Can resistance tests show if you are resistant to Fuzeon before you start taking it?

Theoretically a resistance test could indicate if you were resistant to Fuzeon before taking it. However, there are a number of things to keep in mind....

First of all, there are really only two ways at this point in time to develop resistance to Fuzeon. One would be if you were taking Fuzeon and you had incomplete viral suppression (just as could happen to any of the other antiviral drugs). The second theoretical way to acquire Fuzeon resistance would be to "inherit" it from someone else who already had Fuzeon resistance such as through unsafe sex or unsafe needle sharing. With Fuzeon being so new and not used in high volume, the likelihood of acquiring resistance from someone else would be quite small. Since there aren't other fusion inhibitors in clinical use, there's no chance of cross-resistance from other drugs in the class.

So at this point in time, it's unlikely that a resistance test would be worthwhile since there's little chance of underlying resistance before starting Fuzeon.