Effect of OROS controlled-release delivery on the pharmacokinetics and pharmacodynamics of oxybutynin chloride

A Population Pharmacokinetic Model of (R)- and (S-) Oxybutynin and Its Active Metabolites After Oral and Intravesical Administration to Healthy Volunteers

Oxybutynin is a racemic anticholinergic drug used for the symptomatic treatment of detrusor overactivity. The formation of active metabolites related to tolerability problems depends on the route of administration. The objective of this evaluation was to develop a pharmacokinetic model for oral/intravesical administration as the basis for simulations with different dosages. Data from a published changeover clinical study with 18 healthy adults receiving a single oral dose of 5 mg immediate-release oxybutynin and single and multiple intravesical doses of 10 mg oxybutynin solution was evaluated. Enantioselective plasma concentrations of oxybutynin and N-desethyloxybutynin (NDO) were used to establish a population pharmacokinetic model using nonlinear mixed-effects modeling with NONMEM 7.4.1. For both enantiomers, the data were described well by a 2-compartment model for oxybutynin with an additional compartment for NDO. Oxybutynin absorption was modeled by transit compartments for oral and first-order absorption for intravesical application. Bioavailability of the more active (R)-enantiomer was 7% for oral and 10%-22% for intravesical administration. In simulations, intravesical doses of 5 to 15 mg (R)-oxybutynin administered 2 to 3 times daily decreased peak-trough fluctuations of NDO to 8% compared with 24% after oral administration. The NDO/oxybutynin ratio was reduced from 17 after oral administration to unity. Chronic intravesical versus oral administration of (R)-oxybutynin generates distinctly lower and less variable concentrations of (R)-NDO. Pharmacokinetic simulations suggest that exposure for 12.5 mg (R)-oxybutynin administered twice daily might not compromise efficacy and tolerability compared with exposure for standard thrice-daily administrations. This assumption needs to be assessed in clinical studies.

Insights into the Management of Overactive Bladder with Transdermal Oxybutynin: A Practical Review

Overactive bladder (OAB), clinically defined as urinary urgency, with or without incontinence, generally accompanied by an increase in urinary frequency and nocturia, after any local disease or metabolic disorder that would explain these symptoms have been ruled out, is a highly prevalent condition that affects millions of men and women worldwide. Not only can the symptoms of OAB be very bothersome, but OAB can have significant detrimental effects on many aspects of individuals' lives, representing a particularly impactful health burden to quality of life and productivity. Besides a wide range of conservative treatments, the clinical efficacy of which remains an open issue, antimuscarinics are the mainstay of pharmacotherapy for this condition but anticholinergic troublesome side effects like dry mouth, and the patient's perception of lack of efficacy and poor adherence, are common reasons of abandonment of treatment. An alternative to oral administration treatment, with a lower incidence of dry mouth and other anticholinergic adverse effects, might be attractive to patients and a real treatment option for physicians. Delivery of oxybutynin directly through the skin with oxybutynin transdermal (OXY-TDS) avoids the first-pass hepatic metabolism that occurs with orally administered oxybutynin and prevents the appearance of anticholinergic adverse events. OXY-TDS being equally effective than oral treatment improves adherence, persistence, and patient satisfaction. The aim of this review is to focus on evidence available of the use of OXY-TDS in the management of patients with OAB, and to help clinicians in the challenges involved in the treatment options for patients with this condition.

A Guide to Medications Inducing Salivary Gland Dysfunction, Xerostomia, and Subjective Sialorrhea: A Systematic Review Sponsored by the World Workshop on Oral Medicine VI

BACKGROUND

Medication-induced salivary gland dysfunction (MISGD), xerostomia (sensation of oral dryness), and subjective sialorrhea cause significant morbidity and impair quality of life. However, no evidence-based lists of the medications that cause these disorders exist.

OBJECTIVE

Our objective was to compile a list of medications affecting salivary gland function and inducing xerostomia or subjective sialorrhea.

DATA SOURCES

Electronic databases were searched for relevant articles published until June 2013. Of 3867 screened records, 269 had an acceptable degree of relevance, quality of methodology, and strength of evidence. We found 56 chemical substances with a higher level of evidence and 50 with a moderate level of evidence of causing the above-mentioned disorders. At the first level of the Anatomical Therapeutic Chemical (ATC) classification system, 9 of 14 anatomical groups were represented, mainly the alimentary, cardiovascular, genitourinary, nervous, and respiratory systems. Management strategies include substitution or discontinuation of medications whenever possible, oral or systemic therapy with sialogogues, administration of saliva substitutes, and use of electro-stimulating devices.

LIMITATIONS

While xerostomia was a commonly reported outcome, objectively measured salivary flow rate was rarely reported. Moreover, xerostomia was mostly assessed as an adverse effect rather than the primary outcome of medication use. This study may not include some medications that could cause xerostomia when administered in conjunction with others or for which xerostomia as an adverse reaction has not been reported in the literature or was not detected in our search.

CONCLUSIONS

We compiled a comprehensive list of medications with documented effects on salivary gland function or symptoms that may assist practitioners in assessing patients who complain of dry mouth while taking medications. The list may also prove useful in helping practitioners anticipate adverse effects and consider alternative medications.

Development of a Novel Simplified PBPK Absorption Model to Explain the Higher Relative Bioavailability of the OROS® Formulation of Oxybutynin

A new minimal Segmented Transit and Absorption model (mSAT) model has been recently proposed and combined with intrinsic intestinal effective permeability (P _eff,int ) to predict the regional gastrointestinal (GI) absorption (f _abs ) of several drugs. Herein, this model was extended and applied for the prediction of oral bioavailability and pharmacokinetics of oxybutynin and its enantiomers to provide a mechanistic explanation of the higher relative bioavailability observed for oxybutynin's modified-release OROS® formulation compared to its immediate-release (IR) counterpart. The expansion of the model involved the incorporation of mechanistic equations for the prediction of release, transit, dissolution, permeation and first-pass metabolism. The predicted pharmacokinetics of oxybutynin enantiomers after oral administration for both the IR and OROS® formulations were in close agreement with the observed data. The predicted absolute bioavailability for the IR formulation was within 5% of the observed value, and the model adequately predicted the higher relative bioavailability observed for the OROS® formulation vs. the IR counterpart. From the model predictions, it can be noticed that the higher bioavailability observed for the OROS® formulation was mainly attributable to differences in the intestinal availability (F _G ) rather than due to a higher colonic f _abs , thus confirming previous hypotheses. The predicted f _abs was almost 70% lower for the OROS® formulation compared to the IR formulation, whereas the F _G was almost eightfold higher than in the IR formulation. These results provide further support to the hypothesis of an increased F _G as the main factor responsible for the higher bioavailability of oxybutynin's OROS® formulation vs. the IR.

An update on the use of transdermal oxybutynin in the management of overactive bladder disorder

Antimuscarinic medications are used to treat nonneurogenic overactive bladder refractory to nonpharmacologic therapy. Side effects such as dry mouth, constipation, blurred vision, dizziness, and impaired cognition limit the tolerability of therapy and are largely responsible for high discontinuation rates. Oxybutynin is a potent muscarinic receptor antagonist whose primary metabolite after first-pass hepatic metabolism is considered largely responsible for its associated anticholinergic side effects. Transdermal administration of medications bypasses hepatic processing. Specifically with oxybutynin, whose low molecular weight permits transdermal administration, bioavailability of the parent drug with oral administration is less than 10%, whereas with transdermal delivery is a minimum of 80%. The result has been an improved side effect profile in multiple clinical trials with maintained efficacy relative to placebo; however, the drug may still be discontinued by patients due to anticholinergic side effects and application site reactions. Transdermal oxybutynin is available as a patch that is changed every 3-4 days, a gel available in individual sachets, or via a metered-dose pump that is applied daily. The transdermal patch was briefly available as an over-the-counter medication for adult women, although at this time all transdermal formulations are available by prescription only.

Transdermal delivery of oxybutynin chloride proniosomal gels for the treatment of overactive bladder

CONTEXT

Overactive bladder (OAB) is a common problem and anticholinergic drugs are first-line therapy, but they have side effects.

OBJECTIVE

Development of oxybutynin chloride (OC) proniosomal gels and analyses of its efficacy for OAB treatment.

MATERIALS AND METHODS

Phase separation coacervation was used to prepare proniosomal gels using various non-ionic surfactants, lipids, soy lecithin and isopropyl alcohol. Gels were characterized with regard to entrapment efficiency (EE), vesicle size, surface morphology (using environmental scanning electron microscopy [E-SEM]), stability, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, in vitro skin permeation, in vivo animal studies and histopathology.

RESULTS AND DISCUSSION

EE was 87-92%, vesicle size was 0.38-5.0 μm, and morphology showed some loosened pores in proniosomes after hydration. ATR-FTIR spectroscopy showed no significant shifts in peaks corresponding to OC and excipients. Most formulations exhibited >50% permeation but the cholesterol-containing formulations P3 (Span 20:Span 60 [1:1]) and P4 [Tween 20:Tween 80 (1:1)] had the highest percent cumulative permeation. P3 and P4 also showed faster recovery of cholinergic effects on salivary glands than oral formulations. P3 and P4 had pronounced therapeutic effects in reduction of urinary frequency and demonstrated improvements in bladder morphology (highly regenerative surface of the transitional epithelium).

CONCLUSION

These results suggest that OC could be incorporated into proniosomal gels for transdermal delivery in the treatment of OAB.

Novel targeted bladder drug-delivery systems: a review

The objective of pharmaceutics is the development of drugs with increased efficacy and reduced side effects. Prolonged exposure of the diseased tissue to the drug is of crucial importance. Drug-delivery systems (DDSs) have been introduced to control rate, time, and place of release. Drugs can easily reach the bladder through a catheter, while systemically administered agents may undergo extensive metabolism. Continuous urine filling and subsequent washout hinder intravesical drug delivery (IDD). Moreover, the low permeability of the urothelium, also described as the bladder permeability barrier, poses a major challenge in the development of the IDD. DDSs increase bioavailability of drugs, therefore improving therapeutic effect and patient compliance. This review focuses on novel DDSs to treat bladder conditions such as overactive bladder, interstitial cystitis, bladder cancer, and recurrent urinary tract infections. The rationale and strategies for both systemic and local delivery methods are discussed, with emphasis on new formulations of well-known drugs (oxybutynin), nanocarriers, polymeric hydrogels, intravesical devices, encapsulated DDSs, and gene therapy. We give an overview of current and future prospects of DDSs for bladder disorders, including nanotechnology and gene therapy.

Analysis of the impact of controlled release formulations on oral drug absorption, gut wall metabolism and relative bioavailability of CYP3A substrates using a physiologically-based pharmacokinetic model

Controlled release (CR) formulations are usually designed to achieve similar exposure (AUC) levels as the marketed immediate release (IR) formulation. However, the AUC is often lower following CR compared to IR formulations. There are a few exceptions when the CR formulations have shown higher AUC. This study investigated the impact of CR formulations on oral drug absorption and CYP3A4-mediated gut wall metabolism. A review of the current literature on relative bioavailability (Frel) between CR and IR formulations of CYP3A substrates was conducted. This was followed by a systematic analysis to assess the impact of the release characteristics and the drug-specific factors (including metabolism and permeability) on oral bioavailability employing a physiologically-based pharmacokinetic (PBPK) modelling and simulation approach. From the literature review, only three CYP3A4 substrates showed higher Frel when formulated as CR. Several scenarios were investigated using the PBPK approach; in most of them, the oral absorption of CR formulations was lower as compared to the IR formulations. However, for highly permeable compounds that were CYP3A4 substrates the reduction in absorption was compensated by an increase in the fraction that escapes from first pass metabolism in the gut wall (FG), where the magnitude was dependent on CYP3A4 affinity. The systematic simulations of various interplays between different parameters demonstrated that BCS class 1 highly-cleared CYP3A4 substrates can display up to 220% higher relative bioavailability when formulated as CR compared to IR, in agreement with the observed data collected from the literature. The results and methodology of this study can be employed during the formulation development process in order to optimize drug absorption, especially for CYP3A4 substrates.

Efficacy and safety of oxybutynin topical gel 3% in patients with urgency and/or mixed urinary incontinence: a randomized, double-blind, placebo-controlled study

AIMS

To assess the efficacy and safety of oxybutynin transdermal gel 3% (OTG3%), with propylene glycol for enhanced skin permeation, in patients with urinary incontinence (UI).

METHODS

In this phase 3 study, 626 patients ≥18 years old with urgency and/or mixed UI symptoms and predominantly urgency UI for ≥3 months were randomized 1:1:1 to receive 12 weeks of OTG3% 84 mg, OTG3% 56 mg, or placebo gel applied once daily to abdomen, inner/upper thigh, or upper arm/shoulder. Primary efficacy endpoint was change from baseline to Week 12 in weekly UI episodes recorded in 3-day bladder diaries. Results were compared using analysis of covariance. Adverse events (AEs) were monitored.

RESULTS

Efficacy was assessed in 601 (intent-to-treat) and safety in 626 patients. At 12 weeks, OTG3% 84 mg/day achieved significantly greater improvement versus placebo in weekly UI episodes (mean change from baseline: -20.4 vs. -18.1; P < 0.05(a)), daily urinary frequency (-2.6 vs. -1.9; P = 0.001(b)), and urinary void volume (32.7 vs. 9.8; P < 0.0001(b)). Dry mouth, the most common treatment-related AE, occurred more often with OTG3% 84 mg/day (26/214 [12.1%]) vs. placebo (10/202 [5.0%]) (P = 0.028); 4 OTG3% patients withdrew because of dry mouth. Application site erythema occurred more often with OTG3% 84 mg/day (8/214 [3.7%]) versus placebo (2/202 [1.0%]) (P = NS); 12 OTG patients withdrew because of skin irritation. No serious treatment-related AEs occurred.

CONCLUSIONS

OTG3% 84 mg/day was well tolerated and effective in improving urge incontinence or mixed UI symptoms with a predominance of UI in adults with overactive bladder.

Characterization of bladder selectivity of antimuscarinic agents on the basis of in vivo drug-receptor binding

The in vivo muscarinic receptor binding of antimuscarinic agents (oxybutynin, solifenacin, tolterodine, and imidafenacin) used to treat urinary dysfunction in patients with overactive bladder is reviewed. Transdermal administration of oxybutynin in rats leads to significant binding of muscarinic receptors in the bladder without long-term binding in the submaxillary gland and the abolishment of salivation evoked by oral oxybutynin. Oral solifenacin shows significant and long-lasting binding to muscarinic receptors in mouse tissues expressing the M₃ subtype. Oral tolterodine binds more selectively to muscarinic receptors in the bladder than in the submaxillary gland in mice. The muscarinic receptor binding of oral imidafenacin in rats is more selective and longer-lasting in the bladder than in other tissues such as the submaxillary gland, heart, colon, lung, and brain, suggesting preferential muscarinic receptor binding in the bladder. In vivo quantitative autoradiography with (+)N-[¹¹C]methyl-3-piperidyl benzilate in rats shows significant occupancy of brain muscarinic receptors with the intravenous injection of oxybutynin, solifenacin, and tolterodine. The estimated in vivo selectivity in brain is significantly greater for solifenacin and tolterodine than for oxybutynin. Imidafenacin occupies few brain muscarinic receptors. Similar findings for oral oxybutynin were observed with positron emission tomography in conscious rhesus monkeys with a significant disturbance of short-term memory. The newer generation of antimuscarinic agents may be advantageous in terms of bladder selectivity after systemic administration.

Pharmacokinetics and toxicity of antimuscarinic drugs for overactive bladder treatment in females

INTRODUCTION

Antimuscarinics (AMs) are the mainstay of pharmacological treatment of overactive bladder (OAB), a symptom complex defined by the presence of urinary urgency, usually associated with frequency and nocturia, with or without urgency urinary incontinence. The AMs used to treat OAB differ in their pharmacological profiles, which may affect their potential for causing adverse effects (AEs).

AREAS COVERED

The present article aims to review the literature about pharmacokinetics (PK) of the different AMs used in the treatment of OAB. Furthermore, the AEs related to the use of these drugs and their incidence are presented. This systematic review is based on material searched and obtained via Medline, Pubmed and EMBASE up to March 2012 using the search terms "adverse events, pharmacokinetics, tolerability" in combination with "darifenacin, fesoterodine, imidafenacin, oxybutynin, propiverine, solifenacin, tolterodine, and trospium."

EXPERT OPINION

Antimuscarinics are the first-line pharmacological treatment for OAB. Despite the development of new molecules that improve their efficacy/safety profile, there are some drugs that are pharmacokinetically more appropriate to be prescribed in specific populations such as patients with neurological disease or the elderly. Moreover, research should be encouraged in evaluating antimuscarinics in conjunction with other drugs such as estrogens or beta-agonists. The identification of prognostic criteria for pharmacological therapy would be helpful.

Specific pharmacokinetic aspects of the urinary tract

This chapter reviews the evidence for "specific" pharmacokinetics playing a role in currently marketed drugs intended to treat lower urinary tract (LUT) symptoms. Principles of drug targeting include intrinsic properties of drugs or organs as well as drug formulations to modify drug release or to create confinement of drug presence. Prodrugs and specific formulations to deliver high drug concentrations at the site(s) of action as well as other ways to manipulate drug distribution to achieve enrichment in target tissues are considered. In overactive bladder (OAB), specific formulations for oxybutynin have been introduced to reduce the level of side effects of the active drug. Extended release tablet formulations and a topical gel formulation have been introduced, with efficacy similar to immediate release (IR) tablets, but with a reduction in anticholinergic adverse effects. However, these modifications have not led to outstanding performance parameters compared to other anticholinergic drugs marketed as IR formulations. Urinary excretion is discussed as potential mechanism for targeting LUT symptoms, but no strong indications appear to exist that this mechanism would contribute for currently available drugs. Intravesical administration of drugs is not a preferred option and only considered for drugs like botulinum toxin, where the inconvenient application compensates for a reasonable degree of long-term efficacy in severe refractory OAB. Alpha acid glycoprotein binding is discussed as a potential factor to influence drug tissue distribution, and it is concluded that there is reasonable evidence that for tamsulosin this mechanism is responsible for the difference in free fraction of the drug observed in plasma and prostate, which could contribute to its relative absence of blood pressure effects in patients with LUT symptoms related to benign prostate hyperplasia (LUTS-BPH). The principle of irreversible inhibition of type II 5α-reductase as a tool to develop drugs to reduce prostatic levels of dihydrotestosterone is employed by both dutasteride and finasteride for treatment of LUTS-BPH. Of the mechanisms discussed, the principles employed for the 5α-reductase blockers and tamsulosin in this respect can be considered relatively specific for its urological indication.

The forefront for novel therapeutic agents based on the pathophysiology of lower urinary tract dysfunction: bladder selectivity based on in vivo drug-receptor binding characteristics of antimuscarinic agents for treatment of overactive bladder

We have reviewed the binding of antimuscarinic agents, used to treat urinary dysfunction in patients with overactive bladder, to muscarinic receptors in target and non-target tissues in vivo. Transdermal administration of oxybutynin in rats led to significant binding in the bladder without long-term binding in the submaxillary gland and the abolishment of salivation evoked by oral oxybutynin. Oral solifenacin showed significant and long-lasting binding to muscarinic receptors in mouse tissues expressing the M(3) subtype. Oral tolterodine bound more selectively to muscarinic receptors in the bladder than in the submaxillary gland in mice. The muscarinic receptor binding activity of oral darifenacin in mice was shown to be pronounced and long-lasting in the bladder, submaxillary gland, and lung. In vivo quantitative autoradiography using (+)N-[(11)C]methyl-3-piperidyl benzilate in rats showed significant occupancy of brain muscarinic receptors on intravenous injection of oxybutynin, propiverine, solifenacin, and tolterodine. The estimated in vivo bladder selectivity compared to brain was significantly greater for solifenacin and tolterodine than oxybutynin. Darifenacin occupied few brain muscarinic receptors. Similar findings were also observed with positron emission tomography in conscious rhesus monkeys. The newer generation of antimuscarinic agents may be advantageous in the bladder selectivity after systemic administration.

The evolution of transdermal therapy for overactive bladder

Oxybutynin chloride has been effectively used for treating overactive bladder syndrome for more than three decades. The evolution of different delivery systems led first to intravesical administration, anal suppositories, and then to the commercial development of an extended-release oral formulation of oxybutynin chloride to improve its tolerability while maintaining efficacy. These modes of delivery were associated with decreased antimuscarinic side effects and N-desethyloxybutynin serum levels by avoiding first-pass metabolism in the upper gut and liver. The development of transdermal delivery has carried this evolution even further, with serum levels of desethyloxybutynin < or = oxybutynin and dry mouth rates of 7%, with little constipation. The new development of a transdermal oxybutynin gel has decreased these application site reactions to low levels while maintaining good efficacy.

The pharmacokinetic profile of fesoterodine 8 mg with daytime or nighttime dosing

PURPOSE

Diurnal variation can affect drug pharmacokinetics. Fesoterodine is a new antimuscarinic drug for the treatment of overactive bladder (OAB). We estimated the relative bioavailability of 5-hydroxymethyl tolterodine (5-HMT), the active metabolite of fesoterodine, following nighttime and daytime administration.

METHODS

In this randomized, open-label, two-period, two-treatment crossover, single-dose study, healthy subjects received daytime and nighttime oral dosing of fesoterodine 8-mg sustained-release tablets, separated by a minimum 60-h washout period. Blood samples for 5-HMT PK determination were collected before dosing and at specified intervals up to 48 h postdose. Safety was assessed by adverse event (AE) reports.

RESULTS

Fourteen subjects completed the study. Plasma concentration versus time profiles (AUC) of 5-HMT were similar for daytime and nighttime dosing. Mean AUC(infinity) 5-HMT values were 47.9 and 51.4 ng h/mL for nighttime and daytime dosing, respectively; the mean time to reach maximum concentration (C(max)) values were 3.9 and 5.0 ng/mL, respectively. Nighttime versus daytime AUC(infinity) and C(max) ratios of 5-HMT were 93 and 79%, respectively; 90% confidence intervals (CIs) indicated equivalence for AUC(infinity) but not for C(max). The median time to reach maximum concentration (T(max)) was 5.0 h for both dosing regimens, and the mean terminal elimination half-life (T((1/2))) was 5.9 and 5.7 h for nighttime and daytime dosing, respectively. Seven treatment-related AEs, most commonly headache, occurred in five subjects.

CONCLUSIONS

The AUC values for daytime and nighttime administration of fesoterodine were equivalent. The 21% reduction in the C(max) for nighttime dosing is unlikely to be clinically relevant. No safety issues were apparent. These results support both daytime and nighttime administration of fesoterodine for OAB treatment.

The effects of reformulation: improved therapeutic index

Antimuscarinic agents are the treatment of choice for overactive bladder syndrome. Due to the development of novel delivery systems, extended-release formulations of oxybutynin, tolterodine, and trospium chloride are now available. In addition to the convenience of once-daily dosing, the new formulations of these commonly prescribed agents have improved their therapeutic index, striking a better balance between efficacy and tolerability.

The evolution of transdermal/topical overactive bladder therapy and its benefits over oral therapy

Multiple antimuscarinic agents are available for the treatment of overactive bladder. Many of the agents have undergone reformulation in an attempt to improve patient adherence and drug tolerability. Oxybutynin evolved from an immediate-release pill to a once-daily oral preparation, and is now available as a transdermal patch and gel. This article discusses the clinical impact of oxybutynin reformulation and reviews the evolution and benefits of transdermal therapy.

The evolution of transdermal/ topical overactive bladder therapy and its benefits over oral therapy

Multiple antimuscarinic agents are available for the treatment of overactive bladder. Many of the agents have undergone reformulation in an attempt to improve patient adherence and drug tolerability. Oxybutynin evolved from an immediate-release pill to a once-daily oral preparation, and is now available as a transdermal patch and gel. This article discusses the clinical impact of oxybutynin reformulation and reviews the evolution and benefits of transdermal therapy.

Stereoselective pharmacokinetics of oxybutynin andN-desethyloxybutyninin vitroandin vivo

In vitro studies and the multiple applications of an oxybutynin (OXY) transdermal delivery system to Japanese healthy volunteers were conducted to characterize the stereoselectivity in the pharmacokinetics of OXY and its metabolite, N-desethyloxybutynin (DEOB). In human liver microsomes, (R)-OXY and (R)-DEOB were eliminated slightly slower than the corresponding (S)-enantiomers. The production of DEOB from OXY for the (R)-enantiomer was also slower than that for the (S)-enantiomer. In human P450-expressing liver microsomes, OXY was metabolized mainly by CYP3A4 among five cytochrome P450s (CYPs) tested (CYP2C9, CYP2C19, CYP2D6, CYP3A4 and CYP3A5) and the kinetics were slightly different for the enantiomer. The unbound fraction of (R)-OXY in plasma was almost two times higher than that of (S)-OXY, whereas (R)-DEOB was bound to plasma protein more than (S)-DEOB. No differences were observed in the blood-plasma concentration ratios for the enantiomers. After multiple applications of the transdermal delivery system, the plasma concentrations of (R)-OXY were lower than those of (S)-OXY. These data indicate that for the stereoselectivity of OXY, the unbound fraction of each OXY enantiomer was a major factor and the metabolism in liver had a minimal effect.

Estimation of the impact of noncompliance on pharmacokinetics: an analysis of the influence of dosing regimens

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Patient compliance is better with formulations that require less frequent dosing than with formulations that require more frequent dosing. Intramuscular risperidone and long-acting oxybutynin are two examples of medicines reformulated for less frequent dosing. However, it is not clear whether better compliance with less frequent dosing regimens translates to improved therapeutic outcome.

WHAT THIS STUDY ADDS

At equivalent daily doses and typical patterns of compliance, fortnightly intramuscular depot administrations of risperidone provide better pharmacokinetic coverage than once-daily oral dosing. Once-daily dosing of oxybutynin is no better at maintaining pharmacokinetic exposure than twice-daily dosing at half strength. The use of simulated compliance data as input to pharmacokinetic models is useful to assess the impact of noncompliance on internal drug exposure.

AIMS

To determine whether, for oxybutynin and risperidone, drug exposure is better with less frequent dosing regimens than with regimens that require more frequent dosing.

METHODS

Pharmacokinetic models of oxybutynin (5 mg twice-daily and 10 mg once-daily) and risperidone (2 mg once-daily orally and 25 mg fortnightly intramuscular injection) were developed. Simulations of multiple doses were performed by use of stochastic models of dose-taking compliance and clinic visit attendance.

RESULTS

At therapeutic concentrations and with typical patterns of noncompliance, intramuscular injections of risperidone resulted in a 41% (SD 12%) greater pharmacokinetic coverage than the oral dose, 76% (SD 10%) vs. 35% (SD 7%). No discernable differences were evident between once- and twice-daily formulations of oxybutynin, 29.2% (SD 10%) vs. 29.0% (SD 13%).

CONCLUSIONS

For equivalent doses for each drug, the longer acting preparation of risperidone, but not oxybutynin, is pharmacokinetically more forgiving of noncompliance than the shorter acting counterparts. Further analysis is required to confirm whether these observations are valid clinically.

Randomized Trial of Oxybutynin Extended Versus Immediate Release for Women Aged 65 and Older with Overactive Bladder: Lessons Learned from Conducting a Trial

OBJECTIVE

This trial was designed to investigate the effectiveness of extended release versus immediate release oxybutynin in reducing symptoms of overactive bladder in a community-dwelling female population over the age of 65.

METHODS

This was a prospective randomized 12-week, open-label study. The primary outcome was number of micturitions per 24 hours, 12 weeks after treatment. The a priori sample size estimate was 60 patients per group.

RESULTS

Of the 318 women approached, only 72 women (23%) were enrolled over 34 months (33 in the immediate release group, and 39 in the extended release group). The study was stopped prematurely because of recruitment difficulties and an interim analysis revealing the need for a much larger sample than had been estimated to show a significant difference between treatments. After 12 weeks of treatment, there was no difference between the oxybutynin extended release and immediate release groups in the number of micturitions per 24 hours or in other outcomes.

CONCLUSION

This study did not demonstrate differences between oxybutynin extended release and immediate release and in reducing symptoms of overactive bladder or quality of life, possibly because the study did not reach the necessary sample size. The difficulty in recruiting subjects for the trial likely resulted from the onerous study requirements (4 study visits required over 12 weeks) and the downtown location of the study centres: these factors would cause particular difficulties for women over age 65 with overactive bladder, for whom travelling may be a problem. Evidence is needed to guide prescribing for older patients, but designing research to obtain adequate sample sizes is difficult. Studies in older subjects should ensure that a much larger budget is allocated for recruitment than would be allocated for studies in younger subjects, that meticulous attention is paid to issues of transport and access, and that support is provided for subjects who agree to take part research.

The effects of external heating on the permeation of oxybutynin through human epidermal membrane

The transdermal delivery system (TDS) of oxybutynin (OXY) is widely used for the treatment of overactive bladder patients. This report aimed to assess the effect of external heating on the pharmacokinetics of OXY after transdermal administration. Franz-type diffusion cell experiments at room temperature, 36 and 45 degrees C were performed to estimate the permeations of OXY through human epidermal membrane with an isosorbide dinitrate (ISDN) formulation as a reference. The fluxes of OXY at 36 and 45 degrees C were only approximately 1.2-fold higher than that at room temperature, while those of ISDN with heating were more than 2.5 times as high as that without heating (p<0.001). These results indicate that the influence of heating on the permeation of OXY from the TDS of OXY may be minimal.

Current and emerging investigational medical therapies for the treatment of overactive bladder

Overactive bladder (OAB) is a chronic distressing condition characterised by urinary urgency with or without urge incontinence, usually with frequency (voiding at least eight times daily) and nocturia. It affects millions of people worldwide independent of age, sex and race. The prevalence increases with age and is relatively higher in women compared with men. The treatment of OAB is aimed at reducing the debilitating symptoms so as to improve the overall quality of life for patients. Anticholinergic agents targeting the muscarinic receptors in the bladder represent the mainstay of pharmacotherapy for the treatment of OAB. Besides their status as the current standard of care, use of antimuscarinic drugs is limited by certain side effects, particularly dry mouth and constipation; therefore, various attempts have been made to improve the organ selectivity of these drugs to overcome the side effects. These include the development of new antimuscarinic agents with structural modifications and the use of innovative drug delivery methods. The advancement in the drug delivery systems extends to the long-term therapeutic efficacy with improved tolerability and patient compliance; however, future prospective therapies are aimed at novel targets with novel mechanisms of action, including beta3-adrenoceptor agonists, K+ channel openers, 5-HT modulators and botulinum toxin, which are currently under different stages of clinical development. Among other investigational therapies, neurokinin receptor antagonists, alpha-adrenoceptor antagonists, nerve growth factor inhibitors, gene therapy and stem cell-based therapies are of considerable interest. The future for the development of new modalities for the treatment of OAB looks promising.

Pharmacokinetics/Pharmacodynamics Analysis of the Relationship between the in Vivo Micturition Pressure and Receptor Occupancy of (R)-Oxybutynin and Its Metabolite in Rats

To elucidate the relationships between the pharmacokinetics and pharmacological effects of oxybutynin ((R/S)-OXY), the micturition pressure and the plasma concentration profiles of (R)-OXY and (R)-N-desethyloxybutynin ((R)-DEOB), a pharmacologically active metabolite, after administration by three different routes (i.v., p.o. and transdermal) in rats were measured and analyzed using an inhibitory effect E(max) model with their in vitro pharmacological effects. The plasma exposure ratios of (R)-DEOB to (R)-OXY calculated from the AUCs were somewhat different among the routes administered. (R)-OXY and (R)-DEOB equally inhibited the acetylcholine-induced contractions in vitro. The micturition pressure, measured using the cystometric method in vivo, exhibited saturation against the dose administered. The inhibitory effect E(max) model well described the relationship between the micturition pressure and the receptor occupancy calculated from the plasma concentrations and pA(2) values and resulted in an extremely small receptor occupancy (0.206%) to exhibit half of the maximum effect. The estimated receptor occupancy profiles suggested a sufficient and long-lasting receptor occupation after transdermal administration of (R/S)-OXY, while the receptor occupancy diminished rapidly after the i.v. and p.o. administration. These data indicate that transdermal administration of (R/S)-OXY would be useful to achieve suitable pharmacological effects without excess plasma concentrations.

Muscarinic receptors in the bladder: from basic research to therapeutics

Muscarinic receptor antagonists (antimuscarinics) serve as the cornerstone in the pharmacological management of overactive bladder (OAB) by relieving the symptoms of urgency, frequency and incontinence. These drugs operate primarily by antagonizing post-junctional excitatory muscarinic receptors (M(2)/M(3)) in the detrusor. The combination of pharmacological and gene knockout studies has greatly advanced our understanding of the functional role of muscarinic receptors in the bladder. M(3) receptors produce direct smooth muscle contraction by a mechanism that relies on entry of extracellular calcium through L-type channels and activation of a rho kinase. M(2) receptors, which predominate in number, appear to facilitate M(3)-mediated contractions. M(2) receptors can also produce bladder contractions indirectly by reversing cAMP-dependent beta-adrenoceptor-mediated relaxation, although the physiological role of beta-adrenoceptors in detrusor relaxation is controversial. Emerging evidence suggests that muscarinic receptors in the urothelium/suburothelium can modulate the release of certain factors, which in turn may affect bladder function at the efferent or afferent axis. Currently, oxybutynin, tolterodine, darifenacin, solifenacin and trospium are the five major antimuscarinics approved for the treatment of OAB. Comparative clinical studies have shown that oxybutynin and solifenacin may be marginally more effective than tolterodine, although the latter seems to be better tolerated. Pharmacokinetic-pharmacodynamic analyses using plasma concentrations of 'total drug' indicate that, at therapeutic doses, the clinical efficacy of darifenacin and solifenacin may be driven primarily by selective M(3) receptor occupation, whereas the pharmacodynamic effects of pan-selective molecules (such as tolterodine, trospium) may potentially involve multiple receptors, including M(2) and M(3). Furthermore, high M(3) receptor occupation is the likely explanation for the greater propensity of darifenacin and oxybutynin to cause dry mouth and/or constipation. Although the recently introduced drugs represent a significant improvement over older drugs, especially with respect to the convenience of dosing schedule, their overall efficacy and tolerability profile is still less than optimal and patient persistence with therapy is low. Recent advances in basic research have not yet offered a clear discovery path for improving the therapeutic index of antimuscarinic molecules. There is still an unmet need for an antimuscarinic medicine with superior clinical effectiveness that can translate into better persistence on therapy.

Oxybutynin in Detrusor Overactivity

Oxybutynin has been used for the management of detrusor overactivity for over 30 years and has withstood medical scrutiny and the test of time throughout the world. Although several agents in the class of bladder relaxants have only recently been studied, oxybutynin's effectiveness in reducing urinary frequency and urge urinary incontinence is unquestioned in the medical literature. Oxybutynin is extremely safe and effective in almost every population including children, the elderly, and those who have neurogenic bladder. With more preparations available and more dosing flexibility than any other anticholinergic medication on the market, oxybutynin remains the "gold standard" for first-line therapy for patients who have detrusor overactivity.

Treatment of the overactive bladder syndrome with muscarinic receptor antagonists - a matter of metabolites?

Antagonists of muscarinic acetylcholine receptors, such as darifenacin, oxybutynin, propiverine, solifenacin, tolterodine, and trospium, are the mainstay of the treatment of the overactive bladder syndrome. Fesoterodine is a newer drug awaiting regulatory approval. We briefly review the pharmacological activity of their metabolites and discuss how active metabolites may contribute to their efficacy and tolerability in vivo. Except for trospium, and perhaps solifenacin, all of the above drugs form active metabolites, and their presence and activity need to be taken into consideration when elucidating relationships between pharmacokinetics and pharmacodynamics of these drugs. Moreover, the ratios between parent compounds and metabolites may differ depending on genotype of the metabolizing enzymes, concomitant medication, and/or drug formulation. Differential generation of active metabolites of darifenacin or tolterodine are unlikely to influence the overall clinical profile of these drugs in a major way because the active metabolites exhibit a similar pharmacological profile as the parent compound. In contrast, metabolites of oxybutynin and propiverine may behave quantitatively or even qualitatively differently from their parent compounds and this may have an impact on the overall clinical profile of these drugs. We conclude that more comprehensive studies of drug metabolites are required for an improved understanding of their clinical effects.

Transdermal drug delivery treatment for overactive bladder

Overactive bladder is commonly treated with oral anticholinergic drugs such as oxybutynin chloride. Although oral anticholinergic agents have been effective in controlling urinary urgency and incontinence, adverse events, particularly dry mouth, often cause patients to discontinue oral therapy and to endure incontinence. Oxybutynin can be delivered transcutaneously, maintaining the efficacy of oral oxybutynin while significantly minimizing side effects (e.g., dry mouth) that may complicate therapy. By avoiding hepatic and gastrointestinal metabolism of oxybutynin, less N-desethyloxybutynin (N-DEO) is produced and this compound is deemed to be responsible for anticholinergic side effects such as dry mouth. This novel oxybutynin formulation offers patients with OAB and urge urinary incontinence a well-tolerated option for managing the symptoms of overactive bladder.

Effect of the proton pump inhibitor omeprazole on the pharmacokinetics of extended-release formulations of oxybutynin and tolterodine

This study assessed the effect of the proton pump inhibitor omeprazole on the bioavailability of the extended-release formulations of oxybutynin and tolterodine. Forty-four healthy volunteers received each of 4 treatments in a 4-period crossover design. The treatments consisted of osmotically controlled extended-release oxybutynin chloride tablets at 10 mg/d or extended-release tolterodine tartrate capsules at 4 mg/d, with and without preceding treatment with 20 mg omeprazole daily for 4 days. Blood samples collected predose and at scheduled time points for 36 hours postdose were analyzed for oxybutynin and its active metabolite, N-desethyloxybutynin, or tolterodine and its active 5-hydroxymethyl metabolite, as appropriate. The AUCinfinity ratios for oxybutynin and its metabolite with and without prior omeprazole fell within the 80% to 125% range (accepted as the criterion for bioequivalence), as did those for tolterodine and its active moiety. The peak concentration ratios for oxybutynin and metabolite also conformed to this range; those for tolterodine did not. Increasing gastric pH with omeprazole does not substantially alter the pharmacokinetic properties of extended-release oxybutynin but may alter those of extended-release tolterodine.

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.

Preclinical Assessment of the Feasibility of Applying Controlled Release Oral Drug Delivery to a Lead Series of Atypical Antipsychotics

In this paper, we present a preclinical approach for evaluating the feasibility of applying controlled-release (CR) oral drug delivery to increase the duration of exposure and lower the C(max) of compounds in a lead series of short half-life atypical antipsychotics. Three lead compounds in the series had demonstrated potential pharmacological benefits for the treatment of psychosis, in preclinical studies. However, the compounds showed evidence of insufficient half-lives to enable a once-a-day (QD) product using immediate-release (IR) oral delivery. To evaluate and compare the potential for oral CR delivery to extend the duration of action and thereby enable QD administration, the in vitro solubility and permeability, and the duodenal and colonic absorption of three compounds in the series were measured. Based on the results, one candidate was selected for advancement that showed moderate in vitro solubility, but had the highest in vitro permeability and ratio of colonic to duodenal bioavailability (0.9) in the rat. The results from this study provided evidence that a CR drug delivery system could be used to extend the duration of exposure of the compounds in the series and a scientific basis for selecting one of the three compounds as a candidate.

Oxybutynin: an overview of the available formulations

Overactive bladder (OAB) is a common problem presented to by physicians. Standard treatment with antimuscarinic medication is directed at suppressing involuntary detrusor contractions by blocking the binding of acetylcholine to muscarinic receptors in the bladder. Oxybutynin chloride is the first of several antimuscarinic medications to be marketed for OAB. Although efficacious for treating OAB symptoms, the side effects and suboptimal dosing regimen decrease its utility. To improve patient compliance and tolerability, alternative delivery systems for oxybutynin have subsequently been developed and include a once-daily formulation and a transdermal system. The currently available formulations of oxybutynin are the subject of this review.

Management of overactive bladder with transdermal oxybutynin

In clinical trials, transdermal oxybutynin (OXY-TDS) has shown comparable efficacy and improved tolerability when compared with conventional pharmacotherapy. Systemic anticholinergic adverse effects are comparable to those with placebo, most likely owing to avoidance of first-pass hepatic metabolism and conversion of oxybutynin to N-desethyloxybutynin. OXY-TDS has predictable pharmacokinetic absorption and elimination parameters, as shown in both in vitro and in vivo studies. Consistent plasma concentrations of oxybutynin avoid labile peak and trough concentrations seen with immediate-release formulations, paralleling extended-release drug delivery. This novel drug delivery system has unique dermatologic skin application site reactions, including erythema and pruritus. Skin reactions are usually mild and can be minimized by varying the site of patch application. Most eczematous dermatologic reactions can be appropriately treated with a moderately potent topical corticosteroid cream. A small percentage of patients will discontinue therapy as a result of bothersome application site skin reactions.

Advantages for transdermal over oral oxybutynin to treat overactive bladder: Muscarinic receptor binding, plasma drug concentration, and salivary secretion

To clarify pharmacological usefulness of transdermal oxybutynin in the therapy of overactive bladder, we have characterized muscarinic receptor binding in rat tissues with measurement of plasma concentrations of oxybutynin and its metabolite N-desethyl-oxybutynin (DEOB) and salivation after transdermal oxybutynin compared with oral route. At 1 and 3 h after oral administration of oxybutynin, there was a significant increase in apparent dissociation constant (Kd) for specific [N-methyl-3H]scopolamine ([3H]NMS) binding in the rat bladder, submaxillary gland, heart, and colon compared with control values. Concomitantly, submaxillary gland and heart showed a significant decrease in maximal number of binding sites (Bmax) for [3H]NMS binding, which lasted until 24 h. Transdermal application of oxybutynin caused dose-dependent increases in Kd values for specific [3H]NMS binding in rat tissues. The increment of Kd values by transdermal oxybutynin was dependent on the application time. Plasma concentrations of oxybutynin and DEOB peaked at 1 h after oral oxybutynin. In contrast, plasma concentrations of oxybutynin increased slowly, depending on the transdermal application time of this drug until 12 h. Suppression of pilocarpine-induced salivation in rats due to transdermal oxybutynin was significantly weaker and more reversible than that by oral oxybutynin, which abolished salivary secretion. The present study has shown that transdermal oxybutynin binds significantly to rat bladder muscarinic receptors without producing both long-lasting occupation of exocrine receptors and cessation of cholinergic salivation evoked by oral oxybutynin. Thus, the present study provides further pharmacological basis for advantage of transdermal over oral oxybutynin in the therapy of overactive bladder.

In vivo demonstration of muscarinic receptor binding activity of N-desethyl-oxybutynin, active metabolite of oxybutynin

The present study was undertaken to characterize in vivo muscarinic receptor binding of N-desethyl-oxybutynin (DEOB), active metabolite of oxybutynin (anticholinergic agent), in the bladder, submaxillary gland, heart and colon of rats, in relation to the plasma concentrations and inhibition of salivation. In the in vitro experiment, DEOB, as well as oxybutynin, inhibited the concentration-dependently specific [3H]N-methylscopolamine (NMS) binding in rat tissues and the affinity of DEOB in the rat bladder, submaxillary gland and colon was significantly (about 2 times) greater than that of oxybutynin. Following i.v. injection of DEOB (2.73-27.3 micromol/kg), there were dose- and time-dependent increases in the apparent dissociation constant (Kd) for specific [3H]NMS binding in the bladder, submaxillary gland, heart and colon of rats, compared with control values, and the effect was similar to that by i.v. injection of oxybutynin (2.54-25.4 micromol/kg). Plasma concentrations of DEOB and oxybutynin in these rats showed dose- and time-dependent increases. The pilocarpine-induced salivary secretion in rats was equipotently reduced by the i.v. injection of DEOB and oxybutynin. In conclusion, it has been shown that intravenously injected DEOB, as well as oxybutynin, binds significantly to muscarinic receptors in rat tissues including the bladder and salivary gland and the receptor binding activity of DEOB is roughly similar to that of oxybutynin.

Effect of controlled-release delivery on the pharmacokinetics of oxybutynin at different dosages: severity-dependent treatment of the overactive bladder

OBJECTIVE

To assess the pharmacokinetics of a controlled-release formulation of oxybutynin (OROS-O, ALZA Corp., Mountain View, CA) at different dosages, compared with immediate-release oxybutynin (IR-O), and to determine the pharmacodynamic properties in the severity-dependent reduction of urge urinary incontinence (UUI).

PATIENTS AND METHODS

In all, 105 patients were enrolled in this multicentre, randomized, double-blind study. Individual dose titration was used to assess the minimum effective, maximum tolerated or maximum allowed dose of either OROS-O or IR-O. Blood samples were collected during maintenance therapy with frequent sampling to analyse for R-oxybutynin and R-desethyloxybutynin concentrations. Pre-dose plasma levels before dosing were obtained as the minimum concentrations achieved at steady state during the dosing regimen. In parallel, UUI episodes were assessed at baseline and during maintenance therapy at the final dose level.

RESULTS

For both IR-O and OROS-O, initial R-oxybutynin plasma concentrations increased in a dose-dependent fashion. For comparable dosages pre-dose plasma levels were higher for OROS-O than IR-O. After one dose of IR-O plasma concentrations peaked at approximately 27-fold after 1 h and decreased to baseline levels within 4-8 h. In contrast, plasma concentrations of R-oxybutynin remained constant for up to 24 h after taking OROS-O at all doses. The overall percentage reduction in weekly UUI episodes was 84% (to 4.8 episodes) and 88% (to 3.1 episodes) for OROS-O and IR-O, respectively (P < 0.05). Patients who titrated to final dose levels of 10, 15 and 20 mg OROS-O differed in their weekly UUI episodes at baseline (14.5, 30.3 and 42.0). Because of individual dose titration, UUI episodes/week were profoundly reduced at all applied doses (1.9-2.0, respectively). Fewer patients reported moderate to severe dry mouth with OROS-O than with IR-O (25% vs 46%, P < 0.05).

CONCLUSION

The pharmacokinetics of OROS-O are proportional to dose, with minimal fluctuations between peak and trough concentrations, as associated with IR-O. In clinical practice OROS-O may thus facilitate the highly effective severity-dependent treatment of UUI with flexible dose adaptations based on the patients' needs.

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.

Urinary incontinence: newer pharmacotherapeutic trends

PURPOSE OF REVIEW

Urinary incontinence is an under-reported epidemic with profound effects on quality of life. With recent pharmacologic advances, the belief that incontinence is an inevitable part of aging should be abandoned. Because many patients are unaware of curative options, they fail to report their symptoms and increase their risk of developing associated comorbid disease. Failure to diagnose and treat this disease in a timely manner increases society's economic burden associated with incontinence.

RECENT FINDINGS

Pharmacologic treatment of urge incontinence previously had limited treatment success because efficacious drugs were poorly tolerated, resulting in low patient compliance. Tolerance continues to be improved due to innovative new drugs and alternative delivery systems. While previous pharmacologic management of mild stress incontinence consisted of off-label agents with limited effectiveness, newly introduced drug therapy adds a viable, nonsurgical option for women with stress incontinence.

SUMMARY

The goal of this review is to update the clinician on the efficacy and tolerability of established and investigational pharmacologic modalities of therapy.

Drug effects on salivary glands: dry mouth

OBJECTIVE

To identify drugs associated with the complaint of dry mouth.

MATERIALS AND METHODS

MEDLINE was searched for papers 1980-2002 using keywords, oral, mouth, salivary, drugs, dry mouth and xerostomia, and relevant secondary references were hand-searched.

RESULTS

Evidence was forthcoming for a number of xerogenic drugs, especially antimuscarinic agents, some sympathomimetic agents, and agents affecting serotonin and noradrenaline uptake, as well as a miscellany of other drugs such as appetite suppressants, protease inhibitors and cytokines.

CONCLUSION

Dry mouth has a variety of possible causes but drugs--especially those with anticholinergic activity against the M3 muscarinic receptor--are the most common cause of reduced salivation.

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.