Takatsuka Yashiki

Estimation of drug absorption rates using a deconvolution method with nonequal sampling times

A method affording direct estimation of the drug absorption rate from blood level data using arbitrary time intervals has been derived based on the staircase input principle. In the derivation, the drug was assumed to follow linear kinetics where the plasma concentration of the drug after an impulse input is expressed by a multiexponential function. Drug absorption was assumed to occur at a constant rate during each subsequent sampling interval. The absorption rate profiles obtained by the method using several numerical examples were expressed as a set of rectangular pulses. Divergence in the profiles reflected blood sampling measurement errors rather than errors due to the deconvolution. Smoothing of the rate profiles by calculating the mean of the absorption rates between adjacent time intervals gave realistic results. Absorption rate profiles for theophylline obtained by the method using published data gave information on the initiation and termination of the absorption as well as the extent of absorption from the dosage form.

High-performance liquid chromatographic determination of lansoprazole and its metabolites in human serum and urine

A simple and sensitive high-performance liquid chromatographic method with ultraviolet detection is described for the simultaneous determination of lansoprazole and its metabolites in human serum and urine. The analytes in serum or urine were extracted with diethyl ether-dichloromethane (7:3, v/v) followed by evaporation, dissolution and injection into a reversed-phase column. The recoveries of authentic analytes added to serum at 0.05-2 micrograms/ml or to urine at 1-20 micrograms/ml were greater than 88%, with the coefficients of variation less than 7.1%. The minimum determinable concentrations of all analytes were 5 ng/ml in serum and 50 ng/ml in urine. The method was successfully applied to a pharmacokinetic study of lansoprazole in human.

Quantitation of a new potent angiotensin II receptor antagonist, TCV-116, and its metabolites in human serum and urine

A sensitive high-performance liquid chromatographic (HPLC) method is described for the determination of a new potent antihypertensive agent, TCV-116, and its two metabolites (M-I and M-II) in human serum or urine. After pre-treatment of the specimens, the analytes were determined using a column switching technique, except for the metabolites in urine which were determined by gradient elution mode HPLC. The quantitation limits for TCV-116, M-I and M-II were all 0.5 ng/ml in serum, and 0.5, 10 and 110 ng/ml in urine, respectively. The methods were applied to clinical trials of TCV-116.

High-performance liquid chromatographic determination of busulfan in human serum with on-line derivatization, column switching and ultraviolet absorbance detection.

A high-performance liquid chromatographic (HPLC) method is described for the determination of busulfan in human serum using on-line derivatization and column switching. Busulfan was extracted from serum with a mixture of diethyl ether and dichloromethane. After the evaporation of the organic layer, the reconstituted residue was injected into the HPLC system and busulfan was derivatized with sodium diethyldithiocarbamate on the first short column. The back-flushed derivative was then separated on the second column. Finally, after column switching, the heart-cut fraction containing the derivative was further analysed on the third column and monitored with ultraviolet absorbance detection at 278 nm. The lower limit of quantitation in serum was 10 ng/ml.

Determination of manidipine enantiomers in human serum using chiral chromatography and column-switching liquid chromatography

A stereoselective and highly sensitive method using chiral chromatography and successive column-switching liquid chromatography is described for the determination of manidipine enantiomers in human serum. A human serum sample obtained after ingestion of manidipine was extracted twice with a mixture of n-hexane-diethyl ether under alkaline conditions. The enantiomers in the extract were separated on a chiral stationary phase column (Chiralcel OJ), and the effluents containing the respective enantiomers were collected. Each fraction was then analysed by column-switching liquid chromatography. The proposed stereoselective method offered high sensitivity: detection limits for both isomers were 0.2 ng/ml in human serum, both at a signal-to-noise ratio of 3. The method is suitable for the pharmacokinetic studies of manidipine enantiomers.

Column-switching techniques for high-performance liquid chromatography of ibuprofen and mefenamic acid in human serum with short-wavelength ultraviolet detection

Column-switching techniques for high-performance liquid chromatography of two acidic drugs, ibuprofen and mefenamic acid, in human serum with short-wavelength ultraviolet detection are described. The method involved extraction of the analyte from acidified serum followed by the chromatographic analysis using column switching. Three ODS columns were used each with different mobile phase, utilizing the difference of ion-pair formation or of ionization caused by pH change. The method offered high sensitivity and selectivity, with short-wavelength ultraviolet detection at 221 nm for ibuprofen and at 219 nm for mefenamic acid. The detection limits were 0.5 ng/ml (2.4 pmol/ml) for ibuprofen and 0.1 ng/ml (0.4 pmol/ml) for mefenamic acid using 1 ml of serum, both at a signal-to-noise ratio of 3. With some modifications, the principle of the method would be applicable to other acidic compounds in biological fluids.

Determination of manidipine and its pyridine metabolite in human serum by high-performance liquid chromatography with ultraviolet detection and column switching

A highly sensitive and selective high-performance liquid chromatographic method using column switching is described for the determination of the dihydropyridine calcium antagonist manidipine (I),2-[4-(diphenylmethyl)-1-piperazinyl]ethyl methyl (+/- )-1,4-dihydro-2,6-dimethyl-4-(m-nitrophenyl)-3,5- pyridinedicarboxylate, and its pyridine metabolite (II), 2-[4-(diphenylmethyl)-1-piperazinyl]ethyl methyl 2,6-dimethyl-4-(m-nitrophenyl)-3,5-pyridinedicarboxylate, in human serum. The method is based on the combination of the column-switching technique and ion-pair chromatography. In the first ODS column, I and II are preseparated from endogenous substances in serum with a mobile phase containing sodium nonane sulphonate as an ion-pair reagent. After column switching, in the second ODS column, the heart-cut fraction containing I and II is further separated from the co-eluted substances through the first column with a mobile phase containing no ion-pair reagent. By using microbore columns with a diameter of 2.1 mm, the sensitivity is almost double that given by conventional bore columns with a diameter of 4.6 mm. The method offers high sensitivity and selectivity with short-wavelength ultraviolet detection at 230 nm. The detection limits of both I and II are 0.1 ng/ml using 1 ml of serum. The method is suitable for the pharmacokinetic study of I.2HCl after oral administration to man.

Sensitive determination of methotrexate in monkey plasma by high-performance liquid chromatography using on-line solid-phase extraction

A high-performance liquid chromatographic method was developed for the sensitive determination of methotrexate (MTX) in monkey plasma using direct injection and on-line solid-phase extraction. After application of a 100-microliters aliquot of plasma to a pre-treatment column, the column was washed with 0.02 M phosphate buffer (pH 7) to eliminate plasma proteins and endogenous substances, and subsequently the adsorbed MTX was eluted. The MTX fraction was transferred to an analytical column by a column-switching (heart-cutting) technique, and MTX was analyzed using ion-pair chromatography with tetrabutylammonium bromide. More than 50 injections could be performed onto one pretreatment column. The accuracy, precision, reproducibility and linearity were satisfactory over a wide range of MTX concentrations (5-1000 ng/ml). The quantitation limit was 5 ng/ml with a signal-to-noise ratio of 5. The method was suitable for the pharmacokinetic study of MTX in monkey.

Sensitive high-performance liquid chromatographic determination of chlorpheniramine in human serum using column switching

A sensitive method for the determination of chlorpheniramine in human serum was developed using column-switching high-performance liquid chromatography (HPLC) with ultraviolet detection at 210 nm. The analyte was extracted with diethyl ether from alkalinized serum. After evaporation of the organic layer, the reconstituted residue was analyzed by HPLC using a heart-cut technique. Good recoveries of the analyte from spiked human serum samples were obtained with a coefficient of variation below 7%. A good linear response was obtained for the concentration range 0.5-50 ng/ml, with a correlation coefficient higher than 0.999. The lower limit of quantitation for chlorpheniramine in human serum was 0.5 ng/ml. The method was satisfactorily applied to the determination of chlorpheniramine in human serum after oral administration of chlorpheniramine maleate.

Sensitive high-performance liquid chromatographic determination of EM523, a new erythromycin derivative, in human plasma and urine with ultraviolet detection using column switching

A sensitive high-performance liquid chromatographic (HPLC) method using column switching is described for the determination of EM523 (I), a new erythromycin derivative, in human plasma and urine. The analyte was extracted from alkalinized plasma or urine with a mixture of n-hexane and acetone. After the evaporation of the organic layer, the reconstituted residue was injected into the HPLC system and separated on the first column. After column switching, the heart-cut fraction contamination the analyte was further separated on the second column and monitored by ultraviolet absorbance at 210 nm. The detection limits were 1 ng/ml in plasma and 10 ng/ml in urine. The method was applied to the clinical trials of I.