In two clinical studies, no primary protease inhibitor (PI) resistance was reported in antiretroviral-naive patients taking a Kaletra (lopinavir/ritonavir) based regimen once daily (QD) or twice daily (BID) in combination with other antiretroviral agents. These data were presented at the 15th International AIDS Conference (IAC) in Bangkok, Thailand, an Abbott release said.

The majority of patients in both studies maintained an undetectable viral load of less than 50 copies per milliliter (as measured by HIV RNA).

In study 720, no primary PI resistance has been reported through five years (252 weeks) of follow up in patients new to therapy (ARV-naive). Consistent with these findings, a separate trial of 190 ARV-naive patients, study 418, which evaluated Kaletra dosed once daily versus Kaletra dosed twice daily in combination with other agents, demonstrated no confirmed lopinavir resistance through one year (48 weeks) of therapy. The adult recommended dosage of Kaletra is 400/100 mg (three capsules or five milliliters of oral solution) twice daily with food.

"These resistance data, though based on a relatively small number of patients, are important because of the long duration of follow-up. They demonstrate that it is possible to achieve long term viral suppression while minimizing resistance. This may be especially important for ARV-naive patients, whose first regimen may be the best opportunity for success long-term," said Charles Hicks, lead study investigator, Duke University Medical Centre, Durham, NC.

Data from this randomized, open-label, study of patients new to therapy showed an HIV treatment regimen based on a once-daily dose of Kaletra had comparable viral suppression when compared to a twice-daily dose through one year (48 weeks). Patients received either Kaletra (800 mg lopinavir/200 mg ritonavir) once daily or Kaletra (400 mg lopinavir/100 mg ritonavir) twice daily. Patients in both arms also received once-daily emtricitabine and tenofovir.

In an intent-to-treat analysis (ITT), which categorizes any patient who does not complete the study as a treatment failure, the data showed 70 per cent of patients in the once daily group and 64 per cent of patients in the twice daily group achieved HIV RNA less than 50 copies per milliliter at week 48. These data demonstrated comparable effectiveness between the once-daily regimen and the twice-daily regimen of Kaletra with emtricitabine and tenofovir. Mean increases in CD4 cell count from baseline to the one-year visit were 185 and 188 cells per cubic millimeter in the once-daily and twice-daily arms, respectively, the release says.

Data also show that of 15 patients who had genotypic resistance testing results available (HIV RNA greater than 500 copies per milliliter), no patient (0/8 in the once-daily arm and 0/7 in the twice daily arm) was confirmed to have developed lopinavir resistance or tenofovir resistance. The incidence of emtricitabine resistance was low (2/8 in the once daily arm and 1/7 in the twice daily arm). Twenty-two patients (11 in the once-daily arm and 11 in the twice daily arm) had samples available for resistance testing (HIV RNA > 500 copies/mL) at any time between week 12 and week 48. Resistance testing results were available for 27 samples from 15 of the 22 patients.

"Kaletra dosed once daily was comparable in virologic efficacy to Kaletra dosed twice daily for patients new to therapy. This patient population could benefit from the development of more treatment options that provide once daily dosing schedules without sacrificing efficacy," said Jean-Michel Molina, lead study investigator, Department of Infectious Diseases, Saint-Louis Hospital, University of Paris, Paris, France.

"As part of our commitment to the HIV community, Abbott continues to explore additional treatment options with an aim to offer dosing flexibility to patients. In this study, a majority of patients had undetectable viral load, and no protease inhibitor resistance was detected after one year," said Scott Brun, global project head, Antiviral Global Project Team, Abbott
Laboratories.