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SAN ANTONIO -- The use of investigational combination therapies to treat erectile dysfunction (ED) had mixed outcomes, according to results from two trials presented here.

In the phase II COCKTAIL study, investigators found that while the combined use of low-intensity shockwave therapy (LiST) and autologous platelet-rich plasma (PRP) was safe, the combination did not lead to statistically significant improvements in erectile function compared with saline and sham LiST treatment, reported David Velazquez, a fourth year medical student at the University of Chicago Pritzker School of Medicine.

In a second study, however, Nikolaos Pyrgidis, MD, of the University Hospital of the LMU Munich in Germany, reported that combining LiST with the phosphodiesterase type 5 (PDE5) inhibitor tadalafil to treat patients with severe ED significantly improved erectile function compared with sham therapy plus tadalafil.

Both studies were presented at the annual meeting of the American Urological Association.

COCKTAIL

was a single-center, phase II study that enrolled men with mild to moderate ED, as indicated by International Index of Erectile Function (IIEF) scores of 12 to 25, who were randomized to receive PRP plus LiST or saline plus sham LiST.

"Shockwave therapy involves administering low-intensity shockwaves directly to the corpus cavernosum to induce microtrauma and stimulate angiogenesis to promote better penile blood flow," Velasquez explained. "Platelet-rich plasma in a similar fashion involves the patient's own platelets, which have a concentration of growth factors and cytokines, injected back into the corpus cavernosum to stimulate better erectile function."

While both therapies have been studied as monotherapy, he said the idea behind combining the two is that it will improve erectile function through physical mechanisms such as wound healing, tissue regeneration, and vascular remodeling.

Shockwave therapy and PRP for ED are both considered investigational. However, the recommend the use of LiST in patients with mild vasculogenic ED or as an alternative first-line therapy for patients who don't want or are not suitable for oral vasoactive therapy.

The trial included 56 patients with a median age of 55 years. Patients who were previously taking PDE5 inhibitors were allowed to continue to take them during the course of the study, Velasquez explained, since that suggested these patients continued to experience mild to moderate ED.

Participants in the PRP/LiST group received weekly LiST over the course of 5 weeks, and two PRP injections -- one in the first week and one in the last week of the study. Participants in the saline/sham arm followed the same schedule and received treatment in the same manner. Follow-ups occurred at months 3 and 6.

Velasquez explained that sham LiST was achieved by wrapping a tourniquet over the LiST probe, with an ultrasound cover over that, so that patients could hear the shockwaves being administered without actually receiving the treatment.

Regarding safety, no adverse events (penile bruising, swelling, edema, allergy, or penile fracture) were observed in either group.

In terms of efficacy, there were no significant differences in IIEF scores from baseline to 3 months to 6 months within groups or between groups.

However, Velasquez observed there was a trend toward improved efficacy in both treatment groups at 3 months. He noted that the proportion of patients achieving a minimal clinically important difference in IIEF scores -- at least 7 points -- was similar between treatment groups (about 60% in each), "meaning that we likely have a high placebo effect."

The findings indicate that combined use of PRP and shockwave therapy "is safe, yet its clinical efficacy in treating ED may be insignificant due to small sample size," Velazquez concluded. "Further investigations with larger cohorts are necessary to explore the potential efficacy of combined PRP/LiST."

Shockwave Therapy and Tadalafil

In the second study, Pyrgidis and colleagues included 51 patients who had severe vasculogenic ED that only partially responded to the highest available dose of PDE5 inhibitors and remained severe after a washout period from PDE5 inhibitors or any other treatment.

Of these 51 patients, 34 were randomized to 12 sessions of LiST (three times weekly) plus daily tadalafil (5 mg) for 4 weeks, while 17 were randomized to sham LiST and tadalafil. After treatment, patients were evaluated at 1 and 3 months.

In the LiST/tadalafil group, IIEF scores increased from 7.7 at baseline to 12.1 at 1 month and 12.9 at 3 months, while the sham/tadalafil group's IIEF scores increased from 8.8 at baseline to 10.2 at 1 month and to 10.8 at 3 months.

A comparison of the groups after adjusting for baseline values showed that LiST/tadalafil increased IIEF scores by 3.2 points at 1 month and 3.1 points at 3 months, with both results statistically significant (P<0.001).

The number of patients achieving the 7 points or more improvement in IIEF scores that is considered the minimum clinically important difference in the LiST/tadalafil arm was two at 1 month (6%) and six (18%) at 3 months. None of the patients in the sham therapy arm achieved that mark.

No adverse events were reported during treatment and follow-up.

"For patients not willing to try any invasive treatment -- such as intracavernosal injections -- the combination of LiST and tadalafil may be considered an acceptable short-term option," Pyrgidis concluded. "Of course, further studies are needed to corroborate our findings."

He acknowledge several limitations to the study, including the low number of participants, short follow-up, and definition of severe vasculogenic ED based on medical history and clinical examination rather than by penile ultrasound measures.