The use of solid probe chemical ionization mass spectrometry and gas chromatography-chemical ionization mass spectrometry in quantitation of drugs in biological fluids. Determination of tolbutamide and its metabolites in human plasma

Inhibitory effect of nicotine and its metabolites on tolbutamide hydroxylation in rat liver microsomes

A simple HPLC/fluorescence method to detect hydroxytolbutamide (a major metabolite of the anti-diabetic drug tolbutamide) has been developed. The effects of nicotine and some of its metabolites on tolbutamide hydroxylation is described. An extraction procedure with diethyl ether was followed by isocratic HPLC analysis of tolbutamide hydroxylation with a binary mobile phase composed of 10 mM monobasic sodium phosphate in methanol (45:55, v/v, apparent pH 2.28). A detection limit of sub-nanogram amounts (0.353 ng) of hydroxytolbutamide was obtained with fluorescence detection at 226 nm for excitation and 318 nm for emission. Overall precision values for hydroxytolbutamide was determined with coefficients of variation of 1.4-4.6% when nanogram levels of the metabolite were analyzed. Differential inhibitory responses were demonstrated for tolbutamide hydroxylation to nicotine and its metabolites. Tolbutamide hydroxylation was apparently inhibited by cotinine and relatively less inhibited by nicotine. Nornicotine, however, caused very little inhibition of tolbutamide hydroxylation. The implication is that nornicotine may not share similar affinity for the substrate binding site for tolbutamide. The results also suggest that heavy smokers may experience reduction in tolbutamide metabolism. The assay system itself will be useful for future studies of tolbutamide, and possibly related sulfonylureas.

Simple high-performance liquid chromatographic method for the determination of tolbutamide and its metabolites in human plasma and urine using photodiode-array detection

A high-performance liquid chromatographic method has been developed for the determination of tolbutamide and its metabolites in human plasma and urine. The compounds examined were extracted with diethyl ether from the acidified biological fluid. Chlorpropamide was used as internal standard, and 235 nm was chosen as the wavelength for diode-array detection. A study of the relationship between the capacity factor and the mobile phase composition and pH showed that acetonitrile-2-propanol-0.1% orthophosphoric acid (17: 17: 66, v/v) was the best eluent on a C8 reversed-phase column. The method is precise, sensitive and suitable for pharmacological investigations.

High-performance liquid chromatographic assay of tolbutamide and carboxytolbutamide in human plasma

A high-performance liquid chromatographic method was developed for the simultaneous measurement of tolbutamide and its major metabolite, carboxytolbutamide, in plasma. The assay involves the ether extraction of 1 ml of plasma, using chlorpropamide and an internal standard. The extract is dried, the residue is taken up in acetonitrile, and 5 micro l is injected into a reversed-phase column. The mobile phase consisted of 35% acetonitrile and 65% 0.05 M phosphoric acid buffer (pH 3.9). A fixed-wavelength detector was set at 254 nm. The sensitivity limits for the tolbutamide and carboxytolbutamide assay were 2 and 0.1 microgram/ml, respectively. The ratio of carboxytolbutamide to tolbutamide in plasma obtained from a subject given a 500-mg tolbutamide tablet was 1:20.

Mass spectrometry of medicines. Quantitative determination by direct probe inlet system mass chromatography

A fundamental study was performed to establish a method of quantitative analysis using mass chromatography by the direct inlet system. The samples were aspirin, phenacetin and caffeine, which are often used as cold medicines, and barbital, allobarbital, phenobarbital and phenytoin which are difficult to analyse by gas chromatography in their intact states. N-acetylsulfamine and ethyl p-aminobenzoate were used as internal standards. Direct inlet mass chromatography was performed by an on-line system of the Shimadzu LKB-9000 and the GC-MSPAC 300. The ratio of the cumulative ions of certain peaks of sample and the internal standard was studied. It was found that, whether the sample is a pure reagent or a mixture, the ratio of cumulative ions of a peak specific to the sample and of a selected peak of the internal standard is proportional to the sample size, the error being less than +/- 3.5% for aspirin, phenacetin and caffeine, and less than +/- 2.7% for barbital, allobarbital and phenobarbital. The same relationship was observed for the phenobarbital and phenytoin mixed in rat plasma, the error being less than +/- 2.0%. It can be concluded that this method is applicable to the quantiative determination of medicines in urine, body fluids and other biological samples.

Mass spectrometry of N-methylsulfonylureas. A re-examination

Some confusion has arisen in the literature regarding the electron impact mass spectrum of N-methyltolbutamide. The situation is complicated by the thermal lability of this compound which causes the formation of the corresponding N-methylsulfonamide. We present here spectral data at relatively low probe temperatures (and without an intervening gas chromatographic system) which we believe define the mass spectrum of N-methyltolbutamide more accurately than before. Similar data are presented for the analogous N-methylacetohexamide and show a rearrangement process for both substances not reported previously for this class of compounds.

Determination of phenylbutazone, tolbutamide and metabolites in plasma and urine using chemical ionization mass spectrometry

Quantitative analytical procedures for the analysis of phenylbutazone and tolbutamide levels in plasma have been developed which involve the addition of deuterium labeled internal standards to plasma followed by extraction and direct sample insertion into a mass spectrometer operating under chemical ionization conditions. Peak height ratios used to calculate plasma levels were determined by using either selected ion monitoring or repetitive scan data. The scan approach was used in a related procedure for the simultaneous determination of tolbutamide and two metabolites from urine. The accuracy, precision and sensitivity of the direct sample insertion approach to drug level measurement has been determined. Examples are given of data obtained in the course of pharmacokinetic studies in which this analytical approach appears to offer advantages in the analysis of multicomponent mixtures encountered in drug-drug interaction studies.