This is an exploratory clinical study to presume the optimum usage and dosage for a therapeutic confirmatory study by evaluating the efficacy and safety of TPN171H 5mg, 10mg, 20mg or placebo administered orally in patients with erectile dysfunction. In conclusions, Patients with erectile dysfunction (ED) were administered placebo, TPN171H 5mg, 10mg or 20mg 30 minutes to 4 hours before sexual intercourse for 8 weeks.

This is a Phase II study in 240 ED patients, which consists of 3 part: 1) a 4-week run-in period without any ED treatment; 2)randomization to 8 weeks of treatment with TPN171H or placebo; and 3) a 1-week follow-up period for continued adverse event monitoring.

The effects of TPN171H on ED will be evaluated using the IIEF-EF and SEP diaries. The IIEF-EF will be administered at baseline and at 4-week intervals following initiation of treatment, meanwhile the SEP diary will be completed by patients after each sexual attempt throughout the study.

Inclusion Criteria:

• Male patients aged ≥22 with ED, defined as an inability to achieve or maintain a penile erection sufficient for satisfactory sexual intercourse, evident for at least 3 months;
• Patients whose IIEF-EF domain score is < 26;
• Patients in a stable, heterosexual relationship for at least 3 months and during the study;
• Patients who are willing to stay away from any other medicines or treatments for ED during this study period;
• Patients who are willing to have 4 or more attempts of sexual intercourse each month, demonstrated compliance with the study protocol, including drug administration, diary completion, and scheduled study visits, during the qualifying trial;
• Patients who are willing to take proper contraceptive during the study and within 3 months after the study completed;
• Patients who have voluntarily decided to participate in this study, and signed the informed consent form.

Exclusion Criteria:

• Patients with anatomical malformations of the penis;
• Patients with primary hypoactive sexual desire;
• Patients with ED, which is caused by any other primary sexual disorder, like hypopituitarism, hypothyroidism, or hypogonadism.
• Patients with ED ,which is caused by spinal injury or have had a radical prostatectomy or other surgery ;
• Patients who have a penile implant;
• Patients who have a history of hypersensitivity to other PDE5 inhibitors or who have not responded to them;
• Patients with the following cardiovascular disease:

Myocardial infarction or stroke within the last 6 months; Unstable angina or angina occurring during sexual intercourse; New York Heart Association Class 2 or greater heart failure in the last 6 months; Uncontrolled hypotension (<90/60mmHg), or uncontrolled hypertension (≥160/95mmHg); Orthostatic hypotension.

• Patients administered with the following medications:

Nitrate/Nitric oxide (NO) donors; Androgens, anti-androgen, trazodone; Agents that significantly affect the CYP3A4 intermediary metabolism.

• Diabetic patients whose FBS is over 1.5 fold of normal value, or whose HbA1c exceeds 9%, or with diabetes complications, such as diabetic nephropathy, peripheral neuropathy;
• Patients with hepatic or renal dysfunction as per the following: AST, ALT≧2*ULN, serum creatinine exceeds 20% of the upper limit of normal value;
• Patients with active gastrointestinal ulcers and bleeding disorders;
• Patients who have a history of NAION, or with a known genetically degenerative retinopathy, including retinitis pigmentosa;
• Patients who have a history of sudden decrease or loss of hearing;
• Patient with a history of malignancy;
• Patients with a major refractory psychiatric disorder or significant neurological abnormalities;
• Patients with alcohol addiction or persistent abuse of drugs of dependence;
• Patients who are participating or discontinued participation in the past 3 months from any other clinical trial, or are planning to father a baby or are in a relationship with a pregnant partner.
• For other reasons besides the aforementioned cases, patient whose participation is deemed inappropriate due to clinically significant findings according to the medical decision of the principal investigator or the study personnel.