Competitive rate nephelometric immunoassay for determination of theophylline, phenobarbital, and dilantin in serum.

The theophylline, phenobarbital and dilantin were measured in serum by rate nephelometric immunoassay with the Beckman Immunochemistry System (ICS, Beckman Inc. Brea., CA 92621). The procedures required less than three minutes after proper calibration and dilution, and only 42 microliters of serum theophylline and 100 microliters of serum for phenobarbital and dilantin per determination. It is simple and needs only pipetting and dilution with automatic dispenser and diluter. Day to day variation was determined by analyzing on 30 days two control sera containing theophylline level I (12 micrograms/ml 18-micrograms/ml) and level II (30 micrograms-38 micrograms/ml). The average theophylline level I concentration was 14.5 micrograms/ml, with a standard deviation of 0.70 micrograms/ml, and a coefficient of variation of 4.8%. The average theophylline level II concentration was 32.2 micrograms/ml, with a standard deviation of 1.89 micrograms/ml, and a coefficient of variation of 5.9%. Results attained in patients were compared with results of enzyme immunoassay procedure (EMIT, Syva Corp.). For theophylline, r-0.957, for phenobarbital, r=0.936, and for dilantin, r=0.972.