Urodynamic studies have been used by urologists as a tool to study lower urinary tract function for over 50 years. In patients with BPH, several changes can occur when the hyperplastic prostate tissue obstructs the urethral orifice. Specifically, urethral resistance to flow rises, urinary flow rate drops, and detrusor pressure rises.
Kirby and associates found a mean increase in urinary flow rates of 2.7 mL/s after 1 yr when comparing patients taking 5 or 10 mg of finasteride per day with patients taking placebo (40). Furthermore, patients who continued in the study taking 5 mg/d for 3 yr (open extension) demonstrated improved maximal urinary flow rates from 8.7 mL/s to 13.8 mL/s and decreased mean maximal subtracted voiding pressure from 72 cm H2O to 49 cm H2O. However, the authors concluded that the maximal therapeutic effects are not seen until after 1 yr of therapy.
In 1996, Lepor and the Veterans Affairs Cooperative Studies Benign Prostatic Hyperplasia Study Group published a manuscript detailing the efficacy of terazosin, finasteride, or both in treating BPH. Placebo, terazosin (10 mg/d), finasteride (5 mg/d), and combination fina-
steride/terazosin therapy were compared after 1 yr of treatment. The investigators found that peak urinary flow rates were equally affected by finasteride and placebo. Furthermore, finasteride and terazosin combination therapy was no more effective than terazosin alone in improving flow rates. They concluded that in BPH, terazosin was effective therapy, whereas finasteride was not, and that the combination of terazosin/finasteride treatment was no more effective than terazosin alone.
In 1999, Schafer and associates in the Finasteride Urodynamics Study Group found that, compared with placebo-treated patients, finasteride-treated patients experienced a significant decrease in detrusor pressure at maximum flow and a significant increase in maximum flow rate (41). Patients in this study who had enlarged prostate glands (> 40 mL volume) demonstrated greater improvement in urodynamic parameters.
Additionally, Roehrborn and associates evaluated the PLESS data in 1999 and found that baseline PSA and prostate volume were both good predictors of posttreatment changes in symptom scores and flow rates (42). Baseline PSA levels > 1.4 ng/mL and enlarged prostate glands were parameters predictive of effective patient response to long-term finasteride treatment.
Collectively, these studies suggest that careful patient evaluation is essential in properly selecting individuals who will demonstrate urodynamic improvement as a result of finasteride therapy. Patients with small prostate glands (< 40 mL volume) and low baseline PSA (< 1.4 ng/mL) display marginal urodynamic improvement with the same treatment.
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