AUA 2009: Generics Not Equal to Brand-Name Drugs for Overactive Bladder

Martha Kerr

May 03, 2009

May 3, 2009 (Chicago, Illinois) — A comparison of brand-name oxybutynin with generic substitutes for overactive bladder shows that the bioequivalence in generic formulations can vary from 80% to 125% of the branded drug, investigators announced here at the 2009 annual meeting of the American Urological Association.

Steven A. Kaplan, MD, from the Department of Urology at Weill Cornell Medical Center in New York, and colleagues evaluated 156 consecutive patients with overactive bladder, 87 women and 69 men. Subjects were switched from brand-name Detrol LA, Vesicare, Enablex, or Sanctura XR to generic oxybutynin, either by their primary care physician or because of insurance reasons.

Patients completed 3-day diaries prior to the switch and after 8 weeks of treatment with the generic drug. Treatment-related changes were assessed by 24-hour daytime and nocturnal micturitions, development of urge and urge incontinence and International Prostate Symptom Score (IPSS) in men. Safety was assessed by changes in postvoid residual urine and adverse events.

In women, there was a doubling of daytime frequency of urination, a slight 20% increase in nocturia, and a 46.3% increase in urge incontinence.

In men, there was a 2.4-fold increase in daytime frequency, a 40% increase in nocturia, and a 40.6% increase in urge incontinence. In addition, there was a 3.7-point increase in IPSS.

Postvoid residual volume increased 14.7 mL in women and 19.7 mL in men. In addition, there were increased adverse effects in both sexes. Incidence of dry mouth increased 23.1% in women and 14.3% increase in men, and incidence of constipation increased 32.1% in women and 34.6% in men.

"Switching from Detrol LA and Vesicare to generic oxybutinin resulted in the greatest changes in safety and efficacy" (P < .01), Dr. Kaplan told Medscape Urology after his presentation.

"In 1984, 12% of prescriptions were generic. In 2007, 65% were generic, and it's been growing about 12% per year compared with branded prescriptions," he commented.

"Bioequivalence can vary from 80% to 125% of the brand-name drug. Bioequivalence does not equal therapeutic equivalence," he warned. "The approval process is much different for generic drugs.

"When we looked at changes in [prostate specific antigen] (PSA) levels among men on Avodart switched to the generic formulation, we saw a greater than 0.75 ng/mL increase at 3 months in 34% of men. That is an increase that would ordinarily trigger a biopsy, but I put them back on the brand-name drug. The PSA came down in all cases, and none of them needed a biopsy."

"This is a much more serious problem than I was aware of," AUA spokesman Kevin T. McVary, MD, professor of urology at Northwestern University Feinberg School of Medicine in Chicago, Illinois, commented in an interview with Medscape after listening to Dr. Kaplan's findings. "Cost drives the process of generic prescriptions over brand-name dispensation, so I don't see the situation changing unless the word gets out.

"Generics are an important part of our healthcare system, but the generic houses are under scrutiny," Dr. McVary pointed out.

"The findings on increasing PSA level, especially as a trigger for unnecessary biopsy, is particularly compelling.... I am going to have to review my prescribing habits.... And urology is just a small piece of the healthcare world. If this is true with cardiovascular drugs, for example, the implications are huge," Dr. McVary said.

"I always sign my prescriptions 'dispense as written,' which we can opt to do in New York," Dr. Kaplan said. "When the insurance companies call me on it, I just tell them that the science supports it."

In the meantime, "looking at how generic drugs are approved is a start," Dr. Kaplan said.

Dr. Kaplan and Dr. McVary have disclosed no relevant financial relationships.

American Urological Association (AUA) 104th Annual Scientific Meeting: Abstract 1870. Presented April 28, 2009.

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