Tenofovir Disoproxil Fumarate 300mg is an oral prodrug used primarily in the treatment of HIV and chronic hepatitis B infections. It is converted in the body to its active form, tenofovir diphosphate, which acts as a nucleotide analog reverse transcriptase inhibitor (NtRTI). It works by competing with the natural substrate, deoxyadenosine 5’-triphosphate, for incorporation into viral DNA, causing premature chain termination during viral DNA synthesis. This inhibition prevents the replication of HIV and hepatitis B viruses, reducing viral load and slowing disease progression. The drug has a favorable pharmacokinetic profile for once-daily dosing and limited toxicity to human DNA polymerases.