Shire has flagged the promise of existing and new drugs as evidence that AbbVie's $46 billion offer undervalued the company.

The company is the latest British firm to be targeted by a US group seeking lower taxes. 

Shire is taking a leaf out of AstraZeneca's playbook by disclosing long-range internal forecasts - a tactic used successfully by its larger rival in fending off a $118 billion bid from Pfizer. 

Chief executive Flemming Ornskov said that the company's current products would generate sales of at least $7 billion by 2020, with $3 billion more coming from drugs still in the pipeline.

Shire also said that in the medium term it expected sales of $6.5 billion by 2016. 

The company, best known for hyperactivity and rare-disease drugs, had said on Friday it was targeting sales of more than $10 billion by 2020 without giving details. 

Ornskov said that actual sales could be far above $10 billion, since the long-term forecasts did not include revenue from future deal-making or from two recent transactions. 

"M&A will clearly add growth to the profile," he said, noting that the London-listed company had done six deals since he took over 13 months ago. 

Shire is a serial acquirer, buying rare disease specialist Viropharma for $4.2 billion last November in its biggest deal yet - and Ornskov said further "large" deals were possible. 

As with AstraZeneca's earlier upbeat long-term forecasts, many industry analysts view Shire's $10 billion sales prediction as optimistic, with Credit Suisse saying its own estimates suggested sales of around $8 billion by 2020. 

Nonetheless, the confident performance may encourage AbbVie to dig deeper after the two companies confirmed a series of approaches following a Reuters report last week.

Analysts estimated the US company could make the deal pay at a price of up to $55 a share, or $55 billion, compared to AbbVie's most recent rejected cash-and-shares offer on May 30 of just over $46. 

Key drugs that Ornskov expects to drive continued strong growth include its best-selling hyperactivity medicine Vyvanse, which is now also being tested as a treatment for binge eating, as well as a much-anticipated drug for dry eye disease calledl ifitegrast, which it sees as a potential $1 billion-plus seller. 

Shire's strategy copies AstraZeneca's in another way, too, by highlighting the execution risks associated with AbbVie's plan to cut its tax bill through redomiciling in Britain for tax purposes - an industry-wide ploy that has sparked growing political concerns. 

Such "inversions" by US companies have moved centre-stage in the pharmaceuticals sector this year, with those firms still paying high tax rates anxious to strike deals that will help them compete with rivals now enjoying lower taxes. 

Whether Shire, long viewed as a likely takeover target, escapes the clutches of a larger predator is uncertain and the company is widely seen as more vulnerable to a takeover by AbbVie - or another company - than AstraZeneca. That reflects both its smaller size, which makes it a more manageable target for a wider range of players, and the lack of attendant political issues in Britain, where the company has a relatively small workforce. 

Although established in Britain in 1986 and listed in London, Shire conducts most of its business in the US and has been resident in Ireland for tax purposes since 2008. Other companies that industry sources say have looked at Shire in the past include Allergan, itself the target of a takeover approach by Valeant. 

Sources suggest Shire could also appeal to groups such as Bristol-Myers Squibb and Gilead Sciences. 

Ornskov declined to comment on whether Shire had received approaches from companies other than AbbVie. 

For AbbVie CEO Richard Gonzalez, Shire fits the bill in one important respect: it offers a way to reduce his firm's over-reliance on rheumatoid arthritis drug Humira, the world'stop-selling medicine, which accounted for 58% of the company's sales in the first quarter.
Humira's US patent lapses in late 2016, although it may take years for other drugmakers to develop their own versions of the antibody treatment.
AbbVie itself raised in 2014 profit forecast today, citing strong recent business performance.