Determination of tolbutamide and chlorpropamide in biological fluids

Interaction between tolbutamide and ketoconazole in healthy subjects

A possible interaction between tolbutamide and ketoconazole was studied in seven healthy volunteers. Treatment for 1 week with 200 mg oral ketoconazole increased the elimination half-life (from mean +/- s.d. 3.7 +/- 0.4 to 12.3 +/- 1.9 h) and AUC(0.12 h) of tolbutamide (from 309 +/- 27 to 546 +/- 20 micrograms ml-1 h) by 25 +/- 64 and 66 +/- 15%, respectively. The percentage blood glucose reduction was also increased when tolbutamide and ketoconazole were coadministered.

The effect of food on the bioavailability and pharmacodynamics of tolbutamide in diabetic patients

The effect of food on the rate and extent of absorption of tolbutamide in diabetic patients was studied by varying the time of drug administration in relation to the ingestion of a standard meal. Serum levels of tolbutamide, insulin and glucose and related bioavailability parameters were compared following the administration of a single dose of tolbutamide 0.5 g to diabetic patients 30 min prior to and immediately before a standardized meal. A placebo dosage form was also administered to determine baseline glucose and insulin response to the meal. The 700 calorie standard meal was composed of 41% carbohydrate, 18% protein, and 41% fat. Administration of the drug with the meal resulted in a 6% (statistically significant) decrease in the extent of absorption, as determined by measurement of the area under the tolbutamide serum level-time curve from zero to infinity. Serum levels of tolbutamide were also significantly higher 0.5 h after drug administration when the drug was taken with the meal. Except for these two minor effects, no other differences between the drug treatments were observed in any other parameters of tolbutamide absorption or in the postprandial glucose and insulin serum levels. Therefore, the small differences found were judged to be clinically meaningless. These findings demonstrate that administration of tolbutamide 0.5 g tablets 30 min prior to or with a standard meal results in equivalent therapeutic actions.

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.

The regulation of glucose-induced insulin secretion by pre-stimulus glucose level and tolbutamide in normal man

The relationship between the pre-stimulus glucose level and immunoreactive insulin responses to a glucose challenge (20-g IV) was studied in normal subjects. When the steady-state pre-stimulus glucose concentration was lowered by a 0.33 mU.kg-1.min-1 insulin infusion or raised by a 900 mg/min glucose infusion, no effect on first phase insulin secretion (mean delta 3-5 min insulin level) was observed. In contrast, the second phase response (10-60 min insulin area after glucose pulse) to intravenous glucose fell during insulin infusion and increased during the glucose infusion. Overall, a linear relationship was found between the change of pre-stimulus glucose or level from the control to that during the insulin or glucose infusion and the change in second phase response (r = 0.65, n = 14, p less than 0.02). The effect of tolbutamide infusion (7 mg.m-2.min-1) when compared with saline control was to increase both first phase (+54 +/- 13 mU/l, n = 8, p less than 0.001, mean +/- SEM) and second phase (+972 +/- 256 mU. min-1.l-1, p less than 0.01) insulin secretion. It is concluded that the first phase response to a glucose pulse is independent of the steady-state pre-stimulus glucose concentration and is directly enhanced by tolbutamide; in contrast, second phase is related to both the steady-state pre-stimulus glucose level and tolbutamide. These findings suggest that changes in basal or pre-stimulus plasma glucose during therapy with sulphonylurea drugs may be expected to influence the second phase insulin responses to glucose challenge.

Effect of naproxen on glucose metabolism and tolbutamide kinetics and dynamics in maturity onset diabetics

1 The influence of the nonsteroidal anti-inflammatory drug naproxen on glucose metabolism and on tolbutamide pharmacokinetics and pharmacodynamics has been studied in ten maturity-onset diabetics. 2 Comparison of both plasma glucose decay curves and insulin responses during an intravenous glucose tolerance test before and after eight 12 hourly doses of naproxen revealed that naproxen had no significant influence on fasting glucose levels or on rates of glucose elimination. 3 When the subjects were given a combination of naproxen and tolbutamide for 3 days naproxen had no influence on tolbutamide absorption, protein binding, disposition or pharmacological effect. 4 Treatment with tolbutamide in maturity-onset diabetics need not be modified if concurrent administration of naproxen is contemplated.

Tissue distribution and metabolism of drugs VI: Effect of second drugs on pancreatic distribution and insulin-releasing activity of sulfonylureas in perfused rat pancreas

The distribution of sulfonylureas and their insulin-releasing potency as a pharmacological response were studied in isolated perfused rat pancreas. Sulfonylurea concentrations in the perfused pancreas in the presence or absence of a second drug were determined after perfusion for 15 min. Sulfonylureas could be distributed throughout the pancreas readily, and the tissue sulfonylurea concentration was reduced by the addition of sulfaphenazole, sulfadimethoxine, and salicylic acid. The insulin secretion rate stimulated by tolbutamide also was reduced by these three drugs; sulfanilamide, which could not displace the tolbutamide distribution, did not affect the tolbutamide-mediated secretion of insulin. These results document the importance of drug concentration in the tissue or receptor site with regard to insulin secretion and show that the sulfonylurea-mediated secretion of insulin can be modified easily by concomitant perfusion of a second drug that displaces sulfonylurea in the pancreas. These findings suggest that the drug interaction at the target organ or receptor site should be understood to provide adequate drug therapy.

Specific and sensitive high-performance liquid chromatographic determination of glyburide

A specific and sensitive high-performance liquid chromatographic method has been developed for the rapid determination of intact glyburide in dog serum. With butylparaben as an internal standard, 1 ml of acid-buffered serum was extracted with toluene and an aliquot of the toluene was evaporated to dryness. The redissolved residue was chromatographed on a microparticulate reversed-phase column, and quantitation was achieved by monitoring the UV absorbance of the eluate at 228 nm. The response was linear, and the lower detection limit was approximately 20 ng/ml. Assay precision, as estimated by analyzing replicate samples of a laboratory standard, was better than 6% (CV). The utility of the analytical methodology for the determination of this highly potent sulfonylurea in pharmacokinetic studies in the dog was demonstrated.

Gas chromatographic determination of glibenclamide in plasma

A gas-chromatographic method for glibenclamide determination in plasma is described. It involves derivatization of the drug with dinitrofluorobenzene and the use of an electron-capture detector. The quantitative evaluation is performed using tolbutamide as internal standard. Characteristics and specificity of the method for the principal metabolite of glibenclamide are examined.

Simple, rapid and micro high-pressure liquid chromatographic method for the simultaneous determination of tolbutamide and carboxy tolbutamide in plasma

A rapid high-pressure liquid chromatographic (HPLC) assay is described for the quantitative analysis of tolbutamide and its major metabolite, carboxy tolbutamide in plasma. An aliquot (25--100 microliter) of plasma was prepared for chromatography by deproteinization as follows. One volume of plasma and 2.5 volumes of acetonitrile were vortex mixed for a few seconds and then centrifuged for approx. 1 min. A 50-microliter sample of the clear supernatant was injected into the chromatograph. A mu Bondapak C18 reversed-phase column was used with a mobile phase acetonitrile--0.05% phosphoric acid (45:55) at a flow-rate of 1.5 ml/min. The column effluent was monitored by a variable-wavelength UV detector set at 200 nm. Tolbutamide and its metabolite had retention times of 5.75 and 3.25 min, respectively. The procedure yuelds reproducible results with sensitivity adequate for routine clinical monitoring of plasma levels or for single-dose pharmacokinetic studies. A number of commonly used drugs do not interfere with the method. A single plasma sample can be analyzed in approx. 9 or 10 min.

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.

GLC determination of acetohexamide and hydroxyhexamide in biological fluids

A sensitive and specific GLC assay was developed for acetohexamide and hydroxyhexamide, its major metabolite, in plasma and urine. The assay uses tolbutamide as a mass internal standard. Compounds are extracted from acidified plasma or urine with toluene, converted to methylated derivatives with dimethyl sulfate, and measured by GLC using a flame-ionization detector. With GLC-mass spectrometry, the compounds measured are the N-methylsulfonamides resulting from GLC pyrolysis. Plasma and urine data are presented from a bioavailability study to demonstrate the utility of this method.

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.

The effects of tolbutamide on the myocardium in experimental diabetes

The effects of chronic tolbutamide treatment were examined in a diabetic animal model in which abnormal myocardial function and composition have previously been demonstrated. Eight diabetic dogs were given tolbutamide 250 mg/day orally and compared with seven untreated diabetics, five healthy dogs receiving tolbutamide, and eight normal controls. After one year, resting hemodynamic studies in the intact anesthetized state showed that treated diabetic dogs had a significantly higher left ventricular end-diastolic pressure of 12.1+/-1.3 mm Hg associated with normal end-diastolic volume, compared to 6.1+/-0.8 mm Hg in untreated diabetics (P less than 0.01) and 6.3+/-0.5 in normals. Stroke work and ejection fraction were similar to normals. Acute volume expansion revealed a larger rise of left ventricular end-diastolic pressure in treated and untreated diabetics than normals, without a significant stroke volume response in treated diabetics. Enhanced stiffness of myocardium appeared to be related to interstitial accumulation of periodic acid-Schiff staining material, further intensified in treated diabetics by triglyceride accumulation observed on electron microscopy and by chemical analysis. Thus treatment of diabetes with tolbutamide, despite improved glucose tolerance, effected further reduction of left ventricular function and altered morphology of myocardium.