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Generic Urologic Drugs Less Effective

Two small observational studies suggest that switching from branded to generic urologic drugs led to deterioration of efficacy and more side effects.

In one study, investigators studied 257 men with lower urinary tract symptoms (LUTS) that was treated for at least 6 months with branded medication – alpha-blocker in 169 men and 5 alpha-reductase inhibitor (5ARI) in 88 men. The patients were switched from a branded drug to generic substitute as required by the patient’s insurance company or by the patient’s primary care physician.  After the switch the men were followed for a year.

The mean baseline symptom score (IPSS) for patients on alpha-blocker was 8.9, after the switch to generic drug it increased to 12.9 at six months and 13.2 at 12 months.

For 5ARI, the mean IPSS was 11.3 which increased to 14.7 at six months and 16.2 at 12 months after the switch.

The mean PSA value increased from 1.1 to 1.7 ng/mL in the 12 months after switching from Avodart (dutasteride) to generic finasteride and from 1.2 to 1.5 ng/mL in men switched from Proscar to generic finasteride.

A third of patients in the Avodart group had more than a 0.75 ng/mL rise in PSA after the switch, as did 14% of the Proscar group.

Dr. Steven Kaplan, M.D. of Weill Cornell Medical College in New York said “The PSA changes after the switch to generic finasteride could have been sufficient to trigger unnecessary biopsies.”

Side effects which include dizziness, nasal congestion, and ejaculatory dysfunction also increased by 2% to almost 5% after the switch from branded to generic alpha-blocker.  Because of adverse effects, 26 men were switched back to the branded alpha-blocker.

In the second study, 87 women and 69 men with overactive bladder were switched from a branded anticholinergic drug to generic oxybutynin.  After the switch, the women had 29.4% increase in the rate of urge incontinence and similar increases in frequency and nocturia.  Men had increased rates of urge incontinence, nocturia and frequency. Postvoid residual increased by 15 mL in women and by 18.9 mL in men after the switch.

Following conversion from branded to generic drugs, the frequency of dry mouth and constipation increased in women by 36.4% and 23.01%, respectively, and by 39.5% in men.

“These findings should not consider generic drugs as bad or that it should go away.  People should understand what generic drugs are and make their decisions accordingly.” said Dr. Kaplan.

Generics drugs have been gaining popularity. Prescriptions of generic drugs increased by 12% a year from 2004 to 2008 whereas prescriptions for branded drugs decreased by 6% a year.  In 2008, generic drugs accounted for 2.4 billion prescriptions compared to 1.4 billion branded drugs.

Manufacturers of generic drugs only need to demonstrate the bioequivalence of their drugs vis a vis the branded version.  In the U.S. the definition of bioequivalence encompasses the range from 80% to 125% of the active compound.

That definition means that generics within a specific drug class can vary substantially in the bioavailability of the active compound and that generic versions of individual drugs within the class may exhibit just as much variability.

“The bottom line is that bioequivalence does not mean therapeutic equivalence,” said Dr. Kaplan.

Note that these studies were published as abstracts and presented orally at a conference.  These data and conclusions should be considered to be preliminary.

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