Recently, Ganshorn and Kurz 5 reported that the plasma binding of the su1£onamide drugs, su1£amethoxidiazine and su1£ame-thoxine, was greater in adult plasma than in plasma from cord blood. Since the su1£on-amides are bound mainly to plasma albumin, l we investigated the interaction of sulfaphenazole with albumin isolated by starch block electrophoresis from cord plasma and from the plasma of neonates and adults. Our results show that sulfaphenazole has a lower affinity for plasma albumin isolated from cord and neonatal blood than for adult human plasma albumin. However, this reduced affinity ap-
their ability to induce ataxia, to decrease locomotor activity, and to afford protection against electroshockand strychnine-induced convulsions in mice. In general, the compounds described herein failed to afford protection at an acceptable dose (<50 mg/kg) against convulsions induced by either method. However, many compounds induced ataxia, as judged by impairment of ability to traverse a suspended rod, and decreased motor activity. The data for the more interesting compounds are summarized in Table I; comparable data for Mannich base 1 are included.
The binding of phenylbutazone to plasma albumins from man, rat, rabbit and dog has been measured at 37°C by equilibrium dialysis. Species differences were found both in the number of phenylbutazone binding sites per albumin molecule and the affinity of such sites for the drug. Using the binding parameters from this study we have shown how it is possible to estimate the effect of plasma albumin binding on the distribution of a drug in the body. These calculations suggest that although phenylbutazone has a stronger affinity for human plasma albumin than for plasma albumins from the other 3 species it is unlikely that the longer biologic half life of the drug in man can be attributed solely to a difference in plasma binding. Using the binding parameters for human plasma albumin the effect of complete displacement of phenylbutazone from plasma and tissue binding sites on the concentration of free drug in plasma has also been estimated.
A novel assay procedure has been developed for the determination of sulfonamide drugs with the general formula ArSO2NH2 where Ar = aryl (either homocyclic or heterocyclic). The assay depends on the displacement of a spin-labeled sulfonamide from the active site of bovine carbonic anhydrase B and can detect concentrations of sulfonamide as low as 0.3 µg/ml. This technique can also be used to assay low concentrations of carbonic anhydrase in hemolysates of red blood cells without prior removal of the hemoglobin or isolation of the enzyme.
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