FRANKFURT (Reuters) - Germany's Merck KGaA (>> Merck KGaA) reported second-quarter adjusted core earnings above expectations on Thursday as the benefits of acquiring high-tech chemicals maker AZ Electronic Materials outweighed a drop in revenue from its best-selling drug.

Merck's quarterly adjusted earnings before interest, taxes, depreciation and amortisation (EBITDA) rose 6 percent to 899 million euros (628 million pounds), above the 887 million euros expected on average by analysts.

Sales of multiple sclerosis (MS) treatment Rebif, its biggest medicine, dropped a currency-adjusted 12 percent in the quarter.

Rebif, an established injectable drug against MS, is battling stiff competition from a new generation of oral drugs against the debilitating disease.

Currency-adjusted sales of cancer drug Erbitux also declined slightly in the quarter, hurt by lower prices in some European countries.

That was offset by a strong dollar boosting the value of overseas revenues and by higher sales of lab supplies for the biotech industry, up 11 percent gain when adjusted for currency swings.

The German diversified chemicals and healthcare group repeated its forecast for adjusted earnings before interest, taxes, depreciation and amortisation (EBITDA) to reach 3.45-3.55 billion euros for 2015, up from 3.39 billion last year.

The forecast does not include the $17 billion acquisition of Sigma-Aldrich Corp (>> Sigma-Aldrich Corporation) which is expected to be wrapped up soon.

(Editing by Maria Sheahan and Balazs Koranyi)

By Ludwig Burger

Stocks treated in this article : Sigma-Aldrich Corporation, Merck KGaA