INTRODUCTION:

The International Continence Society's Standardization Sub-Committee classified overactive bladder (OAB) as urgency with or without urge incontinence, typically accompanied by frequency and nocturia.¹In the absence of a urinary tract infection or other obvious pathology, overactive bladder (OAB), a lower urinary tract symptom (LUTS) complex that includes urgency, frequency, and nocturia along with or without urgency urinary incontinence, is becoming more common as people age.^2-3 The main pharmacotherapeutic choices for OAB are antimuscarinic drugs, which block cholinergic-receptor activation in the bladder. Oxybutynin, tolterodine, propiverine, solifenacin, darifenacin, and trospium chloride are among the antimuscarinics now used to treat OAB.⁴

Antimuscarinics, however, have side effects (AEs) that affect long-term treatment compliance and persistence, such as constipation, dry mouth, impaired vision, and drowsiness. In terms of effectiveness and tolerability, none of the drugs currently on the market are perfect.⁵ Festrerodine is a new competitive muscarinic-receptor antagonist that was just approved as a prolonged-release tablet to treat OAB.⁶

Mechanism of Action:

Fesoterodine is an antagonist of muscarinic receptors that is competitive, specific, and nonselective. It lowers smooth muscle tone in the bladder by blocking acetylcholine from binding to these receptors, which enables the bladder to hold large amounts of urine and lessens the frequency of incontinence episodes.⁷

Pharmacokinetics:

Fesoterodine is well absorbed when taken orally. It functions as a prodrug and is quickly and extensively hydrolyzed by nonspecific plasma esterases to produce its active metabolite, 5-hydroxymethyl Tolterodine (5-HMT), which has antimuscarinic properties.⁸

Drug Interactions:

A CYP3A4 inhibitor (ketoconazole), an inducer (rifampicin), and substrates (erhinylesrradiol and levonorgestrel) were given in order to evaluate the drug-drug interactions of fesorerodine.⁹Fesoterodine may exacerbate adverse events (AEs) such constipation, dry mouth, sleepiness, and urine retention when taken concurrently with other antimuscarinics and other medications with anticholinergic qualities (such as amantadine and tricyclic antidepressants). Therefore, when giving patients antimuscarinics, care must be taken. Fesoterodine is already being administered.¹⁰

Analytical Method Development:

A written proof that offers a high degree of assurance that a certain process will consistently deliver the intended outcome at the rule and quality level has already established, according to ICH Q2 R1 method validation. To put it simply, it's the process of demonstrating that analytical techniques support the identity, quality, purity, and potency of drug substances and drug products and are appropriate for the intended use. When novel procedures are developed and applied by several analysts in various laboratories, method validation is required. the performance requirements necessary for method validation.^11,12

Method Validation:

In analytical chemistry, method validation is a crucial procedure that guarantees the accuracy and dependability of a method. Strict guidelines for confirming analytical processes are set by regulatory bodies including the U.S. Food and Drug Administration (FDA) and the International Council for Harmonization (ICH). These recommendations heavily emphasize elements such as system appropriateness, which assesses whether the system is operating correctly prior to starting an analysis, and method robustness, which assesses the technique's ability to function consistently under minute changes in experimental settings.¹³

Parameters of Method Validation:

1. Accuracy

2. Precision

3. Linearity

4. Specificity

5. Range

6. Limit of Detection

7. Limit of quantification

8. Robustness

9. Ruggedness.¹⁴

Accuracy:

The accuracy can be defined as the degree to which the method's test results closely resemble the actual value. It is a gauge of how accurate the analytical technique is.¹⁵

Precision:

The analytical method's repeatability under typical operating conditions is measured by precision. The degree of agreement between a set of measurements made from several identical samples under particularconditions is expressed by the precision of an analytical procedure.¹⁶

Linearity:

The ability of an analytical method to yield test results that are linearly proportional to the analyte concentration in samples within an acceptable range is known as linearity.¹⁷

Specificity:

Specificity is the ability of a method to identify particular analytes in a complex mixture without interference from other mixture components.¹⁸

Range:

The range of the analytical procedure is the interval between the greatest and lowest analyte concentration in the sample for which the analytical technique has been demonstrated to have an appropriate degree of precision, accuracy, and linearity.¹⁹

Limit of Detection:

The limit of detection (LOD) of an analytical method is the lowest concentration of an analyte in a sample that is detectable but not directly quantifiable.²⁰

Limit of Quantification:

The limit of quantitation is the lowest analyte concentration in a sample that, under normal circumstances, can be detected with a sufficient degree of accuracy and precision using the stated method.²¹

Robustness:

An analytical technique's robustness, which demonstrates how dependable it is under normal working settings, is its capacity to tolerate small but deliberate changes in method parameters.²²

Ruggedness:

An analytical method's ruggedness is the degree of repeatability of test results achieved by analysing the same samples under multiple typical test conditions, such as different laboratories and different analysts.²³

Chromatographic Technique:

UV spectrophotometry:

The majority of multicomponent analysis uses UV spectrophotometric techniques, which eliminate the need to separate interferents and enable the measurement of additional analytes. This cuts down on study time and expenses.²⁴

Principle UV visible spectroscopy

The UV-visible concept of spectroscopy is based on the idea that different spectrums are produced when chemical compounds absorb ultraviolet or visible light. The interactions between light and matter are the focus of spectroscopy. A spectrum develops as a result of matter being stimulated and de-excited when it absorbs light.²⁵

High Performance Liquid Chromatography (HPLC)

High-performance liquid chromatography (HPLC), sometimes referred to as high-pressure liquid chromatography, is a method used in analytical chemistry to separate, identify, and quantify specific components in mixtures. Liquid solutions that have been dissolved from food, chemicals, pharmaceuticals, biological, environmental, and agricultural sources, among other sources, may be the source of the mixtures.²⁶

The mobile phasemixes of various solventsis supplied by high pressure pumps and flows through the system, gathering the sample mixture along the way. The sample mixture is then delivered into a column, which is a cylinder that contains the stationary phasesolid adsorbent particles. Variable rates of component migration are caused by various interactions between the components of the sample and the adsorbent material. Separation results from the species' varying rates of migration out of the column and onto particular detectors, like UV detectors. A graph called a chromatogram is produced by the detector. Chromatograms are graphical depictions of signal strength vs time or volume, with peaks signifying sample components. Based on quantity, each sample has a retention duration and matching area.²⁷

Ultra-High Performance Liquid Chromatography (UHPLC):

Particles smaller than the 2.5–5 μm size typically used in HPLC are separated using columns in UHPLC. Reducing column packing is the guiding principle of UHPLC, which functions on the same principles as HPLC. Particle size improves efficiency, which in turn improves resolution. Smaller particle column separations are more effective per unit of time; however, this efficiency cannot be maximized at higher linear velocities or mobile phase flow rates. This feature can limit speed, peak resolution, and smaller particles.

The effectiveness of the chromatographic process is closely correlated with the reduction of particle size. His band broadening theory states that the diameter of the particle packed into the analytical column determines both the linear velocity and the height equivalent of a theoretical plate (HETP). A chromatographic system connected to a spectroscopic system through a suitable interface, like LC-MS/MS, is the hyphenated technique. The performance characteristics of UHPLC technology are widely recognized to significantly enhance detection.²⁸

Reverse Phase High Performance Liquid Chromatography (RP HPLC):

RP-HPLC uses hydrophobic interactions between a polar mobile phase and a non-polar stationary phase to separate compounds. Reverse-phase chromatography uses a non-polar (hydrophobic) stationary phase, commonly modified silica with long carbon chains (like C18 or C8), and a polar mobile phase, typically water combined with organic solvents like methanol or acetonitrile.²⁹

Reported Method forFesoterodine Fumarate:

In 2021 D Sangeetha was developed by Stability-Indicating RP-HPLC Method for the Estimation of Process-Related Impurities and Degradation Products in Fesoterodine Fumarate by Using a Mass Spectrometric Compatible Mobile Phase. The objective of the present work was to Develop a sensitive, selective, accurate and precise stability-indicating HPLC method for Quantification of degradation products and process-related impurities in fesoterodinefumarate Extended-release tablets. The degradation profile was studied by conducting forced Degradation studies and all the degradation products formed during degradation were Separated. A chromatographic separation was achieved by using Waters Symmetry С18, 250 Х 4.6 mm, 5 µm column, maintained at 30°C. Mobile phase A (0.05% trifluoroacetic acid in Water) and mobile phase B (90% of 0.02% TFA in methanol and 10% of water) were used in Gradient elution mode. A total of 75µL of each solution was injected and peak responses were Quantified at 220nm. The method was found specific, precise, accurate, linear, rugged, robust and sensitive. During stability studies of fesoterodine fumarate extended-release tablets, one Unknown impurity at relative retention time 1.37 was found increasing beyond theIdentification threshold. This impurity was isolated by using Preparative HPLC and structure Was elucidated using mass and NMR spectroscopy. This method is a simple, inexpensive HPLC method that can be used as a routine quality control test for the estimation of impurities infesoterodine fumarate extended-release tablets.³⁰

Table No.1 Chromatographic parameters for Stability-Indicating RP-HPLC Method

Parameters	Description
Column Name	C18 (250mm × 4.6mm, 5µm)
Mobile Phase	A (0.05% trifluoroacetic acid in water) and B (90% of 0.02% TFA in methanol and 10% of water)
Flow Rate	1.0mL/min
Detection Wavelength	254nm
Retention Time	1.37min

In 2012 A. P Rajput was developed by Stability Indicating HPLC Method for the Enantiomeric Separation of Fesoterodine Fumarate in Drug Product and Drug Substance Using Chiral Stationary Phase. A chiral liquid chromatographic method was developed for the enantiomeric purity of Fesoterodine Fumarate in drug substance as well as in drug product. The chromatographic Separation was achieved on Chiralpak IC-3. Column using a mobile phase system consisting of n-hexane, isopropyl alcohol, and diethyl amine in the ratio of 950:50:1 (v/v/v). The mobile phase was pumped through column at the flow rate of 1 mL min. Addition of diethyl amine in the mobile phase enhanced chromatographic efficiency and resolution between the enantiomers. The resolution between the enantiomers was found to be more than three. The developed method was subsequently validated and proved to be accurate, specific, and precise. The experimentally established limit of detection and quantification for (S)-enantiomer of Fesoterodine were found to be 0.509µgmL and 1.316 µg mL respectively for 20µl injection volumes. The percentage recoveries of (S)-enantiomer was ranged between 95 to 105% in drug product as well as in drug substance. The proposed method was found to be suitable and accurate for the quantitative determination of chiral purity of Fesoterodine Fumarate in drugs substance as well as in drug product.³¹

Table No.2 Chromatographic Parameters for Enantiomeric Purity Determination

Parameters	Description
Column Name	IC-3, (250mm X 4.6mm, 3µm)
Mobile Phase	n-hexane, isopropyl alcohol and diethyl amine in the ratio of 950: 50:1 (v/v/v)
Flow Rate	1.0mL/min
Detection Wavelength	253nm
Retention Time	10.3min

In 2012 B.V Rami Reddy was developed by A Validated stability indicating HPLC Assy Method for Determination of Fesoterodine Fumarate. A novel stability indicating reverse phase. high performance liquid chromatographic method has been developed for quantitative determination of Fesoterodine Fumarate, new antimuscarinic agent forthe treatment of overactive bladder. The chromatographic separation was achieved using an Inertsil ODS-3V (150min x 4.6mm x 5µm) in isocratic mode employing Buffer (1.15g of Ammonium dihydrogen orthophosphate, 2.0mL. Triethylamine in 1000mL of water. Adjust pH of the solution to 3.040.05 with Orthophosphoric acid solution) and Methanol in the ratio of 42:58(v/v) with a 10mL/min flow rate was chosen. Detector wavelength monitored at 210nm The column temperature was maintained at 30°C.Fesoterodine Fumarate was exposed to thermal, photolytic, acid, base and oxidative stress conditions. Considerable degradation of the drug substance was found to occur under acid, base and oxidative stress conditions. Peak homogeneity data of Fesoterodine Fumarate obtained by photodiode array (PDA) detection demonstrated the specificity of the method in the presence of degradants. The degradation products were well resolved from main peak of Fesoterodine Fumarate thus proved the stability, indicating power of the method. The developed method was validated as per International Conference on Harmonization (ICH) guidelines with respect to specificity, precision, linearity, accuracyand robustness. Regression analysis showed correlation coefficient value greater than 0.999. Accuracy of the method was established based on the recovery obtained between 96.9%.and 101.5% for Fesoterodine Fumarate.³²

Table No.3 Validated Stability-Indicating HPLC Method Parameters for Fesoterodine Fumarate

Parameters	Description
Column Name	ODS-3V (150 × 4.6 mm, 5 µm)
Mobile Phase	Triethylamine: Methanol (42:58 v/v)
Flow Rate	1mL/min
Detection	210 nm
Retention Time	1.36 min

CONCLUSION:

A review of the literature suggests that fesoterodine is an efficacious and well-tolerated treatment option for patients with OAB. Antimuscarinic therapy is likely to remain first-line pharmacological ther-apy for OAB. There is an increased need to show efficacy and safety of these drugs in older people. The condition affects more of them and is, perhaps, more severe in older people. There are increasing num-bers of older people in the populations of the developed world and expectations of healthy aging are changing. Fesoterodine shows evidence of efficacy in the com-munity-dwelling elderly and has data in 'older' old people, albeit not in those who might be described as frail. Fesoterodine also appears to be tolerable in this age group and treatment with fesoterodine does not lead to an excess of adverse events related to cognitive dysfunction in a largely unselected group of older adults.

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Received on 31.03.2026 Revised on 04.05.2026

Accepted on 01.06.2026 Published on 10.07.2026

Available online from July 25, 2026

Asian Journal of Pharmaceutical Analysis. 2026; 16(3):219-223.

DOI: 10.52711/2231-5675.2026.00033

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