A big one-time gain and a tax benefit helped drugmaker Merck & Co. more than double its second-quarter profit, raise the lower end of its profit forecast and easily top analysts' expectations. The maker of popular Type 2 diabetes pill Januvia and cholesterol medicines Vytorin and Zetia said Tuesday that net income increased to $2 billion, or 68 cents per share, from $906 million, or 30 cents per share, in the same quarter a year earlier. Merck, based in Whitehouse Station, New Jersey, said its earnings, adjusted for one-time gains and costs, were 85 cents per share.