July 9, 2002
Intensification is the concept of adding one more drug to a regimen for patients who are beginning to experience a viral breakthrough. A few years ago, the idea was heresy. However, the idea has regained some popularity due to the availability of drugs with relatively high barriers to resistance and high potency, along with the realization that it may not be possible to change all of the drugs in a regimen too many times before running out of drugs.
The two drugs most often studied for intensification are abacavir (Ziagen) and tenofovir (Viread). In fact, two of the pivotal studies that led to the licensing of tenofovir were intensification studies. They showed sustained drops of viral load of about 0.6 log over more than a year after intensifying with tenofovir.
Marshall Kubota presented the results of a study designed to explore the use of abacavir as intensification. This was a retrospective examination within an open-label, prospective, community-based multicenter study of abacavir use. Patients were identified for whom abacavir was added as a single agent, qualifying as intensification. The investigators identified 128 of 533 treatment-experienced patients who added abacavir as a single agent. Baseline viral load was 3.82 log (about 8,000). Of the 128, 96 completed at least 16 weeks of therapy. Ten (9 percent) were felt to have had hypersensitivity reactions. Of those who completed 16 weeks, the median drop in viral load was 0.96 log. Sixty-eight percent had viral loads below 400 copies at 16 weeks.
These results are encouraging, although limited by the short follow up. They confirm results seen in CAN 3009, another exploratory study with 48 weeks of follow up. The rate of hypersensitivity seems higher than in other studies, but it may represent some degree of over-reporting.
There are a number of limitations to the trial. It was designed to include a wide variety of patients, rather than restricting it to those who met narrow study criteria. This made it very useful for exploring a concept, but studies of this sort must be confirmed. Follow up is limited, and viral resistance results are not yet available. One concern might be evolution of multiple resistance mutations over time in those patients who are not fully suppressed. However, for patients on therapy with relatively low viral loads but with detectable viremia, it may be reasonable to add abacavir, rather than changing the whole regimen.
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