Radioimmunoassay of glipizide in human plasma

Simultaneous determination of glipizide and its four hydroxylated metabolites in human urine using LC-MS/MS and its application in urinary phenotype study

Cytochrome P450 (CYP) 2C9 and CYP2C19 genetic mutant could influence the plasma concentration of glipizide in human subjects, which refers to glipizide safety and adverse effects in clinic practice. A further study to investigate the relationship of the concentrations between glipizide and its metabolites in human with different CYP mutants was valuable. We firstly develop a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of glipizide and its hydroxylated metabolites in human urine. After simple protein precipitation with methanol including 4'-OH-tolbutamide and gliclazide (both are internal standards), the analytes were chromatographed on a reversed-phased column with a mobile phase of 0.1% formic acid in acetonitrile and 0.1% formic acid in water by a gradient elution. The ion transitions of the precursor to the product ion were principally protonated ions [M+H]⁺ at m/z 446.4→m/z 321.1 for glipizide, m/z 462.2→m/z 321.1 for the four hydroxylated forms of glipizide, m/z 287.2→m/z 188.0 for 4'-OH-tolbutamide, and m/z 324.1→m/z 127.1 for gliclazide. The method was linear over a concentration range of 0.02-20.0ng/mL. The intraday and inter-day variances were less than 9.9%, and accuracy was within ±6.8%. The method was successfully applied to the urinary phenotyping study in volunteers after a single oral administration of 5-mg glipizide tablet, and two new hydroxycyclohexyl metabolites of glipizide (OH-gp), 4-cis-OH-gp and 3-trans-OH-gp, were found in this study.

Stripping voltammetric quantification of the anti-diabetic drug glipizide in bulk form and pharmaceutical formulation

The electrochemical behavior of glipizide at the hanging mercury drop electrode (HMDE) was studied in B-R universal buffers of pH 1.7-11. The voltammograms exhibited a well-defined 4-electron irreversible cathodic peak which attributed to reduction of the two C=N of the pyrazine ring of glipizide molecule. Glipizide was found to has an interfacial adsorptive character onto the mercury electrode surface. A monolayer surface coverage of 1.02x10(-10)mol cm(-2) was estimated and hence each adsorbed glipizide molecule occupied an area of 1.63 nm(2) onto the mercury electrode surface. A simple and precise square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure was described for quantification of bulk glipizide with a limit of detection of 1.5x10(-10)M and a limit of quantitation of 5x10(-10)M. The proposed procedure was successfully applied for quantitation of glipizide in its pharmaceutical formulation (Minidiab tablets) without interference from excipients.

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.

High-performance liquid chromatographic determination of glipizide in human plasma and urine

A sensitive and selective high-performance liquid chromatographic method for determination of intact glipizide in human plasma or urine has been developed. The plasma and urine samples were acid-buffered, before tolbutamide was added as internal standard. The samples were extracted with benzene, and the organic layer was evaporated to dryness. The residue was dissolved in equilibrated mobile phase (acetonitrile-0.01 M phosphate buffer pH 3.5, 35:65), and an aliquot of 20 microliters was chromatographed on a Spherisorb ODS reversed-phase column. Quantitation was achieved by monitoring the ultraviolet absorbance at 275 nm. The response was linear (0-1000 ng/ml) and the detection limit was 5-10 ng/ml in plasma or urine. The within-assay variation was less than or equal to 10%. No interferences from metabolites or endogenous constituents were observed. The utility of the assay was demonstrated by determining glipizide in samples from a diabetic subject receiving a therapeutic dose of 5 mg of the drug.

Serum gliclazide concentration in diabetic patients. Relationship between gliclazide dose and serum concentration

Serum levels of gliclazide were determined by radioimmunoassay in seven healthy controls and in 18 diabetic in-patients receiving single oral dosing and consecutive dosing over 5 days. Following a single oral dose of 40 mg in the seven controls and eight diabetic patients, and 120 mg in ten diabetic patients, the serum levels of gliclazide peaked on average at 2 h, followed by a slow decline, the t1/2 being 16.5 h in the volunteers, 12.3 h in the diabetic patients receiving 40 mg, and 10.5 h in those receiving 120 mg. During consecutive administration, the serum levels both at fasting and at the peak reached a plateau in 2 days and no further accumulations were observed. The steady-state peak levels of gliclazide in the diabetic patients revealed a strongly positive correlation with the dose per m2 body surface area (r = 0.78, P less than 0.001), and their steady-state fasting levels correlated positively but weakly with the dose per m2 body surface area (r = 0.48, P less than 0.05). Thus, measuring either the fasting or the peak concentration of gliclazide will be useful for monitoring drug concentration in the serum. Pharmacokinetics of gliclazide will contribute to the elucidation of the relationship of serum level and clinical effectiveness in diabetic subjects.

Effect of guar gum on glipizide absorption in man

The effect of 4.75 g guar gum, a fibre preparation, on the absorption of 2.5 mg glipizide has been studied in 10 healthy volunteers given a standard breakfast. Three different experimental protocols were used: glipizide without guar gum (Treatment 1), glipizide with guar gum (Treatment 2) and guar gum 30 min after the drug together with breakfast (Treatment 3). The serum glipizide at 30 minutes was higher during Treatment 2 than Treatment 3 (p less than 0.01), but neither differed from the control treatment. The AUCs for glipizide were calculated up to 8 hours. They did not differ significantly between the treatment, although there was a non-significant trend to lower values during Treatment 3. Serum insulin and blood glucose levels were determined up to 3 h. Corresponding to differences in the glipizide concentration, serum insulin was highest and blood glucose lowest at 30 minutes during Treatment 2. According to this single dose study, guar gum does not have any substantial deleterious effect on the absorption of glipizide. The lack of effect may be due to the complete gastrointestinal absorption of glipizide.