INTRODUCTION:

As shown in Figure 1, Cobicistat is a pharmacokinetic enhancer that has gained approval as a booster to be co-administered with antiretroviral drugs for HIV/AIDS therapy¹.Unlike other boosters like ritonavir, cobicistat has no antiviral activity though it boosts the pharmacokinetics of administered drugs by inhibiting CYP3A enzymes². This inhibition results in higher plasma levels of drugs that are metabolized by CYP3A enzyme thus enhance the therapeutic effect of those drugs. For this reason, the quality and purity of cobicistat is very important since it is a component of fixed-dose combination products³. For this reason, the quality and purity of cobicistat is very important since it is a component of fixed-dose combination products³.

Impurities in pharmaceutical compounds can be from the synthesis of raw materials, intermediates, degradation products and processing. These impurities can influence the safety and effectiveness of drugs that can cause negative side effects. Hence, the need to perform an in-depth analysis of impurities has become mandatory for the registration of pharmaceutical drugs. Impurity profiling therefore entails the assessment of these unwanted species in order to keep their levels below the set regulatory standards such as the ICH Q3A and Q3B⁴.

Figure 1: Chemical Structure of Cobicistat

Moreover, most of the drugs such as cobicistat have chiral centers leading to the formation of stereoisomers; these are enantiomers. Although impurity profiling and chiral purity assessment are significant for cobicistat, the existing analytical techniques may not be sensitive or specific enough for a detailed study^5,8. In this present work, it is proposed to design and optimize a new analytical technique for the determination of impurities and enantiomeric composition of cobicistat. The method development process includes the chromatographic conditions’ optimization^9,11. The assay of the developed method is performed as per ICH guidelines and the parameters studied are Linearity, Accuracy, Precision, LOD, LOQ and Robustness¹². These validation parameters are important to prove that the method can be applied for daily QC and to meet regulatory requirements^13,14.

Experimental Work:

Material:

Gift sample of Cobicistat was received from Shreya scientific Chemicals, India. Acetonitrile used in the present study was of HPLC grade and was obtained from Merck, India. Potassium dihydrogen phosphate, Dipotassium hydrogen phosphate and Orthophosphoric acid used in the preparation of the sample were of analytical reagent grade obtained from Merck, India. High pure water prepared with the help of Millipore Milli Q plus purification system.

Instrumentation:

The LC system that was used for method development, forced degradation studies, and method validation was Waters, alliance 2695 HPLC system having UV/PDA detector with Empower chromatography software or its equivalent.

Method Development:

Chromatographic conditions:

The chromatographic column adopted was from Waters using symmetry C18 (250mm x 4.7mm, 3.0μ). The mobile phase consists of a mixture Mobile phase-A: Mobile phase-B: Buffer: Methanol: Acetonitrile: Tetrahydrofuran in the ratio of (55:20:12:13 v/v). The mobile phase was pumped from the solvent reservoir through to the column with a flow rate of 0.9ml/min for 65 min and the column temperature was held at 450C. As for the injection volume, it was 10(μl). Mobile phase was used as diluents in preparation of the standard and test samples as described in the literature¹⁵. All impurities were prepared in diluent, and cobicistat was prepared individually in diluent at 0.1% level solution and pass through the HPLC-PDA detector. The PDE of Cobicistat and its impurities are at a maximum of 258nm.Therefore, the development studies were carried forward to be attained at 258nm¹⁶.

Preparation of Standard solution:

For the different analytical methods used in this study, preparation of the following solutions was done^17,18. Transferring to make a dilute orthophosphoric acid solution. Into 25mL volumetric flask, 0mL of orthophosphoric acid was pipetted and diluted to 10mL with water and then made up to the mark with water and mixed well¹⁹. Thus, a diluent buffer was made by dissolving. Dissolve 74g of di-potassium hydrogen phosphate in 1000mL of water, and then adjust the pH of the solution to 7.00±0.05 with the dilute orthophosphoric acid solution, and filtering through. 0.45μm nylon membrane filter, and degassing. The diluent was a degassed mixture of acetonitrile and the diluent buffer in a 1: At the1 v/v ratio²⁰. Another buffer was prepared by dissolving 2.72g of potassium dihydrogen phosphate dissolved in 1000ml of water and the pH of the solution was brought down to 2.20±0.05 with the dilute orthophosphoric acid solution and the filtrate was collected after filtering through Whatmans filter paper of grade 0.45μm nylon membrane filter and degassing. The mobile phases used included Buffer for Mobile phase-A and a mixture of Buffer, Methanol, Acetonitrile, and Tetrahydrofuran in the ratio of 55: The ratio of the v/v/v/v used in the preparation of Mobile phase-B is 20:12:13²¹.

Reference Solution:

About 25.0mg of Cobicistat Sodium standard is taken and quantitatively transferred in to a 100mL volumetric flask. It is then dissolved in 50mL of diluent and then the volume is made up to the required mark using diluent with adequate shaking. From this solution, 1. This means, 0mL of the preparation is taken and mixed with 50mL of diluent and from this 5. To obtain the final concentration, 0mL of the previously diluted solution is diluted 1: 50 with diluent while mixing well in each step ²².

Cobicistat and its impurities:

Pharmaceutical substances’ impurity profiling is critical since it determines the safety and efficacy of the drugs ²³. The impurities that may be found in Cobicistat, an antiretroviral drug used in the treatment of HIV infection include; each of them has to be defined, measured and regulated in compliance with the requirements of the pertinent legislation^24,26.

Forced degradation study:

To check that the developed HPLC method is stability indicating, samples of Cobicistat sodium were prepared were affected by such treatments as acid, base, oxidation, light and heat. To analyse the degraded samples, a photodiode array detector was used as indicated by the literature²⁷.

a) Acid and Alkaline breakdown:

For the study on forced degradation investigation in an acidic medium of Cobicistat, the medication was dissolved to arrive at the required concentration in 0. 1N HCl solution. The deterioration solution was heat treated at 70ºC for 24hours to enhance deterioration of the interfaces. Subsequently, to have a final concentration of 100mcg/ml, a part of the deteriorated solution was taken in a 10ml volumetric flask to which adequate volume was added to the volumetric mark with 0.75N and 1.5N HCl. After the storage of the solution at room temperature for 2hours, the solution was neutralized using the correct base. For HPLC analysis the final concentration was 10mcg/ml, therefore a portion of the neutralized solution was diluted to this concentration with the mobile phase. Equally, 1 N NaOH was used to cause deterioration in an alkaline environment²⁸.

a) Oxidative force degradation:

For the oxidative degradation, 10ml volumetric flask was prepared with hydrogen peroxide (3.0%, 10%) up to the mark level with aliquot of the stock solution to obtain 100mcg/ml as the final concentration. The flask was left open to air at room temperature for 2 hours. Therefore, a 10mcg/ml final concentration was obtained through dilution of an adequate amount of the mentioned solution with mobile phase²⁹.

c. Thermal Force degradation studies:

Thermal stress degradation for Cobicistat was done where API was exposed to dry heat at 70ºc for 24hours. After heating, the sample was allowed to cool to room temperature and then made up to 10ml with the suitable solvent. The solution was then diluted with the mobile phase to give a concentration of 10mcg/ml for the HPLC analysis³⁰.

RESULT AND DISCUSSIONS:

HPLC Method development and Optimization:

The analytical procedure employed a Waters Symmetry C18 column (250mm x 4.7mm, 3.0µm) kept at room temperature to achieve efficient separation, focusing on the accurate quantification of Cobicistat. Optimization involved refining the mobile phase composition, pH, and flow rate, particularly using stressed samples to enhance method robustness.

During the analysis, the mobile phase was delivered to the column at a flow rate of 0.9mL/min over a 65-minute duration. The chromatographic separation produced peaks that were distinct and well resolved, without any signs of tailing. To further assess method robustness, small, deliberate modifications in mobile phase composition, pH, and flow rate were introduced. These adjustments confirmed that the method maintained stable performance, highlighting its resilience under minor experimental variations^31,32.

Method Validation:

The analytical method was validated by following various parameters such as specificity, Solution Stability, Precision, limit of quantitation (LOQ), limit of detection (LOD), linearity, accuracy, selectivity, robustness/ruggedness and Force degradation studies.

Specificity:

The data assesses the specificity of an analytical method by evaluation the retention times, RT ratios, purity angles, and purity thresholds of various impurities in a sample. Morpholine thiazole Facid + HOBT and cobicistat show high specificity with minimal interference, indicated by low purity angles and appropriate thresholds. Thiazole methanol and Methyl thiazole amino impurities demonstrate good separation with low to moderate interference. However, Morpholine N-oxide impurity exhibits significant specificity issues due to its high purity angle and substantial overlap with other compounds. Isomeric impurities such as S, S, R-isomer and S, R, S-isomer, also show considered overlap, making separation challenging. The Dimethyl impurity, with late elution and a high purity angle, indicates potential separation difficulties. While the method is effective for some impurities, optimization is needed to improve the separation and quantification of impurities with high interference and significant overlap. Figure 3 shows the chromatogram peak for specificity of cobicistat and its impurities.

Figure 2: Chromatogram for Specificity of Cobicistat and its impurity Solution Stability

Solution stability:

Studies were done which focus on levels of degradation in concentrations (S, S, R, R, R, R and S, R, S) 48hours under storage conditions. Spiked sample and reference solutions initially demonstrated consistent isomer concentrations at room temperature (24 to 26°C). Concentrations in the spiked sample also decreased minimally over 48h for S, S, R-Isomer and R, R, R-Isomer, whereas concentrations of analytes other than Timbys’ll lodged near theoretical values except slight decrease exhibited by all isomers. Fig 3, 6 shows that isomer concentrations in solutions stored for the same period at 2-8°C decreased slightly only R, R, Isomers. The observed results support the robustness of the method for accurate measurement impurities was stable across tested conditions.

Figure 3: Chromatogram of Solution Stability of solution stability study of spiked sample solution stored at room temperature (24⁰C to 26 ⁰C) after 24 Hrs.

Figure 4: Chromatogram of Solution Stability of solution stability study of spiked sample solution stored at room temperature (24⁰C to 26 ⁰C) after 48 Hrs.

Figure 5: Chromatogram of Solution Stability of solution stability study of spiked sample solution stored at room temperature (240C to 260C) after 24 hrs.

Figure 6: Chromatogram of Solution Stability of solution stability study of spiked sample solution stored at room temperature (2-80C) after 24 hrs.

Precision:

The precision of S, S, R-isomer, R, R, R-isomer and S, R, S-isomers (3isomeric impurities) were checked at LOQ by multiple injections. The average %RSD for the S, S, and R- isomer was 2.7% with peak areas ranging from 1937 to 2059. The %RSD was 3.1% for the R, R, R-isomer, and peak areas varied from 2701 to 2891. The %RSD for peak areas of the S, R, S-isomer were 3.9%, with ranges between 2812 and 3069 (%). The method provided reproducible and accurate results from injection to injection, which included the QC level of NVP in all five matrices due to low levels (< 1percentage) of isomeric impurities (figure 7).

Figure 7: A chromatogram of precision of cobicistat and its chiral impurity

Limit of quantitation and Limit of detection:

The Limit of Detection and Limit of Quantitation of S, S, R-isomer, R, R, R-isomer, and S, R, S-isomers affirm the specificity, sensitivity, and precision of the developed analytical method. While the S, S, R-isomer at 0.000038mg/mL (0.002% of the test concentration) is detected with a signal-to-noise ratio of 3:1:1, the R, R, R-isomer is detected with 0.000056mg/mL (0.002%) concentration and same ratio is detected S, R, S-isomer whose value is 0.000063mg/mL (0.003%) is the found highest concentration among the them. The R is queitite at 0.000125mg/mL (0.01%) with a signal to noise ratio of 9.6:1, R, R, R-isomer is quantitated 0.000185mg/mL (0.001%) with the ratio of 10.1:1 and S, R, S-isomer which has 0.000209mg/mL (0.01%) have same ratio 10:1:1. In Fig 8 and 9 LOD and LOQ level chromatogram of cobicistat and its chiral impurity respectively is shown.

Figure 8: Chromatogram for LOD of Cobicistat and its impurity

Figure 9: Chromatogram for LOQ of Cobicistat and its impurity

Linearity:

To assess the linearity of the calibration curve, least squares linear regression analysis was conducted. Calibration curves across the 1–200 µg/mL concentration range showed a reliably linear response. This table was then linear regression analyzed (peak region vs. concentration) triplet-controls on to the resulting curve The correlation coefficient (n=3) is higher than 0.999 for all of the concentration levels tested, as are %RSD values lower than 2% (Table1).

Accuracy:

The percentage recoveries for the S, S, R-isomer and S, R, S-isomer demonstrate the accuracy and reliability of the analytical method. For the S, S, R-isomer, with a theoretical concentration of 0.0001247mg/mL, the measured recoveries ranged from 89.7% to 92.9%, averaging 90.9% with a %RSD of 1.9%. For the S, R, S-isomer, with a theoretical concentration of 0.0002089 mg/mL, the measured recoveries ranged from 104.5% to 107.0%, averaging 105.7% with a %RSD of 1.2%. These results confirm the method’s high accuracy and precision, with low variability in measurements, ensuring robust and reliable quantification of these impurities for quality control.

Robustness:

The study assessed the robustness of a chromatographic method by evaluating key parameters such as resolution between the S, R, S-isomer and cobicistat, cobicistat peak area, theoretical plates, and tailing factor across six injections. Under actual conditions (0.6mL/min flow rate, 350C column temperature, 450:550 buffer to acetonitrile ratio, and pH 9.0 buffer), the mean peak area was approx. 40,088, 519.774 with %RSD values of 1.2 for resolution, 1.8 for peak area, 1.0 for theoretical plates, and 33.3 for tailing factor. At a low flow rate (0.5mL/min), the mean peak area was 4,764,949.3 with slightly higher %RSD values but still acceptable robustness. Under high flow conditions (0.7mL/min), the mean peak area was 48,663,416 with %RSD values of 1.3 for resolution, 1:7 for peak area, 0.2 for theoretical plates, and 3082 for tailing factor. Despite variations in flow rate column temperature, and mobile phase composition, the method exhibited consistent chromatographic performance, and mobile phase composition, the method exhibited consistent chromatographic performance with minor fluctuations in measured parameters, demonstrating its robustness.

High Recovery Percentages of S, R, S-Isomer and Significance:

The average recovery percentage for the S, R, and S-isomer was 105.7%, with a range of 104.5% to 107.0%. These results highlight how sensitive and accurate the approach is in measuring impurities at low concentrations. Since high recovery guarantees precise detection and constant pharmaceutical product quality, it is important for regulatory compliance. The findings confirm that the technique reduces analyte loss and possible variability, giving important chiral impurity quantification confidence.

Oxidative degradation studies:

The purity of Cobicistat was significantly reduced to 38.38% by oxidative degradation, and a notable N-oxide impurity peak that accounted for 60.15% emerged. This emphasizes how vulnerable the sample is to oxidative stress and how crucial it is to handle and store it carefully. Oxidative circumstances caused the most significant deterioration in comparison to other stress conditions (such as acidic and UV light), providing information about the stability profile of Cobicistat. This result is consistent with other research highlighting the reactivity of comparable chemicals in oxidative environments, which may jeopardize the effectiveness of treatment.

Forced degradation studies:

This study evaluates the purity and related retention times (RRT) of impurities in different stress condition to find out stability. The sample started at 98.64% purity, but then two new impurities formed as the opposing conditions caused it to become less pure: - under alkaline (at a mere 0.43%, dropped to), and with thermal treatment [which way below pristine] had just left of [94.36%]. Oxidative stress results purity to 38.38%, having a large peak Identity as N-Oxide impurity (60.15%). Acidic and UV aqueous conditions had only minor impact, keeping the level of purity high (98.62%, 98.51% respectively), with a very small increase in impurities; This reinforces the sensitivity of this sample to oxidizing conditions and moderate stability under other circumstances, providing knowledge for future handling and storage.

CONCLUSIONS:

This research presents the development and validation of a quick, reliable, and precise HPLC method for routine analysis of cobicistat and its major impurities, with demonstrated stability throughout the process. The stability and selectivity of the stress testing results showed that it was feasible. The method proposed, is suitable for analysis of samples obtained during accelerated stability trails by effectively separating cobicistat from its degradation products and related substances.

An accurate and reliable HPLC technique for the thorough characterization of Cobicistat and its impurities, including chiral and degradation-related impurities, was developed and validated in this study. Key isomers including S, R, S-isomer, and R, R, R-isomer were resolved by the approach with remarkable specificity and great sensitivity, as shown by low LOD and LOQ values. The excellent recovery rates for important isomers, especially the S, R, and S-isomer (105.7%), highlighted how reliable the method is for measuring contaminants at low concentrations. Cobicistat high vulnerability to oxidative stress was demonstrated by forced degradation experiments, which showed a dominating peak of N-oxide impurity (60.15%) and a decline in purity to 38.38%. Favorable stability under UV, acidic, and thermal conditions preserved purity levels over 94% and offered information on the best storage settings. The accuracy (%RSD < 3.9%) and linearity (R2 > 0.999) of the validation parameters further validated the method's appropriateness for regular quality control. Its industrial usefulness was further supported by robustness testing, which revealed constant performance with slight experimental differences. The results highlight the significance of controlling oxidative degradation and are consistent with earlier research on antiretroviral drugs. This approach ensures therapeutic safety, efficacy, and regulatory compliance by offering a trustworthy framework for impurity profiling of comparable pharmaceutical molecules. To improve Cobicistat formulations, future research should investigate oxidative stability improvements.

FUTURE DIRECTION:

The study on cobicistat impurity and chiral impurity profiling sets the path for significant breakthroughs in pharmaceutical quality control and drug safety. Future studies should test the new analytical approach on other fixed-dose combination medications that contain cobicistat in an effort to increase its applicability. Given the widespread usage of cobicistat in antiretroviral regimens, extending its assessment across different formulations will validate the method's dependability and generalizability, guaranteeing thorough impurity profiling across a range of treatment combinations. It is advised to incorporate sophisticated analytical methods like LC-MS or LC-MS/MS to improve sensitivity and specificity. Particularly in complicated medication formulations, these instruments can offer more accurate detection and quantification of breakdown products and trace contaminants. Additionally, these methods can improve chiral purity evaluations, which are essential for avoiding racemic combinations that could compromise the safety and effectiveness of medications. These developments will bring cobicistat impurity analysis into compliance with state-of-the-art scientific and regulatory norms. Cobicistat vulnerability to oxidative stress has been brought to light by forced degradation tests, which show that it degrades significantly in oxidative environments. To guarantee medication efficacy, particular storage and stability guidelines are required. In order to shield cobicistat from oxidative destruction, future studies should concentrate on investigating the best possible packaging materials and environmental factors, such as the use of antioxidants or inert atmospheres. On the basis of these results, guidelines for controlling light, temperature, and humidity during storage and transit ought to be created. This will guarantee consistent therapeutic results and assist preserve medication stability.

FINANCIAL SUPPORT AND SPONSORSHIP:

This Research Article did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CONFLICTS OF INTEREST:

No competing interests to declare.

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Received on 10.11.2024 Revised on 08.03.2025

Accepted on 11.05.2025 Published on 01.12.2025

Available online from December 06, 2025

Research J. Pharmacy and Technology. 2025;18(12):6042-6048.

DOI: 10.52711/0974-360X.2025.00873

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Creative Commons License.

Component	Slope	Intercept	Correlation coefficient (R)	R2	Intercept value w.r.to 100% standard response (%)
S, S, R-Isomer	16024049.4208	789.7638	0.9999	0.9998	0.78
R, R, R-Isomer	16672231.0692	6843.8132	0.9999	0.9999	0.82
S, R, S-Isomer	14752920.5120	809.0352	0.9999	0.9997	0.86