PF-4455242

PF-4455242 is a selective, short-acting (non-"inactivating") antagonist of the κ-opioid receptor. Discovered by Pfizer in 2009, it was pursued in a phase I clinical trial for the treatment of bipolar disorder, and was also investigated as a treatment for depression and substance abuse. However, development was stopped in September 2010 due to toxicology findings in animals that had been exposed to the drug for three months.