CLINICAL PHARMACOLOGY
Mechanism Of Action
Tolterodine acts as a competitive antagonist of acetylcholine at postganglionic muscarinic receptors.
Both urinary bladder contraction and salivation are mediated via cholinergic muscarinic receptors.
After oral administration, tolterodine is metabolized in the liver, resulting in the formation of 5-
hydroxymethyl tolterodine (5-HMT), the major pharmacologically active metabolite. 5-HMT, which
exhibits an antimuscarinic activity similar to that of tolterodine, contributes significantly to the
therapeutic effect. Both tolterodine and 5-HMT exhibit a high specificity for muscarinic receptors,
since both show negligible activity or affinity for other neurotransmitter receptors and other potential
cellular targets, such as calcium channels.
Pharmacodynamics
Tolterodine has a pronounced effect on bladder function. Effects on urodynamic parameters before and
1 and 5 hours after a single 6.4 mg dose of tolterodine immediate release were determined in healthy
volunteers. The main effects of tolterodine at 1 and 5 hours were an increase in residual urine,
reflecting an incomplete emptying of the bladder, and a decrease in detrusor pressure. These findings
are consistent with an antimuscarinic action on the lower urinary tract.
Cardiac Electrophysiology
The effect of 2 mg BID and 4 mg BID of DETROL immediate release (tolterodine IR) tablets on the QT
interval was evaluated in a 4-way crossover, double-blind, placebo- and active-controlled
(moxifloxacin 400 mg QD) study in healthy male (N=25) and female (N=23) volunteers aged 18–55
years. Study subjects [approximately equal representation of CYP2D6 extensive metabolizers (EMs) and
poor metabolizers (PMs)] completed sequential 4-day periods of dosing with moxifloxacin 400 mg QD,
tolterodine 2 mg BID, tolterodine 4 mg BID, and placebo. The 4 mg BID dose of tolterodine IR (two
times the highest recommended dose) was chosen because this dose results in tolterodine exposure
similar to that observed upon coadministration of tolterodine 2 mg BID with potent CYP3A4 inhibitors
in patients who are CYP2D6 poor metabolizers [see DRUG INTERACTIONS]. QT interval was
measured over a 12-hour period following dosing, including the time of peak plasma concentration
(Tmax) of tolterodine and at steady state (Day 4 of dosing).
Table 2 summarizes the mean change from baseline to steady state in corrected QT interval (QTc)
relative to placebo at the time of peak tolterodine (1 hour) and moxifloxacin (2 hour) concentrations.
Both Fridericia's (QTcF) and a population-specific (QTcP) method were used to correct QT interval for
heart rate. No single QT correction method is known to be more valid than others. QT interval was
measured manually and by machine, and data from both are presented. The mean increase of heart rate
associated with a 4 mg/day dose of tolterodine in this study was 2.0 beats/minute and 6.3 beats/minute
with 8 mg/day tolterodine. The change in heart rate with moxifloxacin was 0.5 beats/minute.
Table 2. Mean (CI) change in QTc from baseline to steady state (Day 4 of dosing) at T
(relative to placebo)
Drug/Dose |
N |
QTcF
(msec) (manual) |
QTcF
(msec)
(machine) |
QTcP
(msec)
(manual) |
QTcP
(msec)
(machine) |
Tolterodine
2 mg BID* |
48 |
5.01
(0.28, 9.74) |
1.16
(-2.99, 5.30) |
4.45
(-0.37, 9.26) |
2.00
(-1.81, 5.81) |
Tolterodine
4 mg BID* |
48 |
11.84
(7.11, 16.58) |
5.63
(1.48, 9.77) |
10.31
(5.49, 15.12) |
8.34
(4.53, 12.15) |
Moxifloxacin
400 mg QD† |
45 |
19.26‡
(15.49, 23.03) |
8.90
(4.77, 13.03) |
19.10‡
(15.32, 22.89) |
9.29
(5.34, 13.24) |
*At Tmax of 1 hr; 95% Confidence max Interval.
†At Tmax of 2 hr; 90% Confidence Interval.
‡The effect on QT interval with 4 days of moxifloxacin dosing in this QT trial may be greater than typically
observed in QT trials of other drugs. |
The reason for the difference between machine and manual read of QT interval is unclear.
The QT effect of tolterodine immediate release tablets appeared greater for 8 mg/day (two times the
therapeutic dose) compared to 4 mg/day. The effect of tolterodine 8 mg/day was not as large as that
observed after four days of therapeutic dosing with the active control moxifloxacin. However, the
confidence intervals overlapped.
Tolterodine's effect on QT interval was found to correlate with plasma concentration of tolterodine.
There appeared to be a greater QTc interval increase in CYP2D6 poor metabolizers than in CYP2D6
extensive metabolizers after tolterodine treatment in this study.
This study was not designed to make direct statistical comparisons between drugs or dose levels. There
has been no association of Torsade de Pointes in the international post-marketing experience with
DETROL or DETROL LA [see WARNINGS AND PRECAUTIONS].
Pharmacokinetics
Absorption
In a study with 14C-tolterodine solution in healthy volunteers who received a 5 mg oral
dose, at least 77% of the radiolabeled dose was absorbed. Cmax and area under the concentration-time
curve (AUC) determined after dosage of tolterodine immediate release are dose-proportional over the
range of 1 to 4 mg. Based on the sum of unbound serum concentrations of tolterodine and 5-HMT
("active moiety"), the AUC of tolterodine extended release 4 mg daily is equivalent to tolterodine
immediate release 4 mg (2 mg bid). Cmax and Cmin levels of tolterodine extended release are about 75%
and 150% of tolterodine immediate release, respectively. Maximum serum concentrations of tolterodine
extended release are observed 2 to 6 hours after dose administration.
Effect Of Food
There is no effect of food on the pharmacokinetics of tolterodine extended release.
Distribution
Tolterodine is highly bound to plasma proteins, primarily α -acid glycoprotein. Unbound
concentrations of tolterodine average 3.7% ± 0.13% over the concentration range achieved in clinical
studies. 5-HMT is not extensively protein bound, with unbound fraction concentrations averaging 36% ±
4.0%. The blood to serum ratio of tolterodine and 5-HMT averages 0.6 and 0.8, respectively,
indicating that these compounds do not distribute extensively into erythrocytes. The volume of
distribution of tolterodine following administration of a 1.28 mg intravenous dose is 113 ± 26.7 L.
Metabolism
Tolterodine is extensively metabolized by the liver following oral dosing. The primary
metabolic route involves the oxidation of the 5-methyl group and is mediated by the cytochrome P450
2D6 (CYP2D6) and leads to the formation of a pharmacologically active metabolite, 5-HMT. Further
metabolism leads to formation of the 5-carboxylic acid and N-dealkylated 5-carboxylic acid
metabolites, which account for 51% ± 14% and 29% ± 6.3% of the metabolites recovered in the urine,
respectively.
Variability in Metabolism
A subset of individuals (approximately 7% of Caucasians and approximately
2% of African Americans) are poor metabolizers for CYP2D6, the enzyme responsible for the
formation of 5-HMT from tolterodine. The identified pathway of metabolism for these individuals
("poor metabolizers") is dealkylation via cytochrome P450 3A4 (CYP3A4) to N-dealkylated
tolterodine. The remainder of the population is referred to as "extensive metabolizers."
Pharmacokinetic studies revealed that tolterodine is metabolized at a slower rate in poor metabolizers
than in extensive metabolizers; this results in significantly higher serum concentrations of tolterodine
and in negligible concentrations of 5-HMT.
Excretion
Following administration of a 5 mg oral dose of 14C-tolterodine solution to healthy
volunteers, 77% of radioactivity was recovered in urine and 17% was recovered in feces in 7 days.
Less than 1% (< 2.5% in poor metabolizers) of the dose was recovered as intact tolterodine, and 5% to
14% (<1% in poor metabolizers) was recovered as 5-HMT.
A summary of mean (± standard deviation) pharmacokinetic parameters of tolterodine extended release
and 5-HMT in extensive (EM) and poor (PM) metabolizers is provided in Table 3. These data were
obtained following single and multiple doses of tolterodine extended release administered daily to 17
healthy male volunteers (13 EM, 4 PM).
Table 3. Summary of Mean (±SD) Pharmacokinetic Parameters of Tolterodine Extended Release
and its Active Metabolite (5-Hydroxymethyl Tolterodine) in Healthy Volunteers
|
Tolterodine |
5-Hydroxymethyl Tolterodine |
tmax*
(h) |
Cmax
(μg/L) |
Cavg
(μg/L) |
t1/2
(h) |
tmax*
(h) |
Cmax
(μg/L) |
Cavg
(μg/L) |
t1/2
(h) |
Single dose
4 mg† |
EM |
4 (2–6) |
1.3 (0.8) |
0.8 (0.57) |
8.4 (3.2) |
4 (3–6) |
1.6 (0.5) |
1.0 (0.32) |
8.8 (5.9) |
Multiple
dose 4 mg |
EM |
4 (2–6) |
3.4 (4.9) |
1.7 (2.8) |
6.9 (3.5) |
4 (2–6) |
2.7 (0.90) |
1.4 (0.6) |
9.9 (4.0) |
PM |
4 (3–6) |
19 (16) |
13 (11) |
18 (16) |
‡ |
‡ |
‡ |
‡ |
Cmax = Maximum serum concentration; tmax = Time of occurrence of Cmax ;
Cavg = Average serum concentration; t1/2 = Terminal elimination half-life.
*Data presented as median (range).
†Parameter dose-normalized from 8 to 4 mg for the single-dose data.
‡= not applicable. |
Drug Interactions
Potent CYP2D6 Inhibitors
Fluoxetine is a selective serotonin reuptake inhibitor and a potent inhibitor
of CYP2D6 activity. In a study to assess the effect of fluoxetine on the pharmacokinetics of tolterodine
immediate release and its metabolites, it was observed that fluoxetine significantly inhibited the
metabolism of tolterodine immediate release in extensive metabolizers, resulting in a 4.8-fold increase
in tolterodine AUC. There was a 52% decrease in Cmax and a 20% decrease in AUC of 5-
hydroxymethyl tolterodine (5-HMT, the pharmacologically active metabolite of tolterodine). Fluoxetine
thus alters the pharmacokinetics in patients who would otherwise be CYP2D6 extensive metabolizers of
tolterodine immediate release to resemble the pharmacokinetic profile in poor metabolizers. The sums
of unbound serum concentrations of tolterodine immediate release and 5-HMT are only 25% higher
during the interaction. No dose adjustment is required when tolterodine and fluoxetine are coadministered.
Potent CYP3A4 Inhibitors
The effect of a 200 mg daily dose of ketoconazole on the pharmacokinetics
of tolterodine immediate release was studied in 8 healthy volunteers, all of whom were CYP2D6 poor
metabolizers. In the presence of ketoconazole, the mean Cmax and AUC of tolterodine increased by 2-
and 2.5-fold, respectively. Based on these findings, other potent CYP3A4 inhibitors may also lead to
increases of tolterodine plasma concentrations.
For patients receiving ketoconazole or other potent CYP3A4 inhibitors such as itraconazole,
miconazole, clarithromycin, ritonavir, the recommended dose of DETROL LA is 2 mg daily [see DOSAGE AND ADMINISTRATION].
Warfarin
In healthy volunteers, coadministration of tolterodine immediate release 4 mg (2 mg bid) for 7
days and a single dose of warfarin 25 mg on day 4 had no effect on prothrombin time, Factor VII
suppression, or on the pharmacokinetics of warfarin.
Oral Contraceptives
Tolterodine immediate release 4 mg (2 mg bid) had no effect on the
pharmacokinetics of an oral contraceptive (ethinyl estradiol 30 μg/levo-norgestrel 150 μg) as
evidenced by the monitoring of ethinyl estradiol and levo-norgestrel over a 2-month period in healthy
female volunteers.
Diuretics
Coadministration of tolterodine immediate release up to 8 mg (4 mg bid) for up to 12 weeks
with diuretic agents, such as indapamide, hydrochlorothiazide, triamterene, bendroflumethiazide,
chlorothiazide, methylchlorothiazide, or furosemide, did not cause any adverse electrocardiographic
(ECG) effects.
Effect Of Tolterodine On Other Drugs Metabolized By Cytochrome P450 Enzymes
Tolterodine immediate
release does not cause clinically significant interactions with other drugs metabolized by the major
drug-metabolizing CYP enzymes. In vivo drug-interaction data show that tolterodine immediate release
does not result in clinically relevant inhibition of CYP1A2, 2D6, 2C9, 2C19, or 3A4 as evidenced by
lack of influence on the marker drugs caffeine, debrisoquine, S-warfarin, and omeprazole. In vitro data
show that tolterodine immediate release is a competitive inhibitor of CYP2D6 at high concentrations (K
1.05 μM), while tolterodine immediate release as well as the 5-HMT are devoid of any significant
inhibitory potential regarding the other isoenzymes.
Clinical Studies
DETROL LA Capsules 2 mg were evaluated in 29 patients in a Phase 2 dose-effect study. DETROL
LA 4 mg was evaluated for the treatment of overactive bladder with symptoms of urge urinary
incontinence and frequency in a randomized, placebo-controlled, multicenter, double-blind, Phase 3, 12-
week study. A total of 507 patients received DETROL LA 4 mg once daily in the morning and 508
received placebo. The majority of patients were Caucasian (95%) and female (81%), with a mean age of
61 years (range, 20 to 93 years). In the study, 642 patients (42%) were 65 to 93 years of age. The study
included patients known to be responsive to tolterodine immediate release and other anticholinergic
medications, however, 47% of patients never received prior pharmacotherapy for overactive bladder.
At study entry, 97% of patients had at least 5 urge incontinence episodes per week and 91% of patients
had 8 or more micturitions per day.
The primary efficacy assessment was change in mean number of incontinence episodes per week at
week 12 from baseline. Secondary efficacy measures included change in mean number of micturitions
per day and mean volume voided per micturition at week 12 from baseline.
Patients treated with DETROL LA experienced a statistically significant decrease in number of urinary
incontinence per week from baseline to last assessment (week 12) compared with placebo as well as a
decrease in the average daily urinary frequency and an increase in the average urine volume per void.
Mean change from baseline in weekly incontinence episodes, urinary frequency, and volume voided
between placebo and DETROL LA are summarized in Table 4.
Table 4. 95% Confidence Intervals (CI) for the Difference between DETROL LA (4 mg daily)
and Placebo for Mean Change at Week 12 from Baseline*
|
DETROL LA
(n=507) |
Placebo
(n=508)† |
Treatment
Difference, vs . Placebo
(95% Cl) |
Number of incontinence
episodes/ week |
Mean Baseline |
22.1 |
23.3 |
-4.8‡ |
Mean Change from
Baseline |
–11.8 (SD 17.8) |
–6.9 (SD 15.4) |
(–6.9, –2.8) |
Number of
micturitions/day |
Mean Baseline |
10.9 |
11.3 |
-0.6‡ |
Mean Change from
Baseline |
–1.8 (SD 3.4) |
–1.2 (SD 2.9) |
(–1.0, –0.2) |
Volume voided per
micturition (mL) |
Mean Baseline |
141 |
136 |
20 |
Mean Change from
Baseline |
34 (SD 51) |
14 (SD 41) |
(14, 26) |
SD = Standard Deviation.
*Intent-to-treat analysis.
†1 to 2 patients missing in placebo group for each efficacy parameter.
‡The difference between DETROL LA and placebo was statistically significant. |