INTRODUCTION:

Sitagliptin (Figure 1) is an anti-diabetic agent which is an oral dipeptidyl peptidase-4 inhibitor which exerts its actions in type 2 diabetes patients by slowing the inactivation of incretin hormones. Sitagliptin (C₁₆H₁₅F₆N₅O); Mol. Wt. 407.314 g/mol) is chemically (R)-4-oxo-4- [3-(trifluoromethyl)- 5,6-dihydro [1,2,4]triazolo [4,3-a] pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl) butan-2-amine. Spectrophotometric methods were developed^2-17 but no derivative spectrophotometric techniques were developed and therefore in the present study the authors have proposed new first derivative spectrophtotmetric methods for the determination of Sitagliptin in pharmaceutical dosage forms and the methods were validated¹⁸.

Figure 1: Chemical structure of Sitagliptin

MATERIALS AND METHODS:

Sitagliptin is available as film coated tablets under the brand name Januvia, Janumet, Istamet, Istavel, Zita and Steglujan. Double beam spectrophotometer (Shimadzu Model No. UV - 1800) was used for the present study. For this study quartz cells are used and all the solutions were scanned at 200-400 nm range. Gift samples of Sitagliptin were obtained from SUN Pharma (India). 25 mg of Sitagliptin was accurately weighed and transferred in to a 25 ml volumetric flask and dissolved in methanol (1000 µg/ml) and a series of dilutions were prepared with respective buffers as per the requirement. Reagents such as phosphate buffer (pH 5.0), phosphate buffer (pH 8.0), acetate buffer (pH 4.7), 0.1 N NaOH, borate buffer (pH 9.0) and were prepared as per IP 2010.

Method validation¹⁸

A series of Sitagliptin solutions 5-100 µg/ml were prepared using different reagents such as phosphate buffer pH 5.0 (Method I), phosphate buffer pH 8.0 (Method II), acetate buffer pH 4.7 (Method III), 0.1 N NaOH (Method IV) and borate buffer pH 9.0 (Method V) and scanned against their reagent blank at range of 200-400 nm. Sitagliptin has shown its λ_max at 267 nm in all methods and the individual zero order spectra of Sitagliptin obtained were converted into their first order derivative spectra by the inbuilt software of the instrument. The resultant derivative spectra have shown both maxima and minima and therefore the amplitude was considered for the construction of calibration curve. The amplitude was plotted on y-axis against concentration on the x-axis for all the methods. Precision study was conducted with all the reagents for Method I, II, III, IV and V using six replicates of the same concentration (n=6) and the standard deviation followed by the percentage relative standard deviation was calculated whereas the accuracy studies were carried out by standard addition method (50%, 100% and 150 %) and the recovery was calculated.

Assay of Sitagliptin tablets

Two different brands of Sitagliptin were procured and extracted with methanol and further dilutions were made with respective reagents and the assay was carried out for all the methods.

RESULTS AND DISCUSSION:

New first derivative spectrophotometric (D₁) techniques were developed for the determination of Sitagliptin in different reagents such as phosphate buffer pH 5.0 (Method I), phosphate buffer pH 8.0 (Method II), acetate buffer pH 4.7 (Method III), 0.1 N NaOH (Method IV) and borate buffer pH 9.0 (Method V) respectively. The first derivative spectra of Sitagliptin were shown in Figure 2. Sitagliptin obeys Beer-Lambert’s law over the concentration range 5-100 µg/ml in all the methods (Table 1) and the calibration curves were shown in Figure 3. The % RSD in both precision and accuracy studies were found to be less than 2 indicating that the methods are precise (Table 2) and accurate (Table 3). The assay of marketed formulations (Tablets) was shown in Table 4.

Figure 2: Overlay first derivative spectra of Sitagliptin (D₁)

Table 1: Linearity of Sitagliptin – First derivative spectroscopy

Conc. (µg/ml)	Method I	Method II	Method III	Method IV	Method V
5	0.003	0.003	0.003	-	0.003
10	0.005	0.005	0.007	0.008	0.005
20	0.011	0.011	0.014	0.015	0.011
40	0.021	0.022	0.029	0.03	0.021
60	0.032	0.033	0.042	0.045	0.032
80	0.043	0.045	0.055	0.058	0.042
100	0.053	0.054	0.068	0.075	0.052

Figure 3: Calibration curves of Sitagliptin

Table 2: Precision study of Sitagliptin

Conc.(µg/ml)	Statistical parameters: Mean ± SD (% RSD)
	Method I	Method II	Method III	Method IV	Method V
10	0.0054 ± 0.0005 (0.09)	0.0056 ± 0.0008 (0.14)	0.0078 ± 0.0008 (0.10)	0.008 ± 0.0005 (0.05)	0.0054 ± 0.0005 (0.09)
10
10
10
10
10

*Mean of three replicates

Table 3: Accuracy studies of Sitagliptin

Spiked Conc.

(µg/ml)

Formulation

Total Conc.

(µg/ml)

Conc. obtained (μg/ml) [% Recovery] (% RSD)

Method

Method II

Method

III

Method

14.89

[99.27]

(0.35)

14.75

[98.33]

(0.29)

14.82

[98.80]

(0.32)

14.92

[99.47]

(0.73)

14.89

[99.20]

(0.52)

19.28

[96.4]

(0.36)

19.26

[96.3]

(0.34)

19.9

[99.5]

(0.29)

19.58

[97.9]

(0.86)

19.01

[95.05]

(0.34)

24.39

[97.56]

(0.54)

24.88

[99.2]

(0.19)

24.1

[96.4]

(0.43)

24.55

[98.2]

(0.99)

24.21

[96.84]

(0.33)

*Mean of three replicates

Table 4: Assay of Sitagliptin (Labeled claim: 50 mg)

Observed amount (mg)						% Recovery
Method	I	II	III	IV	V	I	II	III	IV	V
Brand I	49.84	49.89	49.90	49.78	49.85	99.68	99.78	99.8	99.56	99.7
Brand II	49.86	49.85	49.92	49.89	49.90	99.72	99.7	99.84	99.78	99.8

*Mean of three replicates

CONCLUSION:

The new spectrophotometric methods were validated for the determination of Sitagliptin and found to be simple, precise and accurate and the methods can be successfully applied for the determination of Sitagliptin in pharmaceutical dosage forms.

ACKNOWLEDGMENT:

The authors are grateful to M/s GITAM (Deemed to be University), Visakhapatnam for providing the research facilities and SUN Pharma (India) for providing the gift samples of Sitagliptin.

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Received on 14.03.2020 Modified on 18.04.2020

Research J. Pharm. and Tech 2020; 13(6): 2838-2842.

DOI: 10.5958/0974-360X.2020.00505.3