INTRODUCTION:

Lansoprazole {2-[[[3-methyl-4-(2,2,2-trifluoroethoxy)-2-pyridinyl]methyl]sulfinyl]1H benzimidazole} as shown in (Figure 1)⁶ is a substituted benzimidazole with anti-secretory and anti ulceractivities . It is effective in treating various peptic diseases, especially those resistant to treatment with histamine H2 receptor antagonists; therefore it is successfully used for the treatment of duodenal ulcer, gastric ulcer, reflux Oesophagitis and Zollinger–Ellison syndrome ¹.Naproxen is chemically 2-Naphthaleneacetic acid,6-methoxy-α-methyl-,(s)-(+)-(s)-6-Methoxy-α-methyl-2-naphthaleneacetic acid as shown in (Figure 1)⁷. Naproxen is a non steroidal anti-inflammatory drug (NSAID) commonly used for the reduction of moderate to severe pain, fever, inflammation and stiffness. It works by inhibiting both the COX-1 and COX-2 enzymes. Like other NSAIDs, Naproxen is capable of producing disturbances in the gastrointestinal tract ².

Lansoprazole Naproxen

Figure 1: Chemical Structure of Lansoprazole and Naproxen

On literature survey it was found that LAN and NAP was estimated independently or in combination with other drugs by several methods as HPTLC³, LC-MS in human plasma⁴,LC- electrospray Tandem Mass Spectrometry⁵. On literature survey it was found that LAN and NAP was estimated independently or in combination with other drugs^8-19.

There was no UV- spectrophotometric method had been develop for the determination of LAN and NAP in combined dosage form. The combination of both is used in the treatment of rheumatoid arthiritis and oesteoarthiritis. The lansoprazole in this medication helps reduce the risk of stomach ulcers in people who may be at risk for them while receiving treatment with an NSAID’S. So an attempt was taken to develop and validate an economic, rapid Absorption Ratio method for the determination of naproxen and lansoprazole in combined tablet dosage form.

MATERIALS AND METHODS:

Drugs and chemicals:

Lansoprazole was procured from Lupin pharmaceuticals Limited, India. Naproxen was procured from Glenmark Pharmaceutical Limited, India. Methanol was of analytical grade. All other chemicals used were of analytical grade. The pharmaceutical dosage form used in this study was junior lanzol-30 labelled to contain 30mg LAN and naprosyn labelled to contain 250mg of NAP.

Apparatus

Analysis was carried out on UV -Visible Spectrometer (LAB INDIA 3200) with 1cm quartz cells. An analytical balance (Roy electronics– LCBCNS) was used for weighing the samples.

Figure 2: λ_maxof Lansoprazole

Figure 3: λ_max of Naproxen

Figure 4: Linearity study of Lansoprazole

Figure 5: Linearity study of Naproxen

Figure 6: Iso Absorptive point for Lansoprazole and Naproxen

Method Development

Absorption Ratio Method

Preparation of standard stock solution

The standard stock solutions of 1000µg/ml of LAN and NAP were prepared by accurately weighing 50mg drugs separately in methanol in 50ml volumetric flask. The working dilutions were in the range of 10-35 µg/ml for naproxen and 5-30 µg/ml for LAN respectively were prepared by further dilutions for calibration curves (Figure no 4 and 5).

Determination of Iso-absorptive point and wavelength of maximum

The isobestic point (where both the drugs show equal absorbance) was obtained from the overlain spectra of LAN and NAP. The overlain spectra showing isobestic point at 275nm as (Figure 6). Thus 275nm was selected as λ_1.The λ₂was selected at 284 nm which was λ_max for LAN.

Preparation of standards for test for linearity

A calibration curve was plotted over a concentration range of 5-30µg/ml for LAN and 10-35µg/ml for NAP. Accurately measured standard stock solution of LAN (0∙5,1∙0,1∙5,2∙0,2∙5,3∙0) and standard stock solution of NAP (1∙0,1∙5,2∙0,2∙5,3∙0,3∙5) were transferred to a separate series of 10mL of volumetric flask and diluted to the mark with methanol. The different concentration of solutions were scanned over the range of 200 nm to 400 nm and absorbance at 284 nm and 271 nm for LAN and NAP were measured respectively (Figure 2 and 3 ) in the quantitative mode of the instrument and the absorptivity was calculated. From the absorbance value the absorptivity value at respective wavelength i.e. λ₁ (275nm) and λ₂(284 nm) was calculated by dividing absorbance and respective concentration. Similarly for LAN the absorbance value was recorded at 275 and 284 nm and the absorptivity was calculated. The concentration of LAN and NAP were calculated by using the following equations.

C_x = (Q_M- Q_Y) A₁/ (Q_X- Q_Y) a_x1^20-26

Where, A₁and A₂are the absorbance of the mixture at 275 nm and 284 nm respectively; a_x1and a_y1are absorptivities of LAN and NAP respectively at 275 nm; a_x2and a_y2are absorptivities of LAN and NAP respectively at 284 nm.

Q_M= A₂/ A₁

Q_{X =}a_x2/a_x1and

Q_Y= a_y2/ a_y1

Analysis of commercial formulation

Commercially products in the combination of Lansoprazole and Naproxen are not available currently. Ten tablets of lansoprazole and naproxen were accurately weighed separately and its contents crushed to fine powder. Powder equivalent to 30mg of lansoprazole and 250mg of naproxen was weighed and dissolved in methanol, sonicate for 10min, mixed well and filtered through Whatman’s filter paper no.41. After rejecting first few ml, different of tablets sample were prepared by serial dilution technique and analyzed at 275nm and 284nm. Then the absorbances were recorded at the respective wavelengths as shown in Table no.1.

Table 1: Analysis of commercial formulation:

Formula-tion

Drug

Label claim

% Label claim

( mean ± SD)

Tablet

Lansoprazole

naproxen

30mg

250mg

100∙13 ± 0∙000985

100∙16 ± 0∙012757

Table 2: Linearity study for Lansoprazole and Naproxen

S.NO.	Parameter (units)	Lansoprazole	Naproxen
i.	Linearity range (µg/ml)	5-30 µg/ml	10-35µg/ml
ii.	Correlation coefficient (r²)	0.998	0.999
iii.	Slope	0.040	0.054
iv.	Intercept	0.022	0.022

Method Validation

Recovery studies

To study the accuracy of the proposed methods, recovery studies were carried out by standard addition method at three different levels (80%, 100% and 120% of the test concentration as per ICH guidelines) as shown in table no.3. A known amount of drug was added to pre analyzed capsule powder and percentage recoveries were calculated. The result of recovery studies was satisfactory.

Linearity and range

The six point calibration curve that were constructed were linear over the concentration range between 5-30 µg/ ml for LAN and 10-35 µg/ ml for NAP respectively. Each concentration was repeated for 3 times as shown in Table no.2.

Table 3: Validation parameter

		Lansoprazole	Naproxen
i.	Interday Precision
	(1^st d)	92%±0∙014365	96%±0∙0021886
	(2^nd d)	86%±0∙000323	97%±0∙003265
	(3^rd d)	88%±0∙001235	97%±0∙000354
	Intraday precision
	(1^st h)	87%±0∙000242	98%±0∙001895
	(2^nd h)	86%±0∙001093	97%±0∙002953
	(3^rd h)	88%±0∙014588	94%±0∙002653
ii.	Recovery
	80%	87%±0∙002138	67%±0∙009667
	100%	100%±0∙000603	69%±0∙000666
	120%	99%±0∙00361	78%±0∙001234
iii.	LOD (mg/ ml)	0∙525mg/ ml	0∙0455mg/ ml
iv.	LOQ(mg/ ml)	0∙151mg/ ml	1∙753mg/ ml
v.	Robustness	86%±0∙001201	98%±0∙000153

Precision

The precision of the method, as intra-day repeatability was evaluated by performing six independent assays of the test sample preparation and calculating the RSD %. The intermediate (interday) precision of the method was checked by performing same procedure on different days by another person under the same experimental conditions as shown in Table no.3.

LOD and LOQ

The LOD and LOQ of lansoprazole and Naproxen are calculated by Mathematical equation.

LOD= 3.3×standard deviation ÷ slope

LOQ=10×standard deviation ÷ slope

The LOD of lansoprazole and Naproxen were found to be 0∙04µg/ml and 0∙5µg/ml and the LOQ of lansoprazole and Naproxen were found to be 0∙15μg /ml and 1∙7μg/ml as shown in Table no.3.

Robustness

Robustness of proposed method was performed by changing the UV analyst and remaining condition was keeping constant as shown in Table no.3.

RESULTS AND DISCUSSION:

In a quantitative assay of two components in admixture by absorbance ratio method, absorbances are measured at any two wavelengths, one being the iso absorptive point of two components and other being the wavelength of maximum absorption of one of the two components. Thus, two selected wavelengths for this method were 275 nm (iso-absorptive point) and 284nm λ_max of LAN. The absorbencies and absorptivity at these wavelengths were determined and substituted in equation 1 to obtain the concentration of both the drugs.

CONCLUSION:

All these factors lead to the conclusion that the absorption ratio method development is accurate, precise, simple, sensitive and rapid and can be applied successfully for the estimation of LAN and NAP in bulk and in pharmaceutical formulations without interference. The relative standard deviation (RSD) for all parameters was found to be less than one, which indicate that the validity of method are also within the limit so the proposed method can be used for routine quantitative simultaneous estimation of both the drug.

ACKNOWLEDGEMENT:

The authors are thankful to Lupin Pharmaceuticals Limited, India and Glenmark Pharmaceuticals Limited, India for the gift sample of LAN and NAP and also thankful to the project guide and management, Invertis Institute of Pharmacy, Invertis University, Bareilly to providing the equipment and facility for entire duration of research work.

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Received on 30.04.2013 Modified on 25.05.2013

Asian J. Research Chem. 6(8): August 2013; Page 745-748