In recent years, many antibody drugs that play an important role in the pharmacotherapy of several diseases have been developed. Antibody drugs exhibit immunogenicity in vivo leading to the development of antibodies against the antibody drug (anti-drug antibody). Nonetheless, other factors also affect the pharmacokinetics of antibody drugs. Recently, therapeutic drug monitoring (TDM) of infliximab was introduced for personalized medicine. However, the usefulness of TDM in antibody therapy remains unclear. In addition to intervention studies, real-world data analysis is important. Unlike small-molecule drugs, antibody drugs do not have a uniform molecular weight; therefore, using the conventional analysis methods, it is impossible to determine the true pharmacokinetic outcomes of these agents. To analyze structural changes of antibody drugs in the body, new technologies are necessary. In the future, along with the development of new drugs, the establishment of novel analytical methods is essential to facilitate the promotion of personalized medicine.