DUTASTERIDE AND TAMSULOSIN HYDROCHLORIDE
Clinical safety rating: safe
Other antihypertensive drugs can have additive effects Can cause retrograde ejaculation and orthostatic hypotension.
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.
| Metabolism | Dutasteride is extensively metabolized by CYP3A4 and CYP3A5; tamsulosin is primarily metabolized by CYP2D6 and to a lesser extent by CYP3A4. |
| Excretion | Dutasteride: 40% as metabolites in feces (mainly via bile), 5% in urine. Tamsulosin: 76% in urine as unchanged drug and metabolites, 24% in feces. |
| Half-life | 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). |
| Protein binding | Dutasteride: >99.5% bound to albumin and alpha-1-acid glycoprotein. Tamsulosin: 94-99% bound to alpha-1-acid glycoprotein. |
| Volume of Distribution | Dutasteride: Vd 300-500 L (total body, large tissue distribution). Tamsulosin: Vd 0.2 L/kg (approx 14-30 L, moderate distribution). |
| Bioavailability | Dutasteride: Oral bioavailability ~60% (enhanced with food). Tamsulosin: Oral bioavailability ~30% (increased with food; formulation designed for consistent absorption). |
| Onset of Action | Dutasteride: Clinical effect on DHT levels within 1-2 weeks; symptom improvement over 3-6 months. Tamsulosin: Onset of action within 1-2 hours after oral administration. |
| Duration of Action | Dutasteride: Duration of suppression of DHT persists for months after discontinuation due to long half-life. Tamsulosin: Duration of action ~24 hours with once-daily dosing, but maximal effect on urinary flow occurs within 2-6 hours. |
One capsule (dutasteride 0.5 mg / tamsulosin hydrochloride 0.4 mg) orally once daily, approximately 30 minutes after the same meal each day.
| Dosage form | CAPSULE |
| Renal impairment | 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. |
| Liver impairment | 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. |
| Pediatric use | Safety and efficacy in pediatric patients have not been established. Use is not recommended in patients under 18 years of age. |
| Geriatric use | 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. |
| 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.
| FDA category | Animal |
| Breastfeeding | 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. |
| Teratogenic Risk | 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. |
■ FDA Black Box Warning
None
| Common Effects | Retrograde ejaculation |
| Serious Effects |
["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"]
| Precautions | ["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"] |
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| Fetal Monitoring | Monitor maternal blood pressure and heart rate for tamsulosin-related orthostatic hypotension. Assess fetal growth and anatomy via ultrasound if inadvertent exposure occurs. No specific monitoring for dutasteride required if pregnancy excluded. |
| Fertility Effects | Dutasteride may reduce semen volume and sperm count due to decreased dihydrotestosterone; effect reversible upon discontinuation. Tamsulosin has no known effects on fertility. |