Used as an antiviral agent, particularly effective against human immunodeficiency virus (HIV) and hepatitis B virus (HBV). It shows activity in treating these viral infections, especially in patients with chronic conditions. The compound works by inhibiting reverse transcriptase (for HIV) or the viral polymerase with reverse transcriptase activity (for HBV), thereby preventing viral replication. Due to its structural similarity to nucleotides, it gets incorporated into viral DNA, causing chain termination. It is used in combination therapy with other antiretrovirals to control viral load, reduce complications, and improve patient outcomes. Its phosphonate group enhances cellular uptake and activation, making it effective even in cells with low kinase activity.