The present invention relates to a novel solid composition, useful for treating hepatitis, in particular hepatitis C, comprising at least one interferon alpha and at least one grafted poly(glutamic acid) having an average molar mass ranging from 26,000 to 40,000 g/mol, preferably approximately 33,000 g/mol and carrying grafts of alpha-tocopherol at an average molar grafting rate ranging from 4.5 to 5.5%, preferably approximately 5%, the interferon alpha and said grafted poly(glutamic acid) being present in a grafted poly(glutamic acid)/interferon alpha weight ratio ranging from 21 to 125.It also relates to the use of such a solid composition for the preparation of a liquid composition by the addition of an aqueous liquid.
