What should never be combined with Lamivudine due to duplicate therapy concerns?

Combining Lamivudine with Emtricitabine presents a concern for duplicate therapy because both medications are nucleoside reverse transcriptase inhibitors (NRTIs) that have similar mechanisms of action and therapeutic profiles. Since both drugs target the same viral enzyme and share substantial overlapping activity against HIV, their combined use does not provide a significant benefit and could increase the risk of side effects without enhancing therapeutic effectiveness.

On the other hand, the other options represent different NRTIs or classes that do not share this duplicate mechanism. For example, Stavudine and Didanosine are also NRTIs but have different structures and adverse effect profiles, which means they can be used in combination with Lamivudine to provide a more comprehensive treatment regimen. Tenofovir, belonging to a different class of antiretroviral medications (nucleotide reverse transcriptase inhibitors), can also be used safely with Lamivudine for effective HIV treatment.