Comparative efflux of saquinavir, ritonavir and lopinavir from primary human cells

Therapeutic drug monitoring is an important element in the management of drug treatment in HIV-1 infected patients. We have examined the effect of temperature on the egress of HIV-1 protease inhibitors from primary T lymphocytes to determine optimum conditions to be adopted in the processing of blood samples in order to accurately estimate intracellular or plasma drug concentrations. Peripheral blood mononuclear cells or U937 cells were incubated with radiolabelled saquinavir, ritonavir or lopinavir at a concentration of 1 µM. The cells were washed and resuspended in RPMI medium (without radiolabelled drug) and further incubated at 37°C, room temperature (21°C) or at 4°C. We observed that release of drug ensued upon the removal of cells from bathing media containing drug, with the rate of efflux being slower at 4°C and fastest at 37°C for all the protease inhibitors. There was a more rapid efflux of saquinavir and ritonavir than lopinavir from both cultured monocytic and primary human cells. The rank order of the partition coefficient of the drugs were lopinavir > saquinavir > ritonavir. All factors that may limit optimal estimation of cell-associated drug concentrations must be considered so that intracellular concentrations of drug can be accurately estimated.