On the surface, the lack of Kaletra mutations might be considered to be a good thing. However, without information about its resistance profile, it is difficult to determine which protease inhibitor people can switch to if they start therapy with Kaletra and eventually fail the drug. Fortunately, another study presented at the 8th CROI helped shed some light on this situation. Upon testing samples collected from people who had failed other protease inhibitors in the past, researchers at Abbott concluded that people who are no longer responding to Kaletra may benefit from switching to either Fortovase (saquinavir) or Agenerase (amprenavir). On the other hand, patients failing Kaletra were less likely to respond upon switching to Norvir (ritonavir) or Crixivan (indinavir).
What about patients who have failed other protease inhibitors in the past and need to switch to Kaletra? Of all the mutations that can arise during therapy with other protease inhibitors, 11 are associated with cross-resistance to Kaletra. As a rule of thumb, researchers have determined that HIV containing six or fewer of these 11 mutations will still likely respond to Kaletra. Strains of HIV containing seven or more of these 11 mutations are less likely to respond to Kaletra therapy. Many laboratories currently conducting drug-resistance testing are aware of this new information, so people hoping to use Kaletra as a salvage protease inhibitor can benefit from the information produced by these tests.