Process for the preparation of concentrated liquid formulations containing biomolecules

It is disclosed an improved multi-step process for the preparation of a highly concentrated liquid formulation containing biomolecules comprising the steps of (a) a first ultrafiltration UF1; (b) a first diafiltration DF1; (c) a second diafiltration DF2; and (d) a second ultrafiltration UF2; wherein an aqueous solution of one or more salts, as liquid medium B, is used for step (b) and water or an aqueous solution of one or more salts, as liquid medium C, is used for step (c), wherein the one or more salts used for step (b) are the same or different from the one or more salts used for step (c) and wherein the liquid medium B has an ionic strength which is higher than the ionic strength of the liquid medium C. The process according to the present invention allows the preparation of well-defined highly concentrated formulations containing biomolecules, particularly proteins, intended for pharmaceutical or non-pharmaceutical use. Unwanted excipient(s) of the starting liquid biomolecule formulation, may be reduced under solution conditions, to very low levels or levels lower than the detection limit.