A formulation for use in an implantable infusion device includes between about 5 mg/ml and about 500 mg/ml (e.g., about 10-25 mg/ml) of a TNF inhibitor polypeptide, 10 mM-25 mM of a phosphate or citrate buffer, has an ionic strength of the combined buffer and an optional salt of the equivalent of about 0.1-0.2 NaCl (e.g., about 0.15 M), 5% to 10% of a carbohydrate (e.g., trehalose or sucrose), has a pH of between 6 and 7, is fluid at room temperature and at 37° C., and has a viscosity of less than about 10 centipoise (e.g., between about 1 centipoise and 9 centipoise, between about 1 cp and about 5 cp, between about 1 cp and about 3 cp, or between about 1 cp and about 2.5 cp) at room temperature.