INTRODUCTION:

As with all angiotensin II receptor antagonists, Irbesartan is indicated for the treatment of hypertension. Irbesartan may also delay progression of diabetic nephropathy and is also indicated for the reduction of renal disease progression in patients with type 2 diabetes.¹ hypertension and micro albuminuria (>30 mg/24 hours) or proteinuria (>900 mg/24 hours. Irbesartan is a non-peptide compound, chemically described as a 2-butyl-3-[p-(o-1H-tetrazol-5-ylphenyl)benzyl]-1,3-diazaspiro[4.4]non-1-en-4-one.²

Literature survey reveals few HPLC³, Derivative⁴ and UV- spectrophotometry⁵, LC/MS/MS⁶ and HPTLC⁷ methods reported for the estimation of Irbesartan in blood serum and in ocular fluids. However there is no simple and accurate method reported for the determination of Irbesartan in pharmaceutical formulation by Visible spectrophotometry.

Structure of Irbesartan

MATERIALS AND METHODS:

Instruments used:

An Elico model SL 164 UV-Visible double beam spectrophotometer with 1 cm matched quartz cell was used for recording spectra and absorbance measurements.

Reagents: All reagents used were of analytical grade and were obtained from s.d. fine chemicals, Mumbai. Naproxen was kindly supplied by Hetero drugs Pvt. Ltd. (India). Naproxen tablets were purchased from a local market.

EXPERIMENTAL:

Preparation of standard Naproxen solution:

Standard solution of Naproxen (1000μg/ml) was prepared by dissolving 100mg in methanol and diluting to the mark in a 100ml volumetric flask.

Working standard solution of 100μg/ml was prepared by further dilution of the above standard stock solution

Method A: Using phenol red:

Aliquots of the working standard solution of Irbesartan (60-80µg/ml) were prepared and from that 1ml of sample was accurately measured and transferred in to a series of volumetric flasks by means of a micropipette. To each of the above aliquots, 1ml of 100µg/ml of phenol red solution in methanol was added and mixed thoroughly. The volume was brought up to 5ml mark with methanol, mixed thoroughly and after 10 min absorbance of each species was measured at 422nm against reagent blank. A calibration graph was constructed by plotting the absorbance against the concentration of the drug as shown in Fig. 1

Fig-1: Using phenol red

Method B: By using bromocresol green:

Aliquots of the working standard solution of naproxen(120-160µg/ml) were prepared and from that 1ml of sample was accurately measured and transferred in to a series of volumetric flasks by means of a micro burette. To each of the above aliquots, 1ml 180µg/ml of bromocresol green solution in methanol was added and mixed thoroughly. The volume was brought up to 5ml mark with methanol, mixed thoroughly and after 10 min absorbance of each species was measured at 417 nm against reagent blank. A calibration graph was constructed by plotting the absorbance against the concentration of the drug as shown in Fig. 2.

RESULTS AND DISCUSSION:

Determination of absorption maximum:

Irbesartan was treated with phenol red and bromocresol green. To determine the absorption maxima, 100μg/ml of drug concentration was prepared from that dilution was made to 80μg/ml of drug solution. 1ml of 80μg/ml of drug solution with 1ml of 100μg/ml of phenol red was mixed. The volume was made up to 5ml with methanol. The λmax was seen at 422nm. Similarly 1ml of 160μg /ml of drug solution was mixed with 1ml of 180μg /ml of bromocresol green. The volume was made up to 5ml with methanol. λmax was found to be 417nm.

Fig-3: Absorption spectrum of Irbesartan with phenol red

Fig-4: Absorption spectrum of Irbesartan with Bromocresol green

Optimization of reaction conditions:

Optimum reaction conditions for quantitative determination of drug were achieved through a number of preliminary experiments. This was done by measuring the absorbances of a series of solutions at 422nm and 417nm(Method A and B) by varying one and fixing the other parameters. These conditions were incorporated in the procedure.

Stability:

The resultant coloured products of the proposed methods were found to be stable for more than four hours, which was sufficient time to make proper determination of Irbesartan drug.

Table1. Analytical parameters of spectrophotometric methods.

PARAMETERS	METHOD A	METHOD B
λmax	422nm	417nm
Beers law limit(µg/ml)	60-80 µg/ml	120-160µg/ml
Sandells sensitivity(µg/ml)	0.0433	0.0952
Regression equation*
Slope	0.2184	0.0857
Intercept	0.0128	0.0733
Correlation coefficient	0.9994	0.9984
%relative standard Deviation	0.7523	1.06
% rang of error	0.0058	0.0099
Limit of dection (µ/ml)	0.035	0.1567
Limit of quantification( µ/ml)	0.119	0.5218
Stability	4	4

**Y=bX+c where Y is the absorbance and X is the concentration of the drug in µg/ml^* average of six determinations

Table2. Determination of Irbesartan in formulations by the proposed and Reference Method

Tablet Brand name	Labeled Amount	Method A	Method B
Avapro	300mg	99.91	99.23
Irbest	150mg	99.90	99.20

Optical characteristics and validation of the method:

Optical characteristics such as Beer’s law limits and Sandell’s sensitivity for Irbesartan are given in Table 1. Data of the regression analysis using the least squares method made for the calibration curves are also given in the same table. The accuracy and precision of the proposed methods were checked by analyzing six replicate samples within the Beer’s law range containing the same amount of each drug. The lower values of RSD indicate the good precision and reproducibility of the methods. The validity of the proposed procedure for the determination of irbesartan in their pure state was checked by analyzing this drug using the proposed methods. The results obtained for pure drug were reproducible with low relative standard deviations (RSD). The LOD and LOQ for naproxen by the proposed method were determined by using calibration standards. LOD and LOQ were calculated as 3.3 and 10 respectively, where b is the slope of the calibration curve.(Table 1)

Applicability of the method:

The applicability of the proposed spectrophotometric methods for the assay of Irbesartan was tested by analyzing various available commercial formulations. The results given in Table 2 of the analysis showed that the data are consistent with the label claim of the formulations. The calibration curves showed a linear response over the concentration ranges used in the general procedures. The RSD values for the reproducibility and recovery studies show that the methods are precise and accurate. Hence, these methods can be adopted for the routine quality control of Naproxen in bulk and in formulations.

CONCLUSIONS:

To summarize, our studies showed a possibility to use phenol red and bromocresol green as a reagents for the spectrophotometric determination of Irbesartan. The determination procedures are characterized by low detection limits, simplicity, cheap and good reproducibility. The statistical analyses showed that the data from the proposed methods are in good agreement with those of the reported methods. The color reaction does not require stringent conditions nor any specific reagent or buffer. The colored species was stable for more than four hours, which is sufficient time for the analyst to perform the analysis. Moreover they do not require any pretreatment of the drug and tedious extraction procedure. Hence, the data presented in the thesis by spectrophotometric methods for the determination of naproxen in its pure and dosage form demonstrate that the proposed methods are accurate, precise and linear. Thus it can be extended for routine analysis of Irbesartan in bulk and pharmaceutical dosage.

ACKNOWLEDGEMENTS:

Authors are thankful to Hetero drugs Pvt. Ltd. (India) for providing the gift samples of drug and also thankful to Chairman of Vijaya college of pharmacy, Hyderabad for providing laboratory facilities to carry out this research work.

REFERENCES:

1. Lewis EJ, Hunsicker LG, Clarke WR, Berl T et all. Collaborative Study Group. Renoprotective effect of the angiotensin-receptor antagonist irbesartan in patients with nephropathy due to type 2 diabetes. N Engl J Med:2001:345(12): 851–60.

2. Rossi S, editor. Australian Medicines Handbook2006. Adelaide: Australian Medicines Handbook; 2006.

3. HPLC determination of irbesartan in human plasma: its application to pharmacokinetic studies. Biomed chromatogr :2009:23(6):568-572.

4. Vetuschi C, GiannandreaA, CarlucciG et al. Determination of hydrochlorothiazide and irbesartan in pharmaceuticals by fourth-order UV derivative spectrophotometry. Farmaco:2005:60(8):665-670.

5. Sridharan D, Thenmozhi A, Rajamanickam V et al.Simultaneous Estimation of Irbesartan andHydrochlorothiazide in Combined Pharmaceutical Dosage Form by UV Spectroscopy using Multicomponent Mode of Analysis. International Journal of ChemTech Research:2010:2(2):876-879.

6. Prasad S V S G ,Savithiri Shivakumar, Sudhir T et al. Lc/ms/ms method for the simultaneous estimation of losartan potassium and irbesartan in rat plasma., international journal of pharmacy and pharmaceutical sciences:2009: 1(1):123.v.

7. Sane R T, Francis M and Pawar S. Determination of irbesartan in pharmaceutical dosage forms by HPTLC. Indian Drugs:2002: 39(1): 32-35.

Received on 30.06.2011 Modified on 17.07.2011

Research J. Pharm. and Tech. 4(10): Oct. 2011; Page 1567-1569