The study is a prospective, randomized, double-blind, placebo-controlled drug study to evaluate the pattern of erectile function recovery after robotic assisted laparoscopic prostatectomy (RALP). We hope to illustrate that early and continuous therapy with either Sildenafil citrate or pentoxyfylline after nerve sparing RALP will promote improved erectile function.

Evaluation of erectile function with the International Index of Erectile Function Questionnaire (IIEF) and measurement of penile length any time between the prostate biopsy and 3 days prior to RALP will be performed.

Patients will undergo a unilateral or bilateral nerve sparing-RALP.

Patients will be randomized to receive either 25mg Viagra twice daily, 400mg pentoxifylline twice daily or placebo twice daily, starting on the first postoperative day after surgery and continuing for one year. The biostatistician generates a table of random numbers. 120 subjects anticipated to enroll at Brooke Army Medical Center will be divided into 3 groups, sildenafil, pentoxifylline or placebo. The randomization table will be given to the research pharmacist.

Patients will have their erectile function evaluated at 3 months, 6 months, 9 months, and 12 months with IIEF and sexual intercourse diary. These visits are routine for post-operative care following a RALP, however, completion of the IIEF and sexual intercourse diary are being performed for study purposes.

Patients will stop therapy at 12 months and penile length will be re-measured. Measurement of penile length will be done for study purposes at the standard 1 year post-operative follow up visit.

Patient will undergo a 6 week washout period during which neither drug will be used, then repeat analysis of erectile function with IIEF will be performed, after which they may restart standard erectile dysfunction therapy as desired. This washout period and follow up will be for study purposes.

Inclusion Criteria:

1. Patients who have had a prostate biopsy positive for prostate cancer.
2. Patient must be age 30 - 89 years.
3. Patient must be willing to sign the Institutional Review Board approved consent.
4. Patient must have had (or be about to undergo) bilateral or unilateral nerve sparing RALP.
5. Patient must have an International IIEF equal to or greater than 21.

Exclusion Criteria:

1. Patients with known unstable angina, uncontrolled hypertension, congestive heart failure, or cardiovascular accident within the preceding 2 weeks.
2. Patients being treated with nitrate therapy.
3. Patients with significant renal or hepatic impairment, cerebrovascular disease.
4. Patients with prior erectile dysfunction as indicated by the initial IIEF.
5. Patients younger than 30 years of age.
6. Patients who did/will not have a unilateral or bilateral nerve sparing radical prostatectomy.
7. Patients who have had a prior reaction to Sildenafil or pentoxifylline.
8. Patients taking any potent inhibitor of cytochrome P450 3A4 (e.g., ketoconazole, itraconazole, erythromycin, etc.).
9. Patients with a clinically significant abnormality on preoperative ECG that in the opinion of the investigator may increase the patient's cardiovascular risk in this study.
10. Patients with a history of left ventricular outflow obstruction (e.g. aortic stenosis, idiopathic hypertrophic subaortic stenosis).
11. Patients with resting hypotension (BP < 90/50 mm Hg), or resting hypertension (BP > 170/110 mm Hg).
12. Patients with retinitis pigmentosa.
13. Patients with a bleeding disorder.
14. Patients with active peptic ulceration.
15. Patients with conditions that may predispose to priapism (e.g. sickle cell anemia, multiple myeloma, or leukemia).
16. Patients who have previously experienced non-arteritic ischemic optic neuropathy (NAION).

Must have a prostate