Used in combination with ritonavir, lopinavir is a key antiretroviral medication in the treatment of HIV-1 infection. It works by inhibiting the HIV protease enzyme, preventing the virus from maturing and producing infectious particles. This helps reduce viral load and slow disease progression. It is commonly prescribed as part of highly active antiretroviral therapy (HAART), especially in resource-limited settings due to its availability in fixed-dose combinations. It has also been studied in the management of other viral infections, though with limited success. Lopinavir/ritonavir was widely used during the early stages of the COVID-19 pandemic, but clinical trials did not show significant benefit against SARS-CoV-2.