Updated from 2:10 p.m. EDT

Shares of King Pharmaceuticals ( KG) were among the best-performing health and pharmaceutical stocks Monday after the company agreed to be acquired by Mylan Laboratories ( MYL) for about $4 billion in stock.

King shareholders will receive 0.9 shares of Mylan for each King share they own. Based on Friday's closing prices, King shareholders would receive about $16.66 a share. Mylan said that a key component of the transaction was gaining access to King's cardiovascular sales force, which currently markets Altace, a hypertension drug that had approximately $450 million in sales during the 12 months ended March 31. Shares of King Pharmaceuticals traded up $2.52, or 24.3%, to $12.89. Shares of Mylan Labs traded down $3, or 16.2%, to $15.51.

Omnicare ( OCR) fell after it reported weaker-than-expected second-quarter earnings and warned that full-year financial results would fall short of expectations. The pharmaceutical care provider earned 58 cents a share during the second quarter on sales of $1.01 billion. Analysts polled by Thomson First Call had expected it to earn 63 cents a share on sales of $1 billion. The company cited pricing pressures and drug pricing issues for the shortfall. Looking ahead, it now expects full-year earnings of $2.35 to $2.45 a share. Analysts had expected it to earn $2.60 a share. Shares of Omnicare traded down $8.87, or 23.2%, to $29.22.

Shares of Humana ( HUM) rose after the company reported better-than-expected second-quarter earnings and sales and upped its third-quarter earnings guidance. Excluding items, the health insurer earned 42 cents a share on sales of $3.43 billion. Analysts had expected it to earn 39 cents a share on sales of $3.36 billion. Looking ahead, it forecast third-quarter earnings of 43 cents to 44 cents a share. Analysts were looking for it to earn 39 cents a share. Shares of Humana traded up 87 cents, or 5.1%, to $17.92.

Coventry Health Care ( CVH) rose after it posted better-than-expected second-quarter earnings and said its third-quarter earnings results would top expectations. The health insurer earned 93 cents a share during the second quarter on sales of $1.31 billion. Analysts had expected it to earn 87 cents a share on sales of $1.32 billion. Looking ahead, it now expects third-quarter earnings of 93 cents to 95 cents a share on sales of $1.32 billion to $1.34 billion. Analysts were looking for it to earn 92 cents a share on sales of $1.35 billion. Shares of Coventry Health Care traded up $3.67, or 7.4%, to $53.30.

Shares of Beckman Coulter ( BEC) fell after the company reported weaker-than-expected second-quarter earnings. The medical equipment company earned 88 cents a share during the second quarter on sales of $597.3 million. Analysts had expected it to earn 89 cents a share on sales of $602.2 million. Looking ahead, it forecast third-quarter earnings of 69 cents to 74 cents a share on sales of $577.6 million to $593.6 million. Analysts were looking for it to earn 73 cents a share on sales of $575.6 million. Shares of Beckman Coulter traded down $5.59, or 9.7%, to $52.21.

Other health care volume movers included Pfizer ( PFE), down 56 cents to $31.74; ImClone Systems ( IMCL), down $9.62 to $56.42; Boston Scientific ( BSX), up $2.12 to $35.71; Schering-Plough ( SGP), up 81 cents to $19.56; Elan ( ELN), down $1.97 to $19.83; and Anthem ( ATH), down 64 cents to $88.16.