The use of a compound of formula (I) wherein: ring C is phenyl or carbon-linked heteroaryl selected from pyridyl, pyrazinyl, pyrimidinyl and pyridazinyl; and wherein said phenyl or heteroaryl is substituted as defined herein; A-B is selected from NHCO, OCH2, SCH2, NHCH2, trans-vinylene, and ethynylene; R1 is linked to ring C at a carbon ortho to the position of A-B attachment and is defined herein; n is 1 or 2; R?2 and R3¿ are alkyl, haloalkyl or together from cycloalkyl or halocycloakyl as defined herein; in the manufacture of a medicament for use in the elevation of PDH activity in warm-blooded animals such as humans is described. Salts and esters of compounds of formula (I) are also described.