Oral formulations and lipophilic salts of methylnaltrexone

A pharmaceutical composition for oral administration comprising a solid dosage of (i) methylnaltrexone, or a pharmaceutically acceptable salt thereof, and (ii) and an amphiphilic pharmaceutically acceptable excipient comprising a saturated or unsaturated, branched or unbranched, cyclic or acyclic C4-30 aliphatic group that is optionally substituted, wherein when the methylnaltrexone, or the pharmaceutically acceptable salt thereof, and the amphiphilic pharmaceutically acceptable excipient are in solution, the apparent octanol/water partition coefficient for methylnaltrexone is at least 0.25 at a pH between 1 and 4.