Sueharu Nakano

Evaluation of applicability of SLFIA method to monitoring carbamazepine concentration in plasma. Comparison with EMIT and HPLC methods.

Concentrations of carbamazepine (CBZ) in plasma were measured by AMES TDATM carbamazepine kit, a newly developed substrate-labeled fluorescent immunoassay (SLFIA). The study produced results which showed good correlation with those of homogeneous enzyme immunoassay (EMIT) and high-performance liquid chromatography (HPLC). There was a significant correlation in the plasma concentrations between SLFIA and EMIT methods (n= 92, r= 0.994, p<0.01), whereas a high correlation between SLFIA and HPLC was also found (n=92, r= 0.990, p<0.01).For the determination of plasma concentrations of antiepileptics in the clinical field, SLFIA procedure seems to have considerable advantages over hitherto available method: This method requires only 50μl of plasma for a single determination and is quite a simple method for monitoring plasma concentrations of antiepileptics.Concentrations of CBZ in plasma after administration of CBZ alone were compared with those after concurrent administration of antiepileptics, including CBZ, phenobarbital (PB) and phenytoin (PHT). From these results, it was found that plasma concentrations of CBZ administered concurrently with PB and PHT were significantly lower than those after administration of CBZ alone.

Clinical Application of SLFIA Method for Monitoring Plasma Concentration of Antiepileptics

Plasma concentrations of primidone, phenobarbital and phenytoin were assayed by AMES TDATM Kit (Miles-Sankyo Co., Ltd.), the newly developed Substrate-Labeled Fluorescent Immunoassay (SLFIA). The results were compared with those obtained by High-Pressure Liquid Chromatography (HPLC) method, where the SLFIA results showed high correlation with HPLC. The correlation coefficient was over 0.977 both in SLFIA and in HPLC and the coefficient variation was less than 6% in a spiked sample by the SLFIA method in the replicated analysis based on 147 plasma samples obtained from 144 epileptic patients given antiepileptics. The correlation coefficient obtained from the SLFIA method using the spiked sample was also over 0.998.SLFIA procedure in clinical application for determination of plasma concentrations has considerable advantages over hitherto available methods. This method requires only 50μl of plasma for a single determination, which may eliminate deproteinization and extraction steps. These results suggest that SLFIA is a simple method for monitoring plasma concentration of antiepileptics.

Pharmaceutical Tests and Plasma Theophylline Level of Slow-Release Preparation

Plasma theophylline concentration of a slow-release theophylline preparation (SRT: Theona P) was measured by high-pressure liquid chromatography. SRT was administered to 6 healthy adults orally in dose of 100mg. Dissolution test of SRT by the rotating basket method made in accordance with U. S. P. XVIII revealed that the drug tended to dissolve slowly, dissolution rate being about 50% 6 hours after initiation of the experiment. The experiment also demonstrated that plasma concentration of theophylline reached peak about 5 hours after oral administration of SRT on the average, and about 2 hours after use of Aminophylline Tablet (immediate-release preparation).Average maximal plasma theophylline level was 1.32μg/ml for SRT as compared with 1.92μg/ml for Aminophylline. In clinical trial, the plasma concentration of theophylline was not maintained at 10μg/ml after oral administration of SRT and Aminophylline Tablet in dose of 100mg 4 times a day, respectively. The 10-μg/ml level was maintained when SRT single dose was increased to 200mg.

Rectal Absorption of Aminophylline Suppository

Mode of rectal absorption of aminophylline was examined with 3 kinds of suppository bases, macrogol, Vosco H-15, and Vosco S-55. Plasma concentration of theophylline after rectal and oral administration was also measured on the subjects of 5 healthy adults. Measurement was made by the high-pressure liquid chromatography.Drug releasing test was made by the method of Kakemi et al. Physical property, melting point, dissolution time, and other properties of the suppository were measured. The drug releasing test demonstrated that the release of aminophylline from macrogol base was faster than that from Vosco bases (in vitro test). Plasma concentration of theophylline was found higher in the oleaginous base (Vosco) than in the water-soluble base (macrogol). This is contradictory to the finding in vitro test.In the human experiment, the highest mean plasma concentration of theophylline, 1.29 μg/ml., was observed 1 hour after rectal administration. The highest plasma concentration by rectal administration was slightly lower than that by oral administration.