Pharmaceutical stock Mallinckrodt PLC is tumbling on Wednesday after short-seller Citron Research released a new note valuing the stock at $20 and alleging the company “has committed FRAUD by lying to the investing public about the company’s dependence on the Medicare system.”This isn't the first time that Citron has attacked the controversial drug company. Citron’s Andrew Left said Mallinckrodt’s practices were worse than those of Valeant Pharmaceuticals Intl Inc roughly one year ago.Following the new report, Mizuho analyst Irina Koffler stepped up to defend Mallinckrodt. In her note, Koffler says that Citron is actually the one misleading investors.“While a significant number of Acthar-treated patients may be covered by Medicare/Medicaid, we think that the cost of the system is heavily rebated and inaccurately reflected in the dashboards,” Koffler explains.Koffler points out that the dashboards exclude manufacture rebates and price concessions, suggesting inflated cost estimates.In addition, she notes that Acthar prices rose only about 5 percent per unit in 2015 and 0 percent so far in 2016, much less than the prices of number of other generic drugs.Koffler believes that investors should take advantage of the selloff and snatch up the Buy-rated stock on the dip. Mizuho maintains an $89 price target for the stock.Shares traded recently at $61.53, down 9.2 percent on the day.Latest Ratings for MNK DateFirmActionFromToNov 2016Raymond JamesInitiates Coverage OnOutperformAug 2016Deutsche BankMaintainsBuyAug 2016BarclaysMaintainsOverweightView More Analyst Ratings for MNK View the Latest Analyst Ratings