A Clinically Applicable High-pressure Liquid Chromatographic Method for Measurement of Serum Theophylline, with Detailed Evaluation of Interferences

Abstract

A high-pressure liquid chromatographic method for the routine measurement of serum theophylline that is accurate, specific, and sensitive is presented. It is technically simple, requires only 50 microliter serum, and takes relatively little technician time. Values for theophylline in sera obtained by this method correlate well with those obtained by use of a gas-liquid chromatographic method (r = 0.980) and with values obtained by the commonly used spectrophotometric method (r = 0.939) when the latter is free of interference. The assay has been employed for two years in a routine clinical chemistry laboratory, with interassay coefficients of variation of 2.4-3.2%. Interferences have been identified at an incidence rate of 3.8% of all specimens, and interfering substances include cephazolin, chloramphenicol, sulfamethoxazole, and sulfisoxazole. A calculation technic that allows a reliable and clinically useful estimation of a range of concentrations of theophylline in the serum when these interferences are present is described. In contrast, the incidence of interferences with the spectrophotometric method is 4.9%, and in this method the interferences prevent the analysis of theophylline. Of 33 samples having interferences by use of the spectrophotometric method, the high-pressure liquid chromatographic technic yielded precise values for theophylline in 21 and reliable estimates of ranges of concentrations of theophylline in the remaining 12.

Theophylline therapy inhibits neutrophil and mononuclear cell chemotaxis from chronic asthmatic children.

“…Serum IgE was quantified by solid-phase enzyme immunoassay (Johansson, 1978;Yman et al, 1981) using Abbott IgE-EIA kits (Abbott Laboratories, Chicago, II, USA). Plasma theophylline and cAMP measurement Plasma theophylline concentrations were assayed by high-performance liquid chromatography (Ou et al, 1982;Weidner, 1980) and plasma cAMP levels by a competitive protein binding assay (Gilman, 1970), using a cAMP liquid scintillation assay kit from Amersham (Tovey et al, 1974).…”

Drug Interferences with Plasma Assays in Therapeutic Drug Monitoring

“…These drugs include some of the cephalosporins (Agdeppa and Lipton, 1980;Frutkoff et aI., 1982;Kelly et aI., 1978;Robinson et aI., 1978;Weidner et aI., 1980), ampiciIIin and methiciIIin (Lam et aI., 1979;Soldin and Hill, 1977a), sulphamethoxazole (Bowman et al, 1980;McKenzie et aI., 1978;Weidner et aI., 1980), sulphafurazole (sulfisoxazole) [Lam et aI., 1979;Weidner et al, 1980], the trisulphapyrimidines (Bond and Thornton, 1979), and chloramphenicol (Weidner et aI., 1980). Other methods should be selected when these drugs are co-administered with theophylline, otherwise the procedure should be modified to include an extraction step or the change of the internal standard (when the peak of the interfering drug appears very close to the position of the internal standard).…”

“…Modifications, which include a change of the column or of the mobile phase, could eliminate some of the interferences as well (Bowman et aI., 1980;Miksic and Hodes, 1979). 79 Weidner et al (1980) suggested a second reading of a sample with interference at a lower flow rate. This offered complete resolution of some of the peaks which overlapped with either theophylline (a positive interference) or the internal standard (a negative interference).…”