A pharmaceutical composition for use in the treatment of a hearing impairment or imbalance disorder associated with loss of auditory hair cells in a subject in need of treatment, the composition comprising a compound of the following formula, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier: wherein: R 43 is C 6 -C 10 aryl or heteroaryl including 5-10 atoms, each of which is optionally substituted with from 1-5 R m; R 44 is: (i) C 6 -C 10 aryl or heteroaryl including 5-10 atoms, each of which is optionally substituted with from 1-5 R m; or (ii) -Z 4 -(C 1 -C 6 alkyl), wherein: Z 4 is a bond or NH; and the C 1 -C 6 alkyl is substituted with one of the following: (a) heterocyclyl including 5-6 atoms, which is optionally substituted with from 1-3 substituents independently selected from oxo and C 1 -C 6 alkyl; or (b) phenoxy, which is optionally substituted with from 1-5 R m; and R m at each occurrence is, independently: (i) halo; NH 2; NH(C 1 -C 3 alkyl); N(C 1 -C 3 alkyl) 2; hydroxy; C 1 -C 6 alkoxy or C 1 -C 6 haloalkoxy; nitro; or cyano; or (ii) C 1 -C 6 alkyl or C 1 -C 6 haloalkyl. R 43 is C 6 -C 10 aryl or heteroaryl including 5-10 atoms, each of which is optionally substituted with from 1-5 R m; R 44 is: (i) C 6 -C 10 aryl or heteroaryl including 5-10 atoms, each of which is optionally substituted with from 1-5 R m; or (ii) -Z 4 -(C 1 -C 6 alkyl), wherein: Z 4 is a bond or NH; and the C 1 -C 6 alkyl is substituted with one of the following: (a) heterocyclyl including 5-6 atoms, which is optionally substituted with from 1-3 substituents independently selected from oxo and C 1 -C 6 alkyl; or (b) phenoxy, which is optionally substituted with from 1-5 R m; and R m at each occurrence is, independently: (i) halo; NH 2; NH(C 1 -C 3 alkyl); N(C 1 -C 3 alkyl) 2; hydroxy; C 1 -C 6 alkoxy or C 1 -C 6 haloalkoxy; nitro; or cyano; or (ii) C 1 -C 6 alkyl or C 1 -C 6 haloalkyl. (i) C 6 -C 10 aryl or heteroaryl including 5-10 atoms, each of which is optionally substituted with from 1-5 R m; or (ii) -Z 4 -(C 1 -C 6 alkyl), wherein: Z 4 is a bond or NH; and the C 1 -C 6 alkyl is substituted with one of the following: (a) heterocyclyl including 5-6 atoms, which is optionally substituted with from 1-3 substituents independently selected from oxo and C 1 -C 6 alkyl; or (b) phenoxy, which is optionally substituted with from 1-5 R m; and R m at each occurrence is, independently: (i) halo; NH 2; NH(C 1 -C 3 alkyl); N(C 1 -C 3 alkyl) 2; hydroxy; C 1 -C 6 alkoxy or C 1 -C 6 haloalkoxy; nitro; or cyano; or (ii) C 1 -C 6 alkyl or C 1 -C 6 haloalkyl. Z 4 is a bond or NH; and the C 1 -C 6 alkyl is substituted with one of the following: (a) heterocyclyl including 5-6 atoms, which is optionally substituted with from 1-3 substituents independently selected from oxo and C 1 -C 6 alkyl; or (b) phenoxy, which is optionally substituted with from 1-5 R m; and (a) heterocyclyl including 5-6 atoms, which is optionally substituted with from 1-3 substituents independently selected from oxo and C 1 -C 6 alkyl; or (b) phenoxy, which is optionally substituted with from 1-5 R m; and R m at each occurrence is, independently: (i) halo; NH 2; NH(C 1 -C 3 alkyl); N(C 1 -C 3 alkyl) 2; hydroxy; C 1 -C 6 alkoxy or C 1 -C 6 haloalkoxy; nitro; or cyano; or (ii) C 1 -C 6 alkyl or C 1 -C 6 haloalkyl. (i) halo; NH 2; NH(C 1 -C 3 alkyl); N(C 1 -C 3 alkyl) 2; hydroxy; C 1 -C 6 alkoxy or C 1 -C 6 haloalkoxy; nitro; or cyano; or (ii) C 1 -C 6 alkyl or C 1 -C 6 haloalkyl.