An updated literature search yielded several small studies looking at pharmacotherapy (primarily sildenafil) post-prostatectomy to preserve erectile function and eventual return of functional natural erections:
•A recent small study involved 40 men with normal pre-operative erectile function who were randomized to sildenafil or a control 2 weeks post radical prostatectomy (RP). Using the International Index of Erectile Function (IIEF) questionnaire, scores for the sildenafil group were statistically significant for the mean score (25 +/- 6 vs. 17 +/- 9, p < 0.05) and potency rate (87% vs. 56%) at 24 weeks after the surgery.
•In another prospective study with 77 patients, sildenafil or tidalafil (tiw) were evaluated in a postoperative penile rehabilitation protocol. More than 60% of patients discontinued therapy within 6 months.
•In a 2009 restrospective study of 92 patients, researchers attempted to predict success of using oral sildenafil or intracavernosal injection (if oral therapy failed) for penile rehabilitation during 18 months post-prostatectomy. They concluded that approximately 57% of patients using a pharmacological rehabilitation program had return of functional natural erections. The authors noted that "predictors of successful outcome included nerve-sparing surgery, early post-RP presentation, young age (<60), and absence of vascular comorbidities."
Additionally there is a handful of ongoing clinical trials assessing pharmacologic penile rehabilitation, including sildenafil and testosterone.
Sources:
Trials registered with NIH
Pace G et al. Penile rehabilitation therapy following radical prostatectomy. Disabil Rehabil. 2010 Feb 15. [Pubmed abstract]
Lee DJ et al. Penile rehabilitation protocol after robot-assisted radical prostatectomy: assessment of compliance with phosphodiesterase type 5 inhibitor therapy and effect on early potency. BJU Int. 2010 Feb;105(3):382-8. [Pubmed abstract]
Muller A et al. Penile rehabilitation following radical prostatectomy: predicting success. J Sex Med. 2009 Oct;6(10):2806-12. [Pubmed abstract]