Cocktail-Dosing Microdialysis Study to Simultaneously Assess Delivery of Multiple Organic–Cationic Drugs to the Brain

Abstract

Brain microdialysis is a powerful tool to estimate brain-to-plasma unbound concentration ratio at the steady state (Kp,uu) of compounds by direct measurement of the unbound concentration in brain interstitial fluid. Here, we evaluated a method to estimate Kp,uu values of multiple organic-cationic drugs simultaneously, by means of brain microdialysis combined with cocktail dosing. Five cationic drugs (diphenhydramine, memantine, oxycodone, pyrilamine, and tramadol), substrates of the proton-coupled organic cation antiport system, were selected as model drugs, and compared under single-dosing and cocktail-dosing conditions. We selected doses of the drugs at which no significant drug-drug interaction occurs at the proton-coupled organic cation antiport system in the blood-brain barrier (BBB). This was confirmed by uptake studies in hCMEC/D3 cells, an in vitro BBB model. The Kp,uu values after cocktail administration were in the range of 1.8-5.2, and were in good agreement with those after single administration. These results suggest that the microdialysis method with cocktail dosing is suitable to estimate Kp,uu values of several cationic drugs simultaneously, if there is no drug-drug interaction during BBB transport. The method could be useful for evaluating drug candidates with high Kp,uu values at an early stage in the development of central nervous system-acting drugs.

Applicability of free drug hypothesis to drugs with good membrane permeability that are not efflux transporter substrates: A microdialysis study in rats

“…Supplemental kinetic study in rodents may facilitate accurate identification of efflux transporters. Recently, it has been reported that the unbound concentrations of several drugs in the brain were greater than in plasma, suggesting the involvement of active influx transporters in brain uptake 20,57 . Conceivably, drugs that are substrates of influx transporters are also not expected to follow the free drug hypothesis.…”

Involvement of Proton-Coupled Organic Cation Antiporter in Varenicline Transport at Blood-Brain Barrier of Rats and in Human Brain Capillary Endothelial Cells

“…The in vivo brain microdialysis study in rats was performed by the same methods as described previously. 15,[23][24][25] A microdialysis probe CMA12 (CMA, Stockholm, Sweden) was implanted into the striatum region (2.7 mm lateral and 0.8 mm anterior to the bregma, and 3.8 mm depth from the surface of the parietal bone). Brain microdialysis was performed 48 h after surgery.…”

“…The steady-state concentration of varenicline in the brain ISF was estimated according to the reference method, as reported previously. 15,[23][24][25] For further details, see Supplementary Information.…”

“…To examine the effects of depletion of metabolic energy and membrane potential on varenicline uptake, the cells were preincubated with glucose-free transport buffer containing 0.1% NaN 3 (metabolic energy inhibitor) for 20 min 16,25 or K þ -free transport buffer containing 10 mM valinomycin (K þ ionophore) for 10 min. To examine extracellular Na þ dependency, NaCl in the transport buffer was replaced with LiCl or choline chloride.…”

Prediction of human CNS pharmacokinetics using a physiologically-based pharmacokinetic modeling approach

“…It thus appears reasonable to assume that the BBB influx mediated by this transporter is comparable between rat and human, and therefore the human AFs were considered to be similar to rat AFs. The human AF at the BBB, AFin1, was 2.3, which was calculated using a Kpuu,brain ECF (unbound brain ECF -to-plasma concentration ratio) value of 1.7 (Kitamura et al, 2016). The human AFs at the BCSFB, AFout2 and AFout3, were assumed to be 1.9 and 2.3, respectively, which were calculated from a Kpuu,CSF (unbound CSF-to-plasma concentration ratio) value of 1 (Kokki et al, 2014).…”