Introduction: Varenicline (VRC, Figure 1), chemically known as 7,8,9,10-tetrahydro-6,10-methano-6H-azepino[4,5-g]quinoxaline (2R,3R), is a novel centrally acting agent that functions as a highly selective partial agonist of the nicotinic acetylcholine receptor. VRC exhibits both agonistic and antagonistic properties, providing the therapeutic advantage of alleviating nicotine withdrawal symptoms and cigarette cravings during abstinence, while simultaneously blocking the reinforcing effects of nicotine in individuals who relapse. Varenicline tartrate has been approved by the U.S. FDA as a smoking cessation aid. The recommended treatment regimen is 1 mg daily for 12 weeks, beginning with a 1-week titration period.
Figure 1: Chemical Structure of VernacilineTartate
MATERIALS AND METHODS:
1. Chemicals
Varenicline Tartrate was received as a gift sample from Enaltec Pharma, Ambernath, India. All other chemicals and reagents used were of analytical reagent (AR) grade.
2. Instrumentation
A Shimadzu UV-1800 double-beam UV-Visible spectrophotometer (Kyoto, Japan) equipped with computer-operated software UV Probe 2.33 and a pair of 1 cm matched quartz cells was used to measure the absorbance of prepared solutions. An analytical balance (Mettler Toledo, Model JL 1503-C) was used for all weighing purposes.
3. Method
A) UV-Spectroscopy Methods
a) Area Under Curve (AUC) Method:
The AUC method is applicable when sharp peaks or broad spectra are obtained. It involves calculating the integrated absorbance with respect to wavelength between two selected points, λ₁ and λ₂. The software calculates the area enclosed by the spectrum and the horizontal axis. The wavelength range is chosen based on repeated observations to ensure linearity between the area under the curve and analyte concentration. The resulting spectra are used to calculate AUC, which is then plotted against concentration to construct the calibration curve.
4. Experimental Work
A) Solubility Study of Varenicline Tartrate:
25 mg of Varenicline Tartrate was weighed and tested for solubility in 25 mL of distilled water, methanol, and ethanol. It was found to be freely soluble in water; hence, distilled water was selected as the solvent.
B) Determination of λₘₐₓ of Varenicline Tartrate:
10 mg of pure drug was dissolved in a small portion of distilled water and diluted to 10 mL to prepare a standard stock solution (1000 µg/mL). From this stock, 2.5 mL was transferred to a volumetric flask and diluted to 25 mL with distilled water to prepare a 100 µg/mL solution. Further dilutions were made to obtain standard solutions of 2, 4, 6, 8, and 10 µg/mL. The spectrum peak details are shown in Figure 2.
5. Analytical Method Development and Validation1. Linearity:
Linearity defines the concentration range over which the analytical procedure provides a proportional response. Standard solutions of Varenicline Tartrate (2, 4, 6, 8, 10 µg/mL) were prepared in 25 mL volumetric flasks using distilled water. The absorbance maxima and area under the curve were measured at 237.60 nm and over the range of 200–400 nm, respectively, against distilled water as a blank. The calibration curve of Varenicline Tartrate is shown in Figure 3.
Figure 2: Spectrum peak report of Varenicline Tartrate
2. Linerity and range
A) Calibration Curve for Drug :
a) Absorbance maxima method:
In the Experimental conditions described, the graph obtained for the absorbance maxima for pure drug showed linear relationship (Figure 2). Regression analysis was made for the slope, intercept and and correlation coefficient values. The regression equations of calibration curve were y = 0.3069x – 0.3486(r2 =0.994) at 237.60nm for absorption maxima the range was found to be 2-10mm/ml for the UV spectrophotometric analysis. Calibration curve of Varenicline Tartrateis shown in Figure. 3.
Table 1: Calibration curve of Varenicline Tartrate
| CONC. | ABS |
| 2 | 0.231 |
| 4 | 0.84 |
| 6 | 1.603 |
| 8 | 2.14 |
| 10 | 2.65 |
Figure 3: Calibration of Varenicline Tartrate
b) Area Under Curve Method :Under the experimental condition described , the graph obtained for area under curve spectra showed linear relationship (Fig. 4). The range was found to be 2-10 mg/ml for area under curve spectrophotometric analysis.
Figure 4: Area Between 230.40-243 nm selected for Varenicline Tartrate
Table 2: Spectroscopic parameters.
| Parameter | AUC |
| Wavelength Range (nm) | 200 – 400 |
| Concentration Range (mm/ml) | 2-10 |
| Regression Equation | y = 0.3069x-0.3486 |
| Slope (m) | 0.3069 |
| Intercept (c) | 0.3486 |
| Correlation Coefficient (r2) | 0.9945 |
CONCLUSION:
A simple and cost-effective UV spectrophotometric area under the curve (AUC) method has been developed for the determination of Varenicline Tartrate. Due to its low cost and minimal maintenance requirements, this UV spectrophotometric method is particularly suitable for small-scale industries. It can be effectively applied for the qualitative analysis of Varenicline Tartrate where economy, time efficiency, and assurance of therapeutic efficacy are important. The results demonstrate that the method is accurate, precise, and sensitive.
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