Difference Spectrophotometric Method for the Determination of Duloxetine in Bulk and Tablet Dosage Form

 

Mrs. Sheeja Velayudhan Kutty¹, Dr. Yellinah Hari Babu², Aswathy. A.V³, Rubiya. P.A³,Sajitha. S³_.

¹Assistant Professor, Department of Pharmaceutical Analysis, Grace College of Pharmacy, Kodunthirapully.Post, Palakkad, Kerala, India.

²Principal and HOD, Department of Pharmaceutical Analysis, Grace College of Pharmacy, Kodunthirapully Post, Palakkad, Kerala, India.

³Department of Pharmaceutical Analysis, Grace College of Pharmacy, Kodunthirapully Post, Palakkad, Kerala, India

*Corresponding Author E-mail: aswathyav014@gmail.com, sreevaigha2013@gmail.com

A new, simple, rapid, sensitive and economical spectrophotometric method has been developed and validated for estimation of duloxetine in pure and its pharmaceutical formulation like tablet. During the development of formulations containing duloxetine in its solid dosage form, analytical methods will serve as assay method for quantitation of the duloxetine during product developmental stages. The present work consist of estimation of duloxetine by difference spectrophotometry which is based on shifting of λ max by changing the pH of the solution by adding 1M HCl and 1M NaOH the absorption maximum was obtained. Linearity of the response was demonstrated for the drug for a range fulfilling Beer’s law, which is 11-16 μg/ml with the linear regression value of 0.995.  The absorption maxima of duloxetine were obtained at 230 nm in 1M NaOH, and in 1M HCl. The results of analysis have been validated statistically and by recovery studies. Interday and Intraday studies showed high degree of repeatability. Recoveries obtained do not differ significantly from 100% .The method was extended to pharmaceutical formulation and there were no interferences from any excipients and diluents. The full analytical validation was performed according to International Conference on Harmonization Q2R1 guidelines for validation of analytical procedures was found to be satisfactory.

              

 

 

INTRODUCTION:

Duloxetine is chemically methyl[(3s)-3-(naphthalene-1-yloxy)-3-(tiophen-2-yl)propyl]amine.It is under the category of antidepressive agent, dopamine uptake inhibitor, adrenergic uptake inhibitor, and serotonin reuptake inhibitor.¹ Difference spectrophotometry of duloxetine was not revealed in literature.

 

An attempt in the present study has been made to develop simple, accurate and economical method for difference spectroscopy^[6,7] of duloxetine and its pharmaceutical formulations. The simplest and most commonly employed technique for altering the spectral properties of analyte is the adjustment of the pH by means of aqueous solution of acids, alkali.^[2] The result of analysis using the developed spectrophotometric methods for difference spectrophotometry^[3] was found to be satisfactory such that the developed methods can be used for routine analysis of drugs and pharmaceutical dosage form.

 

MATERIALS AND METHODS:

A SHIMADZU model PHARMASPEC-1800UV-Vis spectrophotometer with 1.0 cm matched cells was used for the electronic spectral measurements. Duloxetine and all other chemicals used were analytical reagent grade. Duloxetine pure drug was generously provided by Torrent Pharmaceuticals Pvt. ltd (Ahmadabad, India), as a gift sample. The commercially available capsule duloxetine HCl (Dulot) containing 20mg of Duloxetine was procured from the local market. Freshly prepared 1 N sodium hydroxide, 1 N hydrochloric acid, distilled water was used in the present analysis.

 

Preparation of standard stock solution:

The standard Duloxetine 10mg was weighed accurately and transferred to volumetric flask (100 ml). It was dissolved properly in distilled water by using ultrasonication  and made up to the mark to get a concentration of 100μg/ml.             

 

Preparation of working standard solution:

Working standard solution was prepared by series of dilutions of 1.1-1.6 ml of standard stock solution to 10 ml with 1N HCl and 1N NaOH separately to get concentrations of 11-16μg/ml for Duloxetine. These solutions were used to determine absorption maxima, Beer’s law and linearity.

 

Determination of λ max:                                                                             

By appropriate dilution of two standard drug solutions with 1N HCl and 1N NaOH solutions containing 10 μg/ml of Duloxetine was prepared and was scanned separately over the range of 400 to 200 nm against the reagent blank. From the spectrum obtained, the λ max was found to be 230nm both in acidic and basic solutions.

(Fig.1, Fig.2)

 

Fig.1-Overlay spectra of Duloxetine in 1N HCl at 230nm

 

Procedure for calibration curve:

Working standard solution was prepared to get concentrations of 11-16μg/ml separately using 1N HCl and 1N NaOH and the absorbance were measured at 230 nm both in acidic and basic solutions respectively against reagent blank. Calibration curve was prepared by plotting concentration versus difference in absorbance and found to be linear in the concentration range of 11-16μg/ml. [Fig.3]

 

Fig.2-Overlay spectra of Duloxetine in 1N NaOH at 230nm

 

Fig.3

 

RESULTS AND DISCUSSION:

The method was found to be simple, economical, selective and sensitive. The statistical parameters clearly indicate the reproducibility and accuracy of the method. Analysis of Duloxetine in its dosage forms showed no interference from the common excipients and additives. Difference spectrophotometry by indicating pH of the medium may be recommended for routine and quality control analysis of the investigated drug in tablets.

 

Analysis of tablet formulation:

Ten tablets were accurately weighed and triturate thoroughly to get fine powder. The powder equivalent to 10mg of Duloxetine was weighed and transferred into 100 ml volumetric flask. The contents of the flask were dissolved in the 100ml of the distilled water with the aid of ultrasonication for10 minutes. The solution was filtered through Whatman filter paper no.41 and volume was made up to 100ml with distilled water. From the resultant solution, further dilutions were prepared with 1N HCl and 1N NaOH separately to get final concentration of duloxetine. The absorbance was measured at selected wavelengths and concentration of each analyte was determined with the equation obtained from calibration curve.[Table.1]

 

Table.1

Formulation	Label Claim (mg)	Amount Estimated (mg)	% Amount Estimated	%RSD
Dulot	20	19.99 20.008 19.99	99.99 100.4 99.99	0.59889

 

Method validation ^{[4 , 5]}

Linearity:

Working standard solution was prepared by series of dilutions of 1.1-1.6 ml of standard stock solution to 10 ml of 1N HCl and 1N NaOH separately to get concentrations of 11-16μg/ml for Duloxetine. Solutions were scanned in the wavelength range of 400 – 200nm, and the absorbance was measured at 230 nm both in acidic and basic solutions respectively against reagent blank. Calibration curve was prepared by plotting concentration versus difference in absorbance and found to be linear in the concentration range of 11-16μg/ml.[Table.2]

 

Linearity of Duloxetine by Difference Spectrophotometry

Table.2

Concentration (μg/ml)	Absorbance in 1N NaoH	Absorbance in 1N Hcl	Difference in absorbance
11	0.969	1.668	0.706
12	1.046	1.840	0.794
13	1.108	2.005	0.897
14	1.127	2.115	0.988
15	1.225	2.280	1.055
16	1.234	2.354	1.12

 

Precision:

Precision of the method was determined by performing Interday variation, intraday variation and repeatability studies and expressed in the forms of %RSD. In Interday variation, the absorbances of working standard solutions of Duloxetine (11-16 μg/ml) were measured on three consecutive days. In intraday variation the absorbance were measured three times a day. In repeatability study, six determinations of the fixed concentration of both acidic and basic solutions of the drug were analyzed separately. [Table.3]

 

Table.3

	Concentration (μg/ml)	Amount found(mg)	%RSD*
Intraday (n=3)	11	19.99	0.8490
Interday (n=3)	11 12 13	20.08 20.00 20.003	1.1909 0.2306 0.0011
Repeatability(n=6)	11	19.99	0.5988

 

Accuracy (Recovery studies):

The accuracy of the proposed method was determined by calculating the recoveries of Duloxetine by the standard addition method. It was determined by preparing solutions of different concentrations at 50%, 80% and 100% in which the amount of marketed formulation was kept constant and the amount of pure drug was varied. The amount of Duloxetine was estimated by applying obtained values to the regression line equation. [Table.4]

 

Robustness:

The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal usage. Robustness of the proposed procedures was examined by evaluating the influence of small variation in the solvent on the analytical performance of the proposed methods. [Table.5]

 

Ruggedness:

Ruggedness was ascertained by getting the sample analysed from different analysis and carrying out analysis for interday variation, intraday variation and for different instrument ascertained ruggedness by proposed method. [Table.6]

 

 

Table.4

Drug	Level of Addition	Amount of pure drug Added(mg)	Amount of pure drug recovered (mg)	Percentage recovery	Average percentage recovery	%RSD*
Duloxetin	50%	5 5 5	20 19.9 19.99	100% 99.99% 99.99%	99.993%	0.002
	80%	8 8 8	20 19.9 20	100% 99.99% 100%	99.996%	0.00173
	100%	10 10 10	19.9 20 19.9	99.99% 100% 99.99%	99.993%	0.1336

 

Table.5

Concentration	Absorbance in  0.1N NaoH	Absorbance in 0.1N  Hcl	Difference	Percentage Purity	Percentage  RSD*
11	0.985 0.982 0.982	1.062 1.060 1.061	0.077 0.078 0.079	100% 99.999% 99.999%	0.001

 

Table.6

	Concentration	Absorbance in  1N NaoH	Absorbance in  1N Hcl	Difference	Percentage Purity	Percentage  RSD*
Analyst – 1	12	0.980 0.985 0.98	1.171 1.175 1.18	0.191 0.19 0.208	100% 100% 100.4%	0.0101
Analyst – 2	12	0.988 0.978 0.985	1.188 1.178 1.175	0.2 0.2 0.19	100.4% 100.4% 100%	0.00575
Analyst – 3	12	1.052 1.050 1.055	1.245 1.240 1.255	0.193 0.19 0.2	100% 100% 100%	0.00511

 

Table.7

Parameters	Value
λ max	230nm
Linearity range	11-16µg/ml
Reggression equation	0.089X-0.271
Slope	0.089
Intercept	-0.271
Correlation coefficient	0.995
Molar absorptivity(Mean)	692.79

 

CONCLUSION:

Duloxetine exhibits a substantial difference in absorbance in the two solvents that is in 1NHCl and 1N NaOH. So determination of Duloxetine by difference spectrophotometry was attempted. Beer’s law was obeyed in the concentration range of 11-16μg/ml with a linear regression value 0.995. Interday, Intraday and repeatability studies showed high degree of precision of an analytical method under normal operating conditions. The %RSD for precision, which was less than 2% Indicates that the method is precise. Recoveries obtained do not differ significantly from 100% showed that there was no interference from the common excipients used in the tablet formulation indicating accuracy and reliability of the method.

 

ACKNOWLEDGMENT:

We express our sincere thanks to Torrent pharmaceuticals private limited, Ahmadabad, India for providing the gift sample of Duloxetine, and also we are grateful to the Principal and staffs of Grace College of Pharmacy, Kodunthirapully, Kerala, India for providing the facilities to carry out the present work.

 

REFERENCE:

1.       www.Drugbank/ca.com.

2        AH Beckett, JB Stenlake  practical pharmaceutical chemistry, fourth edition, part two, Page no 293-296.

3        Instrumental methods of analysis Hobart.H.Willard ,et al, seventh edition page no.176.

4        Text on Validation of Analytical Procedures Q2R1 in; ICH, Harmonized Tripartite Guidelines, 1996.

5        Development and validation of analytical methods , edited by Christpher .M. Riley  et al vol.3 .

6        Difference Spectrophotometric Methods for Pioglitazone Hydrochloride and Metformin Hydrochloride,  Journal of Pharmaceutical  Science and Research Vol.3(4), 2011,1122-1126 7. 

7        Developement of Difference Spectrophotometry Method for Estimation of Lercanidipine in Tablet Dosage Form, Research Journal of Pharmaceutical, Biological and Chemical Sciences, July – September 2012 , Volume 3 ,Issue 3, Page No. 149.

 

 

 

Received on 09.12.2013       Modified on 10.01.2014

Accepted on 18.01.2014      © RJPT All right reserved