It is well known that 92% of rapamycin binds to albumin once it is in the blood stream. I was wondering if the 92% Albumin bound rapamycin is no longer potent in immunosuppression and only 8% free rapamycin is active in inhibiting t-cells.
The proportion of the drug (rapa) among cellular components was as follows (mean % distribution +/- SD); RBC 94.5 +/- 4.9%; plasma 3.1 +/- 2.5%; lymphocytes 1.01 +/- 1.02%; and granulocytes 1.0 +/- 0.88%. The free or unbound fraction of RAPA over the plasma concentration range of 5-100 micrograms/L as determined by ultracentrifugation was 2.5 +/- 0.2%. The rapa in all three blood components is in a dynamic equilibrium, with exchange, some fast, some slow, among all those compartments.
