Dutasteride + Tamsulosin

Pharmacogenomics:

Tamsulosin

Tamsulosin is extensively metabolised in the liver by CYP3A4 and CYP2D6 into metabolites. CYP2D6 poor metabolisers have a potential for a significant increase in tamsulosin exposure. The prevalence of CYP2D6 poor metabolisers is approx 7% of Caucasians and 2% of African Americans. Currently, there are insufficient data supporting a recommendation for genetic testing before starting therapy.

CYP2D6 poor metabolisers
Individuals who are CYP2D6 poor metabolisers may result in higher tamsulosin systemic concentration. The US Food and Drug Administration (US FDA) drug label recommends using tamsulosin with caution, particularly in individuals receiving doses higher than 0.4 mg.

Severe: Contraindicated.

Dutasteride + Tamsulosin Should be taken with food. Swallow whole, do not crush/chew/open.

History of orthostatic hypotension. Severe hepatic impairment. Children and adolescents. Pregnancy and lactation.

Patient with large residual urinary volume and/or severely impaired urine flow for obstructive uropathy; coronary heart disease. Patients undergoing cataract or glaucoma surgery. CYP2D6 poor metabolisers (particularly those who are also concurrently taking potent CYP3A4 inhibitors). Not indicated for use in women. Severe renal impairment (CrCl <10 mL/min) and mild to moderate hepatic impairment.

Significant: Intraoperative floppy iris syndrome, orthostatic hypotension and syncope. Rarely, priapism.
Nervous system disorders: Dizziness, vertigo.
Reproductive system and breast disorders: Impotence, decreased libido, ejaculation disorder, breast disorder, gynaecomastia, breast tenderness.

PO: X

Women of child-bearing potential, pregnant or children should avoid handling the cap. Excreted in semen therefore use of condom is recommended. Avoid donating blood during and for at least 6 months after discontinuation of therapy. This drug may cause dizziness and vertigo, if affected, do not drive or operate machinery.

Rule out prostate cancer before initiation of therapy. Perform digital rectal examination, other assessment for prostate cancer or other conditions causing the same symptoms as BPH before and during therapy. Obtain new baseline prostate-specific antigen level after 3 months of treatment then monitor periodically thereafter. Assess for objective and subjective signs of relief of BPH (e.g. improvement in urinary flow, reduction in symptoms of urgency, relief of difficulty in micturition).

Symptoms: Tamsulosin: Acute hypotension, vomiting, diarrhoea.

Management: Supportive and symptomatic treatment. CV support should be given in acute hypotension; lying the patient down may restore blood pressure and heart rate, if insufficient, volume expanders and vasopressors may be given if necessary. Inducing emesis may delay absorption. May perform gastric lavage or administer activated charcoal and an osmotic lavage (e.g. sodium sulfate) for large doses.

Dutasteride: Increased serum concentration with potent CYP3A4 inhibitors (e.g. ritonavir, indinavir, nefazodone, itraconazole, oral ketoconazole).
Tamsulosin: Enhanced hypotensive effect with anaesthetic agents, PDE5 inhibitors (e.g. sildenafil, tadalafil, vardenafil) and other α₁-adrenoreceptor antagonists. Increased plasma concentration with strong CYP3A4 inhibitors (e.g. ketoconazole) or to a lesser extent, with strong CYP2D6 inhibitors (e.g. paroxetine) or a combination of both CYP3A4 and CYP2D6 inhibitors (e.g. amiodarone, cimetidine, imatinib). Decreased plasma concentration with furosemide. Increased elimination rate with diclofenac and warfarin.

Decreased rate and extent of absorption with food (within 30 minutes of a meal).

May cause decreased serum PSA levels by approx 50% within 3-6 months of use.

Description:
Mechanism of Action: Dutasteride, a 4-azo analogue of testosterone, is a competitive, selective inhibitor of both type 1 and type 2, 5α-reductase isoenzyme which results to the inhibition of testosterone to dihydrotestosterone conversion, thus significantly decreasing serum dihydrotestosterone levels.
Tamsulosin antagonises the α_1A-adrenoreceptors, which mediate the smooth muscle tone in the prostate. This results in the relaxation of smooth muscle in the bladder neck and prostate leading to an improved urine flow and reduced symptoms of benign prostatic hyperplasia (BPH).
Pharmacokinetics:
Absorption: Dutasteride: Absorbed from the gastrointestinal tract. Bioavailability: Approx 60%. Time to peak plasma concentration: 1-3 hours.
Tamsulosin: Absorbed from the gastrointestinal tract and almost completely available. Food decreases rate and extent of absorption. Time to peak plasma concentration: 6-7 hours (fed state); 4-5 hours (fasting).
Distribution: Dutasteride: Volume of distribution: 300-500 L. Plasma protein binding: Approx 99% to albumin; approx 97% to α₁-acid glycoprotein; >96% to semen protein.
Tamsulosin: Volume of distribution: Approx 16 L. Plasma protein binding: 94-99%, mainly to α₁-acid glycoprotein.
Metabolism: Dutasteride: Extensively metabolised in the liver by CYP3A4 and CYP3A5 into 6-hydroxydutasteride (similar activity to parent drug), and 4-hydroxydutasteride and 1,2-dihydrodutasteride metabolites.
Tamsulosin: Extensively metabolised in the liver by CYP3A4 and CYP2D6 into metabolites; further metabolised via conjugation into glucuronide or sulfate.
Excretion: Dutasteride: Mainly via faeces (40% as metabolites, approx 5% as unchanged drug); trace amounts via urine (<1% as unchanged drug). Terminal elimination half-life: Approx 3-5 weeks.
Tamsulosin Mainly via urine (76%, <10% as unchanged drug); faeces (21%). Elimination half-life: Approx 10-15 hours.

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 6918296, Dutasteride. https://pubchem.ncbi.nlm.nih.gov/compound/Dutasteride. Accessed Feb. 27, 2026.

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 129211, Tamsulosin. https://pubchem.ncbi.nlm.nih.gov/compound/Tamsulosine. Accessed Feb. 27, 2026.

Store below 30°C.

Drugs for Bladder & Prostate Disorders

G04CA52 - tamsulosin and dutasteride ; Belongs to the class of alpha-adrenoreceptor antagonists. Used in the treatment of benign prostatic hypertrophy.

Whirl-Carillo M, Huddart R, Gong L et al. An Evidence-Based Framework for Evaluating Pharmacogenomics Knowledge for Personalized Medicine. Clin Pharmacol Ther. 2021 Sep;110(3):563-572. doi: 10.1002/cpt.2350. Accessed 27/02/2026. PMID: 34216021

Annotation of FDA Label for Tamsulosin and CYP2D6. ClinPGx. https://www.clinpgx.org. Accessed 27/02/2026.

Annotation of HCSC Label for Tamsulosin and CYP2D6. ClinPGx. https://www.clinpgx.org. Accessed 27/02/2026.

Anon. Dutasteride. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 14/01/2021.

Anon. Tamsulosin. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 14/01/2021.

Buckingham R (ed). Dutasteride. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 14/01/2021.

Buckingham R (ed). Tamsulosin Hydrochloride. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 14/01/2021.

CYP2D6 - Tamsulosin. UpToDate Lexidrug, Pharmacogenomics Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 27/02/2026.

Duodart 0.5 mg/0.4 mg Capsules (GlaxoSmithKline Pharmaceutical Sdn. Bhd.). National Pharmaceutical Regulatory Agency - Ministry of Health Malaysia. https://www.npra.gov.my. Accessed 10/02/2026.

Dutasteride and Tamsulosin. UpToDate Lexidrug, Lexi-Drugs Multinational Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 10/02/2026.

Dutasteride/Tamsulosin Hydrochloride 0.5 mg/0.4 mg Hard Capsules (Accord Healthcare Limited). MHRA. https://products.mhra.gov.uk. Accessed 13/01/2021.

Dutasteride/Tamsulosin Hydrochloride 0.5 mg/0.4 mg Hard Capsules (Milpharm Limited). MHRA. https://products.mhra.gov.uk. Accessed 10/02/2026.

Dutasteride; Tamsulosin. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com. Accessed 10/02/2026.

Jalyn Capsule (GlaxoSmithKline LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 13/01/2021.

Jalyn Capsule (Waylis Therapeutics). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 10/02/2026.

Joint Formulary Committee. Tamsulosin with Dutasteride. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 10/02/2026.