Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE vs FLOMAX
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Dutasteride inhibits both type 1 and type 2 isoforms of 5α-reductase, preventing conversion of testosterone to dihydrotestosterone (DHT), reducing prostate volume. Tamsulosin is a selective antagonist of alpha-1A and alpha-1D adrenoceptors, relaxing smooth muscle in the prostate and bladder neck.
Selective antagonist of alpha-1A and alpha-1D adrenergic receptors in the prostate, bladder base, and bladder neck, leading to relaxation of smooth muscle and improved urinary flow.
treatment of symptomatic benign prostatic hyperplasia (BPH),combination therapy for BPH
Treatment of signs and symptoms of benign prostatic hyperplasia (BPH),Off-label: adjunctive therapy for ureteral calculi expulsion
One capsule (dutasteride 0.5 mg / tamsulosin hydrochloride 0.4 mg) orally once daily, approximately 30 minutes after the same meal each day.
0.4 mg orally once daily, approximately 30 minutes after the same meal each day. If no response after 2-4 weeks, may increase to 0.8 mg once daily.
Dutasteride: Terminal half-life ~5 weeks (3-7 weeks), allowing once-daily dosing; steady-state reached at 3-6 months. Tamsulosin: Terminal half-life ~9-13 hours in healthy subjects, prolonged in elderly (up to 16-19 hours).
Terminal elimination half-life is approximately 14-15 hours (range 6-20 hours) in healthy adults, allowing once-daily dosing.
Dutasteride is extensively metabolized by CYP3A4 and CYP3A5; tamsulosin is primarily metabolized by CYP2D6 and to a lesser extent by CYP3A4.
Extensively metabolized in the liver via CYP3A4 and CYP2D6 enzymes.
Dutasteride: 40% as metabolites in feces (mainly via bile), 5% in urine. Tamsulosin: 76% in urine as unchanged drug and metabolites, 24% in feces.
Primarily hepatic metabolism (CYP3A4, CYP2D6) with <10% excreted unchanged in urine; fecal excretion accounts for ~76% of metabolites.
Dutasteride: >99.5% bound to albumin and alpha-1-acid glycoprotein. Tamsulosin: 94-99% bound to alpha-1-acid glycoprotein.
94-99% bound primarily to alpha-1 acid glycoprotein, with high affinity.
Dutasteride: Vd 300-500 L (total body, large tissue distribution). Tamsulosin: Vd 0.2 L/kg (approx 14-30 L, moderate distribution).
Approximately 16 L/kg (or 16 L for an average 70 kg patient), indicating extensive tissue distribution.
Dutasteride: Oral bioavailability ~60% (enhanced with food). Tamsulosin: Oral bioavailability ~30% (increased with food; formulation designed for consistent absorption).
Oral bioavailability is approximately 90% (capsule) due to extensive absorption, with minimal first-pass metabolism.
No dosage adjustment is required for renal impairment. Tamsulosin is extensively metabolized and renally excreted as inactive metabolites; however, no specific GFR-based adjustments are recommended.
No adjustment required for GFR ≥10 m L/min; insufficient data for GFR <10 m L/min, use with caution.
Dutasteride is contraindicated in patients with severe hepatic impairment (Child-Pugh Class C). For mild to moderate hepatic impairment (Child-Pugh A or B), no dosage adjustment is recommended, but caution is advised.
Child-Pugh Class A: No adjustment. Child-Pugh Class B: Use with caution; consider starting at 0.4 mg once daily. Child-Pugh Class C: Contraindicated.
Safety and efficacy in pediatric patients have not been established. Use is not recommended in patients under 18 years of age.
Not approved for pediatric use; safety and efficacy not established.
No specific dose adjustment is required based on age alone. Elderly patients may be more sensitive to orthostatic hypotension from tamsulosin; monitor blood pressure and advise caution when rising from a seated or lying position.
Same dosing as adults; monitor for orthostatic hypotension and dizziness. Consider starting at 0.4 mg once daily.
None
None.
Orthostatic hypotension/syncope, especially with concurrent antihypertensives,Intraoperative floppy iris syndrome during cataract surgery,Risk of high-grade prostate cancer (increased Gleason score 8-10 with dutasteride),Hepatic impairment may increase exposure,Sexual dysfunction: decreased libido, erectile dysfunction, ejaculation disorders
Orthostatic hypotension and syncope, especially upon initiation or dose increase,Intraoperative floppy iris syndrome (IFIS) during cataract surgery,Priapism (rare),Hepatic impairment,Consideration of prostate cancer before initiating therapy
Hypersensitivity to dutasteride, tamsulosin, or other 5α-reductase inhibitors,Women who are or may become pregnant (risk of fetal harm due to androgen inhibition),Severe hepatic impairment (Child-Pugh Class C),History of orthostatic hypotension
Hypersensitivity to tamsulosin hydrochloride or any component of the formulation,Concomitant use with strong CYP3A4 inhibitors (e.g., ketoconazole) in patients with moderate to severe hepatic impairment
Absorption of tamsulosin is decreased when taken with food; however, the combination product should be taken 30 minutes after a meal to maintain consistent exposure. Avoid grapefruit juice as it may increase tamsulosin concentrations. No specific food interactions with dutasteride.
Grapefruit juice may increase tamsulosin levels; avoid concurrent intake. High-fat meals can decrease absorption; administer 30 minutes after the same meal daily.
Dutasteride is contraindicated in pregnancy due to risk of fetal harm, particularly male genital abnormalities (e.g., hypospadias) from inhibition of dihydrotestosterone. Tamsulosin has no known teratogenic risk. First trimester: Dutasteride exposure may cause feminization of male fetuses. Second and third trimesters: Risk persists; avoid use.
Tamsulosin is FDA Pregnancy Category B. Animal studies revealed no evidence of teratogenicity at doses up to 50 mg/kg/day in rats and 5 mg/kg/day in rabbits (approximately 50 and 30 times the human exposure). There are no adequate and well-controlled studies in pregnant women; use only if clearly needed. First trimester: no known increased risk of major malformations. Second/third trimester: no known specific fetal risks; however, alpha-blockers may cause hypotension in the mother, potentially affecting placental perfusion. No reports of teratogenic effects in humans.
Unknown if dutasteride or tamsulosin are excreted in human milk. Dutasteride is lipophilic and may appear in milk. Tamsulosin likely excreted. M/P ratio not available. Due to potential for adverse effects (e.g., hypotension), breastfeeding is not recommended during therapy.
Tamsulosin is excreted in rat milk at concentrations 20-fold higher than maternal plasma. No human data exist; M/P ratio is not established. Due to potential for adverse effects (e.g., hypotension) in the nursing infant, breastfeeding is generally not recommended. Discontinue drug or bottle-feed, considering importance of therapy to mother.
No dose adjustment studies in pregnancy. Dutasteride should not be used; tamsulosin is not recommended. No pharmacokinetic changes requiring dose adjustment are established, but avoid use.
No specific pharmacokinetic studies during pregnancy. Dose adjustments are not routinely recommended; however, hypotension risk may be increased due to pregnancy-related hemodynamic changes. Use the lowest effective dose and monitor for maternal hypotension to avoid fetal compromise.
Dutasteride/tamsulosin is a fixed-dose combination for benign prostatic hyperplasia (BPH). Dutasteride is a 5α-reductase inhibitor that reduces prostate volume over months; tamsulosin is an α1-adrenoceptor antagonist providing rapid symptom relief. Do not split or crush capsules. Avoid use in women and children. Monitor for orthostatic hypotension, especially when initiating therapy. Assess for drug-drug interactions: CYP3A4 inhibitors (e.g., ketoconazole) increase dutasteride exposure; tamsulosin interacts with other α-blockers, antihypertensives, and PDE5 inhibitors. Counsel patients about risk of postural hypotension and syncope. Advise patients to avoid driving or hazardous activities until they know how the medication affects them. Dutasteride may cause sexual dysfunction (decreased libido, ejaculatory dysfunction, gynecomastia). Tamsulosin may cause intraoperative floppy iris syndrome during cataract surgery; inform ophthalmologist of use. Monitor serum PSA levels: dutasteride decreases PSA by ~50% after 6 months; establish new baseline. Do not use in patients with history of prostate cancer.
First-dose orthostatic hypotension is common; administer at bedtime. Avoid use in patients with history of cataract surgery due to intraoperative floppy iris syndrome (IFIS). Tamsulosin is not recommended for hypertension. Renal impairment does not require dose adjustment. Use caution with strong CYP3A4 inhibitors (e.g., ketoconazole) and PDE5 inhibitors (e.g., sildenafil) due to enhanced hypotensive effects.
Take this medication once daily, 30 minutes after the same meal each day.,Swallow capsules whole; do not crush, chew, or open.,Rise slowly from sitting or lying down to avoid dizziness or fainting.,Avoid driving or operating machinery until you know how the drug affects you.,Inform your doctor if you plan to have cataract surgery, as this drug may cause complications.,Do not donate blood while taking this medication, as it may harm a fetus if given to a pregnant woman.,Women who are pregnant or may become pregnant should not handle crushed or broken capsules.,Report any breast lumps, pain, or nipple discharge, as gynecomastia is possible.,Use condoms if your partner is pregnant, as dutasteride can be absorbed through skin contact with semen.,Keep all appointments for PSA blood tests; the test result will be lower than expected.,Do not take other alpha-blocker medications for blood pressure or prostate problems while on this drug unless prescribed.,Grapefruit juice may increase side effects; limit or avoid consumption.,Do not stop taking this medication suddenly without consulting your doctor.
Take this medication approximately 30 minutes after the same meal each day to maintain consistent absorption.,Avoid getting up too quickly from a sitting or lying position to minimize dizziness.,Inform your ophthalmologist about tamsulosin use before any cataract surgery due to risk of floppy iris syndrome.,Do not drive or operate heavy machinery until you know how this medication affects you.,If you miss a dose, skip it and take the next dose at the usual time; do not double the dose.
"Tamsulosin, an alpha-1 adrenergic antagonist, and fosinopril, an ACE inhibitor, both lower blood pressure through distinct mechanisms, leading to additive hypotensive effects. This synergistic action increases the risk of orthostatic hypotension, dizziness, syncope, and falls, particularly at treatment initiation or dose escalation. The interaction is of clinical concern in elderly patients or those with volume depletion."
"Lofexidine, a central alpha-2 adrenergic agonist, reduces sympathetic outflow and can cause bradycardia and hypotension. Tamsulosin, an alpha-1 adrenergic receptor antagonist, also lowers blood pressure, especially orthostatic. Combined use leads to additive hypotensive effects, increasing risk of symptomatic bradycardia, orthostatic hypotension, syncope, and falls, particularly at therapy initiation or dose titration."
"The combination of tamsulosin and moexipril can lead to an increased risk of hypotension and orthostatic hypotension due to additive vasodilatory effects. Tamsulosin, an alpha-1 adrenergic antagonist, reduces peripheral vascular resistance, while moexipril, an ACE inhibitor, decreases angiotensin II production, further promoting vasodilation. This synergistic effect may cause symptomatic hypotension, dizziness, and syncope, particularly at the initiation of therapy or during dose adjustments."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE vs FLOMAX, answered by our medical review team.
DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE is a Alpha-1 Blocker that works by Dutasteride inhibits both type 1 and type 2 isoforms of 5α-reductase, preventing conversion of testosterone to dihydrotestosterone (DHT), reducing prostate volume. Tamsulosin is a selective antagonist of alpha-1A and alpha-1D adrenoceptors, relaxing smooth muscle in the prostate and bladder neck.. FLOMAX is a Alpha-1 Blocker that works by Selective antagonist of alpha-1A and alpha-1D adrenergic receptors in the prostate, bladder base, and bladder neck, leading to relaxation of smooth muscle and improved urinary flow.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE and FLOMAX depend on the specific clinical indication. These are both Alpha-1 Blocker agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE is: One capsule (dutasteride 0.5 mg / tamsulosin hydrochloride 0.4 mg) orally once daily, approximately 30 minutes after the same meal each day.. The standard adult dose of FLOMAX is: 0.4 mg orally once daily, approximately 30 minutes after the same meal each day. If no response after 2-4 weeks, may increase to 0.8 mg once daily.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE and FLOMAX in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE is classified as Category A/B. Dutasteride is contraindicated in pregnancy due to risk of fetal harm, particularly male genital abnormalities (e.g., hypospadias) from inhibition of dihydrotestosterone. Tamsulosi. FLOMAX is classified as Category C. Tamsulosin is FDA Pregnancy Category B. Animal studies revealed no evidence of teratogenicity at doses up to 50 mg/kg/day in rats and 5 mg/kg/day in rabbits (approximately 50 and 3. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.