$11 billion drugmaker Mylan and US drug giant Pfizer are teaming up to reshape Mylan's business. 3 tough questions from Wall Street analyst show the challenging road ahead.

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Mylan is combining with a unit of US drug giant Pfizer.

• The drugmaker Mylan is combining with a Pfizer unit that makes off-patent drugs like Viagra. The all-stock deal was announced on Monday and aims to revitalize Mylan's flagging stock.
• Three tough questions from Wall Street analysts on a Monday conference call show why the spinoff could face an uphill battle.
• Analysts questioned the deal at a big-picture level and from a growth perspective. They also asked about difficulties in the broader business environment.
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A major deal announced on Monday will combine generic drugmaker Mylan with a unit of Pfizer that makes off-patent products like Viagra.

The all-stock merger is a bid to revitalize Mylan, best known for making the EpiPen allergy shot. Mylan's shares have lost almost half their value over the past year, though they surged 14% on Monday after the deal was announced. Pfizer's stock fell 2%.

The deal is already facing some tough questions from Wall Street.

In a Monday morning conference call, analysts asked crucial questions about the deal, including about investor confidence, growth opportunities and the underlying business model.

Executives occasionally got testy, seeking to portray the spinoff as a transformational new corporate entity.

"This is about enhancing every aspect of our organization, starting with the Board of Directors, starting with management, starting all the way down the line," said longtime Mylan Chairman Robert Coury, who will stay on at the new organization as executive chairman.

Other familiar faces at the top of the new company include Rajiv Malik, a longtime exec at Mylan. Michael Goettler, a pharma industry veteran who serves as group president of Pfizer's Upjohn business, will be the new CEO.

Notable absences from that list include Heather Bresch, Mylan's CEO who led the company during its EpiPen scandal. Bresch will be retiring, the companies said. Mylan CFO Ken Parks is also out and the new company is searching for a CFO.

Read more: The 2 big pharma companies behind Viagra and EpiPen are betting an unusual deal can create a new kind of drug company that you'll actually want to invest in. One slide reveals why.

Read on for the three biggest questions analysts asked that reveal key challenges facing the new company