COCAINE AND COCAETHYLENE BINDING TO HUMAN-MILK

The binding of cocaine and its ethyl analog, cocaethylene, to human mi lk was studied using equilibrium dialysis at 4 degrees C. For cocaine, a low-affinity high-capacity binder was noted (equilibrium constant o f association, K-a, 3.12 X 10(3) L/mol; concentration of binding sites , B-0, 3.85 x 10(-4) mol/L), as well as a very low affinity, high-capa city binder (K-a, 7.54 x 10(2) L/mol; B-0, 1.42 x 10(-3) mol/L). For c ocaethylene, 2 low-affinity, high-capacity binders were suggested: a s tronger (K-a, 3.79 x 10(3) L/mol; B-0, 3.27 x 10(-4) mol/L) and a weak er (K-a, 1.84 X 10(3) L/mol; B-0, 8.91 x 10(-4) mol/L) binder The low- affinity, high-capacity binder for cocaine and cocaethylene seems to b e albumin, while the weaker nonspecific binding may be due to lipids. Up to 55% of cocaine and up to 61% of cocaethylene were bound to milk; such binding, coupled with the lower pH of milk (6.9) relative to tha t of serum (7.4), may enhance the mammary secretion of these 2 basic d rugs, having important consequences for the nursing infant.