1. INTRODUCTION:

Venlafaxine hydrochloride is a structurally novel antidepressant for oral administration. Chemically it is designated 1-[(1RS)-2-(dimethylamino)-1-(4-methoxyphenyl) ethyl] cyclohexanol hydrochloride^1-2. The mechanism of Venlafaxine hydrochloride is referred to as serotonin and noradrenalin reuptake inhibitor (SNRT), because it inhibits uptake of both these amine but, in contrast to older Tricyclic antidepressants (TCAs), Venlafaxine hydrochloride does not interact with cholinergic, adrenergic or histaminergic receptors or have sedative property^3-5. The minimum dose for antidepressant action, initially 75 mg a day is administered and dose is gradually increased up to 225 mg a day, not to exceed 375 mg a day in severe cases^6-8.

A survey of literature has revealed, several analytical methods for the determination of Venlafaxine hydrochloride in pharmaceutical preparation including several spectrophotometric methods^9-14, Reversed-phase High-performance Liquid chromatographic (RP-HPLC) method¹⁵, and stability indicating LC method have been reported^16-17.

So far no Area Under Curve method was reported for the quantitative determination of Venlafaxine hydrochloride in pharmaceutical dosage forms.

The developed method was simple, precise, economical and accurate and the statistical analysis proved that method is reproducible and selective for the analysis of Venlafaxine hydrochloride in bulk drug and tablet formulations.

2. MATERIALS AND METHODS:

2.1 Instruments and reagents:

An analytically pure sample of Venlafaxine hydrochloride was procured as gift sample from Torrent pharmaceuticals Ltd. (Ahmedabad, India). Analytical grade methanol was used as solvent for dilution. A Shimadzu UV-1800 UV / VIS spectrophotometer was used with 1 cm matched quartz cell. Tablet formulation [VENTAB XL (Brand I), Intas Pharmaceuticals Ltd., Ahmedabad and VEXOR (Brand II), Cadila Pharmaceuticals Ltd., Ahmedabad] were procured from a local pharmacy with labeled amount 37.5 mg per tablet.

2.2 Preparation of working standard drug solution:

The standard Venlafaxine hydrochloride (100 mg) was weighed accurately and transferred to volumetric flask (100 ml). It was dissolved properly and diluted up to the mark with methanol to obtain final concentration of 1000 μg/ml and the resulting solution was used as working standard solution.

2.3 Analysis of marketed formulations:

For the estimation of Venlafaxine hydrochloride in tablets formulations by this method, 20 tablets of brand were weighed and triturate to fine powder. Tablet powder equivalent to 100 mg of Venlafaxine hydrochloride was weighed and transfer into 100 ml volumetric flask than dissolved with methanol and further diluted with methanol. It was kept for ultrasonication for 30 min; this was filtered through Whatman filter paper No. 41 and then final dilution was made with methanol to get the final stock solution of 1000 μg/ml. From this stock solution, various dilutions of the tablet solution were prepared and analyzed.

2.4 Area under curve (AUC) method:

The area under curve (AUC) method is applicable, when there is no sharp peak or when broad spectra are obtained. It involves the calculation of integrated value of absorbance with respect to the wavelength between two selected wavelengths λ₁ and λ₂. Area calculation processing item calculates the area bound by the curve and the horizontal axis. The horizontal axis is selected by entering the wavelength range over which the area has to be calculated. This wavelength range is selected on the basis of repeated observation so as to get the linearity between area under curve and concentration. The standard drug solution was diluted, so as to get the final concentration in the range of 20-100 μg/ml and scanned one of this solution in the spectrum mode from the wavelength range 400-200 nm. Then the calibration curve in the wavelength range of 267-278 nm was plotted as concentration against area under curve. Similarly area under curve of sample solution was measured and amount of Venlafaxine hydrochloride was determined from standard calibration curve.

Figure 1: Wavelength range selected for AUC method Venlafaxine hydrochloride

3. RESULT AND DISCUSSION:

The AUC method is advantageous as it is applicable to the drugs which show the broad spectra without a sharp peak.

The method was validated according to International Conference on Harmonization guidelines for validation of analytical procedures^18-20.

The area under curve (AUC) for analysis of Venlafaxine hydrochloride was measured in the wavelength range of 267-278 nm. The polynomial regression data for the calibration plots showed good linear relationship in the concentration range of 20-100 μg/ml with r²=0.998 and given in Table 1.

Recovery studies were carried out at three different levels i.e. 80 %, 100 %, and 120 % by adding the pure drug to the previously analysed tablet powder sample and shown in Table 2. The percentage recovery value indicates non interference from excipients used in formulation.

Table 1: Calibration Parameters

Sr. No	Parameter	Results
1	Wavelength range (nm)	267-278
2	Beer’s Law limits(mg/ml)	20-100
3	Regression equation (y)* Slope (b) Intercept (a)	0.998 0.0231 0.0048
4	Limit of detection (µg / ml)	1.27
5	Limit of quantification (µg / ml)	3.85
6	Intraday precision (% RSD)	0.94
7	Interday precision (% RSD)	1.42

*y = bx + a; when x is the concentration in mg/ml and y is absorbance unit.

Table 2: Recovery study Data

Sample	Label claim (mg)	Amount added (%)	Amount recovered (mg)	Recovery ± SD (%)	% RSD
BRAND I	37.5	0	37.07	98.85 ± 0.78	0.789
	37.5	80	37.34	99.22 ± 0.23	0.231
	37.5	100	37.23	99.28 ± 0.82	0.825
	37.5	120	37.73	100.61 ± 0.28	0.278
BRAND II	37.5	0	37.47	99.92 ± 0.64	0.640
	37.5	80	37.14	99.04 ± 0.91	0.918
	37.5	100	37.39	99.70 ± 0.52	0.521
	37.5	120	37.54	100.10 ± 0.34	0.339

The result of analysis of marketed formulations is shown in Table 3. The reproducibility and accuracy of the method was found to be good, which was evidenced by low standard deviation.

Table 3: Analysis of tablet formulation

Tablet	Label claimed (mg)	Amount found (mg)	%Recovery ± SD
BRAND I	37.5	37.7 ± 0.02	100.53 ± 0.23
BRAND II	37.5	37.3 ± 0.24	99.46 ± 0.86

4. CONCLUSION:

A new, simple and selective area under curve method was developed for the analysis of Venlafaxine hydrochloride in bulk and in pharmaceutical formulation. The developed method was also validated and from the statistical data, it was found that method was accurate, precise, reproducible and can be successfully applied to the pharmaceutical formulation without interference of excipients.

5. ACKNOWLEDGEMENT:

We would like thank to Torrent Pharmaceuticals Ltd, Ahmedabad for providing reference sample of Venlafaxine hydrochloride to facilitate this work and also to the Principal, Bharathi College of Pharmacy, Maddur for providing facilities.

6. REFERENCE:

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18. International Conference on Harmonization (ICH), Validation of Analytical Procedures:Text on Validation of Analytical Procedures Q2A, 1994.

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Received on 10.11.2009 Modified on 13.01.2009

Research J. Pharm. and Tech. 3(2): April- June 2010; Page 500-502