Drug uptake rule challenged 27 August 2008 A study by UK
scientists apparently contradicts a 100-year-old rule thought to
govern the rate at which molecules cross biological membranes.
The researchers have designed an electrochemical technique to
study membrane transport, which they say is more accurate than
previous methods. Overton's rule is widely used by
pharmacologists because it can determine how easily a drug
molecule will enter a cell. Theoretically, molecules with longer
carbon chains - more lipophilic, or hydrophobic, molecules - are
more soluble in fat and so make swifter progress through the
lipid membranes of cells. Patrick Unwin, who led the study at
the University of Warwick, says, 'Overton's rule would have
suggested that as we made the molecules more lipophilic, the
rate of transport would have gone up. We found it went down.' So
far, the researchers have studied the transport of four weak
acids across an artificial membrane. If their results are
mirrored across other molecules and in living