Piper Jaffray analyst David Amsellem recommends bracing for a "significant downward guidance revision" from Valeant Pharmaceuticals (VRX). The company's 2016 guidance implies a revenue and earnings growth rate in the second half of 2016 versus the first half of 7% and 48%, respectively, Amsellem tells investors in a research note previewing the Q3 earnings reports in the Specialty Pharmaceuticals space. The outlook reflects improving dynamics for the gastroenterology and dermatology segments, as well as for emerging markets segments, but the prescription trends "simply do not reflect those hopes," Amsellem writes. Prescriptions for Xifaxan showed a Q3 sequential growth rate of 0.6% versus Q2, while Rx's for the entire gastroenterology business declined by 4% in Q3 versus last quarter, the analyst notes, citing data from IMS. He points out that Valeant's prescriptions in Dermatology declined by 4% in Q3 versus Q2. The analyst has an Underweight rating on shares of Valeant with a $22 price target. The stock closed yesterday at $22.06. The company reports Q3 results on November 8. Within the Specialty Pharmaceuticals sector, Amsellem believes Akorn (AKRX) is best positioned for Q3 upside and a potential upward revision to guidance.