Patent ID: 8758648

Claim:
A method for stabilizing 10-(carboxymethylaminocarbonyl)-3,7-bis(dimethylamino)phenothiazine or a salt thereof, the method comprising causing the 10-(carboxymethylaminocarbonyl)-3,7-bis(dimethylamino)phenothiazine or a salt thereof to be present with the following compounds (2) and (3): (2) a compound represented by the following formula (I): R 1 —N═N—R 2 (I) wherein R 1 is and R 2 is wherein each X is independently hydrogen, halogen, sodium or potassium; each Y is independently hydrogen or SO 3 X; and each Z is independently hydrogen, a methyl group or a methoxy group; and, (3) a quaternary ammonium having a hydrocarbon group with a carbon number of 12 or higher or a salt thereof.