1. A pharmaceutical composition comprising a therapeutically effective amount of a compound of the formula:   in which: R1 is 1-butyl, 2-butyl, cyclohexyl or phenyl and R2 is acetyl or isobutanoyl, and a propellant selected from 1,1,1,2-tetrafluoroethane, 1,1,1,2,3,3,3-heptafluoropropane and a mixture thereof, and ethanol in an amount effective to solubilize the compound of formula (I) and optionally a surfactant. 2. A pharmaceutical composition as claimed in Claim 1 in which the compound of formula (I) is ciclesonide. 3. A pharmaceutical composition as claimed in Claim 1 which is free of surfactant. 4. A pharmaceutical composition as claimed in Claim 1 in which the composition comprises from 3 to 25% by weight of ethanol. 5. A pharmaceutical composition as claimed in Claim 4 in which the composition comprises from 5 to 20% by weight of ethanol. 6. A pharmaceutical composition as claimed in Claim 5 in which the composition comprises from 7 to 12% by weight of ethanol. 7. A pharmaceutical composition as claimed in Claim 6 in which the composition comprises 8% by weight of ethanol. 8. A pharmaceutical composition as claimed in Claim 2 comprising from 1 to 8 mg/ml of ciclesonide. 9. A pharmaceutical composition as claimed in Claim 1 in which the propellant is 1,1,1,2-tetrafluoroethane. 10. A pharmaceutical composition as claimed in Claims 1 in which the propellant is 1,1,1,2,3,3,3-heptafluoropropane. 11. A pharmaceutical composition as claimed in Claim 9 consisting of ciclesonide at a concentration of 1 to 5mg/ml in a blend of ethanol: 1,1,1,2-tetrafluoroethane with a ratio 8:9 by weight. 12. A pharmaceutical product comprising an aerosol vial equipped with a dispensing valve and containing a formulation as claimed in Claim 1. 13. A pharmaceutical composition as claimed in Claim 12 in which the valve is a metered dose dispensing valve. 14. A pharmaceutical composition as claimed in Claim 13 in which the valve comprises a valve ferrule having a rim and associated rim gasket for engaging the aerosol vial and an aperture therethrough; a metering tank having walls defining an exterior, an internal metering chamber, an inlet orifice, an inlet end, and an outlet end; an elongate valve stem having a filling channel, a filling end, a discharge end, and a discharge orifice; wherein the outlet end of the metering tank is in sealing engagement with the valve ferrule, the discharge end of the valve stem passes through both the valve ferrule aperture and the outlet end of the metering tank and is in slidable sealing engagement with the valve ferrule; wherein the filling end of the valve stem passes through and is in slidable engagement with the inlet orifice of the metering tank, and a bottle emptier surrounding the metering tank and filling end of the elongate valve stem and defining a passage between the metering tank and bottle emptier allowing communication between the inlet orifice of the metering tank and the aerosol vial; wherein the valve stem is movable between an extended closed position wherein the filling channel of the valve stem allows open communication, via the inlet orifice, between the interior and the exterior of the metering chamber, and wherein the outlet end of the metering tank is closed, and a compressed open position wherein the inlet orifice of the metering tank is in sealing engagement with the filling end of the valve stem and the discharge orifice of the valve stem allows open communication between the interior and exterior of the metering chamber. 15. A pharmaceutical product as claimed in Claim 14 additionally comprising an adapter having a body for containing the aerosol vial, a nozzle block accommodating the discharge end of the valve stem and a mouthpiece. 16. A pharmaceutical product as claimed in Claim 15 in which the nozzle block has an exit orifice directed towards the mouthpiece, the exit orifice having a diameter in the range 0.20 to 0.33mm. 17. A pharmaceutical product as claimed in Claim 16 in which the exit orifice has a diameter of about 0.28mm. 18. A pharmaceutical product as claimed in Claim 17 in which the exit orifice has a jet length in the range 0.30 to 0.60mm. 19. A pharmaceutical product as claimed in Claim 18 in which the exit orifice has a jet length of 0.50mm. 20. A pharmaceutical aerosol formulation contained in an aerosol canister equipped with a dispensing valve, the formulation comprising a compound of the formula:   in which: R1 is 1-butyl, 2-butyl, cyclohexyl or phenyl and R2 is acetyl or isobutanoyl; and a hydrofluorocarbon propellant; and cosolvent in an amount effective to solubilize the compound of formula (I).