Stocks making the biggest moves premarket: CI, BHC, MNK, DF, MAR, Z & more

Check out the companies making headlines before the bell:

Cigna – The health insurer's $54 billion deal to buy pharmacy benefits manager Express Scripts will be opposed by activist investor Carl Icahn, who issued an open letter to Cigna shareholders. Icahn calls the deal a "folly" and that it carries a "ridiculous" price tag, and adds that Amazon.com represents an "existential threat" to pharmacy benefit managers.

Bausch Health – The company formerly known as Valeant Pharmaceuticals beat Street forecasts on both the top and bottom lines for its latest quarter, as well as slightly raising its adjusted full-year revenue forecast.

Mallinckrodt – The British drugmaker earned an adjusted $1.78 per share for its latest quarter, 30 cents a share above consensus estimates. Revenue also beat analysts' forecasts, and the company raised its full-year sales growth guidance.

Dean Foods – The dairy producer matched forecasts with adjusted quarterly profit of 16 cents per share, with revenue beating forecasts. However, the company slashed its full-year earnings forecast due to non-dairy cost inflation, as well as other factors.

Marriott – Marriott reported adjusted quarterly profit of $1.73 per share, beating the consensus estimate of $1.38 a share. The hotel operator's revenue came in shy of Street forecasts, however, and the company also gave a weaker-than-expected forecast for current-quarter revenue per available room – a key hotel industry metric – although it kept its full year forecast for that metric unchanged.

Hertz Global – Hertz lost 19 cents per share for its latest quarter, smaller than the 24 cents a share loss anticipated by Wall Street. The car rental company's revenue beat estimates, and Hertz said it saw growth across all of its business segments.

Etsy – Etsy fell a penny a share short of forecasts, with quarterly profit of 3 cents per share. The online crafts marketplace operator's revenue beat estimates and it also boosted its full-year guidance for revenue and gross merchandise sales.

Weight Watchers – Weight Watchers reported quarterly profit of $1.10 per share, 13 cents a share above estimates. The weight loss company's revenue beat forecasts. Weight Watchers reported a 28 percent year-over-year jump in subscribers, and raised its full year earnings forecast.

Zillow – Zillow came in 3 cents a share above estimates, with adjusted quarterly profit of 13 cents per share. The real estate website operator's revenue missed forecasts. Zillow also issued weaker-than-expected full-year revenue guidance. Separately, the company announced it was buying Mortgage Lenders of America, currently a Zillow advertiser, for an undisclosed amount.

Twilio – Twilio earned an adjusted 3 cents per share for its latest quarter, compared to analysts' expectations of a 5 cents per share loss. The cloud communications company's results were helped by growth in its voice and messaging products, among other factors.

GlaxoSmithKline – Glaxo named Iain Mackay as the drugmaker's new chief financial officer as of January 14, 2019. Mackay will join Glaxo from his current role as CFO at banking giant HSBC.

Alibaba – Alibaba will reportedly merge its food delivery units and raise funds for the combined business, according to a Reuters report.

Alcoa – Alcoa is asking the U.S. for an exemption on aluminum purchased from Canada. Alcoa said no U.S.-based aluminum producer can meet its specifications and quality requirements for aluminum used in the manufacture of beverage cans.

Allstate, Progressive – The two insurers were rated "outperform" in new coverage at Credit Suisse, saying they are positioned to benefit from telematics technology that tracks precise information about the cars and drivers they insure.