Among patients who had previously shown drug resistance, drug-resistant strains of HIV still existed in blood cells even though the patients were responding successfully to highly active antiretroviral therapy (HAART), Belgian researchers recently observed.

Dr. Chris Verhofstede and Ghent University Hospital colleagues studied 11 patients who were successfully treated with HAART for a mean of 59 months. All patients had a history of suboptimal therapy and had developed drug resistance. Of the patients, 10 still had previously evolved drug-resistant HIV detectable in peripheral blood mononuclear cells.

"We were able to show that all drug-resistant HIV-1 variants that arise during therapy failure remain archived in the cells of the infected person for a very long period of time - at least seven years and most probably much longer," said Verhofstede. The resistance was detectable "even if drug pressure was removed or if a patient subsequently responded well to a new drug combination."

"These findings indicate that once resistance arises against an antiretroviral, the activity of this drug will remain reduced for several years and possibly life-long, even after a withdrawal period of years," said Verhofstede. "Recycling drugs is therefore not an advisable option if other alternatives are available." He further noted that the results "argue against a possible benefit of therapy interruptions as a way to improve the effect of a subsequently introduced salvage regimen containing recycled drugs."

The full study, "Drug-Resistant Variants That Evolve During Nonsuppressive Therapy Persist in HIV-1-Infected Peripheral Blood Mononuclear Cells After Long-Term Highly Active Antiretroviral Therapy," is published in the Journal of Acquired Immune Deficiency Syndromes (2004;35(5):473-483).

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