Tenofovir diphosphate is a key metabolite of tenofovir, primarily used in the treatment of HIV and hepatitis B infections. It functions as a nucleotide reverse transcriptase inhibitor, effectively blocking the replication of the virus by incorporating itself into the viral DNA chain, causing termination of its growth. This mechanism is crucial in reducing the viral load in patients, thereby managing the progression of the disease and improving immune system function. In clinical settings, it is often part of combination therapies to enhance efficacy and reduce the risk of developing drug resistance. Additionally, it is used in pre-exposure prophylaxis (PrEP) regimens to prevent HIV infection in high-risk populations. Its role in antiviral therapy has made it a cornerstone in the global fight against HIV/AIDS and hepatitis B.