and linear regression.

RESULTS

Steady-state plasma concentrations were achieved after the first transdermal application and after the second extended-release oral dose. Mean +/- SD 24-hour oxybutynin areas under the concentration-time curve were comparable during transdermal and oral extended-release treatments, 10.8 +/- 24 vs 9.2 +/- 33 ng x h(-1) x mL(-1), respectively. However, the ratio of area under the curve (N-desethyloxybutynin/oxybutynin) after transdermal administration (1.2 +/- 03) was significantly lower (P < .001) than after extended-release oral administration (4.1 +/- 0.9). Mean plasma concentrations were less variable during transdermal compared with extended-release oral administration. Mean +/- SD saliva output was greater during transdermal than extended-release oral treatment (15.7 +/- 93 vs 12.2 +/- 6.8 g, respectively; P = .02). Lower N-desethyloxybutynin during transdermal application was associated with greater saliva output (r = -059, P = .04). No clinically important treatment-related adverse effects were observed.

CONCLUSIONS

Transdermal oxybutynin administration results in greater systemic availability and minimizes metabolism to N-desethyloxybutynin compared with extended-release oral administration. Lower N-desethyloxybutynin plasma concentration and greater saliva output during transdermal treatment correspond to the reported low incidence of dry mouth in patients with overactive bladder.

The use of tolterodine in children after oxybutynin failure

OBJECTIVE

To assess the safety and efficacy of tolterodine tartrate prescribed to children who previously failed to tolerate oxybutynin chloride.

PATIENTS AND METHODS

We reviewed 34 children, followed for>1 year, who were prospectively crossed-over from oxybutynin to tolterodine because of side-effects. The initial diagnosis was dysfunctional voiding in 31 patients. All patients were placed on a behavioural modification protocol. When their symptoms did not improve after 6 months, treatment with an anticholinergic agent was considered. Urodynamic studies were conducted in 20 patients, confirming uninhibited contractions in 19. The remaining 14 patients were empirically started on antimuscarinic or anticholinergic agents. The 34 patients were treated with oxybutynin for a median (range) of 6 (2-84) months. When significant side-effects were reported, they were crossed over to tolterodine. The efficacy of tolterodine was assessed as defined by the International Children's Continence Society, with tolerability assessed and side-effects documented using a questionnaire.

RESULTS

The mean age at the first dose of tolterodine was 8.9 years; the dose was 1 mg twice daily for 12 patients and 2 mg twice daily for 22. The median treatment with tolterodine was 11.5 months, with 20 (59%) patients reporting no side-effects; six described the same but tolerable side-effects as with oxybutynin. Eight patients discontinued tolterodine because of side-effects after a median (range) of 5 (1-11) months. The efficacy of tolterodine was comparable with that of oxybutynin, as reported by the questionnaire and voiding diaries. The reduction in wetting episodes at 1 year was> 90% in 23 (68%), more than half in five and less than half (or failure) in six patients.

CONCLUSION

Tolterodine is tolerated well in children. In this subgroup of patients who could not tolerate oxybutynin, 77% were able to continue tolterodine treatment with no significant side-effects.

A benefit-risk assessment of extended-release oxybutynin

Oxybutynin is a muscarinic receptor antagonist, which has been available for a number of years in its original immediate-release (IR) formulation. While oxybutynin IR has proven effective for the treatment of overactive bladder, its extended use can be limited by adverse effects, particularly dry mouth. An extended-release (ER) formulation of oxybutynin based on the OROS system has recently become available, which allows once daily administration. In direct comparison to oxybutynin IR, oxybutynin ER has an increased oral bioavailability for the parent compound oxybutynin which is accompanied by a reduced bioavailability for the active metabolite N-desethyl-oxybutynin. The latter has been implicated in mediating a major part of the adverse effects of oxybutynin treatment. Two double-blind, placebo-controlled, randomised studies in patients with overactive bladder have demonstrated that oxybutynin ER has a similar efficacy as oxybutynin IR but with improved tolerability. This is in line with clinical pharmacological studies demonstrating a smaller impairment of saliva production with oxybutynin ER than with oxybutynin IR. Thus, the ER formulation of oxybutynin maintains the therapeutic benefits and concomitantly improves tolerability.

Advances in drug delivery: improved bioavailability and drug effect

Alterations in drug delivery produce substantial changes in the bioavailability of anticholinergic agents. These bioavailability differences change the efficacy and tolerability of this drug class, which consistently enhances patient compliance and overall drug effect. In order for drug delivery to alter successfully the bioavailability of a specific agent, the metabolism of that agent and the effect of the degradatory pathway on drug-parent compound levels need to be established. This will enable researchers to design improved or altered delivery pathways to maximize the benefits of these agents. Intestinal metabolism is known to affect certain agents, specifically oxybutynin chloride. Therefore, delivery techniques have been designed that either substantially lower or totally bypass intestinal (presystemic) metabolism. These alternate paths include extended-release oral, cutaneous, intravesical, and intravaginal routes. In addition, improvements in drug delivery have also been found to influence positively efficacy and tolerability profiles associated with tolterodine tartrate, another anticholinergic agent. A long-acting oral formulation has been shown to increase drug efficacy while decreasing tolerability concerns and side effects such as xerostomia. These salubrious effects are, in part, due to the more stable serum-drug concentrations that are imparted by this long-acting formulation.

Pharmacologic treatment for detrusor overactivity

Recent pharmacologic treatment for detrusor overactivity has resulted in more favorable side effect profiles, not only because of the use of different drug delivery systems for older drugs but perhaps also due to the improved bladder selectivity of newer antimuscarinic agents. These developments translate into higher patient compliance and better long-term results with the newer agents over generic immediate-release oxybutynin for the treatment of the overactive bladder.

Current pharmacotherapeutic strategies for overactive bladder

Overactive bladder (OAB) is a chronic, distressing condition characterised by symptoms of urgency (sudden overwhelming urge to urinate) and frequency (urinating more than eight times daily), with or without urge urinary incontinence (sudden involuntary loss of urine). It affects millions of people of all ages and both sexes world wide, with greater prevalence in women and the elderly. The treatment of OAB is aimed at reducing debilitating symptoms, which have a significant effect on all aspects of an individual's quality of life, including social, domestic, psychological, occupational, physical and sexual functioning. Anticholinergic agents are currently recommended as first-line therapy for OAB. Their use results in significant clinical improvement in patients, although a lack of selectivity for receptors in the bladder may lead to troublesome side effects, including dry mouth, blurred vision, somnolence, dizziness and constipation. Recent research efforts have focused on developing drugs with a reduced propensity for causing these problems. Of the available anticholinergic agents, oxybutynin and tolterodine are the most widely used to treat OAB. Studies directly comparing tolterodine immediate-release (IR) with oxybutynin IR have shown that the two agents have similar efficacy. However, tolterodine IR is significantly better tolerated, particularly with respect to the incidence and severity of dry mouth. An extended-release formulation of tolterodine (4 mg capsules) has recently been developed to allow for once-daily dosing. In addition to greater convenience, tolterodine extended-release has shown enhanced efficacy and tolerability compared with tolterodine IR.

Oxybutynin chloride: alterations in drug delivery and improved therapeutic index

Oxybutynin chloride (Ditropan, Alza) is widely regarded as the most efficient antimuscarinic agent for the treatment of bladder detrusor dysfunction resulting in urinary urgency, frequency and urge incontinence. Oxybutynin metabolism occurs primarily in the proximal gastrointestinal tract and the hepatic circulation and is mediated by the cytochrome P450 3A4 isozyme. The major degradation products are desethyloxybutynin, which possesses pharmacological activity, and phenylcyclohexylglycolic acid, which is metabolically inert. A major limitation to long-term compliance with immediate-release oxybutynin remains the necessity for twice- or thrice-daily dosing regimens to provide sustained pharmacological efficacy. Side effects induced by cytochrome P450 metabolism of oxybutynin into the primary metabolite desethyloxybutynin within the gut wall substantially affect the tolerability of the compound within the individual. The oral osmotic delivery system provides unique advantages for drug delivery and substantially alters the tolerability profile of the oxybutynin chloride compound. This extended-release formulation consists of a two component core encapsulated by a semi-permeable membrane. The osmotic gradient between the surrounding environment and the inner core of the delivery system remains constant and water absorption within the capsule is controlled by the semipermeable membrane causing a controlled release of drug, which is sustained over 24 h. Herein are reviewed the various pre- and post-approval trials which have documented the overall therapeutic index of the oral osmotic oxybutynin (Ortho-McNeil Pharmaceuticals). Subsequent post-market surveillance issues are reviewed as are new developments in oxybutynin delivery.