is at least 4 provided that the compound is other than one where only r 22 31 or r 20 21 are d the abundance can also be a at least 6 b at least 14 c at least 19 d at least 26 e at least 32 f at least 39 g at least 45 h at least 52 i at least 58 j at least 65 k at least 71 l at least 77 m at least 84 n at least 90 o at least 97 and p 100 in another embodiment the present invention provides a novel mixture of deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof wherein the abundance of deuterium in r 1 r 7 is at least 100 in another embodiment the present invention provides a novel mixture of deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof wherein the abundance of deuterium in r 8 r 12 is at least 8 provided that the compound is other than one where only r 22 31 or r 20 21 are d the abundance can also be a at least 15 b at least 24 c at least 31 d at least 38 e at least 46 f at least 54 g at least 62 h at least 69 i at least 77 j at least 85 k at least 92 and l 100 in another embodiment the present invention provides a novel mixture of deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof wherein the abundance of deuterium in r 13 r 18 is at.