Dutasteride (GI198745) In Benign Prostatic Hyperplasia Subjects

Inclusion Criteria: Only subjects who meet all the following criteria during the screening phase will be enrolled in the study. 1. Diagnosis: BPH 2. Age: ≥50 years 3. Gender: Male 4. Estimated prostate volume ≥30cc (by TRUS) 5. I-PSS Symptom Score (total of 7 items) ≥8 points 6. Maximum flow rate (Qmax) ≤15mL/sec (voided volume measured simultaneously ≤150mL)\*\[1\] 7. Patients who meet either of the following regarding tamsulosin HCl use: Patients with tamsulosin HCl use: Patients who have received tamsulosin HCl continuously for at least 4 weeks and who are likely to continue to take tamsulosin HCl without any change to the dosage and administration of the drug until the end of study treatment. Patients without tamsulosin HCl use: Patients who haven't received tamsulosin HCl in the past 4 weeks and who are unlikely to use tamsulosin HCl until the end of study treatment. 8. Outpatients 9. Patients who in person have given written consent Exclusion Criteria: Patients who apply to any of the following criteria during the screening phase will not be enrolled in the study. 1. Post void residual volume \>250mL (by suprapubic ultrasound). 2. History of AUR within the previous 12 weeks. 3. Evidence or history of prostate cancer. 4. PSA \>10ng/mL \[in patients with PSA \>4ng/mL, the presence of prostate cancer should be ruled out by the investigator/subinvestigator. DRE and free/total PSA ratio should be considered, and prostate biopsy be conducted if necessary\]. 5. Previous surgery (including balloon dilatation, thermotherapy and stent placement) or minimally invasive techniques for BPH. 6. Any causes other than BPH, which may in the judgment of the investigator/subinvestigator, affect evaluation of symptoms or urine flow (e.g., neurogenic bladder, bladder neck contracture, urethral stricture, bladder malignancy, acute/chronic prostatitis, acute/chronic urinary tract infection). 7. History of any unstable, serious co-existing medical condition(s) including, but not limited to, myocardial infarction, coronary bypass surgery, unstable angina, cardiac arrhythmias\*\[2\], congestive heart failure or cerebrovascular accident within the previous 6 months; or diabetes mellitus or peptic ulcer uncontrollable with medical treatment. 8. Liver function tests (AST, ALT, AL-P) \>2 times the upper limit of normal. 9. Serum cleatinine \>1.8mg/dL. 10. Use of any antiandrogen (e.g., chlormadinone acetate, allylesterenol) for BPH within the previous 12 months. 11. Use of a1-adrenoceptor blockers excluding tamsulosin HCl (e.g., prazosin HCl, urapidil slow-release capsule formulation, terazosin HCl, naftopidil), plant extract preparations for treatment of BPH (e.g., Eviprostat, cernitin pollen extract), herbal medicines (e.g., hachimi-jio-gan, gosha-jinki-gan), other drugs (e.g., Paraprost), and dietary or herbal supplements (e.g., saw palmetto) for relief of BPH symptoms within the previous 4 weeks. Use of a-adrenoceptor agonists (e.g., pseudoephedrine, phenyle * \[1\] Subjects with voided volume \<150 mL at Qmax measurement cannot be enrolled in the study and may undergo re-measurement of Qmax before the visit for Week 0 for study entry. * \[2\] Of "Degree II" according to "Grading of Side Effects (PMSB Notification No. 80 dated June 29, 1992) or equivalent (Appendix 4).