UV Spectrophotometric Method For The Estimation of Tadalafil in Bulk and Tablet Dosage Form

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ISSN: 0973-4945; CODEN ECJHAO

E-Journal of Chemistry
2010, 7(3), 833-836
UV Spectrophotometric Method for the Estimation of

Tadalafil in Bulk and Tablet Dosage form
MOHAMMAD YUNOOS*, D.GOWRI SANKAR,
B.PRAGATI KUMAR and SHAHUL HAMEED
Nimra College of Pharmacy, Jupudi, Ibrahimpatnam, Vijayawada, India.
University College of Pharmaceutical Sciences,
Andhra University, Visakhapatanam, Andhra Pradesh, India.
yunoos_pharmacyanalyst666@gmail.com
Received 14 October 2009; Accepted 5 December 2009
Abstract: A simple, sensitive, precise and highly accurate UV
spectrophotometric method has been developed for the determination of
tadalafil in bulk and tablet dosage form. Solution of tadalafil in methanol
shows maximum absorbance at 284 nm. Beers law was obeyed in the
concentration range of 2-20 mcg mL-1 with 1.65x104 mol-1 cm-1, the slope,
intercept, correlation coefficient, detection and quantitation limits were also
calculated. The proposed method has been applied successfully for the analysis
of the drug in pure and in its tablets dosage forms. Result of percentage
recovery and placebo interference shows that the method was not affected by
the presence of common excipients. The method was validated by determining
its sensitivity, accuracy and precision which proves suitability of the developed
method for the routine estimation of tadalafil in bulk and solid dosage form.
Keywords: UV Spectrophotometry, Tadalafil, Beers law, Tablet dosage form.
Introduction
Tadalafil, chemically pyrazino [1,2:1,6] pyrido [3,4-b] indole-1,4-dione,6-(1,3-benzodioxol5-yl)-2,3,6,7,12,12 a-hexahydro-2-methyl-, ( 6R,12aR )-( Figure1 ), is an impotence agent. It is
indicated for the treatment of erectile dysfunction1-2. It is a selective inhibitor of cyclic
guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5)3. In previous
studies, only one assay has been reported for the determination of tadalafil in human serum and
urine by LC-MS-MS4.Tadalafil has also been quantified in pharmaceutical preparations,
human serum and biological fluids by HPLC5 with UV detection. Determination of tadalafil by
densitometric (TLC)6 and colorimetric7 methods has also been reported. Although the
ultraviolet spectrophotometric method is the instrumental method of choice commonly used in
industrial laboratories because of their simplicity, selectivity and sensitivity. As of our
knowledge no report has been mentioned in the literature for the determination of tadalafil by
834
M. YUNOOS et al.
UV method. The aim of the present work was to develop simple, rapid, accurate and sensitive
UV spectrophotometric method for the determination of tadalafil in bulk and tablet formulation.
UV analysis of tadalafil was performed in methanol. The spectrum was recorded from 200 nm to
400 nm. The quantitative analysis was carried out at 284 nm. The method was validated and
applied for the determination of tadalafil in tablet dosage form.
CH3
Figure 1. Chemical structure of tadalafil.
Experimental
Pharmaceutical grade of tadalafil was procured from Orchid chemicals and Pharmaceuticals
Ltd., India. All the chemicals were of analytical reagent grade of Merck (Germany) unless
otherwise specified. Methanol was used to prepare all solutions. Freshly prepared solutions were
always employed. Different brands of tablets of tadalafil were supplied from local pharmacy.
Instrumentation
The spectrophotometric measurements were carried out using Elico UV/Visible double
beam spectrophotometer SL-164 with 1 cm matched quartz cells.
Tadalafil stock solution

Standard stock solution was prepared by dissolving 50 mg of tadalafil in 50 mL of methanol
to get concentration of 1000 g/mL solution. It was further diluted to get working standard
solution of 100 g/mL.
Method development
Aliquot of working standard solution was further diluted with methanol to get concentration
of 10 g mL-1 and it was scanned between 200-400 nm which shows the maximum absorbance at
284 nm (Figure 2). The same max was used for the further measurement of the drug.
2.5
Absorbance
ABSORBANCE
2
1.5
1
0.5
0
200 220 240 260 280 300 320 340
Wavelength, nm
Figure 2. UV spectra of tadalafil.
UV Spectrophotometric Method for the Estimation of Tadalafil
835
Procedure for calibration curve

Aliquots of working standard solution were further diluted with methanol to get concentration of
2, 4, 8, 12, 16 and 20 g mL-1. Finally, the prepared standards were measured after standing for
5.0 min at max as recorded in Table 1, in each case against a solvent methanol as blank. A
calibration graph of the absorbance versus the concentration of the drug was plotted (Figure 3).
Absorbance
1
0.8
0.6
0.4
0.2
0
0 2 4 6 8 10 12 14 16 18 20 22 24
CONCENTRATION(Microgm
/m L)
Concentration micro g/mL
Figure 3. Standard plot of tadalafil.
Procedure for dosage forms

For analysis of commercial formulations, twenty tablets containing tadalafil were taken and
powdered. Tablet powder equivalent to 50 mg of tadalafil was transferred to 50 mL volumetric
flask and dissolved in methanol. Then the solution was sonicated for 15 min and filtered through
Whatman filter paper No. 41 and it was further diluted to get the required concentration. The
absorbance of the prepared sample solution was measure against methanol as a blank at 284 nm.
A standard additions technique was also used to confirm the accuracy and precisions
Results and Discussion

The optical characteristics such as Beers law limit, molar absorptivity, Sandells sensitivity,
correlation coefficient, slope and intercept, % Relative Standard Deviation (RSD), % range
of error (0.05 and 0.01 confidence limits) were calculated and are summarized in Table 1.
To ensure the reproducibility and accuracy of the method, recovery studies were carried out
by adding a known quantity of pure drug with preanalyzed sample and contents were
reanalyzed by the proposed method. From the amount of drug found, percentage recovery
was calculated. The results of analysis and recovery studies are given in Table 2.
Table 1. Optical characteristics and precision of the proposed method.
Parameters
Results
284
max, nm
2-20
Beers law limit, g/mL
Molar absorptivity , L mole-1 cm-1
1.65x104
Sandells sensitivity
0.023
(g cm-2 / 0.001 absorbance unit)
Regression equation (Y = a + bC)
Slope (b)
0.0372
Intercept (a)
0.0075
Correlation coefficient (r)
0.0075
Relative standard deviation (%)*
0.28
% Range of error (Confidence limits)
0.05 level
0.2341
0.01 level
0.3462
* Average of eight determinations.
836
M. YUNOOS et al.
Table 2. Assay of tadalafil in tablet dosage form.
Brand
TADIL
Labeled
amount
mg/tablet
10
Estimated Spike
amount level, %
9.98
80
100
120
Amount of
drug
added,mg
4
8
10
Amount of
drug
found,mg
3.98
7.97
10.02
Percentage
Recovery
+ RSD*
99.5 + 0.44
99.6 + 0.29
100.2 + 0.37
*Mean of six determinations.
Conclusion
In this study a simple, rapid, sensitive, accurate and precise UV spectrophotometric method
for the determination of tadalafil in bulk and pharmaceutical formulation has been developed
and validated. It was found that the common excepients present in the formulation did not
interfere with the proposed method and can be used for the routine quality control analysis
of tadalafil in bulk as well as in tablet formulations.
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http://www.e-journals.

ISSN: 0973-4945; CODEN ECJHAO

UV Spectrophotometric Method for the Estimation of

Figure 1. Chemical structure of tadalafil.

Tadalafil stock solution

200 220 240 260 280 300 320 340

Figure 2. UV spectra of tadalafil.

UV Spectrophotometric Method for the Estimation of Tadalafil

Procedure for calibration curve

Figure 3. Standard plot of tadalafil.

Procedure for dosage forms

Results and Discussion

*Mean of six determinations.

Pomerol J M and Rabasseda X, Drugs Today (Barc), 2003, 39, 103-113

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