False-positive results in the radioimmunoassay detection of stilbene derivatives after administration of fluorinated corticosteroids to animals.

During routine inspections, indications were found that the therapeutic use of fluocortolone or dexamethasone can cause false-positive results in the detection of stilbene derivatives by radioimmunoassay (RIA) in samples of animal origin. After experimental application of the fluorinated corticosteroids to rabbits or calves, the assumed false-positive RIA results were confirmed. The kinetics after application of dexamethasone were concomitant with the elimination of radioactive [3H]dexamethasone. Furthermore, it could be demonstrated that [3H]dexamethasone was transformed in the faeces of rabbits and calves. The metabolites formed were not completely separated by the extraction procedure used for the RIA and seemed to be responsible for the false-positive results.

[Penetration kinetics of fluocortolone from a new base for ointment and creme (author's transl)]. / Penetrationskinetik von Fluocortolon aus einer neuen Salben- und Cremegrundlage.

The penetration of fluocortolone from topically administered Syracort ointment and creme was investigated in guinea pigs. Two fluocortolone standards were tested as reference preparations (ointment and creme). 1. Fluocortolone liberation from the ointments and Syracort Creme within 24 h varied between 55% and 62% of the administered dose. The reference creme gave lower drug liberation values (39%). 2. The penetration profile of fluocortolone changed gradually. Non-absorbed portions and the concentrations in the upper layers of the stratum corneum decreased during inunction up to 24 h. Within the same time concentrations in the deeper layers of the skin increased. 3. The two ointments showed comparably good penetration properties, whereas Syracort creme gave flux values higher than those obtained from the reference creme. 4. 24 h after removal of the non-absorbed portion of the ointments a further persistence of the drug could be observed within the skin: 14.3% to 18.5% after additional 6 days. The mean renal elimination rate was found to be 3 days, a total amount between 28% to 30% of the dose was excreted via urine and feaces. Consequently, fluocortolone can be considered a fast penetrating topical which is accumulated especially in the layers of the epidermis and cutis.