Abbott Laboratories on Monday reported that the company's protease inhibitor Kaletra achieves and maintains undetectable HIV viral loads for nearly five years, the Chicago Sun-Times reports. Speaking at a Chicago conference of the American Society of Microbiology, the researchers reported that in a study of 100 patients, 67 of 68 who took the Kaletra as part of first-line therapy and remained on the medication for 252 weeks had undetectable HIV viral loads. Study subjects also did not develop resistance to the medication, indicating that HIV-positive people taking Kaletra "are very, very unlikely to develop resistance to the treatment," said lead investigator Joseph Eron of the University of North Carolina-Chapel Hill. All of the study subjects also took 3TC and d4T as part of combination therapy. Kaletra, approved by the Food and Drug Administration in September 2000, is the most commonly prescribed protease inhibitor in the United States and Europe.