Silodosin (known by the trade names Silosoft, Silodal, Sildoo in India, Urief in Japan, Rapaflo in North America, and Silodyx or Niksol in the European Union) is a medication for the symptomatic treatment of benign prostatic hyperplasia (BPH). It acts as an α1-adrenoceptor antagonist with high uroselectivity (selectivity for the prostate). Medical uses Silodosin is used for the treatment of BPH in adult men. Contraindications According to European labels, silodosin has no contraindications apart from known hypersensitivity. Another source names recurring urinary retention, recurring urinary infections, uncontrolled macrohematuria, bladder stones, hydronephrosis, combination with other α1-antagonists or dopamine agonists, and severe renal or hepatic impairment as contraindications. According to the FDA, silodosin is contraindicated with paxlovid, a drug used in treating COVID-19. Side effects The most common adverse effect is loss of seminal emission. This seems to be caused by silodosin's high selectivity for α1A receptors. Other common adverse effects (in more than 1% of patients) are dizziness, orthostatic hypotension, diarrhoea, and clogged nose. Less common (0.1–1%) are tachycardia (fast heartbeat), dry mouth, nausea, skin reactions, and erectile dysfunction. Hypersensitivity reactions occur in fewer than 0.01% of patients. There have been reports about intraoperative floppy iris syndrome during cataract extractions. These side effects are similar to those of other α1 antagonists. Interactions Combining silodosin with strong inhibitors of the liver enzyme CYP3A4, such as ketoconazole, significantly increases its concentrations in the blood plasma and its area under the curve (AUC). Less potent CYP3A4 inhibitors such as diltiazem have a less pronounced effect on this parameters, which is not considered clinically significant. Inhibitors and inducers of the enzyme UGT2B7, alcohol dehydrogenases, and aldehyde dehydrogenases, as well as the transporter P-glycoprotein (P-gp), may also influence silodosin concentrations in the body. Digoxin, which is transported by P-gp, is not affected by silodosin; this means that silodosin does not significantly inhibit or induce P-gp. No relevant interactions with antihypertensive drugs or with PDE5 inhibitors have been found in studies; although combination with other α1-antagonists is not well studied. Pharmacology Mechanism of action Silodosin has high affinity for the α1A adrenergic receptor in the prostate, the bladder, and the prostatic urethra. By this mechanism it relaxes the smooth muscle in these organs, easing urinary flow and other symptoms of BPH. Pharmacokinetics The absolute bioavailability after oral intake is 32%. Food has little effect on the AUC. When in the bloodstream, 96,6% of the substance are bound