A NEW RP-HPLC METHOD FOR SIMULTANEOUS ESTIMATION OF TOLCAPONE AND QUINAPRIL IN ITS PURE AND PHARMACEUTICAL DOSAGE FORM

A NEW RP-HPLC METHOD FOR SIMULTANEOUS ESTIMATION OF TOLCAPONE AND QUINAPRIL IN ITS PURE AND PHARMACEUTICAL DOSAGE FORM

Ayesha K. Begum ^* and Sabeela Mubashir

Department of Pharmaceutical Analysis, Shadan Women’s College of Pharmacy, Khairatabad, Hyderabad - 500004, Telangana, India.

ABSTRACT: A short selective, precise, accurate, and sensitive method for the estimation of Tolcapone and Quinapril was done by RP-HPLC. The assay of Tolcapone and Quinapril was performed with tablets, and the % assay was found to be 100.19 and 100.45, which shows that the method is useful for routine analysis. The linearity of Tolcapone and Quinapril was found to be linear with a correlation coefficient of 0.999 and 0.999, which shows that the method is capable of producing good sensitivity. The acceptance criteria of precision percent RSD should be not more than 2.0%, and the method show precision 0.2 and 0.7 for Tolcapone and Quinapril, which shows that the method is precise. The acceptance criteria of intermediate precision are RSD should be not more than 2.0%, and the method show precision 0.3 and 0.7 for Tolcapone and Quinapril, which shows that the method is repeatable when performed in different days also. The LOD and LOQ for Tolcapone were found to be 3.07 and 9.98, and LOD and LOQ for Quinapril were found to be 2.95 and 10.00. Therefore, this method can be adopted to estimate Tolcapone as well as Quinapril in other pharmaceutical formulations.

Tolcapone and Quinapril, Validation, stability-indicating method, degradation products

INTRODUCTION: Tolcapone is a drug that inhibits the enzyme catechol-O-methyl transferase (COMT) ¹. It is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa medication ². It is a yellow, odourless, non-hygro-scopic, crystalline compound. Tolcapone is soluble in organic solvents such as ethanol, DMSO, and dimethylformamide (DMF), which should be purged with an inert gas. Tolcapone is sparingly soluble in aqueous buffers ³. Tolcapone is a reversible inhibitor of catechol-O-methyltransferase (COMT; Ki= 0.27 nM for human recombinant COMT), an enzyme that degrades catecholamines, including dopamine and L-DOPA.

Tolcapone crosses the blood-brain barrier and can inhibit both peripheral and central COMT activity. By inhibiting COMT, tolcapone increases L-DOPA efficacy and reduces L-DOPA-induced motor complications in animal models of Parkinson’s disease ^{4, 5}.

Quinapril is the ethyl ester prodrug of the non-sulfhydryl angiotensin-converting enzyme inhibitor quinaprilat. It is used to treat hypertension and heart failure ^{6, 7}. ACE inhibitors are commonly used as first-line therapy in the treatment of hypertension, along with thiazide diuretics or beta-blockers ⁸. Quinapril is indicated for the treatment of hypertension and as an adjunct therapy in the treatment of heart failure. Quinapril prevents the conversion of angiotensin I to angiotensin II by inhibiting of angiotensin-converting enzyme and reduces bradykinin's breakdown. Reduced levels of angiotensin II lead to lower levels of PAI-1, reducing the risk of thrombosis, especially after myocardial infarction. Quinapril hydrochloride is white to off-white amorphous powder that is freely soluble in aqueous solvents ^{9, 10}.

The therapeutic efficacy of Quinapril can be increased when used in combination with Tolcapone. Only few methods were reported for the simultaneous estimation of tolcapone and quinapril by HPLC ^{11, 12}. Hence we had made an attempt to develop a simple, accurate and precise RP-HPLC method for the simultaneous estimation of tolcapone and quinapril.

MATERIALS AND METHODS: Gift samples of tolcapone and quinapril were received from pharma train lab, Hyderabad. KH₂PO₄ was purchased from Final chemicals, whereas water, methanol for HPLC, and orthophosphoric acid were purchased from LICHROSOLV, Merck.

Instrumentation: Waters HPLC (2695 separation module) was used for the separation of tolcapone and quinapril. UV/VIS spectrophotometer (LAB-INDIA UV 12.500⁺) was used for detection. Instruments such as; pH meter used was of Adwa - AD 10100, and the weighing machine was of Afcoset ER-1000A.

Preparation of Buffer and Mobile Phase:

Preparation of 0.1% OPA: Pipette 1ml of orthophosphoric acid dissolved in 1000 ml of HPLC water Ph was adjusted up to 3.0. The final solution was filtered through a 0.44 µm Membrane filter and sonicate it for 10 min.

Preparation of Mobile Phase: Accurately measured 300 ml (30%) of above buffer and 700 ml of Methanol HPLC (30%) were mixed and degassed in an ultrasonic water bath for 10 minutes and then filtered through 0.45 µ filter under vacuum filtration.

Diluent Preparation: The Mobile phase was used as the diluent.

Standard Solution Preparation: Accurately weigh and transfer 50 mg of Tolcapone and 20 mg of Quinapril working standard into a 100 ml clean, dry volumetric flask; add about 7 mL of Diluent and sonicate to dissolve it completely and make volume up to the mark with the same solvent. (Stock solution)

Further pipette 1.5 ml of the above stock solutions into a 10ml volumetric flask and dilute up to the mark with diluent.

Sample Solution Preparation: Accurately weigh 10 tablets crush in mortor and pestle, and transfer equivalent to 50 mg of Tolcapone and 20 mg Quinapril sample into a 100 mL clean, dry volumetric flask; add about 7 mL of Diluent and sonicate it up to 15 mins to dissolve it completely and make volume up to the mark with the same solvent. Then it is filtered through a 0.45-micron Injection filter. (Stock solution)

Further pipette 1.5ml of Tolcapone and Quinapril from the above stock solution into a 10ml volumetric flask and dilute up to the mark with diluent.

Procedure: Inject 20 ml of the standard, sample into the chromatographic system and measure the areas for Tolcapone and Quinapril peaks and calculate the % Assay by using the formulae.

Experimental:

Optimized Chromatographic Conditions:

FIG. 3: STANDARD CHROMATOGRAM OF TOLCAPONE AND QUINAPRIL

System Suitability: All the parameters were evaluated by performing system suitability studies. The recorded responses for suitability studies are depicted in Table 1.

TABLE 1: RESULTS OF SYSTEM SUITABILITY PARAMETERS

TABLE 2: RESULTS OF LINEARITY OF TOLCAPONE AND QUINAPRIL

TABLE 3: RESULTS OF PRECISION FOR TOLCAPONE

TABLE 4: RESULTS OF PRECISION FOR QUINAPRIL

TABLE 5: ACCURACY (RECOVERY) DATA FOR TOLCAPONE

*Average of three determinations

TABLE 5: ACCURACY (RECOVERY) DATA FOR QUINAPRIL

*Average of three determinations

TABLE 7: RESULTS OF LOD

TABLE 8: RESULTS OF LOQ

Degradation Studies:

FIG. 6: CHROMATOGRAM SHOWING ACID DEGRADATION

FIG. 7: CHROMATOGRAM SHOWING BASE DEGRADATION

FIG. 8: CHROMATOGRAM SHOWING PEROXIDE DEGRADATION

FIG. 9: CHROMATOGRAM SHOWING THERMAL DEGRADATION

FIG. 10: CHROMATOGRAM SHOWING PHOTO DEGRADATION

TABLE 9: RESULTS FOR STABILITY OF TOLCAPONE AND QUINAPRIL

TABLE 10: RESULTS OF ASSAY FOR TOLCAPONE AND QUINAPRIL

SUMMARY AND CONCLUSION: From the above, it can be concluded that all validation parameters such as precision, accuracy, linearity and Ruggedness met the predetermined acceptance criteria as mentioned in ICH guidelines. The robustness limit for mobile phase variation and flow rate variation is well within the limit; the % degradation results are in limits. This shows that the method is having good system suitability and precision under a given set of conditions.

Hence, it can be concluded that the developed RP-HPLC method is accurate, precise, rapid, and selective and can be employed successfully for the estimation of tolcapone and quinapril in bulk and pharmaceutical dosage forms.

ACKNOWLEDGEMENT: The authors thankful to PharmaTrain Labs (A Division of HiQ Pharma Labs Pvt. Ltd), Hyderabad, India, for providing gift samples and also to the Department of Pharmaceutical Analysis, Shadan Women’s College of Pharmacy, Khairatabad, Hyderabad, Telangana, India for their encouragement.

CONFLICTS OF INTEREST: There are no conflicts of interest.

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    How to cite this article:

    Begum AK and Mubashir S: A new rp-hplc method for simultaneous estimation of tolcapone and quinapril in its pure and pharmaceutical dosage form. Int J Pharm Sci & Res 2021; 12(6): 3375-80. doi: 10.13040/IJPSR.0975-8232.12(6).3375-80.

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