C.M. Bernards, MD, S. Flack, MBChB
Human clinical studies of intrathecal bolus drug distribution demonstrate that baricity (i.e., the density of the injected fluid relative to the density of CSF) is the most important determinant of drug distribution in CSF. However, the effect of baricity during very slow continuous drug infusions has never been studied in humans or animals. In vitro studies of drug distribution in the Medtronic spinal model suggest that baricity is also the overwhelming determinant of drug distribution during very slow chronic drug infusions. However, the in vitro model cannot account for the effects of drug clearance from CSF, which is a critical determinant of drug distribution during very slow continuous drug infusions. Consequently, to determine the effect of baricity on drug distribution during chronic slow intrathecal infusions it is necessary to study distribution in an animal model.