The US credit ratings agency Moody's has said it is reviewing the credit rating of German chemicals and pharmaceuticals producer Merck KGaA in connection with the company's plans to acquire laboratory products specialist Sigma-Aldrich.

Merck currently has a rating of A3.

Moody's said that while the acquisition makes sense strategically, the purchase price of over €13 billion would more than triple the Darmstadt-based company's debt burden to more than €17 billion.