This invention provides a microemulsion pre-concentrate comprising a difficultly soluble active agent and a carrier medium comprising 1) a hydrophilic phase which comprises dimethylisosorbide and/or a lower alkyl alkanoic ester, 2) a lipophilic phase, and 3) a surfactant. The active agent may be a cyclosporin or a macrolide.In another aspect, this invention provides a pharmaceutical composition for enteral or parenteral administration comprising a macrolide and an acid.