INTRODUCTION:

Chemically, Tolterodine (TOL) is (+)-(R)-(α-(-2-Diisopropylamino)-ethyl))-benzyl)-p-cresol tartarate. It is a tertiary antimuscarinic agent and used in the management of urinary frequency, urgency and incontinence in detrusor instability¹. Capsule formulation containing 4 mg TOL is available in the market. Literature survey revealed that Tolterodine is estimated by HPLC^2-3. No UV spectrophotometric methods have been reported for estimation of TOL in single component formulation. Hence, an attempt has been made to develop new UV methods for its estimation of TOL in its pharmaceutical formulations with good accuracy, simplicity, precision and economy.

Material and Methods:

Instrument: A double-beam Shimadzu UV- Visible spectrophotometer, 1700 Pharmaspec, with spectral bandwidth of 2 nm, wavelength accuracy ± 0.5 nm and a pair of 1-cm matched quartz cells was used to measure absorbance of the resulting solution.

Materials: Standard gift sample of Tolterodine was provided by Cipla Pvt Ltd., Mumbai. Tolterodine capsules were purchased from local market.

Solvent used: Methanol was used as a solvent.

Stock solution: Standard stock solutions of TOL (100 µg/ml) was prepared and used for the analysis.

PROCEDURE:

Method A -- Absorption Maxima Method:

For the selection of analytical wavelength, 20 µg/ml solution of TOL was prepared by appropriate dilution of standard stock solution and scanned in the spectrum mode from 400 nm to 200 nm. From the spectra of drug (Fig. 1), λ _max of TOL, 284.0 nm was selected for the analysis. The calibration curve was prepared in the concentration range of 10-50 µg/ml at 284.0 nm. By using the calibration curve, the concentration of the sample solution can be determined.

Method B-- First Order Derivative Spectroscopy:

In this method, 20 µg/ml solution of TOL was prepared by appropriate dilution of standard stock solution and scanned in the spectrum mode from 400 nm to 200 nm. The absorption spectra thus obtained were derivatized from first to fourth order. First order derivative spectra were selected for analysis of the drug. First order derivative spectra of drug (Fig. 2), showed a sharp peak at 234.0 nm, which was selected for its quantitation. The calibration curve for TOL was plotted in the concentration range of 10-50 µg/ml at wavelength 234.0 nm. The concentration of the drug present in the mixture was determined against the calibration curve in quantitation mode.

Method C-- Area under Curve Method:

For the selection of analytical wavelength, 20 µg/ml solution of TOL was prepared by appropriate dilution of standard stock solution and scanned in the spectrum mode from 400 nm to 200 nm. From the spectra of drug, area under the curve in the range of 289.0-279.0 nm was selected for the analysis. The calibration curve was prepared in the concentration range of 10-50 µg/ml at their respective AUC range. By using the calibration curve, the concentration of the sample solution can be determined.

Fig.-1: Zero order spectra of Tolterodine

Application of the proposed method for the determination of TOL in capsules:

For the estimation of drugs in the commercial formulations, capsule powder equivalent to 10 mg TOL was transferred to 100.0 ml volumetric flask and volume made up to the mark with methanol and ultrasonicated for 10 minutes. The solution was then filtered through a Whatmann filter paper (No. 41). The filtrate was further diluted with methanol to obtain 20 µg/ml of TOL. In Method-A, the concentration of TOL was determined by measuring the absorbance of the sample at 284.0 nm in zero order spectrum modes. By using the calibration curve, the concentration of the sample solution can be determined. Method-B, the concentration of TOL was determined by measuring the absorbance of the sample at 234.0 nm, in first order derivative mode. The results of the capsule analysis were calculated against the calibration curve in quantitation mode. For Method-C, the concentration of TOL was determined by measuring area under curve in the range of 289.0-279.0 nm. By using the calibration curve, the concentration of the sample solution can be determined. Results of capsule analysis are shown in Table No. 1.

Validation:

The methods were validated with respect to linearity, accuracy, precision and selectivity.

Accuracy:

To ascertain the accuracy of proposed methods, recovery studies were carried out by standard addition method at three different levels (80%, 100% and 120%). Percent recovery for TOL, by all the methods, was found in the range of 98.28 % to 100.58 %.

Linearity:

The linearity of measurement was evaluated by analyzing different concentration of the standard solution of TOL. Beer-Lambert’s concentration range was found to be 10-50 µg/ml for all three methods.

Precision:

The reproducibility of the proposed method was determined by performing capsule assay at different time intervals (morning, afternoon and evening) on same day (Intra-day assay precision) and on three different days (Inter-day precision). Result of intra-day and inter-day precision is expressed in % RSD. Percent RSD for Intraday assay precision was found to be 0.2899, 0.3854 and 0.1453 for Method A, B and C, respectively. Inter-day assay precision was found to be 0.2513, 0.3854 and 0.1453 for Method A, B and C respectively.

Fig.-2: First order derivative Spectra of Tolterodine

RESULTS AND DISCUSSION:

The methods discussed in the present work provide a convenient and accurate way for simultaneous analysis of Tolterodine in its pharmaceutical dosage form. Absorbance maxima of Tolterodine at 284.0 nm (Method A) and in the first order derivative spectra, sharp peak at 234.0 nm (Method B) were selected for the analysis. Method C was area under curve (AUC) and the wavelength range for quantitation was 289.0-279.0 nm. Linearity for detector response was observed in the concentration range of 10-50 µg/ml for all three methods. Percent label claim for TOL in capsule analysis, by all the methods, was found in the range of 98.75 % to 99.75 %. Standard deviation and coefficient of variance for six determinations of capsule sample, by all the methods, was found to be less than ± 2.0 indicating the precision of the methods. Accuracy of proposed methods was ascertained by recovery studies and the results are expressed as % recovery. Percent recovery for TOL, by all the methods, was found in the range of 98.28 % to 100.58 % values of standard

deviation and coefficient of variation was satisfactorily low indicating the accuracy of all the methods. Based on the results obtained, it is found that the proposed methods are accurate, precise, reproducible and economical and can be employed for routine quality control of Tolterodine in its capsule formulation.

ACKNOWLEDGEMENTS:

The authors are very thankful to Dr. Avinash D. Deshpande, Director of Pharmacy, Pad. Dr. D. Y. Patil Institute of Pharmaceutical Sciences and Research, Pimpri, Pune for providing necessary facilities. The authors are also thankful to Cipla Pvt Ltd, Mumbai for providing gift samples of Tolterodine.

References:

1. Sweetman. S.C. Martindale, The Complete Drug Reference, Pharmaceutical Press, London, 1999; 32^nd ed: pp. 951.

2. Kumar YR, Ramulu G, Vevakanand V V, Vaidyanathan G, Srinivas K, Kumar MK, Mukkanti K, Reddy MS, Venkatraman S and Suryanarayana MV. A validated chiral HPLC method for the enantiomeric separation of Tolterodine Tartarate. J Pharm Biomed Ana. 2004; 35: 1279-1285.

3. Madhavi A, Reddy GS, Suryanarayana MV and Naidu A. Development and validation of a new analytical method for the determination of related components in Tolterodine Tartarate using LC. Chromatographia. 2008; 68: 399-407.

Received on 16.12.2008 Modified on 25.01.2009

Research J. Pharm. and Tech.2 (2): April.-June.2009; Page 312-314

Method	Drug	Label Claim	Amount of drug estimated (mg/tab)	% Label Claim* ± S.D.	% Recovery*
A	TOL	4	3.97	99.33 ± 0.3028	99.17
B	TOL	4	3.98	99.38 ± 0.3446	99.36
C	TOL	4	3.98	99.46 ± 0.2458	99.35