The present invention relates to a compound of formula (I) including any stereochemically isomeric form thereof, or a pharmaceutically acceptable salt thereof. wherein R1 is —C(═O)O-alkyl, carbonate ester, or —C(═O)-alkyl, ester, or —C(═O)N-alkyl, carbamate ester and wherein R2 is —CH3 or —CD3. The alkyl ester can contain saturated or unsaturated C12 to C26 alkyl carbon. The alkyl carbon chain can have either a straight, branched, noncyclic, cyclic, unsubstituted or substituted structure.