Determination of Favipiravir from Pharmaceutical Dosage Form by Extractive Ion Pair Complex Colorimetric Method

Rele Rajan V.*, Tiwatane Prathamesh P.

Central Research Laboratory D.G. Ruparel College Mahim, Mumbai 400016.

*Corresponding Author E-mail: drvinraj@gmail.com

ABSTRACT:

Simple sensitive and accurate extractive colorimetric method was developed for the estimation of favipiravir in Pharmaceutical dosage forms. The method was based on the formation of colored ion pair complexes by the drugs with thiocynate ions. These ion pair complexes were quantitatively extracted under the experimental condition in chloroform. The absorbance values were measured at 618 respectively. The proposed method was validated statistically. A recovery of method was carried out by standard addition methods. The Beer’s law ranges were found to be 1-12μg/ml, respectively. The low values of standard deviation and percentage RSD indicate high precision of method. Hence the method is useful for routine estimation of favipiravir in tablets respectively.

KEYWORDS: Favipiravir, Cobalt nitrate, Ammonium thiocynate, Chloroform, ethanol.

INTRODUCTION:

Favipiravir, is chemically, 6-fluoro-3-oxo-3,4-dihydropyrazine-2-carboxamide, Formula, C₅H₄FN₃O₂ (molecular weight 157.1g/mol). It becomes a new influenza drug. Favipiravir is a modified pyrazine analog that was initially approved for therapeutic use in resistant cases of influenza. The antiviral targets RNA-dependent RNA polymerase (RdRp) enzymes, which are necessary for the transcription and replication of viral genomes. Favipiravir inhibit replication of influenza A and B, but the drug has shown promise in the treatment of avian influenza, and may be an alternative option for influenza strains that are resistant to neuramidase inhibitors. Favipiravir has been investigated for the treatment of life-threatening pathogens such as Ebola virus, Lassa virus, and nowadays COVID-19.

Active pharmaceutical dosages are urgently required for rising COVID-19 pandemic conditions on global health¹. Pharmaceutical dosages such as remdesivir, chloroquine, and favipiravir are currently undergoing clinical test in different countries for treating corona virus disease^2,3. So far, there is no any specific drug available for the treatment of corona virus due to there is not enough evidence⁴.

It exhibit antiviral activity against alpha-, filo-, bunya-, arena-, flavi-, and noro-viruses^5,6 as well as being active against the influenza virus.

In a pre-pilot trial by University of Wuhan, it was observed that a good recovery rate in corona virus patients in the favipiravir compared to the other drugs⁷, favipiravir is considered as better for as a potential drug for this disease.

According to the literature search, there are published high performance liquid chromatography (HPLC) methods for determining favipiravir assay and impurities in active pharmaceutical ingredients^8-11and miscellaneous^12-14. In both of these methods, a gradient HPLC mode was used for chromatographic separation and the run time was 60 min. favipiravir is not officially available in any pharmacopoeia and there is still a need for validated HPLC and other methods to determine favipiravir in pharmaceutical dosages.

Simple, rapid and reliable ion pair extractive colorimetric method is developed for the determination of favipiravir. This method can be used for the routine analysis. In the proposed methods optimization and validation of this method are reported.

Structure of Favipiravir:

EXPERIMENTAL:

Instrumentation:

A Shimadzu -160 A double beam UV-Visible recording spectrophotometer with pair of 10mm matched quartz cell was used to measure absorbance of solutions.

A Shimadzu analytical balance was used.

Ammonium thiocynate, cobalt nitrate and chloroform of A.R. grade were used in the study.

Preparation of solutions:

Stock solutions of favipiravir (100μg/ml) were prepared in ethanol.

From these stock solutions, working standard solutions (10μg/ml) were prepared by diluting 10ml stock solution to 100μg/ml with ethanol.

Preparation of reagents:

Cobalt thiocynate was prepared by dissolving cobalt nitrate and ammonium thiocynate in 1:2 molar proportions in distilled water.

Experimental:

Into a series of separating funnels appropriate amount of the working standard drug solutions were pipetted out. To each funnel 2.1ml of cobalt thiocynate complex solution was added along with 10ml of chloroform to each funnel. The solutions were shaken for thorough mixing of the two phases and were allowed to stand for separation of the layers. The absorbance value of the chloroform layers were measured against their respective reagent blank at the wavelength of the maximum absorbance (λ max 618nm).

Estimation from tablets:

Twenty tablets of labelled claim 200mg of favipiravir were weighed accurately. Average weight of each tablet of favipiravir was determined. Tablets were crushed into fine powder. An accurately weighed quantity of powder equivalent to 10mg of favipiravir was transferred into a beaker and it was shaken with 50ml of ethanol and filtered. The filtrate and the washing were collected in a 100.0ml volumetric flask. This filtrate and the washing were diluted up to the mark with ethanol to obtain final concentration as 100μg/ml. A 10ml. of this solution was further diluted to give 10μg/ml.

Such solutions were further used for estimation of favipiravir respectively.

Appropriate aliquots of drug solution were taken. The individual assay procedures were carried out for the estimation of drug contents in tablets. The concentration of the drug in the tablets was calculated using calibration curve. Fig. no.1

Fig. No: 1. Calibration curve

The recovery experiment was carried out by standard addition method. The values of optical and regression terms of analysis are given in table no1.

Table 1: Values of results of optical and regression of drug

Parameter	Values
Detection Wavelength (nm)	618
Beer Law Limits (µg/ml)	1-12
Correlation coefficient(r²)	0.9999
Regression equation (y=b+ac)
Slope (a)	0.0005
Intercept (b)	0.006

RESULT:

The extractive spectrophotometric methods are popular due to their sensitivity in assay of the drug and hence ion pair extractive spectrophotometric methods have gain considerable attention for quantitative determination of many pharmaceutical preparations. These proposed methods are extractive spectrophotometric methods for

Table no 2: Results of recovery studies

Amount of Sample Added in (µg/ml)	Amount of Standard Added in (µg/ml)	Total amount recovered	Percentage recovery (%)	Standard deviation	Percentage of relative standard deviation (C.O.V.)
2	0	1.97619	98.80952	0.115011	5.81983
2	2	3.97619	99.40476	0.178174	4.481027
2	4	6.119048	101.9841	0.18545	3.030693
2	6	8.047619	100.5952	0.125988	1.565533
				Mean= 0.151156	Mean= 3.724271

the determination of favipiravir by using chloroform as solvent from its formulations i.e. tablets.

The colour ion –pair complexes are formed and are very stable. The working conditions of these methods were established by varying one parameter at time and keeping the other parameters fixed by observing the effect produced on the absorbance of the colour species. The various parameters involved for maximum colour development for these methods were optimized. The proposed methods were validated statistically and by recovery studies. The optical characteristics such as absorption maxima (nm), correlation coefficient (r) and were calculated and are also summarized in table I. Assay results of recovery studies are given in table no. 2.

Results are in good in agreement with labelled value. The percent recovery obtained indicates non interference from the common excipients used in the formulation.

DISCUSSION:

The reproducibility, repeatability and accuracy of these methods were found to be good, which is evidenced by low values of standard deviations. Colorimetric methods suggested in literature were applied in UV region, need costly reagents for development of chromogen and useful in higher concentration. The proposed methods are simple, sensitive, accurate, precise, and reproducible applicable to even very low concentration as compare to previous methods suggested in literature. They are directly applied to drug to form chromogen. Hence they can be successfully applied for the routine estimation of favipiravir in bulk and pharmaceutical dosage form even at very low concentration in formulation such as tablets. The strong recommendation is made here for the proposed methods for determination of favipiravir from its formulation i.e. tablets.

ACKNOWLEDGMENT:

Authors express sincere thanks to the Principal, D. G. Ruparel College for providing necessary facilities and encouragement for research work.

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Received on 15.03.2021 Modified on 12.05.2021

Asian J. Research Chem. 2021; 14(5):321-323.

DOI: 10.52711/0974-4150.2021.00054