1. INTRODUCTION:

Glimepiride chemically, shown in figure 1, is 3-ethyl-4-methyl-N-[2-[4-[(4-methylcyclohexyl)carbamoylsulfamoyl] phenyl] ethyl]-2-oxo-5H-pyrrole-1-carboxamide is a third generation sulfonylurea derivative which is commonly used in the treatment of non-insulin dependent Type 2 diabetes mellitus.^1,2It is a medium –to-long acting anti-diabetic drug which acts as a secretagogue.³

The primary mechanism of action of glimepiride for lowering blood glucose levels seems to be dependent on stimulating the release of insulin from the functioning pancreatic cells. Glimepiride acts by binding to ATP-sensitive potassium channel receptors on the pancreatic cell surface, which reduces potassium conductance causing depolarization of the membrane. Calcium ion reflux is stimulated by the membrane depolarization through voltage-sensitive calcium channels. This increased intracellular calcium ion concentration induces the secretion of insulin. It can be employed for concomitant use with metformin, thiazolidinedione, insulin and alpha-glucosidase inhibitors for treatment of type 2 (noninsulin dependent) diabetes mellitus. It is completely absorbed from the gastrointestinal tract when it is administered orally. The possible side effects are severe hypoglycemic reactions with coma, seizure, or other neurological impairment. The other reported side effects of sulfonylureas includes clolestatic jaundice, nausea and vomiting, aplastic and hemolytic anemias, agranulocytosis, generalized hypersensitivity reactions, and rashes.^4,5 Molecular formula of glimepiride is C₂₄H₃₄N₄₀₅S with a molecular mass of about 490.617g/mol.⁶It is administered orally; insoluble in water, slightly soluble in methylene chloride(Dichloromethane), very slightly soluble in methanol and soluble in DMSO.⁷ It can be used alone or in combination with atorvastatin, metformin, rosiglitazone and pioglitazone as an agent to treat diabetes mellitus. In the present review, we have complied the published analytical methods reported so far for the determination of glimepiride in pharmaceutical formulations and biological samples. Techniques like spectrophotometry, high-performance chromatography (HPLC), liquid chromatography-mass spectroscopy (LC-MS), liquid chromatography-electrospray ionization-tandem mass spectroscopy (LC-ESI-MS), and thin layer chromatography techniques capillary electrophoresis (CE) have been used for analysis, from which HPLC methods are most extensively used. Overview of these methods for determination of glimepiride is shown in figure 2.

Fig. 1. Structure of glimepride

Fig. 2. Overview of analytical methods for estimation of pioglitazone in biological and pharmaceutical samples.

2. SAMPLE PREPARATION:

2.1 Solubility

According to Biopharmaceutical Classification System (BCS), classification of glimepiride falls under (BCS) class II having low solubility and high permeability. The drug shows low pH dependent solubility. The drug was tested for the solubility in solvents routinely used for analytical method development. It was found to practically insoluble in water, slightly soluble in methylene chloride (Dichloromethane) and very slightly soluble in methanol. It is soluble in DMSO (>10 mg/ml) and in ethanol (<1 mg/ml). In acidic and neutral aqueous media, glimepiride exhibits very poor solubility at 37o C (<0.004 mg/ml). In media pH>7, solubility of drug is slightly increased to 0.02 mg/ml. The melting point of glimepiride is 207°C.⁸The aqueous solubility of the drug is enhanced by various strategies like co-solvent solubilization,⁹micellar solubilization¹⁰ and solvent evaporation method have been proposed.¹¹

2.2 Sample preparation strategies

Sample preparation is the integral part of analytical methodology, and it was reported that approximately about 30% error is contributed from sample analysis was due to sample preparation.¹² The various diluents used for analysis of glimepiride areacetonitrile: 0.02M potassium di-hydrogen phosphate (pH4.5), acetonitrile: 0.2M phosphate buffer (pH 7.4), chloroform, potassium phosphate buffer: methanol (pH6.5), methanol: acetonitrile. In major cases methanol was used as diluent. The sample preparation techniques for the extraction of glimepiride from biological matrices like serum, plasma and urine includeliquid-liquid extraction with diethyl ether, n-butyl ether and ethyl acetate and protein precipitation with methanol.

3. ANALYTICAL METHODS:

3.1 Spectrophotometry

In the literature 15 methods were reported for the estimation of glimepiride using spectrophotometry^13-18, of which 5 methods are for determining glimepiride alone, whereas the remaining are for quantifying glimepiride in combination with other drug substances. Table 1 shows the summary of the reported spectroscopic methods indicating the basic principle, λ_max_,solvent and limit of detection (LOD).

Table 1. Representative Spectrophotometric methods for analysis of glimepiride

Compounds	Method	λ_max	Solvent	LOD	Ref.
Glimepiride	Spectrophotometric method	249	Chloroform	0.4	13
Glimepiride	Simple derivative method	256.3,257.5, 279.0	5*10^-3 molL^-1 Sodium hydroxide solution	1.311	14
Glimepiride, Pioglitazone	Simultaneous equation method	238, 279	HCL buffer +0.5%w/v of SLS	0.171	15
Glimepiride, Pioglitazone	TLC densitometric method	268, 228	Choloform:toluene:ethanol:glacial acetic acid	0.41	16
Glimepiride, Rosiglitazone maleate	Simultaneous equation method	225, 216	0.1 N Sodium hydroxide solution	0.09	17
Glimepiride, Rosiglitazone maleate	Absorbance ratio method	225, 216	0.1 N Sodium hydroxide solution	0.08	18

3.2 Electrochemical methods

Baddawyet.al.²⁸ quantified rosiglitazone, pioglitazone, glimepiride and glyburide conveniently and economically using cyclic voltammetry and differential pulse voltammetry. The authors used glassy carbon electrodes and carbon paste electrodes as sensors for these drugs in Brinton-Robinson as buffer solution. The proposed method was found to be orthogonal to the standard HPLC method. Ion electrodes were prepared by construction of 10% standard drug ion pair with tungstophosphate imbedded as electro active material.

3.3Chromatography

3.3.1 HPLC

3.3.1.1. Biological samples

Nahed m Ei-Enanyet al. developed the method in plasma by using simultaneous method for estimation of rosiglitazone and glimepiride in combined dosage form. The mobile phase used in this method was a mixture of acetonitrile and 0.02 M phosphate buffer of pH 5(60:40, V/V). Nicardipine was used as an internal standard in this method. They performed the validation studies and the LOD was found to be 0.04µg/ml.

3.3.1.2 Pharmaceutical samples

Analytical methods for the determination of Glimepiride in pharmaceutical dosage forms using HPLC^18-24are shown in table 2.

3.4. LC-MS

LC-MS/MS method was developed by Vijaya Bharathi Dasari et al.,²⁵ for determination of Atorvastatin and Glimepiride in human plasma. Samples were extracted by liquid-liquid extraction procedure using diethyl ether. The extraction tubes were shaken for 5 min. Elution of two components was done isocratically on an ACE5CLC₁₈ column and analyzed using multiple reactions monitoring mode.

Another LC-MS/MS study was reported by Srinivasa Rao Polagani²⁶ for simultaneous determination of Atorvastatin, Glimepiride and Metformin in human plasma in which carbamazepine was used as internal standard (IS). Protein precipitation was used for extracting the analytes from the plasma. The samples were separated on a Alltima HP C₁₈ column by using a 60:40(v/v) mixture of acetonitrile and 10mM ammonium acetate (pH 3.0) as the mobile phase at a flow rate of 1.1 ml/min. The linearity range of the proposed method was 4.98-4.94.29ng/mL and was successfully applied to human pharmacokinetic study.

3.5 HPTLC

Sunil R. Dhaneswar et.al.,²⁷ developed an HPTLC method for simultaneous estimation of metformin hydrochloride, Atorvastatin and Glimepiride in bulk and as well as in formulation. They carried out their separation on precoated alumina plates with silica gel 60 F₂₅₄ using water: methanol: ammonium sulphate (1:1:4v/v/v). At 237 nm, the evaluation of separated zones were performed. The linearity of the calibration curve was found to be between 600-2100ng/spot.

Table 2 Reported analytical HPLC methods for determination of glimepiride in combination with other drugs like metformin, pioglitazone and atorvastatin in pharmaceutical dosage forms

Study aim	Mobile phase	Column	Detection	λ_max (nm)	Flow rate (ml/min)	LOD (µg/ml)	Ref.
Simultaneous determination with Metformin and pioglitazone	Methnol:phosphate buffer (pH 4.3) (75:25v/v)	Inertsil-ODS-3(C-18)(250*4.60mm, 5µm)	UV	258	1	-	18
Simultaneous determination with Metformin and pioglitazone	Methanol.Phosphate buffer (pH3.6) (75:25v/v)	C₁₈ column (100*4.6 mm, 5µ)	UV	238	1	-	19
Simultaneous determination with Pioglitazone HCL	Potassium dihydrogen phosphate buffer (pH3.4): acetonitrile (40:60v/v)	C-18 bonded silica column(250*4.6mm, 5µm)	UV	235	0.8	-	20
Simultaneous determination with Pioglitazone HCL	Phosphate buffer:acetonitrile (40:60v/v)	Inertsil ODS C₁₈ column (150*4.6mm, 5µ)	UV	225	1.5	0.11	21
Simultaneous determination with Metformin and Atorvastatin	Methnol:phosphate buffer (pH 3) (75:25 v/v)	C₁₈ (250*4.6mm,5µ)	UV	230	1	0.05	22
Simultaneous determination with Metformin and pioglitazone	Acetonitrile:tetrahydrofuran: buffer (pH 5)(40:50:10v/v)	Inertsil ODS-3V(250 mm*4.6mm, 5µm)	UV	228	1.7	-	23
Simultaneous determination with Glimepiride impurities and pioglitazone	Potassium dihydrogen phosphate(pH3.2).acetonitrile	Cyano column (250*4.6 mm,5µ)	UV	230	0.8	0.005	24

4. CHALLENGES:

As disused earlier, Glimepiride belongs to class -2 of BCS classification and so it possess high permeability and low solubility. So the solubility of glimepiride in water is less and also there would be a problem in selecting the diluents for the analysis of glimepiride. The degradation of the drug in strongly acidic medic is observed over a period of time. For spectrophotometric determination, multi dosage forms with complexity includes the presence of multiple entities and excipients, which may cause considerable challenge to the analytical chemist during the development of an assay procedure. It becomes difficult for the estimation of the individual drugs in these multicomponent dosage forms, so for routine spectrometric methods chemometric methods can be preferred.

5. CONCLUSION:

There are a wide range of techniques are available for the analysis of glimepiride in pharmaceutical formulations and biological samples. The analysis of the published data revealed that HPLC method was extensively for the estimation of glimepiride in various matrices likes urine, plasma and serum. HPLC-MS/MS is recommended for determination of glimepiride in biological samples, because this method combines the HPLC separation ability with MS sensitivity and selectivity which allows the unambiguous identification of glimepiride and its metabolites. HPLC with UV detection is applicable in case of analysis of glimepiride in pharmaceuticals, since this methods provides us accurate results and also cost effective when compared with other more advanced techniques.

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Received on 02.12.2014 Accepted on 23.12.2014

Asian J. Pharm. Ana. 4(4): Oct. - Dec. 2014; Page 178-182