SILODOSIN
Clinical safety rating: safe
Animal studies have demonstrated safety
Silodosin is a highly selective antagonist of alpha-1A adrenergic receptors located primarily in the prostate, bladder base, and proximal urethra. Blockade of these receptors relaxes smooth muscle in these tissues, reducing urinary outflow resistance and improving symptoms of benign prostatic hyperplasia (BPH). It has minimal affinity for alpha-1B receptors, thereby reducing the risk of orthostatic hypotension compared to non-selective alpha blockers.
| Metabolism | Extensive hepatic metabolism primarily via CYP3A4, with minor contribution from CYP2D6 and UGT2B7. Metabolites include KMD-3213G (active, glucuronide conjugate) and others. Approximately 33% of the dose undergoes first-pass metabolism. Biliary excretion of metabolites is significant. |
| Excretion | Renal (33.5% as unchanged drug, 64.3% as metabolites); fecal (<5%) |
| Half-life | Terminal half-life: 11-13 hours; allows once-daily dosing; prolongation in severe renal impairment |
| Protein binding | 94-98%, primarily to albumin and α1-acid glycoprotein |
| Volume of Distribution | 2.5 L/kg; extensive tissue distribution with high prostate concentration |
| Bioavailability | Oral: ~32% (with food); higher under fed conditions; absolute bioavailability 32% |
| Onset of Action | Oral: 1-3 hours for peak effect on urinary symptoms |
| Duration of Action | 24 hours; supports once-daily dosing; effects on IPSS sustained over 24h |
8 mg orally once daily with a meal.
| Dosage form | CAPSULE |
| Renal impairment | eGFR 30-59 mL/min/1.73m2: 4 mg once daily; eGFR <30 mL/min/1.73m2: not recommended. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: 4 mg once daily; Child-Pugh Class C: not studied, avoid use. |
| Pediatric use | Not established; safety and efficacy not evaluated. |
| Geriatric use | Initiate at 4 mg once daily; titrate to 8 mg as tolerated due to increased risk of hypotension. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Other antihypertensive drugs can have additive effects Can cause retrograde ejaculation and orthostatic hypotension.
| Breastfeeding | Unknown if excreted in human milk; low molecular weight suggests potential transfer. No M/P ratio available. Caution advised; use with monitoring for infant hypotension. |
| Teratogenic Risk | No adequate human studies in pregnancy; animal studies show no teratogenic effects at clinically relevant doses. Risk in first trimester cannot be excluded; avoid use in all trimesters unless clearly needed. |
| Fetal Monitoring |
■ FDA Black Box Warning
None
| Common Effects | Retrograde ejaculation |
| Serious Effects |
["Hypersensitivity to silodosin or any component of the formulation","Severe renal impairment (CrCl <30 mL/min)","Concomitant use with strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin, itraconazole, ritonavir)","Severe hepatic impairment (Child-Pugh >9)"]
| Precautions | ["Orthostatic hypotension: Risk is low but may occur, especially at initiation of therapy or with dose increases.","Syncope: Advise patients to avoid situations where injury could occur if hypotension develops.","Intraoperative floppy iris syndrome (IFIS) during cataract surgery: Patients should inform ophthalmologist of silodosin use.","Priapism: Instruct patients to seek immediate medical attention for erections lasting >4 hours.","Hepatic impairment: Not recommended in severe hepatic impairment (Child-Pugh >9).","Renal impairment: Not recommended for CrCl <30 mL/min."] |
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| Monitor maternal blood pressure and heart rate; assess for orthostatic hypotension. No specific fetal monitoring indicated unless maternal hypotension occurs. |
| Fertility Effects | No human data; animal studies show no impairment of fertility. Theoretical effects from alpha-1 blockade not established. |