Flomax (Page 4 of 8)

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)

Figure 1
(click image for full-size original)

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 Parameter0.4 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 BreakfastFastedLight BreakfastHigh-Fat BreakfastFasted
Cmin = observed minimum concentration
Cmax = observed maximum tamsulosin hydrochloride plasma concentration
Tmax = median time-to-maximum concentration
T1/2 = observed half-life
AUCτ = area under the tamsulosin hydrochloride plasma time curve over the dosing interval
Cmin (ng/mL)4.0 ± 2.63.8 ± 2.512.3 ± 6.713.5 ± 7.613.3 ± 13.3
Cmax (ng/mL)10.1 ± 4.817.1 ± 17.129.8 ± 10.329.1 ± 11.041.6 ± 15.6
Cmax /Cmin Ratio3.1 ± 1.05.3 ± 2.22.7 ± 0.72.5 ± 0.83.6 ± 1.1
Tmax (hours)6.04.07.06.65.0
T1/2 (hours)14.9 ± 3.9
AUCτ (ng•hr/mL)151 ± 81.5199 ± 94.1440 ± 195449 ± 217557 ± 257

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 (5.2) and Drug Interactions (7.1)]. 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 (5alpha-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 (8.4)].

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 (8.5)].

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 (8.6)].

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