NANOPORTM technology provides an alternative to frequent injections for the delivery of biotherapeutics (proteins and peptides). A small subcutaneously implantable reservoir is fitted at each end with membranes fabricated to contain pores or channels with diameters (or smallest linear dimension) that are 1 to 5 times the hydrodynamic diameter of the selected drug molecules. Pore diameter is empirically “tuned” with molecular size to enable sustained release of drug molecules held within the reservoir via a constrained passive diffusion mechanism. There are no mechanical or moving parts and the entire volume of the cylindrical reservoir is available for drug loading. NANOPORTM enables concentration gradient independent zero-order release of biopharmaceuticals for up to several months. NANOPORTM is useful for delivery of biopharmaceuticals (peptide and protein drugs) which provide clinical benefit when delivered for prolonged periods.