Studies on prednisolone metabolism in children. 1. A new prednisolone radio immunoassay with prednisolone anti serum against prednisolone 3 oxime bovine serum albumin and plasma prednisolone measurement
Folia Endocrinologica Japonica 57(3): 235-247
A radioimmunoassay using the antiserum of prednisolone-3-oxime-BSA [bovine serum albumin] according to Erlanger's method is described. Antiserum produced by immunizing rabbits with prednisolone-3-oxime-BSA conjugates shows a high affinity for prednisolone (K [binding constant] = 4.2 .times. 109 l/mol) and a higher selectivity (the cross-reactivity to cortisol, 17.alpha.-hydroxyprogesterone, 21-deoxycortisol and 11-deoxycortisol are 17, 1.2, 1 and 1%, respectively) than the antiserum against prednisolone-21-hemisuccinate-BSA reported by others. This method is sensitive to 6 ng/ml of 0.1 ml plasma. In this method, intraassay variability of plasma prednisolone determinations is < 4.1%, interassay variability is < 9.6%. The contamination of endogenous steroids is 1.4 .+-. 1.62 ng/ml (n = 37) in normal controls, and 0.65 .+-. 0.88 ng/ml (n = 14) in several adrenal disorders. Following oral dosage (1 mg/kg per dosage) with prednisolone, the plasma peak values (593 .+-. 63 ng/ml) occurred 1 h after the administration, then plasma levels declined to 163 .+-. 49 ng/ml at 6 h, with the plasma half-life of 2.76 .+-. 0.86 h. The correlation between the plasma peak values and the dosage in the range of 0.5-4 mg/kg per dosage is r = 0.996, P < 0.001 in the same person. This prednisolone radioimmunoassay is accurate, precise, sensitive, specific and suitable for routine clinical monitoring of prednisolone levels. Plasma prednisolone measurement may also be of value in children who have been given a higher dosage than adults.