Tenofovir disoproxil fumarate, an antiretroviral or antiviral medication, is contained in TENVIR. It is a nucleotide reverse transcriptase inhibitor (NRTI) that works by interfering with the normal functioning of enzymes (in HIV reverse transcriptase; in hepatitis B DNA polymerase) that are required for the viruses to reproduce themselves.Disclaimer:For More Information Contact Your Physician