There is no absolute standard in AIDs therapy as drug specfic side effects, patient medication profile, resistance testing, prior failing regimens, and patient adherence must be taken into account. There are guidelines for preferred treatment combinations but they may be highly variable depending on your patient. But generally, preferred NRTIs include FTC, 3TC, and TDF. The pregnancy preferred NRTI is ZDV. Along with this, you also want to take into account the adverse effects of particular NRTIs such as ddI and d4T.