Shares of Gilead (GILD), a leader in the hepatitis C virus treatment space, are sliding this morning after one competitor's hep C drug was granted FDA approval and another's sales disappointed. Additionally, Gilead reported its own news, announcing a shakeup of the roles held by its top executives.

MERCK APPROVAL: Merck (MRK) announced last night that the FDA has approved Zepatier for the treatment of adult patients with chronic hepatitis C virus, or HCV, genotype, or GT, 1 or GT4 infection. Merck has established a list price of $54,600 for a 12-week regimen of Zepatier, which the company said it believes to "be in the range of net prices for other commonly used HCV direct-acting antiviral regimens at 12 weeks of therapy." In contrast, a 12-week regimen of Gilead's Sovaldi is reported to be priced at $84,000. Merck added that it anticipates that this price, as well as its "strategy to seek broad coverage across commercial and public segments," will help broaden and accelerate patient access to treatment.

ABBVIE RESULTS: Meanwhile, Gilead competitor AbbVie (ABBV) announced financial results for the fourth quarter this morning. AbbVie announced Q4 sales of Viekira Pak, its own hep C treatment, of $554M, including U.S. sales of $197M and international sales of $357M. Analysts expected AbbVie to report Q4 Viekira sales of $568.5M, according to a Bloomberg consensus estimate that factored in four forecasts.

EXECUTIVE CHANGES: Additionally, Gilead announced this morning that current chairman and CEO John Martin will assume the role of executive chairman, effective March 10. John Milligan, currently president and COO, will be promoted to CEO and appointed to the company's board.

PRICE ACTION: In morning trading, Gilead shares slipped 3.5% to $84.50, while AbbVie fell 2.4% to $54.53 and Merck gained 1% to $49.75.