Diffusion and flow transfer of theophylline across the blood-brain barrier: pharmacokinetic analysis.

Two possible schemes describing the transfer of theophylline across the blood-brain barrier are investigated. The first, the "diffusion only model," assumes that the rate of transfer is proportional to the difference in free drug concentration in the serum and cerebrospinal fluid. The second, the "diffusion and flow model," has the added feature that drug may be transferred from the CSF to the blood by the continuous secretion of CSF into the blood. Comparison of the results of nonlinear regression for the two proposed schemes indicated that the "diffusion and flow" model best describes the transfer process. The analysis indicates that the parameters obtained for the "diffusion and flow" model are physiologically meaningful.