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Is FDA Approving Too Many Drugs Starting with 'X' and 'Z'?

Posted 16 May 2013 | By Alexander Gaffney, RAC

Regulators with the US Food and Drug Administration (FDA) had a few things to clarify with industry and medical practitioners in the latest issue of the New England Journal of Medicine.

Namely: No, they don't believe that industry has an "insatiable proclivity to include the letters X and Z" in their proprietary names, as some have suggested.


FDA approves final trade names submitted by companies, and among its approval criteria for names is whether they are easily discernible from one another. If a company submitted a trade name application for a drug with the trade name Samplus, but another drug already existed by the name of Simplus, FDA might find cause to reject that name in favor of another.

As with most things, branding efforts are subject to trends and fads, and some industry analysts have observed that it seems like more and more drugs are using the letters "X" and "Z" in their trade names as of late.

To name a few from the last few years: Xofigo, Xtandi, Xarelto, Xalkori, Xgeva, Zaltrap, Zytiga, Zelboraf, Zioptan, and Zometa.

Perceptions and Reality

But, as Carol Holquist and Kellie Taylor, respective director and deputy director of FDA's Division of Medication Errors Prevention and Analysis, write in NEJM, perceptions aren't necessarily indicative of reality.

"Approximately 2% of the more than 6000 approved drug names begin with X or Z," the duo wrote. In addition, they said that a "recent review" conducted by FDA "did not find a disproportionate number of names commencing with X or Z."

Taylor and Holquist did, however, concede the point that names with the same letter have the potential to be confusing. "The relative use of particular letters is an important safety consideration when constructing a name, since most cases of name confusion occur between names that begin with the same letter," they wrote. "Selection of infrequently used letters is prudent, provided the names are uniquely constructed. Discouraging manufacturers from incorporating the letters X and Z unnecessarily restricts name possibilities."

Due Diligence

But they fought back against the perception that FDA was not exercising its due diligence when it came to protecting consumers from similar-sounding names.

"With regard to the trade names Zometa, Xgeva, Zytiga, Xtandi, and Jevtana identified as possibly confusing, each name underwent a thorough safety analysis by the FDA before marketing," they said. "We evaluated the potential for confusion, considering the similarity of the names to other drug names in conjunction with product characteristics (including such attributes as indication for use, product strength, and dosing). We concluded that each name was suitable for approval on these grounds."

However, they did concede that their premarket review may need continuing adjustments, and invited the authors of an earlier critique to come forward with their full concerns. "As regulators, we review the proprietary names of drugs before marketing to ensure that the names are unique and unlikely to cause confusion," Taylor and Holquist concluded. "To best achieve this goal, it is important that our analysis continues to be informed by the safety concerns expressed by clinicians."

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