DEVELOPMENT AND VALIDATION OF STABILITY INDICATING ASSAY METHOD FOR DETERMINATION OF LOXAPINE SUCCINATE IN CAPSULE DOSAGE FORM

DEVELOPMENT AND VALIDATION OF STABILITY INDICATING ASSAY METHOD FOR DETERMINATION OF LOXAPINE SUCCINATE IN CAPSULE DOSAGE FORM

Khushbu A. Thakor ^* and T. Y. Pasha

Department of Chemistry, Parul Institute of Pharmacy and Research, Parul University, Limda, Waghodia, Vadodara - 391760, Gujarat, India.

ABSTRACT: To develop and validate simple, selective, specific, sensitive and accurate stability indicating assay method by RP-HPLC for determination of Loxapine succinate in the capsule dosage form. Several trials are taken by changing mobile phase composition, and ratio and finally the drug was eluted on a C18 Purospher star (250 mm × 4.6 mm, 5 µm) column using mobile phase consisting of water: Methanol: Acetonitrile: TEA:: 40:10:50:1 ratio and pumped at flow rate of 1.0 ml/min using 10 µl injection volume at 254 nm. The Retention time of Loxapine succinate was found to be 10.783 ± 0.02 min. The calibration curve was linear over concentration range of 75-225 µg/ml (r² = 0.999). The accuracy of the method was estimated by recovery studies and % recovery was in a range of 98% to 102%. Stability of Loxapine succinate was studied under different stressed condition like acid, alkali, peroxide, thermal and photolytic conditions. The drug was degraded in all conditions except thermal and photolytic conditions. The developed method was validated as per ICH guidelines.

Loxapine succinate, RP-HPLC, ICH, Validation

INTRODUCTION: Loxapine succinate is a typical antipsychotic drug, member of dibenzoxazepine class and used to treat certain mental or mood disorders (such as schizophrenia). It is a dopamine antagonist and also serotonin 5-HT2 blocker. The exact mode of action of Loxapine succinate has not known. This drug helps in reducing aggression and hallucinations (such as hearing/ seeing things that are not occurred). Loxapine is present in capsules as the succinate salt ^{1, 2, 3}. Its IUPAC name is 8-chloro-6-(4-methyl piperazine-1yl)benzo[b][1,4] benzoxazepine. Its molecular weight is 445.9 gm/mole ^{4, 5}.

FIG. 1: CHEMICAL STRUCTURE OF LOXAPINE SUCCINATE ^{6, 7}

A literature search reveals that the following methods are reported viz. UV method, HPLC method, HPLC-MS/MS, GC-MS method ^{8, 9, 10, 11, 12, 13}. There is a need for developing stability indicating assay method in the capsule dosage form. So, the authors attempted to develop simple, sensitive, selective and specific stability indicating assay method for determination of Loxapine succinate in a capsule dosage form as per ICH guidelines ^{14, 15, 16, 17}.

MATERIALS AND METHODS:

Chemicals and Reagents: Loxapine succinate was provided as a gift sample by Hetero Drugs Ltd., Hyderabad, Andhra Pradesh, India. Capsule dosage form was procured from the local market. All the chemicals and reagents like methanol, acetonitrile, water were of HPLC grade and were procured from Merck Specialties Pvt. Ltd., Mumbai, India.

Instrumentation: HPLC waters Alliance 2695 series, equipped with an autosampler, temperature control, and auto-injector with the capacity to inject 5 µl to 500 µl with PDA detector. Waters HPLC system is equipped with Empower 2 software.

METHODS:

Experimental Conditions: The HPLC system was operated isocratically at a flow rate of 1.0 ml/min at 30°C column temperature for 30 min. The mobile phase was found to be most suitable for analysis was water: Methanol: Acetonitrile: TEA:: 40:10:50:1 ml which was filtered through 0.45 µm PVDF filter. Detection was carried out at 254 nm. The mobile phase is used as a diluent.

Preparation of Standard Solution of Loxapine Succinate: Accurately weighed and Transfer 60 mg of Loxapine succinate into 200 ml volumetric flask. Add diluent about 70% of flask volume. Sonicate to dissolve and volume made up to mark with diluents. Pipette out 10 ml of the stock solution into 20 ml volumetric flask; volume made up to mark with diluents (150 µg/ml). Results were shown in Fig. 3 and Table 1.

Calibration Curve of Loxapine Succinate: Transfer accurately weighed 30 mg of Loxapine into 50 ml volumetric flask. Add 5 ml of diluent. Sonicate to dissolve, volume made up to mark with diluents (600 µg/ml). from 600 µg/ml appropriate aliquots like 2.5 ml, 4 ml, 5 ml, 6 ml, and 7.5 ml taken into 20 ml volumetric flask and made up to mark with diluents, so the resulting solutions become 75, 120, 150, 180 and 225 µg/ml.

Preparation of Sample Solution of Loxapine Succinate: Open 20 capsules and mix and blend powder. Accurately weighed and transferred powder equivalent to 75 mg of loxapine succinate into 50 ml volumetric flask. Add diluent about 50% of flask volume. Sonicate for 30 min with intermitting shaking, volume made up to mark with diluent. Solution filter using 0.45 µm PVDF filter after 5 ml of filtrate discarded. Pipette out 5 ml of the stock solution into 50 ml volumetric flask; volume made up to mark with diluents (150 µg/ml). Results were shown in Fig. 3 and Table 2.

Method Development and Optimization: During the process of method development, several trials were taken using different aqueous phase, organic phase, different column, good peak shape was observed when using the C18 Purospher star (250 mm × 4.6 mm, 5 µm) column and water: Methanol: Acetonitrile: TEA:: 40:10:50:1 as mobile phase at a flow rate of 1.0 ml/min. for the quantitative analytical purpose, the wavelength was selected as 254 nm.

Initially, standard solution 150 µg/ml was injected into column five times and the retention time of Loxapine succinate was found to be 10.783 min. Then the same concentration of sample solution was injected into the system and the resulting chromatogram was recorded.

Method Validation: The developed method was validated as per the USP and ICH guideline Q2(R1).

Specificity: The specificity of the method was evaluated to ensure there was no interference from the placebo components or from products resulting from forced degradation.

Forced Degradation Studies:

Acid Degradation Sample: Accurately weighed and transferred Loxapine succinate equivalent to 75 mg of loxapine into 50 ml volumetric flask. Add 10 ml 1N HCl solution. Keep solution at room temperature for 5 h. After 5 h neutralize with 10 ml of 1N NaOH. Add diluent about 50% of flask volume. Sonicate for 30 min with intermittent shaking, volume made up to mark with diluent. Solution filter using 0.45 µm PVDF filter after 5 ml of filtrate discarded. Pipette out 5 ml of the stock solution into 50 ml volumetric flask, volume made up to mark with diluent. Results are shown in Fig. 4 and Table 3.

Base Degradation Sample: Accurately weighed and transferred Loxapine succinate equivalent to 75 mg of loxapine into 50 ml volumetric flask. Add 10 ml 0.1N NaOH solution. Keep solution at room temperature for 5 h. After 5 h neutralize with 10 ml of 0.1N HCl. Add diluent about 50% of flask volume. Sonicate for 30 min with intermittent shaking, volume made up to mark with diluent. Solution filter using 0.45 µm PVDF filter after 5ml of filtrate discarded. Pipette out 5 ml of the stock solution into 50 ml volumetric flask; volume made up to mark with diluent. Results are shown in Fig. 5 and Table 4.

Peroxide Degradation Sample: Accurately weighed and transferred Loxapine succinate equivalent to 75 mg of loxapine into 50 ml volumetric flask. Add 10 ml 30% H₂O₂ solution. Keep solution at room temperature for 5 h. Add diluent about 50% of flask volume. Sonicate for 30 min with intermittent shaking, volume made up to mark with diluent. Solution filter using 0.45 µm PVDF filter after 5 ml of filtrate discarded.  Pipette out 5 ml of the stock solution into 50 ml volumetric flask; volume made up to mark with diluent. Results are shown in Fig. 6 and Table 5.

Thermal Degradation Sample: Accurately weighed and transferred Loxapine succinate equivalent to 75 mg of loxapine into 50 ml volumetric flask. Keep at 85 ºC for 7 days in vaccum oven. Add diluent about 50% of flask volume. Sonicate for 30 min with intermittent shaking, volume made up to mark with diluent. Solution filter using 0.45 µm PVDF filter after 5ml of filtrate discarded.  Pipette out 5 ml of the stock solution into 50 ml volumetric flask; volume made up to mark with diluent. Results are shown in Fig. 7 and Table 6.

Photolytic Degradation Sample: Put Capsule Sample into UV Chamber for 7 days to complete one ICH cycle accurately weighed and transferred Loxapine succinate equivalent to 75 mg of loxapine into 50 ml volumetric flasks. Add diluent about 50% of flask volume. Sonicate for 30 min with intermittent shaking, volume made up to mark with diluent. Solution filter using 0.45 µm PVDF filter after 5 ml of filtrate discarded. Pipette out 5 ml of the stock solution into 50 ml volumetric flask; volume made up to mark with diluent. Results are shown in Fig. 8 and Table 7.

Results for % degradation and % assay after degradation were shown in Table 8.

Linearity: The concentration range 75, 120, 150, 180 and 225 µg/ml was injected into the system. Linearity was evaluated by linear regression analysis which was obtained by plotting the Loxapine succinate against peak area. The regression coefficient was found to be 0.999. linearity data were shown in Table 9.

Accuracy: The accuracy of the method was determined at three different concentration levels 50%, 100% and 150% of target concentration (150 µg/ml) by recovery studies. The recovery studies were carried out in triplicate on composite blend collected from 20 capsules of Loxapine succinate and analyzed as per the proposed method.

Individual recovery was found to be in the range of 97.0% to 103% and mean recovery was found to be in a range of 98% to 102%. The results of accuracy revealed that the method was accurate. Results for accuracy were shown in Table 10.

Precision: Repeatability study was carried out by estimating six determination of Loxapine succinate with 150 µg/ml. The intraday precision study of loxapine succinate was carried out by estimating the peak response for three determination on the same day with 120 µg/ml, 150 µg/ml and 180 µg/ml concentration and interday precision study of Loxapine succinate was carried out by estimating the peak response for three determination on different days using 120 µg/ml, 150 µg/ml and 180 µg/ml.

SD and % RSD was calculated and found to be within limits. The results of the precision study revealed that the method was precise as shown in Table 11, 12, 13.

Robustness: The Robustness of the analytical method was determined by analysis of aliquots from the homogenous sample by varying the chromato-graphic parameters like change in flow rate, change in column oven temperature, change in mobile phase ratio, change in wavelength, change in HPLC column and their impact on retention time and peak area were studied.

The method was demonstrated to be robust over an acceptable working range of its HPLC operational parameters. Results are shown in Table 14.

RESULTS AND DISCUSSION:

TABLE 1: STANDARD LOXAPINE SUCCINATE

TABLE 2: FOR SAMPLE LOXAPINE SUCCINATE

TABLE 3: FOR ACID DEGRADATION

TABLE 4: FOR BASE DEGRADATION

TABLE 5: FOR PEROXIDE DEGRADATION

TABLE 6: FOR THERMAL DEGRADATION

FIG. 6: CHROMATOGRAM FOR LOXAPINE SUCCINATE- PEROXIDE DEGRADATION

TABLE 7: FOR PHOTOLYTIC DEGRADATION

TABLE 8: FORCED DEGRADATION STUDIES FOR LOXAPINE SUCCINATE

TABLE 9: FOR LOXAPINE SUCCINATE- LINEARITY

TABLE 10: RECOVERY STUDIES FOR LOXAPINE SUCCINATE

TABLE 11: REPEATABILITY STUDY

TABLE 12: INTRADAY PRECISION

TABLE 13: INTERDAY PRECISION

TABLE 14: ROBUSTNESS

TABLE 15: ASSAY OF CAPSULE DOSAGE FORM (LOXAPINE SUCCINATE)

CONCLUSION: This study presents simple and validated stability-indicating HPLC method for the determination of Loxapine succinate in the presence of its degradation products. The developed method is specific, accurate, precise and robust. All the peaks of the degradation products formed during forced degradation studies were well separated from the analyte peak. Hence, the developed method can be used for routine analysis for the determination of Loxapine succinate in capsule dosage forms.

ACKNOWLEDGEMENT: The authors express sincere thanks to Hetero Drugs Ltd., Hyderabad, Andhra Pradesh ­­­­­­­­­­­­for providing a gift sample of Loxapine succinate and Umedica Pvt. Ltd., Vapi for providing necessary facilities to carry out the research work.

CONFLICT OF INTEREST: The authors reveal that there are no conflicts of interest.

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    How to cite this article:

    Thakor KA and Pasha TY: Development and validation of stability indicating assay method for determination of loxapine succinate in capsule dosage form. Int J Pharm Sci & Res 2019; 10(5): 2362-68. doi: 10.13040/IJPSR.0975-8232.10(5).2362-68.

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