<qa>  What is the goal of this study?The objective of this study is to compare the pharmacokinetics of lopinavir tablets administered to pediatric patients as either whole or crushed tablets. The study is a randomized,open-label, crossover study of pediatric subjects already taking lopinavirritonavir tablets as part of their clinical care. THe investigators hypothesize that lopinavir exposure in pediatric patients will be lower after taking a dose of the tablet formulation, crushed and mixed with pudding or yogurt, as compared to the exposure after taking a dose with tablets swallowed whole. 