Vesicare (Solifenacin Succinate) - Description and Clinical Pharmacology

Description

VESIcare^®  (solifenacin succinate) is a muscarinic receptor antagonist. Chemically, solifenacin succinate is butanedioic acid, compounded with (1 S)-(3 R)-1-azabicyclo[2.2.2]oct-3-yl 3,4-dihydro-1-phenyl-2(1 H)-iso-quinolinecarboxylate (1:1) having an empirical formula of C₂₃H₂₆N₂O₂•C₄H₆O₄, and a molecular weight of 480.55. The structural formula of solifenacin succinate is:

Solifenacin succinate is a white to pale-yellowish-white crystal or crystalline powder. It is freely soluble at room temperature in water, glacial acetic acid, dimethyl sulfoxide, and methanol. Each VESIcare tablet contains 5 or 10 mg of solifenacin succinate and is formulated for oral administration. In addition to the active ingredient solifenacin succinate, each VESIcare tablet also contains the following inert ingredients: lactose monohydrate, corn starch, hypromellose 2910, magnesium stearate, talc, polyethylene glycol 8000 and titanium dioxide with yellow ferric oxide (5 mg VESIcare tablet) or red ferric oxide (10 mg VESIcare tablet).

Clinical Pharmacology

Solifenacin is a competitive muscarinic receptor antagonist. Muscarinic receptors play an important role in several major cholinergically mediated functions, including contractions of urinary bladder smooth muscle and stimulation of salivary secretion.

Pharmacokinetics

Absorption

After oral administration of VESIcare to healthy volunteers, peak plasma levels (C_max) of solifenacin are reached within 3 to 8 hours after administration, and at steady state ranged from 32.3 to 62.9 ng/mL for the 5 and 10 mg VESIcare tablets, respectively. The absolute bioavailability of solifenacin is approximately 90%, and plasma concentrations of solifenacin are proportional to the dose administered.

Effect of food

There is no significant effect of food on the pharmacokinetics of solifenacin.

Distribution

Solifenacin is approximately 98% (in vivo) bound to human plasma proteins, principally to ∝₁-acid glycoprotein. Solifenacin is highly distributed to non-CNS tissues, having a mean steady-state volume of distribution of 600L.

Metabolism

Solifenacin is extensively metabolized in the liver. The primary pathway for elimination is by way of CYP3A4; however, alternate metabolic pathways exist. The primary metabolic routes of solifenacin are through N-oxidation of the quinuclidin ring and 4R-hydroxylation of tetrahydroisoquinoline ring. One pharmacologically active metabolite (4R-hydroxy solifenacin), occurring at low concentrations and unlikely to contribute significantly to clinical activity, and three pharmacologically inactive metabolites (N-glucuronide and the N-oxide and 4R-hydroxy-N-oxide of solifenacin) have been found in human plasma after oral dosing.

Excretion

Following the administration of 10 mg of ¹⁴C-solifenacin succinate to healthy volunteers, 69.2% of the radioactivity was recovered in the urine and 22.5% in the feces over 26 days. Less than 15% (as mean value) of the dose was recovered in the urine as intact solifenacin. The major metabolites identified in urine were N-oxide of solifenacin, 4R-hydroxy solifenacin and 4R-hydroxy-N-oxide of solifenacin and in feces 4R-hydroxy solifenacin. The elimination half-life of solifenacin following chronic dosing is approximately 45-68 hours.

Pharmacokinetics in Special Populations

Age

Multiple dose studies of VESIcare in elderly volunteers (65 to 80 years) showed that C_max, AUC and t_1/2 values were 20-25% higher as compared to the younger volunteers (18 to 55 years). (See PRECAUTIONS, Geriatric Use).

Pediatric

The pharmacokinetics of solifenacin has not been established in pediatric patients.

Gender

The pharmacokinetics of solifenacin is not significantly influenced by gender.

Race

The number of subjects of different races studied is not adequate to make any conclusions on the effect of race on the pharmacokinetics of solifenacin.

Renal Impairment

VESIcare should be used with caution in patients with renal impairment. There is a 2.1-fold increase in AUC and 1.6-fold increase in t_1/2 of solifenacin in patients with severe renal impairment. Doses of VESIcare greater than 5 mg are not recommended in patients with severe renal impairment (CL_cr < 30 mL/min) (see PRECAUTIONS, DOSAGE AND ADMINISTRATION).

Hepatic Impairment

VESIcare should be used with caution in patients with reduced hepatic function. There is a 2-fold increase in the t_1/2 and 35% increase in AUC of solifenacin in patients with moderate hepatic impairment. Doses of VESIcare greater than 5 mg are not recommended in patients with moderate hepatic impairment (Child-Pugh B). VESIcare is not recommended for patients with severe hepatic impairment (Child-Pugh C) (see PRECAUTIONS, DOSAGE AND ADMINISTRATION).

Drug-Drug Interactions

Drugs Metabolized by Cytochrome P450

At therapeutic concentrations, solifenacin does not inhibit CYP1A1/2, 2C9, 2C19, 2D6, or 3A4 derived from human liver microsomes.

CYP3A4 Inhibitors

In vitro drug metabolism studies have shown that solifenacin is a substrate of CYP3A4. Inducers or inhibitors of CYP3A4 may alter solifenacin pharmacokinetics.

Ketoconazole Interaction Study

Following the administration of 10 mg of VESIcare in the presence of 400 mg of ketoconazole, a potent inhibitor of CYP3A4, the mean C_max and AUC of solifenacin increased by 1.5 and 2.7-fold, respectively. Therefore, it is recommended not to exceed a 5 mg daily dose of VESIcare when administered with therapeutic doses of ketoconazole or other potent CYP3A4 inhibitors (see PRECAUTIONS, DOSAGE AND ADMINISTRATION).

Oral Contraceptives

In the presence of solifenacin there are no significant changes in the plasma concentrations of combined oral contraceptives (ethinyl estradiol/levogestrel).

Warfarin

Solifenacin has no significant effect on the pharmacokinetics of R -warfarin or S -warfarin.

Digoxin

Solifenacin had no significant effect on the pharmacokinetics of digoxin (0.125 mg/day) in healthy subjects.

Cardiac Electrophysiology

The effect of 10 mg and 30 mg solifenacin succinate on the QT interval was evaluated at the time of peak plasma concentration of solifenacin in a multi-dose, randomized, double-blind, placebo and positive-controlled (moxifloxacin 400 mg) trial. Subjects were randomized to one of two treatment groups after receiving placebo and moxifloxacin sequentially. One group (n=51) went on to complete 3 additional sequential periods of dosing with solifenacin 10, 20, and 30 mg while the second group (n=25) in parallel completed a sequence of placebo and moxifloxacin. Study subjects were female volunteers aged 19 to 79 years. The 30 mg dose of solifenacin succinate (three times the highest recommended dose) was chosen for use in this study because this dose results in a solifenacin exposure that covers those observed upon co-administration of 10 mg VESIcare with potent CYP3A4 inhibitors (e.g. ketoconazole, 400 mg). Due to the sequential dose escalating nature of the study, baseline EKG measurements were separated from the final QT assessment (of the 30 mg dose level) by 33 days.

The median difference from baseline in heart rate associated with the 10 and 30 mg doses of solifenacin succinate compared to placebo was -2 and 0 beats/minute, respectively. Because a significant period effect on QTc was observed, the QTc effects were analyzed utilizing the parallel placebo control arm rather than the pre-specified intra-patient analysis. Representative results are shown in Table 1.

Table 1. QTc changes in msec (90%CI) from baseline at T_max (relative to placebo) ¹

Drug/Dose	Fridericia method (using mean difference)
Solifenacin 10 mg	2 (-3,6)
Solifenacin 30 mg	8 (4,13)

Moxifloxacin was included as a positive control in this study and, given the length of the study, its effect on the QT interval was evaluated in 3 different sessions. The placebo subtracted mean changes (90% CI) in QTcF for moxifloxacin in the three sessions were 11 (7, 14), 12 (8, 17), and 16 (12, 21), respectively.

The QT interval prolonging effect appeared greater for the 30 mg compared to the 10 mg dose of solifenacin. Although the effect of the highest solifenacin dose (three times the maximum therapeutic dose) studied did not appear as large as that of the positive control moxifloxacin at its therapeutic dose, the confidence intervals overlapped. This study was not designed to draw direct statistical conclusions between the drugs or the dose levels.

CLINICAL STUDIES

VESIcare was evaluated in four twelve-week, double-blind, randomized, placebo-controlled, parallel group, multicenter clinical trials for the treatment of overactive bladder in patients having symptoms of urinary frequency, urgency, and/or urge or mixed incontinence (with a predominance of urge). Entry criteria required that patients have symptoms of overactive bladder for ≥ 3 months duration. These studies involved 3027 patients (1811 on VESIcare and 1216 on placebo), and approximately 90% of these patients completed the 12-week studies. Two of the four studies evaluated the 5 and 10 mg VESIcare doses and the other two evaluated only the 10 mg dose. All patients completing the 12-week studies were eligible to enter an open label, long term extension study and 81% of patients enrolling completed the additional 40-week treatment period. The majority of patients were Caucasian (93%) and female (80%) with a mean age of 58 years.

The primary endpoint in all four trials was the mean change from baseline to 12 weeks in number of micturitions/24 hours. Secondary endpoints included mean change from baseline to 12 weeks in number of incontinence episodes/24 hours, and mean volume voided per micturition. The efficacy of VESIcare was similar across patient age and gender. The mean reduction in the number of micturitions per 24 hours was significantly greater with VESIcare 5 mg (2.3; p<0.001) and VESIcare 10 mg (2.7; p<0.001) compared to placebo, (1.4).

The mean reduction in the number of incontinence episodes per 24 hours was significantly greater with VESIcare 5 mg (1.5; p<0.001) and VESIcare 10 mg (1.8; p<0.001) treatment groups compared to placebo (1.1). The mean increase in the volume voided per micturition was significantly greater with VESIcare 5 mg (32.3 mL; p<0.001) and VESIcare 10 mg (42.5 mL; p<0.001) compared with placebo (8.5 mL).

The results for the primary and secondary endpoints in the four individual 12-week clinical studies of VESIcare are reported in Tables 2 through 5.

Table 2. Mean Change from Baseline to Endpoint for VESIcare (5 mg and 10 mg daily) and Placebo: 905-CL-015

Parameter	Placebo (N=253) Mean (SE)	VESIcare 5 mg (N=266) Mean (SE)	VESIcare 10 mg (N=264) Mean (SE)
Urinary Frequency (Number of Micturitions/24 hours) 1
Baseline Reduction P value vs. placebo	12.2 (0.26) 1.2 (0.21)	12.1 (0.24) 2.2 (0.18) <0.001	12.3 (0.24) 2.6 (0.20) <0. 001
Number of Incontinence Episodes/24 hours 2
Baseline Reduction P value vs. placebo	2.7 (0.23) 0.8 (0.18)	2.6 (0.22) 1.4 (0.15) <0.01	2.6 (0.23) 1.5 (0.18) <0.01
Volume Voided per micturition [mL]
Baseline Increase P value vs. placebo	143.8 (3.37) 7.4 (2.28)	149.6 (3.35) 32.9 (2.92) <0.001	147.2 (3.15) 39.2 (3.11) <0.001