Lersivirine is primarily used in the treatment of HIV-1 infection. It functions as a non-nucleoside reverse transcriptase inhibitor (NNRTI), which helps to block the reverse transcriptase enzyme that the HIV virus needs to replicate. By inhibiting this enzyme, Lersivirine effectively reduces the viral load in patients, thereby slowing the progression of the disease. It is often used in combination with other antiretroviral drugs to enhance its efficacy and to minimize the risk of developing drug resistance. This makes it a valuable component in the management of HIV, particularly for patients who may have developed resistance to other NNRTIs.