Bimal Malhotra

A comprehensive non-clinical evaluation of the CNS penetration potential of antimuscarinic agents for the treatment of overactive bladder

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT This study provides antimuscarinic agents for overactive bladder (OAB) display variable association with side effects mediated by the central nervous system (CNS), which may be of particular concern in the elderly. Adverse effects on CNS functioning are related to muscarinic receptor subtype selectivity and the ability of the agent to cross the blood-brain barrier, where P-gp plays a role in limiting permeability. WHAT THIS STUDY ADDS This study provides a parallel investigation of CNS penetration of antimuscarinic OAB agents in vivo and assessment of physical properties and permeability in cell monolayers in vitro. It adds further understanding of the roles of passive transcellular permeability and P-gp in determining CNS penetration of antimuscarinic OAB agents. It also enables a comparison of CNS side-effect profiles of OAB agents with preclinical CNS penetration data. AIMS To assess and compare the mechanisms of central nervous system (CNS) penetration of antimuscarinic overactive bladder (OAB) agents. METHODS Physical properties were computed or compiled from the literature. Rats were administered 5-hydroxymethyl tolterodine (HMT), darifenacin, oxybutynin, solifenacin, tolterodine or trospium subcutaneously. At 1 h postdose, plasma, brain and cerebrospinal fluid (CSF) concentrations were determined using LC-MS/MS assays. Brain and plasma protein binding were determined in vitro. Permeability in the presence and absence of the efflux transporter P-glycoprotein (P-gp) was assessed in RRCK and MDCK-MDR1 transwell assays. RESULTS Oxybutynin displayed extensive CNS penetration, with brain:plasma ratios (B:P), unbound brain:unbound plasma ratios (Kp,free) and CSF:free plasma ratios each >1. Tolterodine (B:P = 2.95, Kp,free = 0.23 and CSF:free plasma = 0.16) and solifenacin (B:P = 3.04, Kp,free = 0.28 and CSF:free plasma = 1.41) showed significant CNS penetration but with some restriction from CNS as indicated by Kp,free values significantly <1. 5-HMT, darifenacin and trospium displayed much lower B:P (0.03-0.16), Kp,free (0.01-0.04) and CSF:free plasma (0.004-0.06), consistent with poor CNS penetration. Permeability in RRCK cells was low for trospium (0.63 × 10(-6) cm s(-1) ), moderate for 5-HMT (11.7 × 10(-6) cm s(-1) ) and high for darifenacin, solifenacin, tolterodine and oxybutynin (21.5-38.2 × 10(-6) cm s(-1) ). In MDCK-MDR1 cells 5-HMT, darifenacin and trospium, were P-gp substrates, whereas oxybutynin, solifenacin and tolterodine were not P-gp substrates. CONCLUSIONS Brain penetration was low for antimuscarinics that are P-gp substrates (5-HMT, darifenacin and trospium), and significant for those that are not P-gp substrates (oxybutynin, solifenacin and tolterodine). CNS adverse events reported in randomized controlled clinical trials show general alignment with the preclinical data described in this study.

Effects of Food on the Clinical Pharmacokinetics of Anticancer Agents: Underlying Mechanisms and Implications for Oral Chemotherapy

Pharmacokinetic interactions between food and orally administered drugs involve changes mainly in the absorption and metabolism of a drug, and may have clinical implications. Such interactions, in particular, may be of major clinical significance for cancer chemotherapy since the majority of anticancer agents are toxic, have a low therapeutic index and are administered long term, most often in combination with other cytotoxic agents. The purpose of this review is to compare the pharmacokinetic profiles of various anticancer drugs, including chemopreventive agents that have been examined previously in fasted and fed conditions, and to discuss the underlying basis/mechanisms of food effect in light of a drug’s physicochemical and pharmacokinetic properties. Clinical pharmacokinetic parameters such as maximum concentration, area under the concentration-time curve, time to maximum concentration and half-life for each drug are compared in fasted and fed states, and specific dietary recommendations are summarised accordingly. In addition, the effects of food on the metabolite kinetics and pharmacodynamic responses, and the potential role of food effect in the modulation of oral biovariability and multidrug resistance have been extensively discussed. Overall, this comprehensive pharmacokinetic analysis indicates that a broad spectrum of food effects is seen among anticancer agents because of diverse factors regulating each drug’s oral bioavailability and its interactions with food. The consideration of such effects is important, as it could lead to more rational pharmacological monitoring and possibly improve the oral chemotherapy of cancer in children, adults and the elderly.

Thorough QT Study with Recommended and Supratherapeutic Doses of Tolterodine

The objective of our study was to determine the QTc effects of tolterodine. A crossover‐design thorough QT study of recommended (2 mg twice daily) and supratherapeutic (4 mg twice daily) doses of tolterodine, moxifloxacin (400 mg once daily), and placebo was performed. Electrocardiograms (ECGs) and pharmacokinetic samples were obtained on days 1–4; time‐matched baseline ECGs were taken on day 0. Mean placebo‐subtracted change from baseline Fridericia‐corrected QT (QTcF) during peak drug exposure on day 4 was the primary end point. Mean QTcF prolongation of moxifloxacin was 8.9 ms (machine‐read) and 19.3 ms (manual‐read). At recommended and supratherapeutic tolterodine doses, mean QTcF prolongation was 1.2 and 5.6 ms (machine‐read), respectively, and 5.0 and 11.8 ms (manual‐read), respectively. The QTc effect of tolterodine was lower than moxifloxacin. No subject receiving tolterodine exceeded the clinically relevant thresholds of 500 ms absolute QTc or 60 ms change from baseline. In conclusion, tolterodine does not have a clinically significant effect on QT interval.

Evaluation of Cognitive Function in Healthy Older Subjects Treated with Fesoterodine

Abstract Objective: To evaluate the cognitive effects of fesoterodine 4 and 8 mg versus placebo in healthy older adults. Methods: This was an active– and placebo–controlled, double–blind, double–dummy crossover study conducted using healthy volunteers (aged 65–85 years) with baseline Mini–Mental State Examination score ≥ 26. The study comprised 4 treatment periods: fesoterodine 4 mg for 6 days; fesoterodine 4 mg for 3 days followed by fesoterodine 8 mg for 3 days; placebo for 6 days; and placebo for 6 days with alprazolam 1 mg on day 6. The treatment sequence was randomized, with a 3– to 6–day washout between periods. Subjects completed computer–based cognitive assessments and the Rey Auditory Verbal Learning Test on day 1 (before dosing) and day 6 (after dosing) of each period. The primary endpoint was the Detection task; secondary endpoints were the Identification task, 1–card learning task, Continuous Paired Associate Learning task, Groton Maze Learning Task, and the Rey Auditory Verbal Learning Test. Results: Among 18 subjects in the per protocol set, changes from baseline to day 6 with fesoterodine 4 and 8 mg were not significantly different from placebo for any endpoint (P < 0.05); alprazolam produced significant impairment in all endpoints versus placebo (P < 0.05). No serious adverse events were reported; the most common adverse events were dry mouth for fesoterodine and sedation for alprazolam. No sedation was reported with fesoterodine. Conclusion: In healthy older adults, fesoterodine 4 and 8 mg once daily had no statistically significant effects versus placebo on any cognitive function assessed, including memory; alprazolam 1 mg produced statistically significant deterioration.

A meta-analysis of the placebo response in antimuscarinic drug trials for overactive bladder

BackgroundThe purpose of this analysis was to characterize the placebo response in antimuscarinic drug trials for OAB, based on changes in commonly-used efficacy endpoints.MethodsPlacebo arm data for incontinence episodes, micturitions, voided volume and study characteristics were extracted from randomized placebo controlled antimuscarinic drug trials in OAB, from studies identified in a prior meta-analysis, and from a systematic review of more recently published studies. Relationships between variables were examined using linear regression, and changes in endpoints were analyzed by a meta-analysis approach. The effect of placebo arm size and magnitude of placebo response on probability of successful study outcome was analyzed using an ANOVA model.ResultsChanges in the placebo arms for all 3 endpoints were substantial and statistically significant, and highly heterogeneous. There were significant associations between baseline and change scores for some but not all of the endpoints. More recent studies tended to have more subjects than earlier studies, and there were positive associations between probability of achieving statistically significant results and size of the placebo arm. The magnitude of changes in placebo arms did not appear to influence the likelihood of the study to be statistically significant.ConclusionThis analysis confirms earlier observation that the placebo response in OAB trials is substantial and highly heterogeneous. There are multiple potential reasons for this; however, these could not be explored in this analysis of study-level data. Two approaches may be used in clinical trials to manage high placebo effect: recruitment of 1) greater numbers of patients and/or 2) more severely affected patients; however, only the former approach is associated with increased probability of successful study outcome.

Safety of intravenous nitroglycerin after administration of sildenafil citrate to men with coronary artery disease: a double-blind, placebo-controlled, randomized, crossover trial.

Objective:Although contraindicated, there are situations when a patient who has recently taken a phosphodiesterase 5 inhibitor (e.g., sildenafil) might need intravenous nitroglycerin (NTG) treatment. This study determined if, and at what dose, intravenous NTG could be administered safely to men with coronary artery disease who had recently ingested sildenafil. Design:Double-blind, placebo-controlled, randomized, crossover trial. Setting:Four clinical practice sites in Canada, Scotland, and the United States. Patients:A total of 34 men (≥35 yrs) with a history of angina pectoris and coronary artery disease (>50% stenosis of at least one coronary artery), most of whom were taking antihypertensives. Interventions:Sildenafil (100 mg) or placebo (single dose; crossover after 3–7 days) followed 45 mins later by escalating doses of intravenous NTG (160 &mgr;g/min maximum). Measurements and Main Results:After sildenafil, there were slightly greater maximum (supine) blood pressure decreases and heart rate increases (e.g., 4 to 6 mm Hg [systolic] and ≤1 beat/min, at NTG doses of ≤80 &mgr;g/min) than after placebo. The median maximum tolerated NTG dose (range) was 80 (0–160) &mgr;g/min for sildenafil vs. 160 (20–160) &mgr;g/min for placebo (adjusted mean ± se, 77 ± 7 vs. 127 ± 7; p < .0001; analysis of variance), and NTG 160 &mgr;g/min was tolerated by eight (25%) and 19 (59%) men, respectively (p = .0008). Treatment-related adverse events were mostly mild/moderate hypotension, headache, and dizziness, which are often associated with NTG alone. Sildenafil and metabolite plasma concentrations were lower than previously reported in healthy men. Conclusions:With close monitoring of blood pressure and heart rate, men with stable coronary artery disease who have taken sildenafil may tolerate intravenous NTG (≤160 &mgr;g/min) with low starting dosage and gradual upward titration. The hemodynamic response might be different in subgroups not specifically examined in the study (e.g., men presenting with acute coronary symptoms). The explanation for the lower than expected plasma concentrations remains uncertain.

Comparison of pharmacokinetic variability of fesoterodine vs. tolterodine extended release in cytochrome P450 2D6 extensive and poor metabolizers

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Tolterodine and 5-hydroxymethyl tolterodine (5-HMT) are equipotent active moieties of tolterodine; 5-HMT is the singular active moiety of fesoterodine. The formation of 5-HMT from tolterodine occurs via CYP2D6, and some subjects are poor metabolizers CYP2D6. On the other hand, the formation of 5-HMT from fesoterodine occurs via ubiquitous esterases. Cross-study comparisons of data from phase 1 studies suggest that active moiety exposures are considerably more variable following tolterodine extended release vs. fesoterodine. WHAT THIS STUDY ADDS This head-to-head study confirmed the findings of reduced pharmacokinetic variability of fesoterodine and further delineates that tolterodine, and not 5-HMT, was the principal source of variability after administration of tolterodine extended release. The data suggest that fesoterodine delivers 5-HMT consistently, regardless of CYP2D6 status, with up to 40% higher bioavailability compared with tolterodine. AIMS Tolterodine and 5-hydroxymethyl tolterodine (5-HMT) are equipotent active moieties of tolterodine; 5-HMT is the singular active moiety of fesoterodine. Formation of 5-HMT from fesoterodine and tolterodine occurs via esterases and CYP2D6 respectively. This randomized, crossover, open-label, multiple-dose study in CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs) compared the pharmacokinetics of fesoterodine vs. tolterodine extended release (ER). METHODS Subjects received fesoterodine and tolterodine ER with a ≥3-day washout period. Treatment comprised 4-mg once daily doses for 5 days escalated to 8-mg once daily for 5 days. Pharmacokinetics of active moieties were compared by drug, dose and genotype. RESULTS Active moiety exposures following fesoterodine and tolterodine ER increased proportional to dose in EMs and PMs. In EMs only, coefficients of variation for AUC and C(max) following fesoterodine (up to 46% and 48% respectively) were lower than those following tolterodine ER (up to 87% and 87% respectively). Following fesoterodine and tolterodine ER administration, active moiety exposures ranged up to sevenfold and 40-fold respectively. Mean urinary excretion of 5-HMT following fesoterodine 4 and 8 mg, respectively, was 0.44 and 0.89 mg in EMs and 0.60 and 1.32 mg in PMs. Following tolterodine ER 4 and 8 mg, it was 0.38 and 0.71 mg respectively (EMs only). Renal clearance was similar regardless of administered drug, dose or genotype. CONCLUSIONS Tolterodine, not 5-HMT, was the principal source of variability after tolterodine ER administration. Fesoterodine delivers 5-HMT with less variability than tolterodine, regardless of CYP2D6 status, with up to 40% higher bioavailability. The pharmacokinetics of fesoterodine were considerably less variable than TER.

Assessment of the Effects of Renal Impairment on the Pharmacokinetic Profile of Fesoterodine

The effects of renal impairment on the pharmacokinetics of a single 4‐mg oral dose of fesoterodine are assessed in 8 healthy subjects and 8 subjects each with mild, moderate, or severe renal impairment. Compared with findings in healthy subjects, the maximum concentration in plasma of 5‐hydroxymethyl tolterodine (5‐HMT), the principal active moiety of fesoterodine, increases by 1.4‐, 1.5‐, and 2.0‐fold and area under the curve increases by 1.6‐, 1.8‐, and 2.3‐fold in subjects with mild, moderate, and severe renal impairment, respectively. There is a clear correlation between the renal clearance of 5‐HMT and creatinine clearance. The median time of observed maximum drug concentration (5–6 hours) and mean terminal half‐life (6–7 hours) of 5‐HMT are unaffected by renal impairment. The unbound fraction of 5‐HMT in plasma (0.43–0.54 ng/mL) is comparable across all groups. In conclusion, because of the involvement of both metabolic and renal elimination pathways, only modest increases in 5‐HMT exposures are observed in patients with renal impairment.

Effects of fesoterodine on the pharmacokinetics and pharmacodynamics of warfarin in healthy volunteers

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Drug-drug interactions with warfarin are common with potentially harmful consequences. Preclinical in vitro studies suggest that fesoterodine or 5-hydroxymethyl tolterodine are not likely to affect warfarin metabolism, but a lack of interaction has not been demonstrated in a clinical study. WHAT THIS STUDY ADDS This study shows that the pharmacokinetics and pharmacodynamics of warfarin 25 mg in healthy adults are unaffected by fesoterodine 8 mg, and that co-administration of warfarin 25 mg and fesoterodine 8 mg is safe and well tolerated. AIMS To confirm the lack of an interaction of fesoterodine 8 mg with warfarin pharmacokinetics and pharmacodynamics in healthy adults. METHODS In this open-label, two-treatment, crossover study, subjects (n= 14) aged 20-41 years with normal prothrombin time (PT) and International Normalized Ratio (INR) were randomized to receive a single dose of warfarin 25 mg alone in one period and fesoterodine 8 mg once daily on days 1-9 with a single dose of warfarin 25 mg co-administered on day 3 in the other period. There was a 10-day washout between treatments. Pharmacokinetic endpoints were area under the plasma concentration-time curve from time 0 to infinity (AUC(0,∞)), maximum plasma concentration (C(max)), AUC from time 0 to the time of the last quantifiable concentration (AUC(0,last)), time to C(max) (t(max) ), and half-life (t(1/2)) for S- and R-warfarin. Pharmacodynamic endpoints were area under the INR-time curve (AUC(INR) ), maximum INR (INR(max)), area under the PT-time curve (AUC(PT)) and maximum PT (PT(max)). RESULTS Across all pharmacokinetic and pharmacodynamic comparisons, the point estimates of treatment ratio (warfarin co-administered with fesoterodine vs. warfarin alone) were 92-100%. The 90% confidence intervals for the ratios of the adjusted geometric means were contained within (80%, 125%). There were no clinically relevant changes in laboratory tests, vital signs or ECG recordings. CONCLUSIONS The pharmacokinetics and pharmacodynamics of warfarin 25 mg in healthy adults are unaffected by fesoterodine 8 mg. Concomitant administration of fesoterodine and warfarin was well tolerated.

Effects of the moderate CYP3A4 inhibitor, fluconazole, on the pharmacokinetics of fesoterodine in healthy subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Available data suggest that fesoterodine dosage should not exceed 4 mg once daily when taken concomitantly with potent CYP3A4 inhibitors, such as ketoconazole. Currently, no information is available on whether dose adjustment is necessary when fesoterodine is administered with a moderate CYP3A4 inhibitor. WHAT THIS STUDY ADDS This study shows that adjustment of fesoterodine dose is not warranted when co-administered with a moderate CYP3A4 inhibitor. AIMS To assess the effects of fluconazole, a moderate CYP3A4 inhibitor, on the pharmacokinetics (PK) and safety/tolerability of fesoterodine. METHODS In this open-label, randomized, two-way crossover study, 28 healthy subjects (18-55 years) received single doses of fesoterodine 8 mg alone or with fluconazole 200 mg. PK endpoints, including the area under the plasma concentration-time curve from 0 to infinity (AUC(0,∞)), maximum plasma concentration (C(max) ), time to C(max) (t(max) ), and half-life (t(1/2) ), were assessed for 5-hydroxymethyl tolterodine (5-HMT), the active moiety of fesoterodine. RESULTS Concomitant administration of fesoterodine with fluconazole increased AUC(0,∞) and C(max) of 5-HMT by approximately 27% and 19%, respectively, with corresponding 90% confidence intervals of (18%, 36%) and (11%, 28%). There was no apparent effect of fluconazole on 5-HMT t(max) or t(½) . Fesoterodine was generally well tolerated regardless of fluconazole co-administration, with no reports of death, serious adverse events (AEs) or severe AEs. Following co-administration of fesoterodine with fluconazole, 13 subjects (48%) experienced a total of 40 AEs; following administration of fesoterodine alone, six subjects (22%) experienced a total of 19 AEs. The majority of AEs were of mild intensity. There were no clinically significant changes in laboratory or physical examination parameters. CONCLUSION Fesoterodine 8 mg single dose was well tolerated when administered alone or with fluconazole. Based on the observed increase in 5-HMT exposures being within the inherent variability of 5-HMT pharmacokinetics, adjustment of fesoterodine dose is not warranted when co-administered with a moderate CYP3A4 inhibitor provided they are not also inhibitors of transporters.