The invention relates to compounds of general formula (I): wherein: each of R1 and R9 is independently selected from: —H, C1-4alkyl, C2-4alkenyl, and halogenated C1-4alkyl; each of R3NA and R3NB is independently selected from: —H, C1-4alkyl, C2-4alkenyl, and halogenated C1-4alkyl; each of R7NA and R7NB is independently selected from: —H, C1-4alkyl, C2-4alkenyl, and halogenated C1-4alkyl; and wherein: each of RA and RB is independently selected from: C1-4alkyl, halogenated C1-4alkyl, and C6-10aryl; or RA and RB are linked to form a group selected from: C1-6 alkylene and C6-10 arylene; and pharmaceutically acceptable salts thereof, which are useful in the treatment of, for example, Alzheimer's disease. In other aspects the invention also relates to novel formulations of 3,7-diamino-10H-phenothiazinium salts.