The Food and Drug Administration sent a warning letter to several drug makers, specially over Gilead Sciences drug Truvada, and Biogen Idec. drug Tysabri on misleading public advertising information.

The products advertising information in question are Gilead´s drug Truvada approved to treat HIV patients and Biogen´s drug Tysabri intended to treat multiple sclerosis.

The agency also issued a letter to privately held Aton Pharma Inc as well as a previously released warning letter to Salix Pharmaceuticals