Drug reference

Silodosin

Alpha-1 adrenergic receptor antagonist (alpha-blocker) · Drug for Benign Prostatic Hyperplasia

START

8 mg OD with food; counsel on retrograde ejaculation risk; check baseline BP (seated and standing); advise first dose at bedtime

TYPICAL MAX

8 mg/day

STOP IF

Severe hypotension, syncope, priapism, severe allergic reaction

WATCH

IPSS score at 4-8 weeks, BP (orthostatic), ejaculatory function, cataract surgery planning (warn ophthalmologist if on silodosin)

CDSCO approvedSchedule HATC G04CA04

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 38min · absorption onset
PEAK: 2.5h · Peak plasma concentration
t½: 13.3h · 13.3 hours
DURATION: 1d · 24-hour coverage

EXCRETION

Fecal (55%); renal (34%, metabolites)

route + CYP

INTERACTIONS

12 major

incl. contraindicated

PREGNANCY

Not indicated for use in women; no data in pregnancy

FDA category + note

Top interactionssee all 12 →

ClarithromycinContraindicatedDatabaseDDInter
ItraconazoleContraindicatedDatabaseDDInter
KetoconazoleContraindicatedDatabaseKimi deep-research + Cla
RitonavirContraindicatedDatabaseDDInter

Available in India

135 branded formulations and 87 fixed-dose combinations. Look up specific brands in the Drugs workspace.

Mechanism

Selective antagonist at alpha-1A adrenergic receptors (highly selective for alpha-1A vs alpha-1B), which predominate in the prostate, bladder neck, and urethra. Relaxation of smooth muscle in these areas improves urine flow and reduces BPH symptoms with minimal effect on vascular alpha-1B receptors (reducing orthostatic hypotension risk).

Indications

Benign prostatic hyperplasia (BPH) - treatment of signs and symptoms

Dosing

Adult: 8 mg once daily with food
Pediatric: Not recommended under 18 years
Renal adjustment: eGFR 30-50: 4 mg OD (US); eGFR <30: contraindicated (EU) / not recommended (US)
Hepatic adjustment: Mild–moderate hepatic: no dose adjustment. Severe (Child-Pugh ≥10): CONTRAINDICATED (FDA §8.7) — Kimi's 'mild-moderate 4 mg' conflated the renal dose.
Geriatric: Standard dosing; increased risk of orthostatic hypotension and ejaculatory dysfunction
Max dose: 8 mg/day

Pharmacokinetics

Onset

Hours to days (symptom improvement)

Peak effect

2.5 hours (Tmax)

Duration

24 hours

Half-life

13.3 hours

Bioavailability

32% (food increases)

Protein binding

96.6%

Metabolism

Hepatic CYP3A4 (major) and alcohol/aldehyde dehydrogenases (glucuronidation and oxidation)

Excretion

Fecal (54.9%); renal (33.5%, primarily as metabolites)

Contraindications

Hypersensitivity to silodosin
Severe hepatic impairment (Child-Pugh C)
Severe renal impairment (eGFR <30 mL/min) (contraindicated in EU, caution in US)
Concurrent use with potent CYP3A4 inhibitors
Concurrent use with other alpha-blockers
Hypotension / orthostatic hypotension

Side effects

Common

Retrograde ejaculation / anejaculation (most characteristic - 20-30%)DizzinessOrthostatic hypotensionNasal congestion / rhinitisDiarrheaHeadache

Serious

Syncope (first-dose phenomenon)
Priapism (rare)
Severe hypotension
Angioedema (rare)
Intraoperative floppy iris syndrome (IFIS) during cataract surgery

Pregnancy & lactation

Pregnancy

Not indicated for use in women; no data in pregnancy

Lactation

Not indicated for use in women

Drug interactions

Clarithromycin

Contraindicated

Database

Significantly increased plasma concentrations of silodosin, leading to an increased risk of orthostatic hypotension and other dose-dependent adverse effects.

Concomitant use is contraindicated. An alternative alpha-blocker or antibiotic should be considered.

Source: DDInter

Itraconazole

Contraindicated

Database

Significantly increased plasma concentrations of silodosin, leading to an increased risk of orthostatic hypotension and other dose-dependent adverse effects.

Concomitant use is contraindicated. An alternative alpha-blocker or antifungal should be considered.

Source: DDInter

Ketoconazole

Contraindicated

Database

Potent CYP3A4 inhibition dramatically increases silodosin levels; severe hypotension risk

Avoid combination

Source: Kimi deep-research + Cla

Ritonavir

Contraindicated

Database

Significantly increased plasma concentrations of silodosin, leading to an increased risk of orthostatic hypotension and other dose-dependent adverse effects.

Concomitant use is contraindicated. An alternative alpha-blocker or antiretroviral should be considered.

Source: DDInter

Other Alpha Blockers

Contraindicated

Database

Additive alpha-blockade; severe hypotension and syncope risk

Do not combine with other alpha-blockers

Source: Kimi deep-research + Cla

Amprenavir

Severe

Database

Drug interaction classified as: metabolism