Plasma protein binding of phencyclidine

Abstract

In healthy male subjects (n = 12) phencyclidine (PCP) free fraction was 22.0 +/- 2.8 % (mean +/- SD). In male patients with mild to moderate alcoholic liver disease (n = 16) free fraction (23.0 +/- 3.4%) was of the same order as in healthy subjects although age and the concentrations of albumin, bilirubin, and high-density lipoproteins were different (P less than 0.05). Free fraction (76.2 /+- 0.06%) in fatty acid free human serum albumin (HSA, 4.4 gm/dl) was far greater than in plasma. Both the increased binding of PCP in plasma over HSA and the lack of a difference in PCP binding between normals and patients was associated with alpha 1-acid glycoprotein (alpha 1-AGP). This protein is an acute-phase reactant that binds cationic drugs and rises nonspecifically in a variety of diseases. Free fraction of PCP in alpha 1-AGP (75 mg/dl) was 36.4 +/- 1.7%. Half of the variance in PCP binding can be accounted for (r = 0.67, P less than 0.01) from percentage of free PCP = 39.24 - 2.18 (albumin) - 0.094 (alpha 1-AGP). Male rats (n = 14, weight = 251 +/- 7 gm) were alternatively assigned to pretreatment with either saline or alpha 1-AGP (11.6 mg) by cardiac puncture. PCP brain concentrations were reduced (11%, P less than 0.05) in the protein-treated group 5 min after cardiac 3H-PCP (0.17 mg) administration, demonstrating that increased plasma protein binding can reduce free drug concentration during the distribution phase and, thereby, the rate and extent of drug distribution.