A process of lowering the viscosity of a solution includes preparing a solution comprising a compound of formula I, at a concentration in the final formulation of between 10 and 250 mM, and a protein having at least one antibody fragment whose concentration is between 50 and 350 mg/mL and whose pH is between 5 and 8. The compound lowers the viscosity of the solution, which is difficult to inject, by a value of at least 15% relative to the viscosity of a solution of at least one protein having at least one antibody fragment of the same concentration and of the same pH not containing the compound.