An implantable device for delivery of a macromolecular drug compound is provided. The device comprises a core having an outer surface and a membrane layer positioned adjacent to the outer surface of the core. The core comprises a core polymer matrix within which is dispersed a drug compound having a molecular weight of about 0.5 kDa or more, the polymer matrix containing a hydrophobic polymer. Further, the membrane layer comprises a membrane polymer matrix within which the macromolecular drug compound is optionally dispersed. The concentration of the macromolecular drug compound in the core is greater than the concentration of the macromolecular drug compound in the membrane layer.