German drug maker Bayer AG says it won't raise its offer for Schiff Nutrition, refusing to engage in a bidding war with British consumer goods company Reckitt Benckiser Group PLC.

Shares of vitamin and nutritional supplement seller Schiff Nutrition International Inc. dropped 5 percent in premarket trading on Tuesday.

The English company on Friday said that it was starting a tender offer to buy Schiff for $1.4 billion, or $42 per share.

Bayer had offered to pay $1.2 billion, or $34 per share, for Schiff on Oct. 30.

Schiff's products include Tiger's Milk nutrition bars, Omega 3 supplement MegaRed, and Airborne immune system health supplements. Its portfolio includes brands in three of the largest health supplement segments — joint care, cardiovascular health and immune support.

Shares of Schiff, which is based in Salt Lake City, fell $2.23 to $41.90 before the market open. Its stock had gained 90 percent since just before the initial offer from Bayer.