Pharmacokinetics and urinary excretion of DMXBA (GTS-21), a compound enhancing cognition

DMXBA (3-(2,4-dimethoxybenzylidene)-anabaseine, also known as GTS-21) is currently being tested as a possible pharmacological treatment of cognitive dysfunction in Alzheimer's disease. In this study, plasma and brain pharmacokinetics as well as urinary excretion of this compound have been evaluated in adult rats. DMXBA concentrations were determined by HPLC. Following a 5 mg kg^-1 iv dose, DMXBA plasma concentration declined bi-exponentially with mean (± SE) absorption and elimination half-lives of 0.71 ± 0.28 and 3.71 ± 1.12 h, respectively. The apparent steady state volume of distribution was 2150 ± 433 mL kg^-1, total body clearance was 1480 ± 273 mL h^-1 kg^-1, and AUC(0-∞) was 3790 ± 630 ng h mL^-1. Orally administered DMXBA was rapidly absorbed. After oral administration of 10 mg kg^-1, a peak plasma concentration of 1010 ± 212 ng mL^-1 was observed at 10 min after dosing. Elimination half-life was 1.740 ± 0.34 h, and AUC(0-∞) was 1440 ± 358 ng h mL^-1. DMXBA peak brain concentration after oral administration was 664 ± 103 ng g^-1 tissue, with an essentially constant brain-plasma concentration ratio of 2.61 ± 0.34, which indicates that the drug readily passes across the blood-brain barrier. Serum protein binding was 80.3 ± 1.1%. Apparent oral bioavailability was 19%. Renal clearance (21.8 mL h^-1 kg^-1) was less than 2% of the total clearance (1480 ± 273 mL h^-1 kg^-1); urinary excretion of unchanged DMXBA over a 96 h period accounted for only 0.28 ± 0.03% of the total orally administered dose. Our data indicates that DMXBA oral bioavailability is primarily limited by hepatic metabolism.