Department of Pharmaceutical Quality Assurance, SND College of Pharmacy, Babhulgaon, Yeola,423401, Maharashtra, India.
Ophthalmic suspensions, particularly corticosteroid formulations, require stringent quality control (QC) measures to ensure their stability, therapeutic efficacy, and safety for patient use. Key physicochemical parameters, such as viscosity, rheological properties, pH, and osmolality, are vital in maintaining the desired characteristics of the suspension. Particle size distribution (PSD) is particularly critical, influencing both the stability and bioavailability of the active pharmaceutical ingredient (API). In addition, chemical parameters such as the assay of the API using High-Performance Liquid Chromatography (HPLC) and impurity analysis help ensure the purity and potency of the formulation. Microbiological testing, including sterility and antimicrobial effectiveness testing (AET), ensures that the product is free from microbial contamination and that preservatives remain effective throughout the shelf life. Advanced techniques like Liquid Chromatography-Mass Spectrometry (LC-MS) are employed to detect impurities and profile metabolites, supporting the drug development process. Stability testing under various conditions is conducted to assess the product’s shelf life and long-term performance. Homogenization techniques, such as high-shear mixing, ultrasonication, and pressure homogenization, are used to ensure particle uniformity, enhancing product stability and therapeutic consistency. This paper discusses the importance of these QC parameters in the development of corticosteroid ophthalmic suspensions and highlights the methods used to ensure product quality, safety, and effectiveness.
Corticosteroid ophthalmic suspensions are widely used in the treatment of ocular diseases, providing localized drug delivery to the eye. The formulation of such suspensions must meet strict quality control standards to ensure the stability, bioavailability, and therapeutic efficacy of the active pharmaceutical ingredients (APIs). These products must maintain their physical properties and effectiveness throughout their shelf life while being safe and comfortable for patients. Corticosteroid ophthalmic suspensions are commonly prescribed for conditions such as ocular inflammation, uveitis, post-surgical inflammation, and allergic conjunctivitis. These conditions often require corticosteroids due to their potent anti-inflammatory effects. The growing use of ophthalmic suspensions in these therapeutic areas underscores the importance of ensuring their quality to achieve effective drug delivery while maintaining patient safety. The quality control of ophthalmic suspensions involves the evaluation of several key physicochemical and chemical parameters, including viscosity, rheological properties, pH, osmolality, and particle size distribution (PSD). These factors are critical in ensuring that the formulation behaves as expected during administration, remains stable in solution, and delivers the API effectively to the target site. The size of the particles in the suspension plays a central role in determining both the therapeutic efficacy and stability of the product. Smaller particles enhance bioavailability, while larger particles may lead to issues like sedimentation and inconsistent dosing. In addition to these physicochemical attributes, chemical testing, including API assays by High-Performance Liquid Chromatography (HPLC) and impurity analysis, is essential to confirm the identity, concentration, and purity of the API. Microbiological testing ensures that the suspension is free from microbial contamination, and stability testing helps predict the product’s behavior under various storage conditions. The incorporation of advanced technologies like Liquid Chromatography-Mass Spectrometry (LC-MS) further enhances the sensitivity and specificity of these analytical methods, providing deeper insights into formulation composition and impurity profiles.
This paper aims to explore the critical QC parameters necessary for corticosteroid ophthalmic suspensions and the methodologies used to ensure that these products meet the required standards for safety, stability, and therapeutic performance.
QUALITY CONTROL PARAMETERS:
Physicochemical Parameters:
Viscosity and Rheology:
Viscosity and rheological properties are critical quality control parameters for corticosteroid ophthalmic suspensions. They influence the product's behavior during administration, its ability to remain on the ocular surface, and overall patient comfort. These properties directly affect the stability, uniformity, and therapeutic performance of the suspension.
Ophthalmic suspensions must have an appropriate viscosity to ensure that the medication remains on the eye's surface long enough for absorption. Viscosity also affects the rate of sedimentation of suspended particles. Typically, suspensions with a viscosity range of 10–50 cPs (centipoise) are preferred for ophthalmic use. Formulations with lower viscosity may cause faster drainage from the eye, reducing therapeutic efficacy. Conversely, higher viscosity could cause discomfort due to impaired blinking or excessive stickiness.
Newtonian vs. Non-Newtonian Fluids:
pH and Osmolality:
The pH scale is a measurement of the concentration of hydrogen ions (H+) in a solution. The highest acidic number on the scale is 0, the neutral number is 7, and the alkaline number is 14.
The pH of human blood is about 7.35. Even seemingly modest pH variations have a major impact on the concentration of hydrogen ions.
Osmosis is the process by which a material in solution moves across a membrane from a region of lower concentration to one of higher concentration in order to create equilibrium.
The concentration of particles dissolved in solution is known as "osmolality" and is measured in osmoles of solute per kilogram of solvent.
Importance: Must match physiological conditions to avoid irritation and maintain drug stability.
Techniques: pH meters and osmometry.
Chemical Parameters:
Assay of Active Pharmaceutical Ingredient (API) By HPLC:
High-Performance Liquid Chromatography, also known as High-Pressure Liquid Chromatography, is a type of column chromatography that is commonly used in biochemistry
and analysis to separate, identify, and quantify active chemicals. It is a widely used analytical method for identifying, measuring, and separating each component of a mixture.
Based on a scale of operation
Preparative HPLC and analytical HPLC
Based on the principle of separation
Affinity chromatography, adsorption chromatography, size exclusion chromatography, chiral phase chromatography, and ion-exchange chromatography.
The mobile phase in normal phase chromatography is nonpolar, whereas the stationary phase is polar. Consequently, the station phase retains the polar analyte. A longer elution time is the result of the solute molecules' enhanced adsorption ability due to their increased polarity.
B. Reversed-phase HPLC:
RP-HPLC has a polar or moderately polar mobile phase and a non-polar stationary phase. The notion of hydrophobic interaction underpins RP-HPLC. The nonpolar stationary phase will hold analytes that are comparatively less polar in a combination of components for a longer period than those that are substantially more polar. As a result, the most polar component elutes the first.
Understanding the Physicochemical Properties of the drug molecule:
When developing a medicinal molecule, its physicochemical properties are crucial. The physical characteristics of the drug molecule, including its solubility, polarity, pKa, and pH, must be assessed before developing a technique. A compound's polarity is a physical property.
Selection of chromatographic conditions:
During the initial stages of method development, basic conditions—such as the detector, column, and mobile phase—are selected to produce the first "scouting" chromatograms for the sample. Typically, this involves using reversed-phase separations with a C18 column and UV detection. At this stage, it's important to decide whether to proceed with an isocratic method or a gradient method.
Impurity and Degradation Product Analysis:
Organic Impurity:
Organic contaminants occur during the production and/or storage of drugs. Impurities can be categorized as source material, by-product, degradation, or enantiomeric.
By Products:
A compound with 100% yield is uncommon, therefore there is always the possibility of by-products. Side reactions, including rearrangement, over-reaction, isomerization, dimerization, and undesired interactions involving starting materials or intermediates with catalysts or reagents, can lead to their formation.
Degradation product impurities:
These are unwanted chemical by-products that form when active pharmaceutical ingredients (APIs) or excipients in a corticosteroid ophthalmic suspension break down over time. Monitoring these impurities is crucial to ensure the safety, efficacy, and stability of the product throughout its shelf life.
Enantiomeric impurities:
These are crucial to monitor because, for many chiral drugs, using a single enantiomer can enhance pharmacological effectiveness and improve the therapeutic index, often resulting in fewer adverse effects.
Techniques: HPLC, Thin-Layer Chromatography (TLC), and Mass Spectrometry (MS), Liquid Chromatography and Mass Spectroscopy (LC-MS)
Microbiological Parameters:
Sterility Testing:
Importance: Ensures the suspension is free from microbial contamination, crucial for ophthalmic applications.
Testing Methods:
Involves filtering the product through a membrane that captures potential microorganisms, which are then cultured on suitable media.
A small volume of the product is directly inoculated into culture media, followed by incubation to detect microbial growth.
Antimicrobial Effectiveness Testing (AET):
The product is inoculated with standardized bacterial and fungal strains, and microbial counts are monitored over time to ensure that the preservative effectively inhibits growth.
Importance: Confirms that preservatives effectively prevent microbial growth over the product’s shelf life.
Common Microorganisms Tested:
Liquid Chromatography and Mass Spectroscopy (LC-MS)
LC-MS is a popular sample analysis technology that combines liquid chromatography (LC) with mass spectrometry (MS). With its extraordinary sensitivity, modern mass spectrometry has made LC-MS a viable alternative to numerous classic immunoassays. This effective approach has significantly increased the efficiency of drug discovery by providing excellent sensitivity and specificity. Furthermore, LC-MS may be used with stable isotope dilution to produce precise and repeatable experiments, ensuring correct findings in a variety of analytical applications.
LC-MS has become one of the most widely used techniques for global metabolite profiling in biological tissues, such as blood plasma, serum, and urine. It is also extensively used to analyze natural products and profile secondary metabolites in plants. This technique provides valuable insights into the complex chemical composition of biological and plant samples, helping to advance research in fields like pharmacology and plant science.
LC-MS is not only used for quantifying API levels but also for identifying degradation products and metabolites of the active drug. The combination of high-resolution mass spectrometry with LC enables the detection of trace amounts of degradation products that may not be visible with conventional analytical methods.
Stability Testing:
Importance: Evaluates the product's shelf life and ensures it maintains efficacy, safety, and quality under various storage conditions.
Condition As Per ICH Guidelines:
Sr. No |
Types of Stability Study |
Condition |
Sampling Period |
1. |
Accelerated Stability Study |
400C±20C/ 25%±5%RH |
1M, 2M, 3M, 6M |
2. |
Long Term Stability Study |
250C±20C/ 40%±5%RH |
3M, 6M, 12M |
3. |
Intermediate Stability Study |
30°C± 2°C/ 65% ± 5%RH |
3M, 6M |
M: Months
Accelerated Stability Testing: Simulates long-term storage conditions in a shorter time frame.
Long Term Stability Testing: Observes product behavior over its intended shelf life.
Parameters Monitored: Physical changes (e.g., pH, Viscosity), Chemical stability (e.g., API degradation Assay of Preservatives), and Microbiological stability.
Stability Condition changes as per Product Markets (Like; US, EU, UK, CANADA, Domestic.)
Particle Size Distribution:
In ophthalmic suspensions, particle size distribution (PSD) is a critical quality control parameter. The size of the particles in the suspension directly impacts its therapeutic performance, safety, and overall effectiveness. The primary goal in formulating ophthalmic suspensions is to ensure that the particles are small enough to remain stable in the formulation and yet large enough to provide the desired controlled release of the active pharmaceutical ingredient (API).
Particle Size Distribution (PSD) is measured using techniques like Laser Diffraction and Dynamic Light Scattering (DLS). Laser diffraction is used for measuring the broad particle size distribution, while DLS provides a more accurate measure of the Z-average diameter and polydispersity index (PDI) of particles.
Importance of Homogenization:
Methods of Homogenization:
Validation of Analytical Methods:
Method validation is a crucial step in ensuring the accuracy and reproducibility of analytical methods. For HPLC, this includes parameters such as accuracy, precision, linearity, and limit of detection (LOD). During the validation of HPLC for API quantification in a corticosteroid ophthalmic suspension, a correlation coefficient of >0.999 was achieved for linearity, confirming the method's robustness. The development of scientific and concrete analytical methods has been significantly advanced by improvements in analytical instruments. These advancements have not only enhanced the precision and sensitivity of analyses but also led to a reduction in both the time and cost associated with analytical procedures. As a result, the role of human intervention in the analysis process has become more focused on interpretation and decision-making, rather than on manual execution. This shift allows for faster and more efficient analysis, ultimately improving productivity and accuracy in scientific research and industry applications.
Linearity and Range:
Linearity refers to how closely a calibration plot of response versus concentration follows a straight line. To assess linearity, measurements are taken at several different concentrations of the analyte. The data is then analyzed using linear least-squares regression. The resulting slope, intercept, and correlation coefficient give important information about the method’s linearity.
Precision:
Precision refers to the consistency of measurements when a series of samples from the same homogeneous source are analyzed under identical conditions. It can be broken down into three categories:
The ICH guidelines recommend that repeatability should be assessed using at least 9 measurements, covering a specified range for the procedure (such as three concentrations with three replicates each), 6 measurements at least, all at 100% of the test concentration.
Accuracy:
The degree to which a measured value resembles the real or expected value is known as accuracy. In a highly accurate method, when a sample with a known “true value” is analyzed, the result should match this true value. Accuracy is typically determined through recovery studies, and there are three common ways to assess it:
It’s important to clearly define how any individual or total impurities will be measured as part of the accuracy assessment
Limit of Detection (LOD):
The Limit of Detection (LOD) refers to the lowest concentration of an analyte that can be reliably detected in a sample, though not necessarily quantified with precision, under the given experimental conditions. The LOD is usually expressed in terms of analyte concentration (e.g., ppm). Several methods, recommended by the ICH, can be used to determine the LOD, depending on the analytical instrument, the nature of the analyte, and the suitability of the method.
Common approaches for determining the detection limit include:
Visual evaluation: Inspecting the sample for a detectable signal.
Analyte signal to noise ratio: Analyte signal to noise ratio.
Standard deviation of the response: Analyzing variations in the measurement response.
The linearity plot's slope standard deviation is: To estimate the limit, use the linearity plot's variability.
One formula for calculating the LOD is;
LOD = 3.3 (? / S)
Where; ? is the standard deviation of the intercepts from the calibration curves.
S is the slope of the linearity plot.
Summary:
The quality control (QC) of corticosteroid ophthalmic suspensions is essential to ensure the safety, efficacy, and stability of the formulation. Various physicochemical and chemical parameters are assessed to maintain product consistency, stability, and therapeutic performance. Physicochemical parameters such as viscosity, rheological properties, pH, and osmolality play a crucial role in the suspension's behavior during administration and its ability to remain stable on the ocular surface. Viscosity directly influences the comfort and stability of the suspension, and pH and osmolality are critical to preventing irritation and maintaining drug stability. Particle size distribution (PSD) is another essential QC parameter, as the size of the particles affects the uniformity, bioavailability, and overall therapeutic effect of the suspension. Chemical parameters, especially the assay of active pharmaceutical ingredients (API) through HPLC, are fundamental in verifying the correct concentration of corticosteroids and ensuring that the formulation complies with regulatory standards. Impurity and degradation product analysis, along with the detection of enantiomeric impurities, are also integral to ensure the product's safety and therapeutic effectiveness. In terms of microbiological testing, sterility testing and antimicrobial effectiveness testing (AET) are mandatory to confirm that the product is free from microbial contamination and that preservatives maintain their efficacy throughout the product’s shelf life. Liquid chromatography-mass spectrometry (LC-MS) has proven to be a highly sensitive and specific analytical technique for drug discovery, metabolite profiling, and impurity detection, thus playing a significant role in the QC of ophthalmic suspensions. It offers detailed insights into the chemical composition and stability of the formulation, which is vital for drug development and safety monitoring. Stability testing is another critical element in QC, as it helps determine the product’s shelf life under various storage conditions. Different stability studies—accelerated, long-term, and intermediate—are conducted to ensure that the formulation maintains its quality over time. Monitoring physical, chemical, and microbiological stability is crucial for ensuring the product’s integrity until the end of its shelf life. Finally, homogenization techniques such as high-shear mixing, ultrasonication, and pressure homogenization are employed to ensure particle uniformity, enhance stability, and maintain consistent therapeutic effects.
Validation of analytical methods ensures that tests for API content, impurity levels, and product stability are accurate and reliable.
CONCLUSION:
Maintaining the quality of corticosteroid ophthalmic suspensions requires a comprehensive approach to quality control, incorporating a wide range of physicochemical, chemical, and microbiological testing. Parameters like particle size distribution, viscosity, and pH are pivotal in ensuring the suspension's stability and therapeutic effectiveness. Advanced analytical techniques such as HPLC, LC-MS, and stability testing are essential for verifying the purity, potency, and safety of the suspension. Homogenization methods play a crucial role in achieving particle uniformity and stability, further ensuring consistent dosing and efficacy. By adhering to rigorous QC standards and utilizing advanced technologies, pharmaceutical manufacturers can produce ophthalmic suspensions that are safe, effective, and stable, meeting both regulatory requirements and patient needs.
REFERENCES
Sumit Wakchaure*, Sonali Waghmare, Pradyumna Ige, A Review Analytical Advances and Challenges in Quality Control Techniques for Corticosteroid Ophthalmic Suspensions, Int. J. of Pharm. Sci., 2024, Vol 2, Issue 12, 1261-1269. https://doi.org/10.5281/zenodo.14365890