Valeant Pharmaceuticals International Inc’s stock plunged as much as 40 percent on Wednesday after an influential short-seller accused the company of using specialty pharmacies to inflate its revenue, an allegation that the drugmaker denied. Citron Research, a short-selling firm run by Andrew Left, alleged that Valeant’s previously undisclosed ties to specialty pharmacies, including Philidor and R&O Pharmacy Inc, helped the company create “phantom sales” of its products or push more product through distribution channels than sales would warrant.