Horizon Pharma has agreed to acquire Vidara Therapeutics via a reverse merger in a tax-driven deal valued at approximately US$660 M. The resulting entity will be named Horizon Pharma plc and will be organised under the laws of Ireland with Horizon’s current shareholders owning approximately 74% of the company. With the acquisition, Horizon will add the immune system modulator Actimmune® (interferon gamma-1b), which is used in the treatment of chroni c granulomatous disease and severe, malignant osteopetrosis, to its portfolio of arthritis drugs.