Inclusion Criteria:
1. Men between the ages of 40 and 65 years;
2. Exclusive heterosexual men, regardless of race or social class.
3. RP due to prostate cancer without metastasis;
4. RP performed less than 60 days before the screening visit;
5. Erectile function prior to normal RP, defined as IIEF questionnaire with more than 22 points in domain A;
6. Stable sexual partner (more than 2 months prior to RP), and intention to maintain the relationship during the study.
7. Continuous use of 5mg Tadalafil from the 30th up to the 60th day after RP.
Exclusion Criteria:
1. Prostate cancer in TNM stage classified as T3 or T4.
2. Perineal and/or open RP;
3. Necessity of other therapy for prostate cancer than RP, including radiation therapy or hormone therapy;
4. Uncontrolled diabetes at screening visit (HbA1C \> 10%);
5. Prior spinal cord injury with lower limb paralysis;
6. Current male hormone use, or hypogonadism, defined by total testosterone below 8 nmol/L (2300 pg/mL) or total testosterone between 8 and 11 nmol/L (2300 and 3170 pg/mL) and free testosterone \< 220 pmol/L (\< 64 ng/dL);
7. Patients with current depression, characterized by use or need for use of antidepressants.
8. Presence of genital lesions (such as severe penile fibrosis or Peyronie's disease) or active sexually transmitted disease (STD) (such as herpes, gonorrhea, candidiasis, HPV, and others) that impair analysis of local adverse effects on the genitalia;
9. Use of topical medications in the genital region that may interfere in the IP evaluation, as well as in its absorption or drug interaction;
10. Possession of penile prosthesis;
11. History of symptomatic hypotension, or diseases that increase the risk of symptomatic hypotension, such as patient with heart diseases (including history of angina and/or heart failure) and nephropathies;
12. Current use of nitrates, such as propatilnitrate (Sustrate®), isosorbide (Monocordil®, Cincordil®, Isordil®), nitroglycerin (Nitradisc®, Nitroderm TTS®, Nitronal®, Tridil®) and isosorbitol dinitrate (Isocord®);ketoconazole; ritonavir; and rifampicin.
13. Findings on ECG and/or laboratory tests that, in the Investigator's criteria, are considered significant and offer risk to the research volunteer's participation or may hinder the study analyses;
14. BP outside the limits considered safe: SBP below 90 mmHg or above 170 mmHg; or DBP below 50 mmHg or above 100 mmHg, except situations such as "white coat syndrome";
15. Diseases that can cause priapism, such as sickle cell anemia, multiple myeloma, or leukemia;
16. Histroy of priapism, defined as painful erection from up to 6 hours.
17. Current relevant diarrhea, defined as duration over four weeks, association with abdominal pain or dysabsortive syndrome, or presence of mucus, pus, or blood in the stool;
18. Known hypersensitivity to tadalafil and/or BZ371A;
19. History of symptomatic Lactose intolorence such as: the necessity of enzymatic treatment, abdominal distension or diarrhea when ingesting products or supplements with lactose;
20. Low adhsesion to 5mg Tadalafil use, characterized by the use of \<80% of the pills between the 30th and 60th day post PR;.
21. Pregnant or lacting partner.
22. Partner in childbearing age which does not accept to get exposed to the treatment
23. Any disease, condition or physical finding that the Investigator considers significant and that increases the risk of the research subject's participation or may interfere with the results, including severe debilitating illness, presence of cancer other than prostate cancer, severe mental illness persistent medication abuse;
