The following general formula (I): [wherein, ring A, R 1, R 2, R 3 and R 4 represent the definitions described in the specification. ] The composition for maintaining the function of platelets which uses the pyridone derivative represented by these, or its salt as an active ingredient.下記一般式(I):[式中、環A、R1、R2、R3及びR4は、明細書中に記載の定義を表す。]で表されるピリドン誘導体またはその塩を有効成分とする、血小板の機能を維持するための組成物。