Tamsulosin is an alpha-adrenoceptor blocker with high specificity for the alpha-1A and alpha-1D subtypes, which are particularly abundant in the prostate and submaxillary tissues. Blockade of these adrenoceptors relaxes smooth muscle in the prostate and improves urinary flow. Blockade of alpha-1D adrenoceptors relaxes the detrusor muscles of the bladder, preventing symptoms of congestion. The specificity of tamsulosin concentrates the effect in the target area and minimizes effects in areas such as the aorta.
Orally ingested tamsulosin is 90% absorbed. Time from ingestion to maximum plasma concentration is 4-7 hours. Tamsulosin is 94%-99% bound to proteins, mainly to the acidic alpha-1-glycoprotein. Tamsulosin is metabolized primarily in the liver by cytochrome P450 enzymes, mainly CYP-3A4 and -2D6. The plasma half-life in fasting patients is approximately 14 hours.