The present invention is directed to novel water-soluble pharmaceutically acceptable, crystalline addition salts of (i) an amine containing one or more hydroxyl and/or carboxylic groups with (ii) amino nicotinic acid derivatives of formula (I) wherein R a , R b , R c and R d independently represent groups selected from hydrogen atoms, halogen atoms, C 1-4 alkyl groups which may be optionally substituted by 1, 2 or 3 substituents selected from halogen atoms and hydroxy groups, and C 1-4 alkoxy groups which may be optionally substituted by 1, 2 or 3 substituents selected from halogen atoms and hydroxy groups, and pharmaceutically acceptable solvates thereof.
