The effect of sodium bisulfite on the removal of drugs and their metabolites interfering with the Porter-Silber reaction in the determination of urinary 17-hydroxycorticosteroids.

In the determination of urinary 17-hydroxycorticosteroids, the urine is saturated with NaHSO3 after hydrolysis with beta-glucuronidase and then extracted with methylene chloride. Sodium bisfulfite removes almost all non-steroidal impurities in the urines from patients medicated with acetylspiramycin, leucomycin, erythromycin, triacetylolenadomycin, rifampicin and tranquilizers such as chlorpromazine, which interfere with the absorption at 410 nm. in the subsquent Porter-Silber reaction. In order to increase the specificity of a routine method, a procedure conducted by Allen has been often employed: The sum of 370- and 450-nm. absorbances is subtracted from twice absorbance at 410 nm. However, the procedure could not be used in the medicated urines mentioned above, because the spectral absorption curve of these drugs and their metabolites in the Porter-Silber reaction was not a straight but a strongly convex or concave line in the 370-450-nm. range. Using the present method, interference with the Porter-Silber reaction was not found in the urines from patients medicated with chloramphenicol, minocycline, chlordiazepoxide, meprobamate, methyprylon, nitrazepam, synthetic penicillins such as hetacillin, oxacillin and cloxacillin, or cephalosporins such as cephalexin and cephalothin. However, to obtain correct values in urines from patients medicated with spironolactone, it was necessary to subject the urines to treatment with methylene chloride before enzyme hydrolysis.