Predictive Power of an In Vitro System to Assess Drug Interactions of an Antimuscarinic Medication: A Comparison of In Vitro and In Vivo Drug-Drug Interaction Studies of Trospium Chloride With Digoxin

Transporter-mediated drug-drug interactions: advancement in models, analytical tools, and regulatory perspective

Drug-drug interactions mediated by transporters are a serious clinical concern hence a tremendous amount of work has been done on the characterization of the transporter-mediated proteins in humans and animals. The underlying mechanism for the transporter-mediated drug-drug interaction is the induction or inhibition of the transporter which is involved in the cellular uptake and efflux of drugs. Transporter of the brain, liver, kidney, and intestine are major determinants that alter the absorption, distribution, metabolism, excretion profile of drugs, and considerably influence the pharmacokinetic profile of drugs. As a consequence, transporter proteins may affect the therapeutic activity and safety of drugs. However, mounting evidence suggests that many drugs change the activity and/or expression of the transporter protein. Accordingly, evaluation of drug interaction during the drug development process is an integral part of risk assessment and regulatory requirements. Therefore, this review will highlight the clinical significance of the transporter, their role in disease, possible cause underlying the drug-drug interactions using analytical tools, and update on the regulatory requirement. The recent in-silico approaches which emphasize the advancement in the discovery of drug-drug interactions are also highlighted in this review. Besides, we discuss several endogenous biomarkers that have shown to act as substrates for many transporters, which could be potent determinants to find the drug-drug interactions mediated by transporters. Transporter-mediated drug-drug interactions are taken into consideration in the drug approval process therefore we also provided the extrapolated decision trees from in-vitro to in-vivo, which may trigger the follow-up to clinical studies.

No. 283-Treatments for Overactive Bladder: Focus on Pharmacotherapy

OBJECTIVE

To provide guidelines for pharmacotherapy to treat overactive bladder syndrome (OAB).

OPTIONS

Pharmacotherapy for OAB includes anticholinergic (antimuscarinic) drugs and vaginal estrogen. Both oral and transdermal anticholinergic preparations are available.

OUTCOMES

To provide understanding of current available evidence concerning safety and clinical efficacy of pharmacotherapy for OAB; to guide selection of anticholinergic therapy based on individual patient characteristics.

EVIDENCE

The Cochrane Library and Medline were searched for articles published from 1950 to the present related to individual anticholinergic drugs. Review articles on management of refractory OAB were also examined. Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies. There were no date or language restrictions. Searches were updated on a regular basis and incorporated in the guideline to 2010.

VALUES

The quality of evidence is rated and recommendations are made using the criteria described by the Canadian Task Force on Preventive Health Care (Table 1).

BENEFITS, HARMS, AND COSTS

Anticholinergics are the mainstay of pharmacotherapy for OAB. Evidence for their efficacy is mostly derived from short-term phase III randomized drug trials. Placebo response is strong, and long-term follow-up and patient subjective outcome data are lacking. Care providers need to be well acquainted with the side effects of anticholinergics and select therapy based on individual patient parameters.

RECOMMENDATIONS

Treatments for overactive bladder: focus on pharmacotherapy

OBJECTIVE

To provide guidelines for pharmacotherapy to treat overactive bladder syndrome (OAB).

OPTIONS

Pharmacotherapy for OAB includes anticholinergic (antimuscarinic) drugs and vaginal estrogen. Both oral and transdermal anticholinergic preparations are available.

OUTCOMES

To provide understanding of current available evidence concerning safety and clinical efficacy of pharmacotherapy for OAB; to guide selection of anticholinergic therapy based on individual patient characteristics.

EVIDENCE

The Cochrane Library and Medline were searched for articles published from 1950 to the present related to individual anticholinergic drugs. Review articles on management of refractory OAB were also examined. Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies. There were no date or language restrictions. Searches were updated on a regular basis and incorporated in the guideline to 2010.

VALUES

The quality of evidence is rated and recommendations are made using the criteria described by the Canadian Task Force on Preventive Health Care (Table 1).

BENEFITS, HARMS, AND COSTS

Anticholinergics are the mainstay of pharmacotherapy for OAB. EVIDENCE for their efficacy is mostly derived from short-term phase III randomized drug trials. Placebo response is strong, and long-term follow-up and patient subjective outcome data are lacking. Care providers need to be well acquainted with the side effects of anticholinergics and select therapy based on individual patient parameters. Recommendations 1. Behavioural management protocols and functional electrical stimulation should be offered in the spectrum of effective primary treatments for overactive bladder syndrome. (I-A) 2. Oral oxybutynin, immediate and extended release, as well as transdermal oxybutynin, may be offered as treatment for overactive bladder syndrome, as they are associated with significant objective clinical improvement at 12 weeks. (I-A) Oxybutynin immediate release has superior cost-effectiveness but more side effects than other anticholinergics. (I-A) Adverse events associated with transdermal oxybutynin are fewer than with oral oxybutynin. (I-A) 3. Tolterodine, immediate and extended release, may be offered as treatment for overactive bladder syndrome, as it is associated with significant objective clinical improvement at 12 weeks. (I-A) 4. Trospium, immediate and extended release, may be offered as treatment for overactive bladder syndrome as it is associated with significant clinical improvement at 12 weeks. (I-A) Trospium is an adequate anticholinergic choice for overactive bladder syndrome patients with pre-existing cognitive impairment (II-B) and for overactive bladder syndrome patients taking concurrent CYP450 inhibitors. (III-B) 5. Solifenacin may be offered as treatment for overactive bladder syndrome, as it is associated with significant objective clinical improvement at 12 weeks. (I-A) Solifenacin may be an adequate anticholinergic choice for elderly overactive bladder syndrome patients or patients with pre-existing cognitive dysfunction. (I-B) 6. Darifenacin may be offered as treatment for overactive bladder syndrome, as it is associated with significant objective clinical improvement at 12 weeks. (I-A) Darifenacin is an adequate anticholinergic choice for overactive bladder syndrome patients with pre-existing cardiac concerns or cognitive dysfunction. (I-B) 7. Overactive bladder syndrome patients should be offered a choice between bladder training, functional electric stimulation, and anticholinergic therapy, as there is no difference in cure rates. Combination therapy does not have a clear advantage over one therapy alone. (I-A) 8. The choice of anticholinergic therapy should be guided by individual patient comorbidities, as objective efficacy of anticholinergic drugs is similar. (I-A) Dose escalation does not improve objective parameters and causes more anticholinergic adverse effects. It is, however, associated with improved subjective outcomes. (I-A) To decrease side effects, switching to a lower dose or using an extended release formulation or a transdermal delivery mechanism should be considered. (I-A) 9. Education on treatment efficacy, realistic expectations, and length of treatment should be offered to patients upon initiation of anticholinergic therapy, as continuation rates for anticholinergic therapy are low. (III-B) 10. Oral or transdermal estrogen supplementation should not be recommended for treatment of overactive bladder syndrome as its effects are comparable to placebo. (I-E) Vaginal estrogen can be suggested for subjective improvements in overactive bladder syndrome symptoms. (III-B) 11. Intravesical botulinum toxin injection and sacral nerve and posterior tibial nerve stimulation are clinically effective options for patients with overactive bladder syndrome unresponsive to conservative options, anticholinergics, or vaginal estrogen. (I-A).

Effect of concomitant administration of trospium chloride extended release on the steady-state pharmacokinetics of metformin in healthy adults

Background

Overactive bladder (OAB) is often associated with a number of co-morbid medical conditions, including diabetes mellitus. This may necessitate several concomitant treatments, thus creating the potential for drug–drug interactions (DDIs). Trospium is renally eliminated, not metabolized via cytochrome P450; therefore, cytochrome P450 DDIs are unlikely. However, coadministration with another renally eliminated drug (e.g., metformin) may theoretically result in a DDI.

Objective

The objective of this study was to evaluate the pharmacokinetics (plasma and urine) and safety/tolerability of the coadministration of trospium chloride extended release (XR) and metformin under steady-state conditions in healthy male and female subjects.

Methods

In a single-centre, randomized, open-label, two-group, two-period study in healthy males and females aged 18–45 years, 44 subjects received oral metformin 500 mg twice daily for 3.5 days during one period, and oral trospium chloride XR 60 mg once daily for 10 days, followed by trospium chloride XR 60 mg once daily for 4 days plus metformin 500 mg twice daily for 3.5 days during the other period. The two periods occurred in a crossover fashion, separated by a 3-day washout period.

Results

Trospium chloride XR coadministration did not alter metformin steady-state pharmacokinetics. Metformin coadministration reduced trospium steady-state maximum plasma concentration (by 34 %) and area under the concentration–time curve from 0–24 hours (by 29 %). Neither drug’s renal clearance was affected. No safety/tolerability issues of concern were observed with coadministration.

Conclusion

No dosage adjustment is necessary for metformin when coadministered with trospium chloride XR.

Once-daily trospium chloride 60 mg extended release in subjects with overactive bladder syndrome who use multiple concomitant medications: Post hoc analysis of pooled data from two randomized, placebo-controlled trials

BACKGROUND

Overactive bladder syndrome (OAB) is associated with various co-morbidities; treatment of these frequently results in multiple medication use (MMU) and the potential for drug-drug interactions, which may lead to adverse events and altered efficacy. With the aging population, the prevalence of MMU is likely to increase in the overall population, an increase due in part to treatment of co-morbidities that are more common in the elderly.

OBJECTIVE

To assess safety and efficacy outcomes with once-daily trospium chloride 60 mg extended release (XR) in subjects with OAB who were taking multiple concomitant medications.

STUDY DESIGN

Post hoc analysis of pooled data from two 12-week randomized, placebo-controlled studies.

SETTING

Urology, urogynaecology, and primary care offices/clinics.

PATIENTS

Subjects aged ≥18 years with OAB for ≥6 months who had baseline urinary frequency of ≥30 toilet voids/3 days; ≥1 'severe' urgency severity rating/3 days (on the Indevus Urgency Severity Scale); and pure urge urinary incontinence (UUI) or mixed incontinence with predominant UUI, with ≥3 UUI episodes/3 days. This analysis utilized data from subjects taking concomitant medications, focusing on those taking seven or more.

INTERVENTION

Once-daily trospium chloride 60 mg XR or placebo.

MAIN OUTCOME MEASURE

Predictors of treatment-emergent adverse events (TEAEs) identified by multivariate logistic regression analysis.

RESULTS

Concomitant medications were being taken by 1135 subjects (placebo, n = 576; trospium chloride XR, n = 559); 427 were taking seven or more (placebo, n = 199; trospium XR, n = 228). Among subjects taking seven or more concomitant medications, there was no significant difference between trospium chloride XR and placebo in the proportion of subjects experiencing one or more TEAEs (64.5% vs 58.3%). Logistic regression analysis indicated that the odds of experiencing a TEAE were influenced by concomitant medication use, but not by randomization assignment to trospium chloride XR or to placebo, suggesting that concomitant drugs contribute more to TEAEs than trospium chloride XR. Compared with subjects taking one to two concomitant medications, the adjusted odds ratio (OR) for experiencing any TEAE was 3.39 (95% CI 2.39, 4.80; p < 0.0001) for subjects taking seven or more concomitant medications. The adjusted OR for experiencing any TEAE for subjects randomized to active treatment compared with placebo was 1.19 (95% CI 0.85, 1.67; p = 0.31). Efficacy in subjects taking seven or more concomitant medications was similar to that in the overall pooled study population.

CONCLUSIONS

Trospium chloride XR does not increase the likelihood of a TEAE compared with placebo. The probability of experiencing a TEAE was significantly influenced by use of multiple concomitant medications. Trospium chloride XR was as effective in subjects with OAB taking seven or more concomitant medications as in the overall pooled study population. The data support the conclusion that trospium chloride XR is safe and effective in patients with OAB taking multiple concomitant medications.

Trospium chloride once-daily extended release is effective and well tolerated for the treatment of overactive bladder syndrome: an integrated analysis of two randomised, phase III trials

BACKGROUND

Trospium chloride is an antimuscarinic agent with a hydrophilic polar quaternary amine structure that is minimally metabolised by hepatic cytochrome P450 and is actively excreted in the urine, each of which confers a potential benefit with regard to efficacy and tolerability.

PURPOSE

We analysed pooled data from two identically designed phase III trials of a once-daily, extended-release (XR) formulation of trospium chloride (trospium XR 60-mg capsules) in subjects with overactive bladder syndrome (OAB).

METHODS

Adults with OAB of > or = 6 months' duration with urinary urgency, frequency and > or = 1 urge urinary incontinence (UUI) episode/day were enrolled in these multicentre, parallel-group, double-blind trials. Participants were randomised (1 : 1) to receive trospium XR 60 mg or placebo for 12 weeks. Primary efficacy variables were changes in urinary frequency and the number of UUI episodes/day. Adverse events (AEs) were recorded throughout.

RESULTS

In total, 1165 subjects were randomised (trospium XR, 578; placebo, 587). At baseline, subjects averaged 12.8 toilet voids/day and 4.1 UUI episodes/day. Compared with placebo, subjects treated with trospium XR had significantly greater reductions from baseline in the mean number of toilet voids/day (-1.9 vs. -2.7; p < 0.001) and UUI episodes/day (-1.8 vs. -2.4; p < 0.001) at week 12. The most frequent AEs considered possibly related to study treatment were dry mouth (trospium XR, 10.7%; placebo, 3.7%) and constipation (trospium XR, 8.5%; placebo, 1.5%). Notably, rates of central nervous system (CNS) AEs were lower with trospium XR vs. placebo (dizziness: 0.2% vs. 1.0%; headache: 1.4% vs. 2.4%).

CONCLUSIONS

Treatment with trospium XR resulted in statistically significant improvements in both of the dual primary and all of the secondary outcome variables. Trospium XR demonstrated favourable rates of AEs, particularly CNS AEs (numerically lower than with placebo) and dry mouth (lower than previously reported with trospium immediate-release, although not compared in a head-to-head study).

The role of p-glycoprotein in limiting brain penetration of the peripherally acting anticholinergic overactive bladder drug trospium chloride

The aim of the present study was to characterize the role of the drug-efflux transporter P-glycoprotein (P-gp) for the disposition of trospium chloride, a widely used anticholinergic drug for the treatment of overactive bladder. P-gp-deficient mdr1a,b(-/-) knockout mice were given either 1 mg/kg trospium chloride orally or 1 mg/kg intravenously to analyze brain penetration, intestinal secretion, and hepatobiliary excretion of the drug. The concentrations of trospium chloride in the brain were up to 7 times higher in the mdr1a,b(-/-) knockout mice compared with wild-type mice (p < 0.05), making P-gp a limiting factor for the blood-brain barrier penetration of this drug. Moreover, the residence time of the drug in the central nervous system was significantly prolonged in mdr1a,b(-/-) knockout mice. Apart from the blood-brain barrier, P-gp also had significant effects on the overall pharmacokinetics of trospium chloride. In the mdr1a,b(-/-) knockout mice, hepatobiliary excretion and intestinal secretion were significantly reduced compared with the wild-type mice. Our study indicates that the multidrug resistance transporter P-gp is a major determinant for the distribution of trospium chloride in the body and highly restricts its entry into the brain.

Digoxin – a therapeutic agent and mechanistic probe: review of liquid chromatographic mass spectrometric methods and recent nuances in the clinical pharmacology attributes of digoxin

Digoxin is an important therapeutic agent for the treatment of congestive cardiac failure. In spite of its narrow therapeutic index, digoxin has been used extensively by the medical community and, lately, the use of digoxin as a mechanistic probe for p-glycoprotein transporter activity has increased. This review describes recent trends in the bioanalysis of digoxin, where scores of liquid chromatographic–mass spectrometric assays have been successfully employed to measure digoxin in preclinical, clinical and mechanistic studies. It provides various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectral conditions, for example, to enable the development of sound bioanalytical methods for digoxin. Some recent updates with regard to clinical pharmacology, absorption and disposition aspects of digoxin have been included. Overall, liquid chromatographic–mass spectrometric assays represent an important tool for many future preclinical, clinical and mechanistic probe studies that would probe digoxin with or without other coadministered substrates.

Trospium chloride treatment of overactive bladder

OBJECTIVE

To review the pharmacology, pharmacokinetics, safety, and clinical application of trospium chloride for the management of overactive bladder (OAB).

DATA SOURCES

Clinical literature including both primary sources and review articles was accessed through MEDLINE, International Pharmaceutical Abstracts, and Cochrane databases from 1980 through January 8, 2009. Search terms included overactive bladder, urge urinary incontinence, muscarinic receptor antagonists, and urinary frequency. Further data sources were identified from bibliographies of selected articles.

STUDY SELECTION AND DATA EXTRACTION

Basic pharmacology data were extracted from animal studies and pharmacokinetic data were gathered from human studies. Multicenter, parallel, randomized, double-blind, placebo-controlled studies were included to describe the efficacy and adverse effects of trospium.

DATA SYNTHESIS

Trospium chloride is an antimuscarinic agent indicated for the treatment of OAB with symptoms of urge urinary incontinence, urgency, and urinary frequency. Trospium has 3 chemical and pharmacokinetic properties unique among antimuscarinic agents: it is a positively charged quaternary ammonium compound with minimal central nervous system penetration; it is not metabolized by the cytochrome P450 system, resulting in a lower tendency for drug interactions; and it is excreted mainly unchanged in the urine as the active parent compound, providing local activity to achieve early onset of clinical effect and prolonged efficacy. In two 12-week, randomized, placebo-controlled clinical studies in adults with OAB, trospium 20 mg twice daily was more effective than placebo in reducing the number of micturitions per 24 hours, reducing the number of urge incontinence episodes per week, and increasing the volume of urine voided per micturition. Placebo-controlled trials report efficacy with trospium in treatment of OAB; comparative trials with other anticholinergic agents are limited. Current therapy of OAB consists primarily of anticholinergic drugs such as oxybutynin, which are associated with therapy-limiting adverse effects. Because the prevalence of OAB is greatest among the elderly, safety considerations regarding renal function must be noted, with dosage adjustment required in patients with severe renal impairment.

CONCLUSIONS

Whether the pharmacodynamic properties of trospium make it superior to other therapies will require considerable additional experience with the drug. For now, it appears to be a feasible alternative for patients who cannot tolerate oxybutynin.

Trospium Chloride: Distinct Among Other Anticholinergic Agents Available for the Treatment of Overactive Bladder

Trospium chloride is an antimuscarinic agent indicated for the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency, and urinary frequency. It has been available in Europe for over 20 years and in the United States since May 2004. Trospium has pharmacologic properties that are distinct from other antimuscarinic agents. The safety and efficacy profiles of trospium and how its pharmacologic properties contribute to these profiles form the basis for this review. The low incidence of adverse event of central nervous system effects and the efficacy parameters of "urgency" and "onset of action" are highlighted.