Tamsulosin is mostly metabolized in the liver by cytochrome P450 (CYP) 3A4 and 2D6, with some metabolism by other CYPs. CYP3A4 can deacetylate tamsulosin to the M-1 metabolite or perform oxidative deamination to the AM-1 metabolite. CYP2D6 can hydroxylate tamsulosin to the M-3 metabolite or demethylate tamsulosin to the M-4 metabolite. Finally, an unknown enzyme can hydroxylate tamsulosin at a different position to form the M-2 metabolite. The M-1, M-2, M-3, and M-4 metabolites can be glucuronidated or the M-1 and M-3 metabolites can undergo sulfate conjugation to form other metabolites before excretion.
来源:DrugBank
代谢
广泛被肝脏中的细胞色素P450酶（具体同工酶未确定）代谢。代谢物在排泄前会进一步发生结合反应。
Extensively metabolized by CYP enzymes (specific isoenzyme[s] not identified) in the liver. Metabolites undergo further conjugation prior to excretion.
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. In vitro results indicate that CYP3A4 and CYP2D6 are involved in metabolism of tamsulosin as well as some minor participation of other CYP isoenzymes. Inhibition of hepatic drug metabolizing enzymes may lead to increased exposure to tamsulosin. The metabolites of tamsulosin hydrochloride undergo extensive conjugation to glucuronide or sulfate prior to renal excretion.
... After a single oral administration of 14C-tamsulosin at a dose of 0.2 mg /to/ four healthy male subjects... unchanged tamsulosin (TMS) and 11 metabolites in 0-24-hr urine samples were quantified. TMS accounted for 8.7% of the dose. Extensive excretion of the sulphate of the O-deethylated metabolite (M-1-Sul) and o-ethoxyphenoxy acetic acid (AM-1) was seen, accounting for 15.7 and 7.5% of the dose respectively.
The metabolism of tamsulosin hydrochloride (TMS), a potent alpha 1-adrenoceptor blocking agent, was studied after a single oral administration to rat and dog. Eleven metabolites (1, 2, 3, 4 and their glucuronides, sulphates of 1 and 3, and A-1) were identified from the urine and bile of rat and dog administered TMS. Unchanged drug and metabolites in urine and bile were quantified in rat and dog dosed with 14C-TMS(1 mg/kg). In rat the main metabolic routes were de-ethylation of the o-ethoxyphenoxy moiety, demethylation of the methoxybenzenesulphonamide moiety, and conjugation of the resultant metabolites by glucuronic acid and sulphuric acid. In dog the main pathways were de-ethylation of the ethoxyphenoxy moiety, conjugation of the de-ethylated product by sulphuric acid, and oxidative deamination of the side chain. The organ responsible for the metabolism of TMS in rat was estimated using 9000g supernatants of liver, kidney, small and large intestine homogenate and plasma. The drug was rapidly metabolized in liver but hardly metabolized in the other organs or plasma.
参考文献：M Chen, V Vijay, Q Shi, Z Liu, H Fang, W Tong. 美国食品药品监督管理局批准的药物标签用于研究药物诱导的肝损伤，《药物发现今日》，16(15-16):697-703, 2011. PMID:21624500 DOI:10.1016/j.drudis.2011.05.007
M Chen, A Suzuki, S Thakkar, K Yu, C Hu, W Tong. DILIrank：按人类发展药物诱导肝损伤风险排名的最大参考药物清单。《药物发现今日》2016, 21(4): 648-653. PMID:26948801 DOI:10.1016/j.drudis.2016.02.015
References:M Chen, V Vijay, Q Shi, Z Liu, H Fang, W Tong. FDA-Approved Drug Labeling for the Study of Drug-Induced Liver Injury, Drug Discovery Today, 16(15-16):697-703, 2011. PMID:21624500 DOI:10.1016/j.drudis.2011.05.007
M Chen, A Suzuki, S Thakkar, K Yu, C Hu, W Tong. DILIrank: the largest reference drug list ranked by the risk for developing drug-induced liver injury in humans. Drug Discov Today 2016, 21(4): 648-653. PMID:26948801 DOI:10.1016/j.drudis.2016.02.015
Oral tamsulosin is 90% absorbed in fasted patients. The area under the curve is 151-199ng/mL\*hr for a 0.4mg oral dose and 440-557ng/mL*hr for a 0.8mg oral dose. The maximum plasma concentration is 3.1-5.3ng/mL for a 0.4mg oral dose and 2.5-3.6ng/mL for a 0.8mg oral dose. Taking tamsulosin with food increases the time to maximum concentration from 4-5 hours to 6-7 hours but increases bioavailability by 30% and maximum plasma concentration by 40-70%.
97% of an orally administered does is recovered in studies, which 76% in the urine and 21% in the feces after 168 hours. 8.7% of the dose is excreted as unmetabolized tamsulosin.
In patients with moderate hepatic impairment, protein binding is altered, resulting in changes in overall plasma concentrations; however, no substantial alterations in intrinsic clearance and concentrations of unbound drug.
