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

Total lignans from Vitex negundo seeds attenuate osteoarthritis and their main component vitedoin A alleviates osteoclast differentiation by suppressing ERK/NFATc1 signaling

The seeds of Vitex negundo have been used for inflammation-related disease treatment in traditional medicine. This study focused on the anti-osteoarthritis (OA) effects of the total lignans of V. negundo seeds (TOV) in monosodium iodoacetate-induced osteoarthritis rats and its pharmacokinetic properties, as well as the effects and potential mechanism of its main components VN1 (6-hydroxy-4-(4-hydroxy-3-methoxy-phenyl)-3-hydro-xymethyl-7-methoxy-3,4-dihydro-2-naphthaldehydeb) and VN2 (vitedoin A) on receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation in bone marrow macrophages (BMMs). TOV significantly attenuated osteoarthritis, leading to an increase in pain thresholds, improvement of knee articular cartilages and chondrocytes loss, and decreased total joint scores and serum levels of TNF-α, interleukin-1β (IL-1β), and prostaglandin E2 (PGE2) in osteoarthritis rats. The half-time (T_1/2 ) was 2.82 h and 1.33 h, and the bioavailability was 15.34%-21.89% and 16.29%-22.11%, for VN1 and VN2, respectively. VN2, rather than VN1, remarkably inhibited tartrate-resistant acid phosphatase (TRAP) activity, reduced the number of TRAP-positive multinuclear cells, diminished the formation of actin ring, and decreased mRNA levels of cathepsin K (CTSK), TRAP, nuclear factor of activated T cell 1 (NFATc1), and osteoclast-associated receptor, as well as downregulated protein levels of p-ERK (phosphorylated extracellular signal-regulated kinase), TRAP, CTSK and NFATc1 in BMMs. These findings suggest TOV has promising therapeutic potential for OA treatment and VN2, in particular, attenuates osteoclast differentiation by suppressing ERK/NFATc1 signaling and actin ring, mainly accounting for the anti-OA efficacy of TOV.

The role of metabolites in bioequivalency assessment. I. Linear pharmacokinetics without first-pass effect

The estimation of bioequivalency using metabolite data was investigated for immediate release formulations with drugs exhibiting linear pharmacokinetics and no first-pass effect. This was accomplished by generating parent drug and metabolite plasma level profiles assuming formation and excretion rate-limited pharmacokinetic models with absorption rate constants obtained from bivariate normal distributions and designated random errors. Simulation results indicated that bioequivalence determination using Cmax of parent drug and metabolite was independent of the metabolite models as evaluated by confidence interval approach. However, a clear difference with respect to the outcome of bioequivalence evaluation arises depending upon the utilization of Cmax values for the parent drug and metabolite. The major reason for this disparity was attributed to the minimal effect of the absorption process for the parent drug on the formation of the metabolite. This phenomenon results in an apparent lower intrasubject variability for Cmax of the metabolite and, in turn, a tighter confidence interval for Cmax of the metabolite in comparison with the parent drug. The simulated results have been found to be in agreement with the bioequivalency data for acetohexamide, allopurinol, procainamide, and sulindac. In all cases, the interval of the 90% confidence limit for Cmax of the metabolite is always smaller than that of the parent drug, regardless of the drug pharmacokinetics and the level of error contained in the data.

Evaluation of hepatic dysfunction in endotoxin pretreated rats using tolbutamide as a marker

The pharmacokinetics of tolbutamide (TB) have been studied in endotoxin pretreated rats with the aim of evaluating TB as a marker for endotoxin effects. Endotoxin dose of 10 mg/kg resulted in a 50% rate of mortality. TB was i.v. administered 24 h. after endotoxin dosing. Clearance (Cl) decreased by approximately 2/3 of its value, area under the curve (AUC) and half-life (t1/2) in the pretreated animals were an average 1.5 times the values for the respective controls. Volume of distribution (Vd) increased by 10% approximately. These findings suggest that endotoxin pretreatment may cause hepatic damage by producing a decrease in Cl and an increase in the t1/2 of TB. But, SGOT levels in pretreated animals were not significantly different. This phenomenon may be explained by the increase in plasma protein binding of TB during endotoxin pretreatment, which decreases the free fraction of the drug in plasma available for metabolism. Endotoxin increased tmax of hydroxy-TB, while no change in Cmax was observed. Since tmax is inversely related to the formation and elimination rates of hydroxy-TB, an increase in tmax may be due to the decrease in both elimination rates. No change in Cmax may be due to the decrease in the rate of formation which is equivalent to the decrease in the rate of elimination of hydroxy-TB.

Simultaneous determinations of tolbutamide and its hydroxy and carboxy metabolites in serum and urine: application to pharmacokinetic studies of tolbutamide in the rat

Methods of analysis of tolbutamide (1) and its hydroxylated (2) and carboxylated (3) metabolites in serum and urine based on high-performance liquid chromatography were developed. The separation was performed on a Apex ODS column in the isocratic mode using a mobile phase composed of 22.5% acetonitrile, 77.5% Sorensen phosphate buffer (pH 7.0), and 0.30 mL of tetrabutylammonium phosphate reagent (Pic A). The compounds were detected at 254 mm. The retention times of 3, 2, 1, and the internal standard chlorpropamide were 3.1, 4.1, 14.8, and 10.0 min, respectively. These conditions were suitable for the simultaneous quantitation of 1, 2, and 3 in serum or plasma samples, but not for the determination of metabolites 2 and 3 in urine. For the analysis of 2 and 3 in urine, the mobile phase was modified to 18% acetonitrile, 82% Sorensen phosphate buffer (pH 7.0), and 0.35 mL of Pic A. Under these conditions, the retention times of the carboxy and hydroxylated metabolites and the internal standard salicylic acid were 4.6, 6.7, and 8.1 min, respectively. These methods were applied to study the pharmacokinetics of 1 administered intravenously and intraperitoneally to the rat. Tolbutamide was almost completely recovered as metabolites 2 and 3 in the urine within 24 h.

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.

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.

Pharmacokinetics of chlorpropamide in epileptic patients: effects of enzyme induction and urine pH on chlorpropamide elimination

The effects of liver enzyme induction and of urine pH on the pharmacokinetics of chlorpropamide have been studied. A single oral dose of chlorpropamide 250 mg was administered to 8 patients on antiepileptic drugs (phenytoin, carbamazepine) and to 8 healthy volunteers. The half-life of chlorpropamide was significantly shorter in the patients (34.4 h) than in the healthy volunteers (50.2 h), but the difference between the groups in the half-life of antipyrine was even more pronounced (5.1 vs 11.4 h). The clearance and volume of distribution of total chlorpropamide were significantly higher in the patients (2.99 ml X h-1 X kg-1 and 126 ml X kg-1) than in the healthy volunteers (1.60 ml X h-1 X kg-1 and 106 ml X kg-1). The unbound fraction of chlorpropamide in serum was also higher in the patients (5.7%) than in the healthy subjects (4.4%). Neither the volume of distribution nor the clearance of the free fraction of chlorpropamide differed significantly between the groups. There was a significant correlation between the half-lives of chlorpropamide and antipyrine, and the half-life of chlorpropamide also had at least as good an inverse correlation with the urinary excretion of unchanged chlorpropamide. The renal clearance of chlorpropamide correlated well with urine pH and was almost 100-fold higher at pH 7 than at pH 5. Both the metabolic and renal clearances of chlorpropamide are important in its elimination. At urine pH higher than 6.5-7, the renal clearance of chlorpropamide represents more than half its total clearance regardless the degree of induction of liver enzymes.

Drug level monitoring: chromatography of some minor groups of drugs

Some important facts about the chromatographic separation of a number of selected categories of drugs are summarized. The data refer to the chromatographic method of choice, stationary phase, mobile phase (carrier gas), detection procedure and (where available) method sensitivity. Also, fundamental instrumental parameters, namely injector, column and detector temperature, carrier gas and mobile phase flow-rate and gradient set-up are reported here. In all cases also the source material used for analysis is specified. The data are presented in table form, each table dealing with a particular category of drugs. The following categories of drugs are being dealt with: anthelmintics, antiarteriosclerotics, antibacterials, anticholinergics and cholinergics, anticoagulants, antidiabetics, antiemetics, antimycotics, antihistamines, antimalarials, antiparasitics, antiparkinsonics, antitussives, antiulcer drugs, antiviral compounds, appetite depressants and immunosuppressives.

Adsorption of sulfonylureas onto activated charcoal in vitro

Adsorption of carbutamide, chlorpropamide, tolazamide, tolbutamide, glibenclamide (glyburide), and glipizide onto activated charcoal was compared in vitro using different charcoal-to-drug ratios. Maximal binding capacities of different sulfonylureas were 0.45-0.52 g/g of charcoal at pH 7.5. The affinity of the second generation derivatives, glibenclamide and glipizide, was considerably higher than that of the first generation derivatives. The affinity of sulfonylureas to charcoal was higher at pH 4.9 than at pH 7.5. Poor water solubility of sulfonylureas at pH 1 prevents the adequate testing in these conditions. Contrary to what has appeared previously, activated charcoal effectively adsorbs different sulfonylureas and can be used to possibly prevent their gastrointestinal absorption.

Effect of activated charcoal on absorption of tolbutamide and valproate in man

The claim that activated charcoal should be ineffective or even contraindicated in intoxication due to tolbutamide is based only on limited in vitro studies. To test the claim, the effect of activated charcoal 50 g on the absorption of tolbutamide and, as a reference, of sodium valproate, was studied in 6 healthy volunteers. Each volunteer swallowed tolbutamide 500 mg and sodium valproate 300 mg with 50 ml water 1 h after a light breakfast, and within 5 min they took in randomized order either a suspension of activated charcoal or water. The absorption of tolbutamide, calculated as the peak concentration and the area under the serum drug concentration-time curve during 0-48 h, was reduced by 90% by charcoal (p less than 0.001). The absorption of valproate in these conditions was reduced on average by 65% (p less than 0.01). In each subject charcoal had a greater effect on the absorption of tolbutamide than of valproate. According to these findings and preliminary in vitro studies on other sulphonylureas high doses of activated charcoal can be recommended for the preventing the absorption of sulphonylureas in acute intoxications. The poor aqueous solubility of these substances at the gastric pH probably delays their gastrointestinal absorption, so that they may be adsorbed on to charcoal even given several hours later.