The recent takeover of high-tech chemicals maker AZ Electronic Materials and a strong U.S. dollar will help Merck KGaA to counter a drop in revenue from its best-selling drug this year, it said on Tuesday. However, shares in the company dropped 1.7 percent, the biggest decline on Germany's blue-chip DAX index, as analysts' expressed concern at a 15.9 percent fall in currency-adjusted sales of multiple sclerosis treatment Rebif -- its biggest medicine -- in the first quarter of this year.