A particulate plug for removing a preservative from a solution, suspension, or emulsion comprising a drug is presented. The plug comprises microparticles of a homopolymer comprising a hydrophilic repeating unit or of a copolymer comprising at least one hydrophilic repeating unit and at least one hydrophobic repeating unit. The microparticles are irregular-shaped rigid aggregates and are sized and packed to yield a hydraulic permeability greater than 0.01 Da. The homopolymers have absorbed portions of a preservative to be removed and/or a drug for delivery in solution, as can the copolymer.