SAN FRANCISCO—Baseline PSA and prostate volume may predict which patients may respond best to botulinum toxin type A (BoNT-A) treatment of lower urinary tract symptoms (LUTS), according to a study presented at the American Urological Association (AUA) annual meeting.

The finding is based on a study of 108 men with moderate to severe LUTS (AUA Symptom Score [AUASS] of 8 or greater) and age 50 or older. The men, who were recruited at seven U.S. sites, were randomized to receive either 100 or 300 units of BoNT-A injected into the prostate transrectally.  The subjects were seen at 4, 8, and 12 weeks, and then again 12-months post-treatment. Investigators assessed total prostate volume (TPV), transition zone volume (TZV), serum PSA, AUASS, Qmax, and post-void residual volume (PVR) at baseline, 12 weeks, and 12 months.

Of the 108 men, 53 received 100 units of BoNT-A and 55 men received 300 units. The mean age of the group was 66 years.

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At baseline, Qmax was 9.8 mL/sec, the AUASS was 19.2, TPV was 50.1 cc, TZV was 24.2 cc, and the PSA was 2.4 ng/mL. Three months later, Qmax was 12.4 mL/min (a 27.7% increase) and AUASS was 11.1 (a 41.1% reduction). No significant changes were observed in TPV, TZV, or PSA.

Baseline PSA and baseline TPV were significantly associated with absolute and percentage changes in AUASS changes at 12 months. TZV was significantly associated with absolute AUASS changes only at three months. PSA levels significantly predicted absolute and percentage changes in Qmax. The greatest responses in AUASS occurred in men with the lowest PSA levels.

“We found that you can change the symptoms and change the flow rate and improve the situation, but it [BoNT-A] does not shrink the prostate,” said lead investigator Kevin T. McVary, MD, Professor of Urology at Northwestern University Feinberg School of Medicine in Chicago. 

The study may give clinicians a better idea of which men with moderate to severe LUTS may benefit the most from this type of therapy. “There was a very consistent pattern here. If your prostate was quite big, the botulinum toxic still works but you are less likely to respond robustly.  Another way to say it is that it works best in the smaller prostates,” Dr. McVary said. “By smaller prostate volumes we mean anything from 20 to 50 grams.”

“This is a good phase 2 trial that gives us guidelines for how it could be used,” commented Anthony Smith, MD, Professor and Chief of Urology at the University of New Mexico in Albuquerque. “We need to know how to use it.  This now gives us some information how to use the treatment and it would still be using it off-label.”