Dipeptide, and tripeptide and tetrapeptide ester derivatives of bioactive agents are provided wherein the parent agents are substrates effluxed by the P-gp transporter. The improved beam front has a profile with a plurality of undulation and the plurality of undulations define a plurality of annular peaks and annular valleys. The system support has a longitudinal extension along which it comprises a plurality of attachment means, evenly spaced apart from each other, for affixing interior equipment components, wherein the spacing of the attachment means is smaller than the spacing of the frame elements.