Correlation of water solubility with octanol-water partition coefficient

Antidepressants Accumulate in Lipid Rafts Independent of Monoamine Transporters to Modulate Redistribution of the G Protein, Gαs

Depression is a significant public health problem for which currently available medications, if effective, require weeks to months of treatment before patients respond. Previous studies have shown that the G protein responsible for increasing cAMP (Gαs) is increasingly localized to lipid rafts in depressed subjects and that chronic antidepressant treatment translocates Gαs from lipid rafts. Translocation of Gαs, which shows delayed onset after chronic antidepressant treatment of rats or of C6 glioma cells, tracks with the delayed onset of therapeutic action of antidepressants. Because antidepressants appear to specifically modify Gαs localized to lipid rafts, we sought to determine whether structurally diverse antidepressants accumulate in lipid rafts. Sustained treatment of C6 glioma cells, which lack 5-hydroxytryptamine transporters, showed marked concentration of several antidepressants in raft fractions, as revealed by increased absorbance and by mass fingerprint. Closely related molecules without antidepressant activity did not concentrate in raft fractions. Thus, at least two classes of antidepressants accumulate in lipid rafts and effect translocation of Gαs to the non-raft membrane fraction, where it activates the cAMP-signaling cascade. Analysis of the structural determinants of raft localization may both help to explain the hysteresis of antidepressant action and lead to design and development of novel substrates for depression therapeutics.

Pharmacodynamics of benzodiazepines after single oral doses: kinetic and physiochemical correlates

Differences among various benzodiazepines in onset and intensity of action after single oral doses are not attributable to differences in blood brain barrier permeability. When given parenterally all benzodiazepines rapidly enter brain tissue and have a rapid onset of action, indicating that passage from blood to brain is not the rate-limiting factor (Arendt et al. 1983). Rather it is the difference in rate of absorption - passage from the gastrointestinal tract to systemic blood - that largely determines the onset of action after single oral doses. This difference in absorption rate in turn depends on the relative lipophilicity as well as the characteristics of the pharmaceutical formulation. There are benefits and disadvantages associated with rapid as well as with slow absorption profiles, depending on the clinical situation and the patient's expectations and particular pattern of drug sensitivity. The suggestion that a drug "works promptly but does not produce initial euphoria" is contradictory, since rapid absorption is the mechanism for both of these effects.