Flomax Clinical Pharmacology

Drug Library
Flomax - Clinical Pharmacology [Tamsulosin]

Incubations with human liver microsomes showed no evidence of clinically significant metabolic interactions between tamsulosin HCI 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 HCI interaction with diclofenac and warfarin were equivocal.

Excretion:

On administration of the radiolabeled dose of tamsulosin HCI to four 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 HCI in plasma range from five to seven hours. Because of absorption rate-controlled pharmacokinetics with FLOMAX capsules, the apparent half-life of tamsulosin HCI is approximately 9 to 13 hours in healthy volunteers and 14 to 15 hours in the target population.

Tamsulosin HCI undergoes restrictive clearance in humans, with a relatively low systemic clearance (2.88 L/ h).

Special Populations

Geriatrics (Age):

Cross-study comparison of FLOMAX capsules overall exposure (AUC) and half-life indicate that the pharmacokinetic disposition of tamsulosin HCI may be slightly prolonged in geriatric males compared to young, healthy male volunteers. Intrinsic clearance is independent of tamsulosin HCI 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.

Renal Dysfunction

The pharmacokinetics of tamsulosin HCI have been compared in 6 subjects with mild-moderate (30 . CLcr < 70 mL/ min/ 1.73m 2 ) or moderate-severe (10 . CLcr < 30 mL/ min/ 1.73m 2 ) renal impairment and 6 normal subjects (CLcr < 90 mL/ min/ 1.73m 2 ). While a change in the overall plasma concentration of tamsulosin HCI was observed as the result of altered binding to AAG, the unbound (active) concentration of tamsulosin HCI, 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 endstage renal disease (CLcr < 10 mL/ min/ 1. 73m 2 ) have not been studied.