A radioimmunoassay for betamethazone. Preparation of a specific antiserum to betamethazone-3 (O-carboxymethyl) oxime-bovine serum albumin and evaluation of method

A radioimmunoassay for the metabolites of the anabolic steroid nandrolone

A new radioimmunoassay for the major metabolites of nandrolone was developed to overcome the interference of certain contraceptive steroids in the original assay of the parent steroid. The new assay gave greater screening capability by increasing retrospective detection and the signal-to-background ratio.

Improvements in the purification of an antisteroid antiserum resistant to conventional immunoadsorption chromatography

Antibodies against dexamethasone, a synthetic steroid, have been induced in rabbits immunized with a 3-carboxymethyloxime dexamethasone derivative conjugated to bovine serum albumin. The antiserum displaying the highest affinity for dexamethasone (KD = 0.5 nM) appeared to be resistant to purification on an agarose matrix bearing the same 3-carboxy-methyloxime dexamethasone derivative. No desorption of active antibodies could be obtained whatever the eluting buffer used. Electrophoretic elution gave only poor results. However a very significant improvement in the purification of these antibodies was achieved by changing the connecting arm for steroid linkage to the agarose beads. A 17-fold purification and a 32% recovery of active specific antisteroid antibodies were obtained using a column bearing a 17 beta-carboxamide dexamethasone derivative. Moreover good results (23-fold purification and 30% recovery) were also obtained with a commercially available preactivated high-performance silica column derivatized with an aminated 3-carboxymethyloxime derivative of dexamethasone. In this case the more efficient diffusion of the eluting solution through the pores of a high performance stationary phase made of small diameter rigid beads probably explained the strikingly improved results, when compared to those obtained with agarose beads bearing the same dexamethasone derivative.

Pharmacokinetic evaluation of betamethasone and its water soluble phosphate ester in humans

Two betamethasone tablet formulations, and betamethasone phosphate solution were compared in a plasma level study. The tablet formulations (A and B) and a solution of betamethasone phosphate (C) were administered in single 2 mg doses to nine volunteers according to a three times repeated Latin square design. Plasma samples were obtained over 72 h following each dose and plasma was analysed for betamethasone by radioimmunoassay. Pharmacokinetic evaluation of the data, obtained according to the one-compartment open model, indicated that there were no significant differences between the extent of absorption, and the first-order elimination rate constants. As would be expected, the solution (C) gave a faster absorption rate than tablets A and B.

An enzyme immunoassay for plasma betamethasone

A sensitive enzyme immunoassay for plasma betamethasone was developed using betamethasone-3-(O-carboxymethyl)oxime-beta-D-galactosidase conjugate as a labelled antigen and 4-methylumbelliferyl-beta-D-galactoside as a fluorescence substrate. The performances of the enzyme immunoassay were compared with that of a radioimmunoassay using 3H-betamethasone and the same antiserum. The minimal detectable level for the enzyme immunoassay was 0.15 pg/tube or 0.15 ng/ml of plasma, which was remarkably more sensitive than the radioimmunoassay level of 10 pg/tube or 2 ng/ml of plasma. The specificity was sufficient, in particular, the cross reactivity of cortisol as 0.008%. However, the precision of the enzyme immunoassay was inferior to that of the radioimmunoassay.