Your question is really about the refinement of options. Combivir + efavirenz was one of the first successful alternatives to protease inhibitor-based regimens. Many subsequent studies have investigated how to improve upon this success. In fact, several studies have tried to see whether lipodystrophy can be decreased while preserving the benefits and success rates of efavirenz + two NRTIs. However, no completed trial has yet directly answered your question.
In the past few years we've seen that the combination of either tenofovir or abacavir + 3TC (lamivudine, Epivir) + efavirenz work excellently. And, for the triple combo using tenofovir, the data show that only 1% of people taking this combination reported any lipodystrophy after two years. Along these same lines was a study of patients who developed lipoatrophy while on d4T (stavudine, Zerit) and then showed improvement after a switch to abacavir.
So now, both tenofovir and abacavir are the "leading contenders" in terms of avoiding lipodystrophy, and even reversing it if it has already occurred.
Coincidentally, since 3TC has always been understood to have low rates of lipoatrophy, this led researchers to study the combination of 3TC + abacavir + tenofovir with the expectation that it would have low rates of lipoatrophy as well. Sadly, though this may be true, there was an unexpectedly high viral rebound rate in patients starting with this combination.
Now, where does AZT fit in? In a study of those who took Combivir + efavirenz, after year one, there is evidence of some fat loss in some patients on AZT. This was not universal and was certainly slower to occur than with a regimen based on d4T + ddI (didanosine, Videx). Nevertheless, some patients can develop lipodystrophy while on AZT-based combinations. This may happen less or, hopefully, not at all on either tenofovir or abacavir. However, it is fair to state that if this has not yet occurred for your patient on AZT, there is no reason to predict that it will occur. However, it is also reasonable to substitute an alternative that has been shown to have low rates of body fat changes, since these alternatives will almost certainly maintain viral suppression.
This issue you raise is important enough that an ongoing study is comparing the success and side effect profiles of AZT vs. tenofovir, both combined with 3TC + efavirenz. So we'll soon have that direct comparison to answer your question. For now, switching to an alternative or continuing the use of AZT are each reasonable approaches.
