Pfizer Inc has reportedly got an approval from the company's board on Sunday to buy Botox-maker Allergan Plc and the announcement of the deal is expected to come out as early as Monday.

The merger will make the combined entity as the world's biggest drug maker, Reuters reported.

Here are the key points from the likely merger:

1) The deal is worth more than $150 billion and it the largest ever in the pharma sector.

2) It will see Pfizer paying 11.3 of its shares for each Allergan share. The cash component in the transaction is below 10% of the total value of the deal.

3) While Pfizer's chief executive Ian Read will be CEO of the combined entity, Allergan's CEO Brent Saunders will hold a "very senior role" overseeing the operations and the integration, according to sources close to the developments.

4) The combined annual sales of the two companies of over $60 billion will be far above the $40 billion annual revenue of Merck & Co, the second largest drugmaker in the US.

5) The deal would also become the largest merger this year surpassing the beer maker Anheuser-Busch InBev's proposed acquisition of SABMiller Plc for $107 billion.

6) It is likely to invite criticism from political circles in the US, as the country headed for presidential elections. The deal will make Pfizer to "redomicile" to Ireland, where the headquarters of Allergen is situated, enabling it to cut its corporate tax payment in the US.

7) The "inversion" deal will allow Pfizer to reduce its tax payments, as it will not be subjected to 35% corporate tax rate in the US, which is among the highest in the world. The tax is 12.5% in Ireland.