A N-oxide pyrazine derivative represented by formula (I) or a salt thereof, or a solvate thereof or a hydrate thereof: wherein: R1 represents a 4-pyridine ring, a halogen atom; R2 represents a hydrogen atom; R3 represents a hydrogen atom; R4 represents: a phenylC 1-3 alkyl group, this group being optionally substituted; R5 represents a hydrogen atom; in the form of a free base or of an addition salt with an acid. Use in Therapy