The Sensex opened almost flat at 8906 - up three points, but soon slipped to a low of 8,935. The index is now down 60 points at 8,842.
Ranbaxy has slumped 12.5% to Rs 181.
DLF and HDFC have tumbled around 3% each to Rs 150 and Rs 1,218, respectively.
ICICI Bank has shed 2.3% at Rs 333. Sterlite and Maruti have slipped 1.3% each to Rs 244 and Rs 655, respectively.
Tata Steel and SBI are down 1% each at Rs 160 and Rs 1,027, respectively.
Tata Motors and Larsen & Toubro have moved up 1.6% each to Rs 142 and Rs 622, respectively.