CLINICAL PHARMACOLOGY
Mechanism Of Action
The symptoms associated with benign prostatic hyperplasia
(BPH) are related to bladder outlet obstruction, which is comprised of two
underlying components: static and dynamic. The static component is related to
an increase in prostate size caused, in part, by a proliferation of smooth
muscle cells in the prostatic stroma. However, the severity of BPH symptoms and
the degree of urethral obstruction do not correlate well with the size of the prostate.
The dynamic component is a function of an increase in smooth muscle tone in the
prostate and bladder neck leading to constriction of the bladder outlet. Smooth
muscle tone is mediated by the sympathetic nervous stimulation of alpha1 adrenoceptors,
which are abundant in the prostate, prostatic capsule, prostatic urethra, and
bladder neck. Blockade of these adrenoceptors can cause smooth muscles in the
bladder neck and prostate to relax, resulting in an improvement in urine flow
rate and a reduction in symptoms of BPH.
Tamsulosin, an alpha1 adrenoceptor blocking agent,
exhibits selectivity for alpha1 receptors in the human prostate. At least three
discrete alpha1 adrenoceptor subtypes have been identified: alpha1A,
alpha1B, and alpha1D; their distribution differs between
human organs and tissue. Approximately 70% of the alpha1 receptors in the human
prostate are of the alpha1A subtype.
FLOMAX capsules are not intended for use as an
antihypertensive drug.
Pharmacodynamics
Urologic pharmacodynamic effects have been evaluated in
neurologically impaired pediatric patients and in adults with BPH [see Use In
Specific Populations and Clinical Studies].
Pharmacokinetics
The pharmacokinetics of tamsulosin hydrochloride have
been evaluated in adult healthy volunteers and patients with BPH after single
and/or multiple administration with doses ranging from 0.1 mg to 1 mg.
Absorption
Absorption of tamsulosin hydrochloride from FLOMAX
capsules 0.4 mg is essentially complete (>90%) following oral administration
under fasting conditions. Tamsulosin hydrochloride exhibits linear kinetics
following single and multiple dosing, with achievement of steady-state
concentrations by the fifth day of once-a-day dosing.
Effect Of Food
The time to maximum concentration (Tmax) is reached by 4
to 5 hours under fasting conditions and by 6 to 7 hours when FLOMAX capsules
are administered with food. Taking FLOMAX capsules under fasted conditions
results in a 30% increase in bioavailability (AUC) and 40% to 70% increase in
peak concentrations (Cmax) compared to fed conditions (Figure 1).
Figure 1: Mean Plasma Tamsulosin Hydrochloride
Concentrations Following Single- Dose Administration of FLOMAX Capsules 0.4 mg
Under Fasted and Fed Conditions (n=8)
The effects of food on the pharmacokinetics of tamsulosin
hydrochloride are consistent regardless of whether a FLOMAX capsule is taken
with a light breakfast or a high-fat breakfast (Table 2).
Table 2: Mean (± S.D.) Pharmacokinetic Parameters
Following FLOMAX Capsules 0.4 mg Once Daily or 0.8 mg Once Daily with a Light
Breakfast, High-Fat Breakfast or Fasted
Pharmacokinetic Parameter |
0.4 mg QD to healthy volunteers; n=23 (age range 18-32 years) |
0.8 mg QD to healthy volunteers; n=22 (age range 55-75 years) |
Light Breakfast |
Fasted |
Light Breakfast |
High-Fat Breakfast |
Fasted |
Cmin (ng/mL) |
4.0 ± 2.6 |
3.8 ± 2.5 |
12.3 ± 6.7 |
13.5 ± 7.6 |
13.3 ± 13.3 |
Cmax (ng/mL) |
10.1 ± 4.8 |
17.1 ± 17.1 |
29.8 ± 10.3 |
29.1 ± 11.0 |
41.6 ± 15.6 |
Cmax/Cmin Ratio |
3.1 ± 1.0 |
5.3 ± 2.2 |
2.7 ± 0.7 |
2.5 ± 0.8 |
3.6 ± 1.1 |
Tmax (hours) |
6.0 |
4.0 |
7.0 |
6.6 |
5.0 |
T½ (hours) |
- |
- |
- |
- |
14.9 ± 3.9 |
AUCτ (ng•;hr/mL) |
151 ± 81.5 |
199 ± 94.1 |
440 ± 195 |
449 ± 217 |
557 ± 257 |
Cmin = observed minimum concentration
Cmax = observed maximum tamsulosin hydrochloride plasma concentration
Tmax = median time-to-maximum concentration
T½ = observed half-life
AUCτ = area under the tamsulosin
hydrochloride plasma time curve over the dosing interval |
Distribution
The mean steady-state apparent volume of distribution of
tamsulosin hydrochloride after intravenous administration to 10 healthy male
adults was 16 L, which is suggestive of distribution into extracellular fluids
in the body.
Tamsulosin hydrochloride is extensively bound to human
plasma proteins (94% to 99%), primarily alpha1 acid glycoprotein (AAG), with
linear binding over a wide concentration range (20 to 600 ng/mL). The results
of two-way in vitro studies indicate that the binding of tamsulosin
hydrochloride to human plasma proteins is not affected by amitriptyline, diclofenac,
glyburide, simvastatin plus simvastatin-hydroxy acid metabolite, warfarin, diazepam,
propranolol, trichlormethiazide, or chlormadinone. Likewise, tamsulosin
hydrochloride had no effect on the extent of binding of these drugs.
Metabolism
There is no enantiomeric bioconversion from tamsulosin
hydrochloride [R(-) isomer] to the S(+) isomer in humans. Tamsulosin
hydrochloride is extensively metabolized by cytochrome P450 enzymes in the
liver and less than 10% of the dose is excreted in urine unchanged. However,
the pharmacokinetic profile of the metabolites in humans has not been
established. Tamsulosin is extensively metabolized, mainly by CYP3A4 and CYP2D6
as well as via some minor participation of other CYP isoenzymes. Inhibition of
hepatic drug-metabolizing enzymes may lead to increased exposure to tamsulosin [see
WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS]. The metabolites
of tamsulosin hydrochloride undergo extensive conjugation to glucuronide or
sulfate prior to renal excretion.
Incubations with human liver microsomes showed no
evidence of clinically significant metabolic interactions between tamsulosin
hydrochloride and amitriptyline, albuterol (beta agonist), glyburide
(glibenclamide) and finasteride (5-alpha-reductase inhibitor for treatment of
BPH). However, results of the in vitro testing of the tamsulosin hydrochloride interaction
with diclofenac and warfarin were equivocal.
Excretion
On administration of the radiolabeled dose of tamsulosin
hydrochloride to 4 healthy volunteers, 97% of the administered radioactivity
was recovered, with urine (76%) representing the primary route of excretion
compared to feces (21%) over 168 hours. Following intravenous or oral
administration of an immediate-release formulation, the elimination half-life
of tamsulosin hydrochloride in plasma ranged from 5 to 7 hours. Because of
absorption rate-controlled pharmacokinetics with FLOMAX capsules, the apparent
half-life of tamsulosin hydrochloride is approximately 9 to 13 hours in healthy
volunteers and 14 to 15 hours in the target population. Tamsulosin
hydrochloride undergoes restrictive clearance in humans, with a relatively low systemic
clearance (2.88 L/h).
Specific Populations
Pediatric use
FLOMAX capsules are not indicated for use in pediatric
populations [see Use In Specific Populations].
Geriatric (Age) Use
Cross-study comparison of FLOMAX capsules overall
exposure (AUC) and half-life indicates that the pharmacokinetic disposition of
tamsulosin hydrochloride may be slightly prolonged in geriatric males compared
to young, healthy male volunteers. Intrinsic clearance is independent of
tamsulosin hydrochloride binding to AAG, but diminishes with age, resulting in
a 40% overall higher exposure (AUC) in subjects of age 55 to 75 years compared
to subjects of age 20 to 32 years [see Use In Specific Populations].
Renal impairment
The pharmacokinetics of tamsulosin hydrochloride have
been compared in 6 subjects with mild-moderate (30≤ CLcr <70
mL/min/1.73 m²) or moderate-severe (10≤ CLcr
<30 mL/min/1.73 m²) renal impairment and 6 normal
subjects (CLcr >90 mL/min/1.73 m²). While a change in the overall plasma
concentration of tamsulosin hydrochloride was observed as the result of altered
binding to AAG, the unbound (active) concentration of tamsulosin hydrochloride,
as well as the intrinsic clearance, remained relatively constant. Therefore,
patients with renal impairment do not require an adjustment in FLOMAX capsules
dosing. However, patients with end-stage renal disease (CLcr <10 mL/min/1.73
m²) have not been studied [see Use In Specific Populations].
Hepatic impairment
The pharmacokinetics of tamsulosin hydrochloride have
been compared in 8 subjects with moderate hepatic impairment (Child-Pugh's
classification: Grades A and B) and 8 normal subjects. While a change in the
overall plasma concentration of tamsulosin hydrochloride was observed as the
result of altered binding to AAG, the unbound (active) concentration of
tamsulosin hydrochloride does not change significantly, with only a modest
(32%) change in intrinsic clearance of unbound tamsulosin hydrochloride.
Therefore, patients with moderate hepatic impairment do not require an
adjustment in FLOMAX capsules dosage. FLOMAX has not been studied in patients
with severe hepatic impairment [see Use In Specific Populations].
Drug Interactions
Cytochrome P450 inhibition
Strong And Moderate Inhibitors Of CYP3A4 Or CYP2D6
The effects of ketoconazole (a strong inhibitor of
CYP3A4) at 400 mg once daily for 5 days on the pharmacokinetics of a single
FLOMAX capsule 0.4 mg dose was investigated in 24 healthy volunteers (age range
23 to 47 years). Concomitant treatment with ketoconazole resulted in an
increase in the Cmax and AUC of tamsulosin by a factor of 2.2 and 2.8,
respectively [see WARNINGS AND PRECAUTIONS and CLINICAL PHARMACOLOGY].
The effects of concomitant administration of a moderate CYP3A4 inhibitor (e.g.,
erythromycin) on the pharmacokinetics of FLOMAX have not been evaluated [see WARNINGS
AND PRECAUTIONS and DRUG INTERACTIONS].
The effects of paroxetine (a strong inhibitor of CYP2D6)
at 20 mg once daily for 9 days on the pharmacokinetics of a single FLOMAX
capsule 0.4 mg dose was investigated in 24 healthy volunteers (age range 23 to
47 years). Concomitant treatment with paroxetine resulted in an increase in the
Cmax and AUC of tamsulosin by a factor of 1.3 and 1.6, respectively [see WARNINGS
AND PRECAUTIONS and DRUG INTERACTIONS]. A similar increase in
exposure is expected in CYP2D6 poor metabolizers (PM) as compared to extensive
metabolizers (EM). A fraction of the population (about 7% of Caucasians and 2%
of African Americans) are CYP2D6 PMs. Since CYP2D6 PMs cannot be readily identified
and the potential for significant increase in tamsulosin exposure exists when FLOMAX
0.4 mg is co-administered with strong CYP3A4 inhibitors in CYP2D6 PMs, FLOMAX
0.4 mg capsules should not be used in combination with strong inhibitors of CYP3A4
(e.g., ketoconazole) [see WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS].
The effects of concomitant administration of a moderate
CYP2D6 inhibitor (e.g., terbinafine) on the pharmacokinetics of FLOMAX have not
been evaluated [see WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS].
The effects of co-administration of both a CYP3A4 and a
CYP2D6 inhibitor with FLOMAX capsules have not been evaluated. However, there
is a potential for significant increase in tamsulosin exposure when FLOMAX 0.4
mg is co-administered with a combination of both CYP3A4 and CYP2D6 inhibitors [see
WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS].
Cimetidine
The effects of cimetidine at the highest recommended dose
(400 mg every 6 hours for 6 days) on the pharmacokinetics of a single FLOMAX
capsule 0.4 mg dose was investigated in 10 healthy volunteers (age range 21 to
38 years). Treatment with cimetidine resulted in a significant decrease (26%)
in the clearance of tamsulosin hydrochloride, which resulted in a moderate
increase in tamsulosin hydrochloride AUC (44%) [see WARNINGS AND PRECAUTIONS
and DRUG INTERACTIONS].
Other Alpha Adrenergic Blocking Agents
The pharmacokinetic and pharmacodynamic interactions
between FLOMAX capsules and other alpha adrenergic blocking agents have not
been determined; however, interactions between FLOMAX capsules and other alpha
adrenergic blocking agents may be expected [see WARNINGS AND PRECAUTIONS
and DRUG INTERACTIONS].
PDE5 Inhibitors
Caution is advised when alpha adrenergic blocking agents,
including FLOMAX, are co-administered with PDE5 inhibitors. Alpha-adrenergic
blockers and PDE5 inhibitors are both vasodilators that can lower blood
pressure. Concomitant use of these two drug classes can potentially cause
symptomatic hypotension [see WARNINGS AND PRECAUTIONS and DRUG
INTERACTIONS].
Warfarin
A definitive drug-drug interaction study between
tamsulosin hydrochloride and warfarin was not conducted. Results from limited in
vitro and in vivo studies are inconclusive. Therefore, caution should be
exercised with concomitant administration of warfarin and FLOMAX capsules [see
WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS].
Nifedipine, Atenolol, Enalapril
In three studies in hypertensive subjects (age range 47
to 79 years) whose blood pressure was controlled with stable doses of
nifedipine, atenolol, or enalapril for at least 3 months, FLOMAX capsules 0.4
mg for 7 days followed by FLOMAX capsules 0.8 mg for another 7 days (n=8 per
study) resulted in no clinically significant effects on blood pressure and pulse
rate compared to placebo (n=4 per study). Therefore, dosage adjustments are not
necessary when FLOMAX capsules are administered concomitantly with nifedipine, atenolol,
or enalapril [see DRUG INTERACTIONS].
Digoxin And Theophylline
In two studies in healthy volunteers (n=10 per study; age
range 19 to 39 years) receiving FLOMAX capsules 0.4 mg/day for 2 days, followed
by FLOMAX capsules 0.8 mg/day for 5 to 8 days, single intravenous doses of
digoxin 0.5 mg or theophylline 5 mg/kg resulted in no change in the
pharmacokinetics of digoxin or theophylline. Therefore, dosage adjustments are
not necessary when a FLOMAX capsule is administered concomitantly with digoxin
or theophylline [see DRUG INTERACTIONS].
Furosemide
The pharmacokinetic and pharmacodynamic interaction
between FLOMAX capsules 0.8 mg/day (steady-state) and furosemide 20 mg
intravenously (single dose) was evaluated in 10 healthy volunteers (age range
21 to 40 years). FLOMAX capsules had no effect on the pharmacodynamics
(excretion of electrolytes) of furosemide. While furosemide produced an 11% to
12% reduction in tamsulosin hydrochloride Cmax and AUC, these changes are
expected to be clinically insignificant and do not require adjustment of the FLOMAX
capsules dosage [see DRUG INTERACTIONS].
Clinical Studies
Four placebo-controlled clinical studies and one
active-controlled clinical study enrolled a total of 2296 patients (1003 received
FLOMAX capsules 0.4 mg once daily, 491 received FLOMAX capsules 0.8 mg once
daily, and 802 were control patients) in the U.S. and Europe.
In the two U.S. placebo-controlled, double-blind,
13-week, multicenter studies (Study 1 [US92-03A] and Study 2 [US93-01]), 1486
men with the signs and symptoms of BPH were enrolled. In both studies, patients
were randomized to either placebo, FLOMAX capsules 0.4 mg once daily, or FLOMAX
capsules 0.8 mg once daily. Patients in FLOMAX capsules 0.8 mg once-daily treatment
groups received a dose of 0.4 mg once daily for one week before increasing to
the 0.8 mg once-daily dose. The primary efficacy assessments included: 1) total
American Urological Association (AUA) Symptom Score questionnaire, which
evaluated irritative (frequency, urgency, and nocturia), and obstructive
(hesitancy, incomplete emptying, intermittency, and weak stream) symptoms,
where a decrease in score is consistent with improvement in symptoms; and 2)
peak urine flow rate, where an increased peak urine flow rate value over
baseline is consistent with decreased urinary obstruction.
Mean changes from baseline to Week 13 in total AUA
Symptom Score were significantly greater for groups treated with FLOMAX
capsules 0.4 mg and 0.8 mg once daily compared to placebo in both U.S. studies
(Table 3, Figures 2A and 2B). The changes from baseline to Week 13 in peak
urine flow rate were also significantly greater for the FLOMAX capsules 0.4 mg
and 0.8 mg once-daily groups compared to placebo in Study 1, and for the FLOMAX
capsules 0.8 mg once-daily group in Study 2 (Table 3, Figures 3A and 3B). Overall
there were no significant differences in improvement observed in total AUA Symptom
Scores or peak urine flow rates between the 0.4 mg and the 0.8 mg dose groups with
the exception that the 0.8 mg dose in Study 1 had a significantly greater
improvement in total AUA Symptom Score compared to the 0.4 mg dose.
Table 3: Mean (±S.D.) Changes from Baseline to Week 13
in Total AUA Symptom Score* and Peak Urine Flow Rate (mL/sec)
|
Total AUA Symptom Score |
Peak Urine Flow Rate |
Mean Baseline Value |
Mean Change |
Mean Baseline Value |
Mean Change |
Study 1† |
FLOMAX capsules 0.8 mg once daily |
19.9 ± 4.9 n=247 |
-9.6‡ ± 6.7 n=237 |
9.57 ± 2.51 n=247 |
1.78‡ ± 3.35 n=247 |
FLOMAX capsules 0.4 mg once daily |
19.8 ± 5.0 n=254 |
-8.3‡ ± 6.5 n=246 |
9.46 ± 2.49 n=254 |
1.75‡± 3.57 n=254 |
Placebo |
19.6 ± 4.9 n=254 |
-5.5 ± 6.6 n=246 |
9.75 ± 2.54 n=254 |
0.52 ± 3.39 n=253 |
Study 2 § |
FLOMAX capsules 0.8 mg once daily |
18.2 ± 5.6 n=244 |
-5.8‡ ± 6.4 n=238 |
9.96 ±3.16 n=244 |
1.79‡ ± 3.36 n=237 |
FLOMAX capsules 0.4 mg once daily |
17.9 ± 5.8 n=248 |
-5.1‡ ± 6.4 n=244 |
9.94 ±3.14 n=248 |
1.52 ± 3.64 n=244 |
Placebo |
19.2 ± 6.0 n=239 |
-3.6 ± 5.7 n=235 |
9.95 ±3.12 n=239 |
0.93 ± 3.28 n=235 |
Week 13: For patients not completing the 13-week study,
the last observation was carried forward.
*Total AUA Symptom Scores ranged from 0 to 35.
â Peak urine flow rate measured 4 to 8 hours post dose at Week 13.
‡Statistically significant difference from placebo (p-value ≤0.050;
Bonferroni-Holm multiple test procedure).
§Peak urine flow rate measured 24 to 27 hours post dose at Week 13. |
Mean total AUA Symptom Scores for both FLOMAX capsules
0.4 mg and 0.8 mg once-daily groups showed a rapid decrease starting at 1 week
after dosing and remained decreased through 13 weeks in both studies (Figures
2A and 2B).
In Study 1, 400 patients (53% of the originally
randomized group) elected to continue in their originally assigned treatment
groups in a double-blind, placebo-controlled, 40-week extension trial (138
patients on 0.4 mg, 135 patients on 0.8 mg, and 127 patients on placebo). Three
hundred twenty-three patients (43% of the originally randomized group) completed
one year. Of these, 81% (97 patients) on 0.4 mg, 74% (75 patients) on 0.8 mg, and
56% (57 patients) on placebo had a response ≥25% above baseline in total
AUA Symptom Score at one year.
Figure 2A: Mean Change from Baseline in Total AUA
Symptom Score (0–35) Study 1
* indicates significant difference from placebo (p-value ≤0.050).
B = Baseline determined approximately one week prior to
the initial dose of double-blind medication at Week 0.
Subsequent values are observed cases.
LOCF = Last observation carried forward for patients not
completing the 13-week study.
Note: Patients in the 0.8 mg treatment group received 0.4
mg for the first week.
Note: Total AUA Symptom Scores range from 0 to 35.
Figure 2B: Mean Change from Baseline in Total AUA Symptom
Score (0–35) Study 2
* indicates significant difference from placebo (p-value ≤0.050).
Baseline measurement was taken Week 0. Subsequent values
are observed cases.
LOCF = Last observation carried forward for patients not
completing the 13-week study.
Note: Patients in the 0.8 mg treatment group received 0.4
mg for the first week.
Note: Total AUA Symptom Scores range from 0 to 35.
Figure 3A: Mean Increase in Peak Urine Flow Rate
(mL/Sec) Study 1
* indicates significant difference from placebo (p-value ≤0.050).
B = Baseline determined approximately one week prior to
the initial dose of double-blind medication at Week 0.
Subsequent values are observed cases.
LOCF = Last observation carried forward for patients not
completing the 13-week study.
Note: The uroflowmetry assessments at Week 0 were
recorded 4 to 8 hours after patients received the first dose of double-blind
medication.
Measurements at each visit were scheduled 4 to 8 hours
after dosing (approximate peak plasma tamsulosin concentration).
Note: Patients in the 0.8 mg treatment groups received
0.4 mg for the first week.
Figure 3B: Mean Increase in Peak Urine Flow Rate
(mL/Sec) Study 2
* indicates significant difference from placebo (p-value ≤0.050).
Baseline measurement was taken Week 0. Subsequent values
are observed cases.
LOCF = Last observation carried forward for patients not
completing the 13-week study.
Note: Patients in the 0.8 mg treatment group received 0.4
mg for the first week.
Note: Week 1 and Week 2 measurements were scheduled 4 to
8 hours after dosing (approximate peak plasma tamsulosin concentration).
All other visits were scheduled 24 to 27 hours after
dosing (approximate trough tamsulosin concentration).