Eventually, resistance may render a drug completely ineffective. Several clinical studies have also shown that developing resistance to AZT can lead to more rapid disease progression. Most of the research on HIV resistance has been done in test tube studies. It is still unclear how much of the information from test tube studies is relevant to human experience. Now, however, there is increasing research on antiretroviral resistance built in to clinical studies.
Studies are underway to see if switching or combining therapies can delay resistance.
Measuring drug resistance is difficult, labor intensive and expensive. Only a few university-based laboratories can perform these tests. As a result, small studies are usually 'nested' within larger studies to look for resistance. New diagnostic tools may soon be available that will make detecting resistance cheaper, less complicated and more widely available. This study showed that people who entered the trial with a high level of AZT resistance progressed significantly faster than without it.