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.

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