The relationship between binding of thiopental to plasma and its distribution into adipose tissue in man, as measured by a spectrophotofluorometric method

Binding in vitro of thiopental to human plasma was measured by a spectrophotofluorometric method as well as by radioactive procedures. At relatively high concentrations of thiopental, binding remains fairly constant. However, below 6 mg/1., per cent binding increases inversely with concentration. This phenomenon, occurring also in vivo hours after thiopental administration, alters the distribution of the drug between plasma and adipose tissue; eventually the adipose tissue to plasma concentration ratios become lower with diminishing plasma concentration. Such a decrease may be considered the result of a passive mechanism which reduces the effectiveness of certain drugs. Administration of dextran to human subjects was found to lower the concentration of thiopental in plasma mainly by increasing blood volume. A spectrophotofluorometric method for the assay of thiopental has been developed. Specificity has been proven by a quantitative thin-layer Chromatographie technique.