Earlier this month, we wrote how IMS data was wreaking havoc with several drugmakers that relied on the firm to calculate market share and sales rep compensation. Novartis was the most notable example, mostly because the drugmaker created a flap after telling its reps that some would have to return bonus money. But Wyeth and Lilly also had trouble, although they told Pharmalot there were no plans to ask reps to fork over any dollars.

Now, Merck can be added to the list. A spokeswoman confirms the difficulties, although the trouble with IMS data is apparently on a regional, not national level. “However, we are working closely with IMS to determine whether sub-national performance reporting corrections will be large enough to impact our various sales compensation plans,” she writes us. “We expect to have corrected information from IMS in a few weeks that will enable us to make any corrections if they prove to be necessary.” There was no word, though, on whether Merck reps will be forced to return bonuses.

Again, the IMS mess is very much a behind-the-scenes, inside baseball drama, but it’s likely to set off a scramble among data firms, such as smaller, up-and-coming operations, to fight for those lucrative and crucial pharma contracts showing market share.