Int J Pharm Pharm Sci, Vol 9, Issue 11, 65-69Original Article


VALIDATED SPECTROPHOTOMETRIC METHOD TO DETERMINE VARDENAFIL AND SILDENAFIL IN PHARMACEUTICAL FORMS USING POTASSIUM IODIDE AND POTASSIUM IODATE

AMIR ALHAJ SAKUR, SHAZA AFFAS

Analytical and Food Chemistry Department, Faculty of Pharmacy, University of Aleppo, Syria
Email: shazaaffas@gmail.com

Received: 08 Jun 2017 Revised and Accepted: 21 Sep 2017

ABSTRACT

Objective: To develop and validate simple, sensitive, precise and free of organic solvents method for the determination of sildenafil (SIL) and vardenafil (VAR) in bulk and pharmaceutical formulation.

Methods: The method is based on the reaction of studied drugs with a mixture of potassium iodide and potassium iodate in an aqueous medium at (25±2 °C) to form yellow coloured triiodide ions (I3-) within 45 min. The reaction is followed spectrophotometrically by measuring the absorbance at 288, 351 nm and 285, 351 nm for sildenafil and vardenafil respectively.

Results: The effects of analytical parameters on the reported systems were investigated. Beer's law of SIL was obeyed in the range of (0.4-12) μg ml-1and (0.6-16) μg ml-1. Molar absorptivity was found to be (67.659 ×103) lmol/cm and (37.955×103) lmol/cm at 288 nm, 351 nm respectively. Beer's law of VAR was obeyed in the range of (0.2-13) μg/ml and (0.5-40) μg/ml. Moreover, molar absorptivity’s were found to be (68.719 ×103) l mol-1 cm-1and (26.691×103) l mol-1 cm-1 at 285 nm, 351 nm respectively.

Conclusion: The proposed method has been applied to determine the components in dosage forms with an average recovery of 98.15% to 103.45% and the results have been found in good agreement with those results obtained by the reference methods.

Keywords: Sildenafil citrate, Vardenafil hydrochloride, Spectrophotometry, Potassium iodide, Potassium Iodate, Triiodide ion

© 2017 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open-access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
DOI: http://dx.doi.org/10.22159/ijpps.2017v9i11.20578

INTRODUCTION

Erectile dysfunction (ED) is one of the most common chronic diseases affecting men and its prevalence increases with aging. It is also the most frequently diagnosed sexual dysfunction in the older male population. Treatment of erectile dysfunction is based on phosphodiesterase type 5 (PDE-5) inhibitors including sildenafil (SIL), and vardenafil (VAR). PDE-5 inhibitors have high efficacy and safety rates, even in difficult-to-treat populations such as patients with diabetes mellitus [1]. Sildenafil citrate was the first drug approved for the treatment of ED in 1998. The United States food and drug administration (FDA) approved tadalafil and vardenafil hydrochloride in 2003 [2].

There are several studies in medical literature reporting the determination of sildenafil citrate in pharmaceuticals, plasma samples, herbal drugs or dietary supplements using liquid chromatography method [1–7], electroanalytical methods [8, 9]gas chromatography [10], Thin layer chromatography [11], capillary electrophoresis [12] and capillary chromatography [13-15]. Many spectrophotometric Methods have also been reported [16–22].

As same as, determination of VAR in bulk, tablet dosage forms, and biological fluids were analyzed using different analytical systems, including HPLC [3, 23–25], capillary electrophoresis [26] capillary chromatography [27] LC-MS [28], and spectrophotometric methods [29, 30]. In the previous studies, the spectrophotometric determination of SIL and VAR depend on UV spectrophotometric method, oxidation of the drug and complex formation. Most of these methods demand organic solvents or organic reagents, unlike the proposed method.

The aim of the present study was to report a new, simple, and environment-friendly method to determination SIL and VAR as raw materials and in pharmaceutical preparations.

MATERIALS AND METHODS

Apparatus

Uv-visible spectrophotometer (JASCO, model V650, Japan) with 1.00 cm quartz cells. Ultrasonic processor (Powersonic, model 405, Korea) was used to sonicate the sample solutions. Adjustable micro­­­­­pipettes covering a volume range from 2 to 5000 μl (ISO-LAB, Germany), used for the preparation of the experimental solutions. Analytical balance (Sartorius, model 2474, Germany). pH meter (CRISON, GLp21/Eu, Spain).

Chemicals and reagents

Pharmaceutical grade sildenafil (99%) and vardenafil (99.5%) were received from XUHUANG, CHINA. Potassium iodate and potassium iodide (Panreac, Germany). All reagents and solvents were of analytical grade. Stock standard solution (1 mg ml-1) of SIL and VAR was prepared by dissolving 25 mg from each of SIL and VAR in double distilled water and diluting to 25 ml with double distilled water. 0.15 M of potassium iodate and 0.2 M of potassium iodide solutions were prepared by dissolving the accurately weighed amount of the pure solid in double distilled water. All other chemicals and reagents were of analytical grade and all solutions were prepared with double distilled water. All solutions are stable for a period of 2 d when stored at (4 °C).

General procedure

Increasing volumes of SIL or VAR working standard solution were transferred into series of 10 ml volumetric flasks that contain 2.5 ml of KI (0.2 M) and 1 ml of KIO3 (0.15 M) for SIL and 3 ml of KI (0.2 M) and 1.0 ml of KIO3 (0.15M) for VAR. The volume was made up to the mark with distilled water and the absorbance was measured after 45 min at 288, 351 nm and 285, 351 nm against a similar reagent blank for SIL and VAR respectively. The standard calibration plot was prepared to calculate the amount of the analyzed drug in bulk samples. All measurements were carried out at room temperature (25±2 °C).

Procedure for pharmaceutical formulations

Twenty individual tablets were weighed and pulverized carefully. An accurately weighed amount of the powder equivalent to 50 mg of SIL or VAR was transferred into 50 ml volumetric flask and dissolve in 50 ml of water. The content of the flask was sonicated for 30 min then diluted to the volume with water. A portion of this solution was centrifuged for 15 min at 5000 rpm then a suitable volume of the supernatant was transferred into 10 ml volumetric flask, and the procedure was continued to use for the analysis of SIL/VAR by the spectrophotometric method after 45 min.

RESULTS AND DISCUSSION

Absorption spectra

Iodide ions convert to free iodine in an acidic medium of VAR or SIL solution, the acidity comes from HCl or H3Cit, then free iodine reacts with a surplus of iodide ions to form yellow complex from triiodide (I3-) (fig. 2, 3) [31].

IO3-+5 I-+6 H+→ 2 I3-+3 H2O

Fig. 1: Absorption spectra of (1) reagent blank against distilled water, (2) SIL (12.0 μg ml-1)+2.5 ml of 0.20 M KI+1.0 ml of 0.15M KIO3 against reagent, Blank, (3) SIL against distilled water

Optimization of reaction conditions

The optimum conditions for the development of method were established by varying one parameter at a time and keeping the others fixed and observing the effect produced on the absorbance of the coloured products.

A volume of 2.5 ml of 0.2 M KI, 1.0 ml of 0.15 M KIO3 and 3.0 ml of 0.20 M KI, 1.0 ml of 0.15 M KIO3 were found to be optimum for maximum colour development for determination of SIL and VAR respectively. Since the absorbances were found to be maximal at the mentioned volumes. The laboratory temperature (25±2 °C), and the time of reaction was 45 min to obtain the optimum absorbance for all the experiments.

Fig. 2: Absorption spectra of (1) reagent blank against distilled water, (2) VAR (13.0 μg ml-1)+3 ml of 0.20 M KI+1.0 ml of 0.15 M KIO3 against reagent, Blank, (3) VAR against distilled water

Analytical method validation

Linearity

At described experimental conditions for determination of SIL and VAR, standard calibration curves with good linearity were obtained. The molar absorptivities, detection limits, and limits of quantification were calculated. The high molar absorptivities of the resulting coloured product indicate the high sensitivity of the method. Values of some analytical characteristics for proposed procedures were shown in table 1.

Accuracy and precision

The accuracy and precision of the proposed procedures were carried out by five determinations at several different concentrations for SIL and VAR. Percentage relative standard deviation (RSD %) as precision and percentage recovery as an accuracy of the suggested procedures were calculated and showed in table 2. The values of relative standard deviations for different concentrations of drugs determined from the calibration curves. These results of accuracy and precision show that the proposed procedures have good repeatability and reproducibility. The proposed method is selective to the assay of SIL and VAR in the presence of various excipients.

Table 1: Analytical parameters of spectrophotometric methods

parameters SIL VAR
288 nm 351 nm 285 nm 351 nm
Linear rang μg. ml-1 0.4-12 0.6-16 0.2-13 0.5-40
ɛ L mol-1 cm-1 67.659×103 37.955×103 68.719×103 26.691×103
Detection limit μg. ml-1 0.07 0.09 0.04 0.08
Limit of quantification μg. ml-1 0.25 0.3 0.13 0.25
Regression equation *(A = m C+b)
m=0.099 m=0.052 m= 0.109 m= 0.044
b= 0.002 b= 0.011 b= 0.012 b= 0.005
Correlation coefficient 0.9996 0.9988 0.9985 0.9994

*With respect to A=mC+b, where C is the concentration (µg. ml-1) and A is the absorbance.

Application to the pharmaceutical dosage forms

The proposed procedures were applied to determine the studied substances in their pharmaceutical formulations. The results in table 3 indicate the high accuracy and precision. As can be seen from table 3, the proposed method has the advantages of being virtually free from interferences by excipients and common degradation products. The results obtained were compared statistically by the student’s t-test (for accuracy) and the variance ratio F-test (for precision) with those obtained by the reference methods [3, 23] on samples of the same batch (table 3). The values of t-and F-tests obtained at 95% confidence level and four degrees of freedom did not exceed the theoretical tabulated value indicating that no significant difference between the proposed method and references method.

Table 2: Accuracy and precision of the determination of SIL and VAR in bulk powder by the proposed method

Drug λ max, nm Mg/ml RSD***% Recovery%
SIL 288 Taken Found Found*±S. D**
0.4 0.403 0.403±0.015 3.69 100.80
2 2.014 2.014±0.039 1.94 100.70
8 8.056 8.056±0.113 1.40 100.70
12 12.130 12.130±0.140 1.15 101.08
351 0.6 0.595 0.595±0.025 4.21 99.16
4 4.067 4.067±0.112 2.75 101.67
10 10.044 10.044±0.192 1.91 100.44
16 16.050 16.050±0.250 1.56 100.31
VAR 285 0.2 0.207 0.207±0.207 4.40 103.45
1 1.026 1.026±0.047 4.58 102.60
8 8.132 8.132±0.130 1.60 101.65
13 12.950 12.950±0.209 1.61 99.615
351 0.5 0.501 0.501±0.021 4.26 100.29
4 4.092 4.092±0.125 3.05 102.30
20 19.631 19.631±0.228 1.16 98.15
40 40.307 40.307±0.363 0.90 100.76

*Average of five determinations, **Standard diviation, ***Relative standard deviation.

Table 3: Determination of SIL and VAR in their pharmaceutical preparations using the proposed and reference methods

Formula Drug

Claim

(mg/tab)

 Found*%±SD*
Proposed method λmax, nm Reference method [3]
288 351
VIGRAVID SIL 25

25.14±1.17

t= 1.02

F=2.30

25.06±1.92

t= 1.35

­­­F=1.64

25.19±0.52

t= 1.22
50

50.14±0.90

t= 1.32

F=2.34

50.75±1.45

t= 1.12

F=1.08

50.33±0.92

t= 1.32
100

101.98±0.49

t= 1.22

F=1.47

101.15±1.92

t= 0.32

F=3.34

101.35±0.89

t= 1.02
285 351 Reference method [23]
FASTFIX VAR 10

9.93±0.67

t= 0.66

F=2.28

9.98±1.97

t= 1.32

F=1.04

9.963±0.72

t= 0.75
20

19.86±1.17

t= 1.32

F=1.79

20.17±1.03

t= 1.81

F=1.34

20.01±0.40

t= 0.36

* Average of five determinations, (four degrees of freedom), At 95% confidence levelt-value is 2.776 and F-value is 6.26, **Supplied by NCPI products، Syria, ***Supplied by UNIPHARMA products, Syria.

DISCUSSION

In this study, the developed spectrophotometric method is free of organic solvents [16-20, 22, 29], rapid, and has more sensitivity than previous methods [16-20, 22, 29, 30]. The proposed method can be carried out without any organic solvents or reagents in contrast with many previous spectrophotometric methods.

All previous reasons make this method easier and cheaper from other spectrophotometric methods.

A comparative summarized study between the proposed methods and previous spectrophotometric methods for determination of SIL and VAR has been provided in table 4 and table 5 respectively.

Table 4: Comparison of the proposed methods with the existing spectrophotometric methods for the determination of Sildenafil citrate

Reference

Ԑ

lmol/cm

 Concentration rang. µg/ml Temp. ˚C Solvent Spectrophotometric Method­­­­ Reagent
[16] 3.75×103 15.0–160 25±1 dichloroethane direct iodine
[16] 2.58×103 15.0–220 50±2 acetonitrile direct TCNQ
[16] 2.41×103 20.0–260 50±2 methanol direct DDQ
[16] 3.05×103 10.0–210 50±2 acetonitrile direct TCNE
[16] 2.25×103 15.0–240 60±2 dichloroethane direct TNF
[16] 3.26×103 20.0–180 60±2 acetonitrile direct chloranilic acid
[16] 3.42×103 28.0–150 60±2 acetonitrile direct chloranil
[16] 2.90×103 15.0–170 60±2 methanol direct bromanil
[17] 1.58×104 1.2–25.0 25±2 chloroform extractive BCG
[17] 9.79×103 1.5–60.0 25±2 chloroform extractive CCR
[18] 1.02×104 3.3–87.0 25±2 Methylene chloride extractive chromotrope 2B
[18] 8.30×103 3.3–96.0 25±2 Methylene chloride extractive chromotrope 2R
[18] 6.83×103 5.0-115.0 25±2 Methylene chloride extractive 3-phenylazo-6-o-carboxyphenylazo-chromotropic acid
[18] 5.42×103 2.5-125.0 25±2 Methylene chloride extractive

bis-3,6-(o-hydroxyphenylazo)-

chromotropic acid
[18] 3.35×103 8.3-166.7 25±2 methylene chloride extractive bis-3,6-(p-N,N-dimethylphenylazo)-chromotropic acid
[18] 2.32×104 0.8-15.0 25±2

Methylene

chloride

 extractive 3-phenylazo-6-o-hydroxyphenylazo-chromotorpic acid
[19] 20.12×103 1.0-40.0 40±2 chloroform extractive BTB
[19] 44.40×103 1.0-50 25±2 chloroform extractive PBP
[19] 24.00×103 3.0-70.0 25±2 chloroform extractive EPPR
[20] 7.86×103 3.0-70.0 25±2 chloroform extractive MCP
[22] 2.28×104 1.3-50.0 25±2 dichloromethane direct BCG
[22] 3.05×104 0.8-27.0 25±2 dichloromethane direct BTB
Proposed method
6.7659×104 0.4-12 25±2 water direct KI+KIO3 (288 nm)
3.7955×104 0.6-16 25±2 water direct KI+KIO3 (351 nm)

Table 5: Comparison of the proposed methods with the existing spectrophotometric methods for the determination of vardenafil hydrochloride

Reference

ԑ

lmol/cm

 Concentration rang. µg/ml Temp. ˚C Solvent Spectrophotometric method­­­­ Reagent
[29] 3.755×104 5-60 25±2 chloroform extractive BCG
[29] 4.079×104 2-20 25±2 alkaline medium direct

acetaldehyde+

sodium nitroprusside
[29] 4.299×103 10-100 25±2 alkaline medium oxidation KMnO4
[30] 3.774×104 4-40 25±2 acidic medium oxidation methyl benzothiazolinone hydrazoneHCL
[30] 4.605×104 4-60 25±2 alkaline medium indirect-oxidation 4-aminoantipyrine+potassium periodate
Proposed method
6.8719×104 O.2-13 25±2 water direct KI+KIO3 (285 nm)
2.6691×104 0.4-40 25±2 water direct KI+KIO3 (351 nm)

We can see this is the unique colorimetric method does not need any organic compound to determine SIL and VAR.

CONCLUSION

The proposed analytical procedures were simple, rapid, accurate and precise, so it can be used for the routine analysis of SIL and VAR in bulk and pharmaceutical formulations. The sample recoveries from all formulations have good agreement with their respective label claims, which suggested non-interference with formulations excipients in the assay. Moreover, the present method is environment-friendly because it does not need any organic reagents or solvents; it is free extractive and very sensitive comparing with other spectrophotometric methods.

CONFLICT OF INTERESTS

The authors declare no conflict of interest

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