NEW YORK -- Valeant Pharmaceuticals and activist investor Bill Ackman have unveiled details of their offer to buy Botox maker Allergan, proposing a cash-and-stock deal that could be worth about US$45 billion -- if they overcome the California-based specialty drug company's reluctance.

Quebec-based Valeant, already one of Canada's largest pharmaceutical companies, says a combination with California-based Allergan would be good for shareholders of both companies.

It's proposing to exchange US$48.30 in cash and 0.83 shares of Valeant per Allergan share -- worth about US$152.89 in total based on Monday stock prices. Allergan Inc. stockholders would own 43 per cent of the combined company.

Allergan shares ended regular trading on Monday at US$142 per share but was about 18 per cent above that in pre-market trade before the Tuesday open, trading at about US$167.31

Valeant shares also rose after the proposal was announced, trading at US$132.25 about 30 minutes before Tuesday's open -- up from $126.1 at the end of Monday's regular session at the New York Stock Exchange. In Toronto, Valeant shares closed Monday at C$138.76.

Ackman's Pershing Square Capital Management LP -- Allergan's biggest stockholder at 9.7 per cent -- has agreed to take only stock in the transaction.

If an acquisition happens, it would give Valeant an array of other cosmetic and eye drugs and add to a string of more than 50 acquisitions that have made it one of Canada's largest drugmakers.

Valeant Chairman and CEO J. Michael Pearson said in a statement that Allergan CEO David Pyott and the company's board have made it clear that they don't want to have talks about a potential combination. But Pearson said he's hoping that the offer being put on the table will enable the two sides "to engage in productive discussions."

On Monday Allergan said in a statement that if it received an offer that its board -- along with financial and legal advisers -- would evaluate it.

Valeant, which is based in Laval, said Tuesday that it anticipates the proposed Allergan deal resulting in more than $2.7 billion in annual cost savings.

Allergan, based in Irvine, Calif., has long been considered one of the star performers in the specialty pharmaceutical sector. "Specialty pharmaceutical" is an industry term that differentiates smaller drugmakers from much bigger companies that sell a wide array of drugs, such as Pfizer and Merck.

Allergan reported revenue of $6.3 billion last year, up 12 per cent from 2012. The company's growth has been driven by expanding use of its blockbuster product, Botox, combined with a broad offering of eye care drugs, skin care formulas and breast implants.

Last year Botox sales rose 12 per cent to nearly $2 billion. First introduced in 1989, the injectable drug is most famous for its ability to smooth wrinkle lines on aging foreheads. But over the years Allergan has racked up more than a half-dozen other approved uses for Botox, including treatment for neck spasms, eye muscle disorders and migraine headaches.

Allergan's shares jumped more than 18 per cent in premarket trading. Valeant's stock rose more than 7 per cent.

Valeant also announced Tuesday that it is raising its full-year earnings forecast to $8.55 to $8.80 per share, up from $8.25 to $8.75 per share. It's also boosting its revenue guidance to a range of $8.3 billion to $8.7 billion. Previously the company predicted revenue of $8.2 billion to $8.6 billion.

Analysts surveyed by FactSet expect 2014 earnings of $9.63 per share on revenue