NRTIs (Nucleoside Reverse Transcriptase Inhibitors) are a class of antiretroviral drugs for HIV treatment, including members like zidovudine and lamivudine. Structurally mimicking natural nucleosides, they are phosphorylated by cellular enzymes into active forms and incorporated into the viral DNA chain, thereby halting DNA synthesis. NRTIs primarily function within cells, inhibiting HIV replication by blocking the activity of reverse transcriptase. Resistance to NRTIs in viruses is typically due to mutations in the reverse transcriptase gene, affecting the drug’s incorporation or the enzyme’s binding capacity.