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Glaxo shares pulled out of a tailspin after the pharma giant defended its second biggest selling drug, Avandia, against claims that it triggers heart attacks.  A sharply worded letter from the company's chief medical officer on the website of medical journal The Lancet pointed out that the increased incidence of heart attacks among Avandia patients—0.6%—was still very small.

And he said it was comparable to two other "gold standard" medicines used to treat type 2 diabetes. GlaxoSmithKline was up 50 cents in trading yesterday, but only after panic among investors wiped $21 billion off its market cap.The diabetes drug accounts for only 7% of Glaxo's shares, the Telegraph reports, suggesting the dive was an overreaction.  (Read more GlaxoSmithKline stories.)