Pharmacokinetic consequences of active drug efflux at the blood-brain barrier. 2006

Stina Syvänen, and Rujia Xie, and Selma Sahin, and Margareta Hammarlund-Udenaes
Division of Pharmacokinetics and Drug Therapy, Department of Pharmaceutical Biosciences, Uppsala University, Box 591, 751 24, Uppsala, Sweden.

OBJECTIVE The objective of this simulation study was to investigate how the nature, location, and capacity of the efflux processes in relation to the permeability properties influence brain concentrations. METHODS Reduced brain concentrations can be due to either influx hindrance, a gatekeeper function in the luminal membrane, which has been suggested for ABCB1 (P-glycoprotein), or efflux enhancement by transporters that pick up molecules on one side of the luminal or abluminal membrane and release them on the other side. Pharmacokinetic models including passive transport, influx hindrance, and efflux enhancement were built using the computer program MATLAB. The simulations were based on experimentally obtained parameters for morphine, morphine-3-glucuronide, morphine-6-glucuronide, and gabapentin. RESULTS The influx hindrance process is the more effective for keeping brain concentrations low. Efflux enhancement decreases the half-life of the drug in the brain, whereas with influx hindrance the half-life is similar to that seen with passive transport. The relationship between the influx and efflux of the drug across the blood-brain barrier determines the steady-state ratio of brain to plasma concentrations of unbound drug, K(p,uu). CONCLUSIONS Both poorly and highly permeable drugs can reach the same steady-state ratio, although the time to reach steady state will differ. The volume of distribution of unbound drug in the brain does not influence K(p,uu), but does influence the total brain-to-blood ratio K(p) and the time to reach steady state in the brain.

UI MeSH Term Description Entries
D010599 Pharmacokinetics Dynamic and kinetic mechanisms of exogenous chemical DRUG LIBERATION; ABSORPTION; BIOLOGICAL TRANSPORT; TISSUE DISTRIBUTION; BIOTRANSFORMATION; elimination; and DRUG TOXICITY as a function of dosage, and rate of METABOLISM. LADMER, ADME and ADMET are abbreviations for liberation, absorption, distribution, metabolism, elimination, and toxicology. ADME,ADME-Tox,ADMET,Absorption, Distribution, Metabolism, Elimination, and Toxicology,Absorption, Distribution, Metabolism, and Elimination,Drug Kinetics,Kinetics, Drug,LADMER,Liberation, Absorption, Distribution, Metabolism, Elimination, and Response
D001812 Blood-Brain Barrier Specialized non-fenestrated tightly-joined ENDOTHELIAL CELLS with TIGHT JUNCTIONS that form a transport barrier for certain substances between the cerebral capillaries and the BRAIN tissue. Brain-Blood Barrier,Hemato-Encephalic Barrier,Barrier, Blood-Brain,Barrier, Brain-Blood,Barrier, Hemato-Encephalic,Barriers, Blood-Brain,Barriers, Brain-Blood,Barriers, Hemato-Encephalic,Blood Brain Barrier,Blood-Brain Barriers,Brain Blood Barrier,Brain-Blood Barriers,Hemato Encephalic Barrier,Hemato-Encephalic Barriers
D002352 Carrier Proteins Proteins that bind or transport specific substances in the blood, within the cell, or across cell membranes. Binding Proteins,Carrier Protein,Transport Protein,Transport Proteins,Binding Protein,Protein, Carrier,Proteins, Carrier
D002627 Chemistry, Physical The study of CHEMICAL PHENOMENA and processes in terms of the underlying PHYSICAL PHENOMENA and processes. Physical Chemistry,Chemistries, Physical,Physical Chemistries
D003198 Computer Simulation Computer-based representation of physical systems and phenomena such as chemical processes. Computational Modeling,Computational Modelling,Computer Models,In silico Modeling,In silico Models,In silico Simulation,Models, Computer,Computerized Models,Computer Model,Computer Simulations,Computerized Model,In silico Model,Model, Computer,Model, Computerized,Model, In silico,Modeling, Computational,Modeling, In silico,Modelling, Computational,Simulation, Computer,Simulation, In silico,Simulations, Computer
D004058 Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially FACILITATED DIFFUSION, is a major mechanism of BIOLOGICAL TRANSPORT. Diffusions
D004364 Pharmaceutical Preparations Drugs intended for human or veterinary use, presented in their finished dosage form. Included here are materials used in the preparation and/or formulation of the finished dosage form. Drug,Drugs,Pharmaceutical,Pharmaceutical Preparation,Pharmaceutical Product,Pharmaceutic Preparations,Pharmaceutical Products,Pharmaceuticals,Preparations, Pharmaceutical,Preparation, Pharmaceutical,Preparations, Pharmaceutic,Product, Pharmaceutical,Products, Pharmaceutical
D004730 Endothelium, Vascular Single pavement layer of cells which line the luminal surface of the entire vascular system and regulate the transport of macromolecules and blood components. Capillary Endothelium,Vascular Endothelium,Capillary Endotheliums,Endothelium, Capillary,Endotheliums, Capillary,Endotheliums, Vascular,Vascular Endotheliums
D006207 Half-Life The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacologic, physiologic, or radiologic activity. Halflife,Half Life,Half-Lifes,Halflifes
D000465 Algorithms A procedure consisting of a sequence of algebraic formulas and/or logical steps to calculate or determine a given task. Algorithm

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