After falling 5.54 per cent to Rs 434.05 in intra-day trade on the BSE, shares of Ranbaxy Lab ended 3.12 per cent lower at Rs 445.20.
On the NSE, the stock settled 3.58 per cent down at Rs 443.10.
On the other hand, shares of Sun Pharma rose 2.68 per cent to close at Rs 587.25 on the BSE.
Sun Pharma and Ranbaxy said they will become the largest pharmaceutical company in India, with an estimated combined revenue of USD 4.2 billion, and the fifth-largest speciality generics company in the world.
As per their agreement, Ranbaxy shareholders will get 0.8 share of Sun Pharma for each share of Ranbaxy, representing an implied value of Rs 457 for each Ranbaxy share.
This is at a premium of 18 per cent to Ranbaxy's 30-day volume-weighted average share price and a premium of 24.3 per cent to Ranbaxy's 60-day volume-weighted average share price, in each case, as of the close of business on April 4, 2014.