Brequinar sodium is primarily used as an inhibitor of dihydroorotate dehydrogenase (DHODH), an enzyme involved in the de novo pyrimidine biosynthesis pathway. This action makes it a potent immunosuppressive agent, as rapidly dividing immune cells depend on this pathway for nucleotide supply. It has been investigated in organ transplantation to prevent graft rejection by suppressing T-cell proliferation.

In oncology, brequinar sodium shows potential as an anticancer agent due to its ability to limit nucleotide availability in fast-growing tumor cells. It has been studied in combination with other chemotherapeutics to enhance cytotoxic effects and overcome drug resistance.

Additionally, brequinar sodium has demonstrated antiviral activity, particularly against RNA viruses such as dengue, Zika, influenza, and SARS-CoV-2, by restricting the pool of pyrimidines needed for viral replication. This has led to interest in its use as a broad-spectrum antiviral therapeutic, especially in early-stage infection.

Research also explores its role in modulating cellular metabolism and immune responses in autoimmune diseases, highlighting its versatility beyond traditional chemotherapy and immunosuppression. Currently, it remains in laboratory and animal trial stages and is not widely approved for human use.