Fostemsavir is primarily used in the treatment of HIV-1 infection, specifically for patients who have limited treatment options due to resistance, intolerance, or safety concerns with other antiretroviral therapies. It is a CD4 attachment inhibitor, which works by blocking the virus from attaching to and entering human immune cells, thereby reducing viral replication. This drug is often prescribed as part of a combination antiretroviral regimen to achieve optimal viral suppression. It is particularly beneficial for heavily treatment-experienced adults with multidrug-resistant HIV-1, offering a new mechanism of action when other therapies have failed. Proper adherence to the prescribed regimen is crucial to maximize its efficacy and prevent the development of resistance.