The present invention relates to pegylated amino acid compounds of formula (I) and pharmaceutically acceptable salts thereof, wherein X, R1, R2, R3A, R3B and n are as defined herein. The present invention also relates to compositions which comprise a pegylated amino acid compound of the invention or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier, in combination with a high concentration of an active biological ingredient (ABI). In embodiments of the invention, the ABI is an anti-PD-1 antibody or antigen binding fragment thereof that specifically binds human programmed death receptor 1 (PD-1). The invention further relates to methods for lowering the viscosity of an aqueous solution of a pharmaceutical composition comprising adding a compound of the invention to the solution. The invention also provides methods for treating a pathological disease or condition, such as cancer, by administering to a subject in need of such treatment a therapeutically effective amount of a pharmaceutical composition of the invention.