Delavirdine mesylate is used in the treatment of HIV-1 infection. It acts as a non-nucleoside reverse transcriptase inhibitor (NNRTI), blocking the reverse transcriptase enzyme that HIV needs to replicate its genetic material. It is typically used in combination with other antiretroviral drugs as part of a highly active antiretroviral therapy (HAART) regimen. This helps reduce the amount of virus in the body, maintain immune function, and slow disease progression. Due to its interaction profile with other drugs and the availability of better-tolerated alternatives, delavirdine mesylate is less commonly used today but may still be considered in specific treatment scenarios.