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Development and validation of stability-indicating RP-HPLC method for the determination of Levocabastine HCl in bulk drug and in ophthalmic suspensions
⁎Corresponding author. Address: 15 Moasbbin Omeir St., Baramkeh, Damascus, Syria. Tel.: +963 (0)988352678. hashim.ani85@gmail.com (Hashem AlAani)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
A new stability-indicating RP-HPLC assay method was developed and validated for quantitative determination of Levocabastine HCl in bulk drugs and in ophthalmic suspensions in the presence of degradation products generated from forced degradation studies. The system consisted of Thermo Hypersil CPS column (CN column) (150 mm, 4.6 mm i.d., 5 μm), and the detection was performed at 210 nm. The mobile phase was a mixture of ethanol–ammonium acetate (pH 3.0; 0.05 M) (40:60, v/v) pumped at 25 °C with a flow rate of 1.2 mL/min. The calibration curve was linear from 50 to 200 μg/mL with R2 > 0.999. The detection limit (DL) and quantitation limit (QL) were 0.9 and 3 μg/mL, respectively. Accuracy (mean recovery: 100.11%) and precision were found to be satisfactory. Stress conditions including acid, alkali hydrolysis, water stress, oxidation, photolysis, and heat were applied. The degradation products did not interfere with the detection of Levocabastine HCl, thus the method can be considered as a stability indicating method. The proposed method can be used for quality control assay of Levocabastine HCl in bulk drug and in ophthalmic suspensions and for the stability studies as a result of the ability of the method to separate Levocabastine HCl from its degradation products and excipients.
Keywords
Levocabastine HCl
RP-HPLC method
Ophthalmic suspensions
Validation
Stability-indicating method
1 Introduction
Levocabastine HCl is chemically (3S, 4R)-1-[cis-4-cyano-4-(4-fluorophenyl) cyclohexyl]-3-methyl-4-phenylpiperidine-4- carboxylic acid monohydrochloride (BP, 2009). (See Fig. 1).
Levocabastine, a piperidine derivative, is a long-acting and potent antihistamine (Sweetman, 2009). It is an antiallergic medication. It inhibits processes in the body that cause allergic symptoms after exposure to an allergen.
Levocabastine ophthalmic is used to treat ocular (eye) symptoms of allergic conditions, such as inflammation, itching, watering, and burning (www.rxlist.com/livostin-drug/patient-images-side-effects.htm, 2013).
Very few methods have been reported for the determination of Levocabastine HCl in the bulk drug by volumetric titration (BP, 2009; USP, 2011). Also, very few methods have been described for the determination of related substances and organic impurities in the Levocabastine HCl in bulk drug using the capillary electrophoresis technique (BP, 2009; USP, 2011).
According to Current Good Manufacturing Practices, all drugs must be tested with a stability-indicating assay method before release. To date, no stability indicating HPLC assay method for the determination of Levocabastine HCl is available in the literature. It was felt necessary to develop a stability-indicating liquid chromatography (LC) method for the determination of Levocabastine HCl as bulk drug and as pharmaceutical dosage forms and to separate the drug from the degradation products under the International Conference on Harmonization (ICH) suggested conditions (hydrolysis, oxidations, photolysis and thermal stress) (Bakshi and Singh, 2002; ICH, 2003). Therefore, the principal objective of this study was to develop a new, simple, economical, precise, and reproducible stability indicating RP-HPLC method with a wide linear range and good sensitivity for assay of Levocabastine HCl in the bulk drug and in the pharmaceutical dosage forms (ophthalmic suspensions).
2 Materials and methods
2.1 Chemicals and solutions
Levocabastine HCl reference substance was purchased from European Pharmacopoeia (EDQM), batch No. 1.1. Levocabastine HCl bulk drug (purity 99.6%) was obtained from Yonsung (Korea). Eye drop, (Livostin 0.05%, batch No. ACB0D00, Johnson & Johnson S.p.A, Italy), was purchased from the market. Ethanol used was of HPLC grade. All other reagents used in this study were of AR grade. Purified water was used for making the solutions.
2.2 Chromatographic conditions
Separations were performed with a HPLC (LA Chrom ELITE, VWR Hitachi, Germany, equipped with L-2130 pump, L-2200 auto sampler, L-2300 column oven, and UV photo diode array detector L-2455). The out-put signal was monitored and processed using EZ Chrom ELITE software.
HPLC system used for reproducibility was a Knauer, Germany, equipped with a 1050 pump, 4050 column oven, and UV photo diode array detector 2850.
The chromatographic column used was Thermo Hypersil CPS column (CN column) (150 mm, 4.6 mm i.d., 5 μm). The mobile phase comprised of a mixture of ethanol–ammonium acetate (pH 3.0; 0.05 M) (40:60, v/v). The pH of the ammonium acetate solution was adjusted to 3.0 with orthophosphoric acid. Solution of 0.05 M NaOH was used as diluent.
The mobile phase was filtered through 0.45 micron membrane filter, degassed in ultrasonic bath and pumped from the respective solvent reservoir to the column at a flow rate of 1.2 mL/min. The column temperature was maintained at 25 °C and the detection wavelength was 210 nm. The injection volume was 20 μL. The column was equilibrated for 60 min prior to the injection of the drug solution.
2.3 Preparation of standard solution
25 mg of Levocabastine HCl Reference Standard was accurately weighed, transferred in a 25 mL volumetric flask, dissolved and diluted to 25 mL with the diluent. From this stock solution, 1 mL was transferred in a 10 mL volumetric flask and diluted with the diluent. This final solution contained 100 μg/mL of Levocabastine HCl.
2.4 Preparation of sample solution
The commercially available eye drop contains 0.05% suspension of Levocabastine (0.5 mg/mL), as Levocabastine HCl. From this well shaken eye drop, 2 mL suspension was carefully transferred in a 10 mL volumetric flask containing about 4 mL of the diluent and sonicated for 5 min to obtain a clear solution. Then the solution was diluted to volume with the same diluent. A sample was filtered using a 0.45 μm nylon syringe filter. The concentration obtained was 100 μg/mL of Levocabastine.
2.5 Calculation
The quantity of Levocabastine (as percentage) in the eye drop was calculated by the following formula:
In which
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AU peak response from the sample solution
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AS peak response from the standard solution
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Mr1 molecular weight of Levocabastine, 420.52
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Mr2 molecular weight of Levocabastine HCl, 457.00
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P potency of reference standard (as percentage).
2.6 Method validation
The proposed RP-HPLC method was validated as per ICH guidelines (ICH, Q2A, 1995; ICH, Q2B, 1996; ICH, Q2 (R1), 1995).
2.7 Procedure for forced degradation study
2.7.1 Diluent
Solution of 0.05 M NaOH.
2.7.2 Stock solution
200 mg of Levocabastine HCl was accurately weighed, transferred in a 200 mL volumetric flask, dissolved and diluted to 200 mL with the diluent. This solution contained 1 mg/mL of Levocabastine HCl.
2.7.3 Water stress degradation
20 mL of water was added to 10 mL of stock solution and was kept at 80 °C for about 3 h in water bath; the solution was allowed to attend ambient temperature. Then volume was made up to 100 mL with the diluent to achieve final concentration of 100 μg/mL.
2.7.4 Acidic degradation
20 mL of 3 M HCl was added to 10 mL of stock solution and was kept at 80 °C for about 3 h in water bath; the solution was allowed to attend ambient temperature. Then solution was neutralized by 20 mL of 3 M NaOH and volume was made up to 100 mL with the diluent to achieve final concentration of 100 μg/mL.
2.7.5 Alkali degradation
3,5,10, and 20 mL of 3 M NaOH were added to four containers, each contained 10 mL of stock solution and were kept at 80 °C for about 3 h in water bath, the solutions were allowed to attend ambient temperature. Then solutions were neutralized by sufficient amount of 3 M HCl (3, 5, 10, and 20 mL) and volume was made up to 100 mL with the diluent to achieve final concentration of 100 μg/mL.
2.7.6 Oxidative degradation
2 and 5 ml of 3% H2O2 and 1,2,5, and 20 mL of 30% H2O2 were added to six containers, each contained 10 mL of stock solution and were kept at 80 °C about 3 h in water bath, the solutions were allowed to attend ambient temperature. Then volume was made up to 100 mL with the diluent to achieve final concentration of 100 μg/mL.
2.7.7 Thermal degradation
10 mL of stock solution was kept at 80 °C for one week. The solution was allowed to attend ambient temperature. Then volume was made up to 100 mL with the diluent to achieve final concentration of 100 μg/mL.
2.7.8 Photodegradation
10 mL of stock solution was exposed to white light for one week. Then volume was made up to 100 mL with the diluent to achieve final concentration of 100 μg/mL.
2.8 Note
Solutions for water stress, acidic, alkali, oxidative, and thermal degradation were kept in the dark in order to avoid the possible effect of light.
3 Results and discussion
3.1 System suitability
System suitability is the checking of a system to ensure system performance before or during the analysis of unknowns. System suitability tests are an integral part of method development and are performed to evaluate the behavior of the chromatographic system. Capacity factor (k′), plate number (N), tailing factor (T), and RSD were evaluated for five replicate injections of the drug at a concentration of 100 μg/mL. The results given in Table 1 were within acceptable limits (FDA, 1994).
| Property | Values | Required limits |
|---|---|---|
| RSD of peak area | 0.241 | RSD ⩽ 1% for n ⩾ 5 |
| RSD of retention time | 0.059 | RSD ⩽ 1% for n ⩾ 5 |
| Tailing factor (T) | 1.48 | T < 2 |
| Capacity factor (k′) | 2.66 | k′ > 2 |
| Theoretical plate (N) | 2630 | plate N > 2000 |
3.2 Method validation
3.2.1 Specificity
Specificity is the ability to assess unequivocally the analyte in the presence of components which may be expected to be present. Typically these might include impurities, degradants, and matrix components (USP, 2007, General chapter <1225>).
It was clear that no peak was observed in the chromatogram of placebo solution at the retention time of Levocabastine HCl. (Figs. 2 and 3).
Also, degradation studies showed that the degradation products did not interfere with the detection of Levocabastine HCl. The peak purity spectra of Levocabastine HCl were recorded using a PDA detector. Peak purities from sample solutions were >0.990. Peak purity >0.990 indicates method specificity (Panchal and Suhagia, 2011).
3.2.2 Accuracy
To study the reliability, the suitability, and the accuracy of the method, recovery experiments were carried out. Known quantities of the pure drug were added to the placebo to make samples at the levels of 50%, 100%, and 200%, and were assayed by the proposed method. Accuracy was calculated as the percentage of recovery and the results are shown in Table 2.
| Level of addition (%) | Concentration (μg/ml) | Recovery (%) |
|---|---|---|
| 50 | 50 | 101.78 |
| 100 | 100 | 99.36 |
| 200 | 200 | 99.19 |
| Mean recovery = 100.11% |
3.2.3 Precision
The precision was demonstrated at three levels: repeatability, intermediate precision, and reproducibility (between laboratories’ precision). Each level of precision was investigated by 3 sequential replicate of injections of three concentrations of 50, 100 and 200 μg/mL. The precision was expressed as relative standard deviation (RSD) or coefficient of variation (CV). The results of three levels of precision are shown in Table 3.
| Precision | Results | ||
|---|---|---|---|
| Concentration (μg/ml) | RSD of peak Area | RSD of Retention time | |
| Repeatability | 50 | 1.514 | 0.064 |
| 100 | 1.470 | 0.224 | |
| 200 | 1.325 | 0.113 | |
| Intermediate precision | 50 | 1.107 | 0.207 |
| 100 | 1.359 | 0.066 | |
| 200 | 0.868 | 0.042 | |
| Reproducibility | 50 | 1.256 | 0.149 |
| 100 | 1.258 | 0.256 | |
| 200 | 0.993 | 0.094 | |
3.2.4 Detection limit (DL) and quantitation limit (QL)
Ratios of 3:1 and 10:1 signal-to-noise were considered acceptable for estimation of the DL and QL, respectively (Ravichandran et al., 2010). So, the limit of detection and the limit of quantitation were determined to be 0.9 and 3 μg/mL, respectively.
3.2.5 Linearity and range
The linearity of measurement was evaluated by analyzing different concentrations of the standard solutions of the Levocabastine HCl. Calibration curve was constructed by plotting average peak area against concentration and then the regression equation was computed. The summary of linearity parameters is shown in Table 4 and Fig. 4. As demonstrated in Fig. 4, the calibration curve covers concentrations of 50% to 200% of the test concentration (50 to 200 μg/mL).
| Linearity parameter | Results |
|---|---|
| Linearity range | 50 to 200 μg/mL |
| Correlation coefficient | 0.99927 |
| Slope | 992 |
| Y Intercept | 4243 |
3.2.6 Ruggedness and robustness
The ruggedness or the degree of reproducibility of the test results in different laboratories was demonstrated by the analysis of the same sample under different conditions of laboratories, analysts, instruments, lots of columns and time.
The robustness of the analytical procedure which is the measure of method’s capacity to remain unaffected by small, but deliberate, variations in method parameters is shown in this study. Robustness (Table 5) was performed in 100% test concentration (100 μg/mL) and was explored using mobile phase composition, mobile phase pH, flow rate, column temperature, wave length, and injection volume.
| Parameter | Variation | Observed value | ||||
|---|---|---|---|---|---|---|
| RSD% of area | RSD% of R.T | Tailing factor (T) | Capacity factor (k′) | Theoretical plate (N) | ||
| Flow rate | 1 mL/min | 0.948 | 0.562 | 1.48 | 2.70 | 2982 |
| 1.4 mL/min | 0.431 | 0.079 | 1.46 | 2.47 | 2474 | |
| Injection volume | 10 μL | 0.624 | 0.056 | 1.44 | 2.58 | 2731 |
| 30 μL | 0.282 | 0.046 | 1.51 | 2.62 | 2403 | |
| M. Phase composition | 45% ethanol | 0.784 | 0.072 | 1.43 | 2.08 | 2344 |
| 35% ethanol | 0.698 | 0.855 | 1.58 | 4.01 | 2539 | |
| pH of M. Phase | 2.8 | 0.814 | 0.066 | 1.49 | 2.84 | 2684 |
| 3.2 | 0.466 | 0.103 | 1.43 | 2.23 | 2644 | |
| Column temperature | 20 °C | 0.596 | 0.062 | 1.54 | 2.72 | 2501 |
| 30 °C | 0.406 | 0.372 | 1.47 | 2.15 | 2377 | |
| Wave length | 205 nm | 0.729 | 0.069 | 1.49 | 2.66 | 2506 |
| 215 nm | 0.549 | 0.066 | 1.48 | 2.69 | 2579 | |
3.3 Mobile phase stability
The stability of the mobile phase was evaluated, so the mobile phase was stored at 4–8 °C for 1 week. The aged mobile phase was compared using a freshly prepared one. The mobile phase was stable up to 1 week at 4–8 °C.
3.4 Standard solution stability
The stability of the standard solution was tested at intervals of 24, 48 h and 1 week at ambient temperature. There were no significant changes in the peak area, retention time, and symmetry of the peak of Levocabastine HCl after 48 h. These results indicate that the standard solution was stable for 48 h at ambient temperature. After one week, about 1% change of peak area of Levocabastine HCl was obtained, and degradation was observed. Fig. 5 shows the chromatogram of standard solution after 1 week.
3.5 Analysis of marketed products
The validated method was applied for the analysis of Levocabastine eye drops from two different manufacturers. In both cases assay obtained was more than 99%. Results are summarized in Table 6.
| Marketed formulation | Labeled amount (mg/mL) | Amount found % |
|---|---|---|
| Livostin 0.05% | 0.5 | 101.17 |
| Local eye drop | 0.5 | 99.62 |
3.6 Result of forced degradation experiments
When stress conditions were applied to Levocabastine HCl, the HPLC results showed that there was no interference between the tested drug and the degradation products. Peak purity results greater than 0.990 indicate that the Levocabastine HCl peak is homogeneous in all stress conditions tested thus establishing the specificity and confirming the stability indicating power of the assay method. Table 7 indicates the extent of degradation, peak purity and assay of Levocabastine HCl under various stress conditions. It was observed that the drug showed extensive degradation in oxidative condition, alkali hydrolysis, and thermal. Figs. 6–18 show the chromatograms obtained after degradation under different stress conditions.
| Stress conditions | Time (h) | Assay of active substance (%) | Peak puritya |
|---|---|---|---|
| Water stress/80 °C | 3 | 98.57 | 1.000 |
| 3 M HCl/80 °C/20 mL | 3 | 99.89 (No degradation) | 1.000 |
| 3 M NaOH/80 °C/20 mL | 3 | 8.48 | 1.000 |
| 3 M NaOH/80 °C/10 mL | 3 | 11.05 | 0.998 |
| 3 M NaOH/80 °C/5 mL | 3 | 31.14 | 1.000 |
| 3 M NaOH/80 °C/3 mL | 3 | 45.71 | 0.999 |
| 30% H2O2/80 °C/20 mL | 3 | (Full degradation) | – |
| 30% H2O2/80 °C/5 mL | 3 | (Full degradation) | – |
| 30% H2O2/80 °C/2 mL | 3 | Below quantitation limit | – |
| 30% H2O2/80 °C/1 mL | 3 | Below quantitation limit | – |
| 3% H2O2/80 °C/5 mL | 3 | 5.43 | 0.991 |
| 3% H2O2/80 °C/2 mL | 3 | 25.90 | 1.000 |
| Thermal/80 °C | 1 week | 25.62 | 1.000 |
| Photo degradation/white light | 1 week | 98.35 | 1.000 |
4 Conclusion
The present developed method is sensitive, rapid, robust, precise and accurate. Application of this method for the analysis of eye drops shows that neither the degradation products nor the excipients, interfere with the analytical determination. This indicates that the proposed method could be used as a stability-indicating method for the determination of Levocabastine HCl either in bulk powder or in pharmaceutical formulations (ophthalmic suspensions).
Acknowledgements
The authors thank the quality control team in Diamond Pharma Pharmaceutical Company especially Mr. Fares Dardar for the support.
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