A study of the interaction of tetracycline with human serum lipoproteins and albumin

The interaction of 7‐[³H]tetracycline at therapeutic concentrations with human serum proteins has been studied by dialysis and by molecular exclusion chromatography. In serum, 53% of tetracycline is in the form of complexes with protein: 54% with albumin; 13% with low density lipoprotein; 19% with high density lipoprotein; 6% with very high density lipoprotein and 8% with other serum proteins. Albumin possesses two binding sites for tetracycline, one a high affinity, low capacity site and the other a low affinity, high capacity site. At therapeutic concentrations three quarters of the tetracycline bound to albumin is associated with the low affinity site. Tetracycline appears to dissolve in the lipophilic portion of the lipoprotein molecule, rather than to be associated with specific binding sites. 1974 Royal Pharmaceutical Society of Great Britain