This is an open-label, crossover, pilot study. Patients that fail their current regimen, and who currently have no adequate treatment options left, will be randomized to start either an alternating triple combination, or to start a continuous quadruple regimen of drugs. After 6 weeks, patients will crossover from either strategy to the other strategy for another 6 weeks. Each period is preceded by an interruption of all antiretroviral therapy for 4 weeks. In the study period when regimens are alternated, two combinations of three drugs with the least possible cross-resistance will alternate every week.