Simultaneous estimation of dutasteride and tamsulosin hydrochloride in tablet dosage form by vierordt’s method

1.1 Objective

The objective of the present study was to develop a simple, precise, accurate and rapid SE method for the estimation of DU and TA in pharmaceutical dosage form.

2.1 Apparatus

Shimadzu 1650 UV–Vis double beam spectrophotometer with uv probe software and 1 cm matched quartz cells were used.

2.2 Materials and reagents

Pharmaceutical grade of dutasteride and tamsulosin HCl was kindly supplied by AN therapeutics, (Pondicherry, India), analytical grade methanol (S.D fine chemical Ltd., Mumbai, India) was used throughout these experiments. The commercial tablets used containing 0.5 mg DU and 0.4 mg TA per tablet were manufactured by cipla Pvt Ltd., (Mumbai, India).

2.3 Standard solutions

Stock solutions of DU and TA were prepared by dissolving in methanol 10 mg of DU and TA separately in a 100 ml volumetric flask, sonicated for 5 min. Final volumes of both the solutions were adjusted with methanol to get stock solutions with the concentration of 100 μg/ml of DU and TA.

2.4 Procedure

25 μg/ml solutions of DU and TA drugs were prepared from stock solutions and scanned individually in the range of 200–400 nm (Fig. 1) and the λ_max values were found to be 240.6 nm for DU (λ₁) and 279.4 nm for TA (λ₂) (Jefferey et al., 1989; Beckett et al., 1997).

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Figure 1

Overlain spectra of DU and TA. (a) UV spectrum of DU; (b) UV spectrum of TA.

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The concentrations of drugs in sample solutions were determined by the SE method using the following formula. $$C_x=A_2{\text{ay}}_1-A_1{\text{ay}}_2/{\text{ax}}_2{\text{ay}}_1-{\text{ax}}_1{\text{ay}}_2$$ $$C_y=A_1{\text{ax}}_2-A_2{\text{ax}}_1/{\text{ax}}_2{\text{ay}}_1-{\text{ax}}_1{\text{ay}}_2$$ Where C_x and C_y are the concentration of DU and TA, ax₁ and ax₂ are absorptivities of DU at 240.6 nm and 279.4 nm, ay₁ and ay₂ are absorptivities of TA at 240.6 nm and 279.4 nm, respectively.

2.5 Determination of absorptivity value

The absorptivity of each solution was calculated by using the following formula (Khan et al., 2010): $$\text{Absorptivity}=\text{Absorbance}/\text{conc}(\text{gm}/100\text{ml})$$ The developed method was validated as per ICH (ICH Q2(R1), 2005) guidelines.

3.1 Specificity

Specificity was studied by measuring the absorbance of DU and TA individually at 240.6 nm and 279.4 nm against the blank and comparing the absorbance of drug solutions to the blank. No interference was observed.

3.2 Linearity

The absorbances were measured for DU and TA in the concentration range of 20, 25, 30, 35, 40 μg/ml and 16, 20, 24, 28, 32 μg/ml at 240.06 nm and 279.4 nm for both the drugs respectively. Calibration graphs were plotted for DU at 240.6 nm and TA at 279.4 nm. (Figs. 2 and 3 respectively) Absorptivity values were calculated for each concentration and presented (Tables 1 and 2).

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Figure 2

Calibration graph for DU.

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Figure 3

Calibration graph for TA.

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3.3 Accuracy

Recovery studies were carried out by measuring the absorbance of added standard solution of both DU and TA in 50%, 100% and 150% levels to the preanalysed sample solutions at 240.6 and 279.4 nm. The amount of DU and TA was calculated and results are presented in Table 3.

3.4 Precision

Inter and intraday precision studies were done by repeated measurements of the absorbance of standard mixed solution in triplicate in same day and single time for three days respectively by the proposed assay method without changing the method procedure. Percentage RSD was calculated and results are presented in Table 4.

3.5 Ruggedness

A study was conducted to determine the effect of variation in analyst to analyst, lab to lab and instrument to instrument in triplicate measurement as per the assay method. % RSD was calculated for each condition and results are presented in Table 5.

3.6 Robustness

Robustness study was carried out by changing the wavelength in ±1 nm from 240.6 nm to 279.4 nm and the results are presented in Table 6.

3.7 Stability

Stability of drug solutions was determined by keeping the drug solution for nine days at room temperature and the absorbance of sample solution in each day was measured. Results are presented in Table 7.

3.8 Apply the developed and validated method to the marketed dosage form

20 Urimax-D Tablets were accurately weighed and powdered and the powder weight equivalent to 1.5 mg of DU and 1.2 mg of TA was transferred to a 50 ml volumetric flask separately and sufficient methanol was added to dissolve it. Then the solutions were sonicated for 15 min. Then final volume was adjusted with methanol and filtered by vacuum filtration. The filtrate was centrifuged at 10,000 RPM for 30 min. Then clear supernatant solutions were transferred to a separate flask without disturbing the sediment. Then absorbance was measured at 240.6 nm and 279.4 nm for minimum six times. Amount of DU and TA in each tablet was calculated and results are presented in Table 8.