THERAPEUTIC SUBSTITUTION COULD MASK BREAKTHROUGH POTENTIAL

THERAPEUTIC SUBSTITUTION COULD MASK BREAKTHROUGH POTENTIAL of new pharmaceuticals early in their clinical use, FDA's Peter Rheinstein, MD, suggested at a March 15 seminar sponsored by the Institute of Alternative Futures. "The danger from therapeutic substitution, even if it's done through formulary boards . . . is that a new product that's out there, which is not markedly different from its predecessors, will be immediately substituted with something that's already out there -- probably something for which there exists generic alternatives," Rheinstein said. Consequently, "there's a real potential for missing a breakthrough." Citing estimates that 10-30% of prescriptions are therapeutically substituted under sets of prearranged conditions, Rheinstein the trend "may increase because of pressures on the health care system." If the practice "increases to any great extent, it brings up a whole new set of problems, and that really is: 'who will pay for research on new drugs?'" After a drug is approved by FDA as safe and effective, it "really needs to be out there for a while in clinical practice before [prescribers] can figure out how it's better, worse, or just plain different from what's already out there," he noted. "The other problem, of course, is that if you substitute very early," the innovator loses sufficient time to recoup its investment. "If that happens, obviously you're going to get less development of drugs that are not markedly superior," Rheinstein suggested. The Medical College of Virginia's Pharmacy and Pharmaceutics Chairman William Barr, PhD, asserted at the March 15 meeting that overall pharmaceutical quality has increased since the advent of generic competition. "Over the past 10-15 years, in which we've had the entry of generic drugs into the marketplace, I would say that quality control is much higher than it was," said Barr, who served on FDA's bioequivalence advisory panel in the autumn of 1986. "The overall quality of drug products that we see in the marketplace has been drastically, dramatically improved because of the more rigid bioavailability and bioequivalence requirements, which have taught all the companies how to do a better job." On the other hand, Barr said studies are needed to determine when different products are interchangeable. "Adequate studies" are needed, he maintained, "[to test] products on the marketplace in a systematic way." Noting that "a bioequivalence study is a one-time study . . . using 16-24 healthy young adult ambulatory males," Barr suggested that subsequent comparative studies be done. When a generic "product gets out on the marketplace and it's been out there two or three years, and five or six or 10 or 15 other products have been out in the marketplace, we don't know how well these products can be interchangeable," he said. "We simply don't know unless we survey them from time to time, and we have not done that kind of a survey." Another unknown is whether there are "subsets" of the patient population "who may not be able to interchange those drugs during therapy," Barr concluded.