Analytical Method Development and Validation for Estimation of Tofacitinib Citrate in Pharmaceutical Dosage Form – A Review

Tofacitinib, an immunomodulator of Janus kinase inhibitor (Jakinib) family, blocks tyrosine kinases of the Janus family. Janus kinase?signal transducer and activator of transcription (JAK/STAT) is an intracellular pathway that drives downstream signaling of several pro?inflammatory pathways. The well?established efficacy of Jakinibs in inflammatory disorders, particularly rheumatoid arthritis (RA) and ulcerative colitis (UC), suggests the potential of their positive effects in a myriad of inflammatory dermatoses as well. Tofacitinib is a synthetic and potent immunosuppressant that is selective inhibitor of pro-inflammatory receptors specifically Janus kinases (JAK).4-7 Tofacitinib is FDA approved second generation DMARD that inhibits Janus activated kinase 1 and 3 (JAK1 and JAK 3).

1.1 Analytical Chemistry:

Analytical chemistry may be defined as the science and art of determining composition of materials in term of the element of composition and quantitative analysis of the substance and chemical species.

Analytical chemistry can be broken down into two general areas of analysis

• Qualitative analysis.
• Quantitative analysis.

1.2 Analytical Method Development:

Analytical method development and validation are essential components in the processes of drug discovery, development, and pharmaceutical manufacturing. Rooted in analytical chemistry, method development encompasses techniques for identifying, separating, and quantifying the chemical constituents of medicinal compounds. The primary goal of analytical method development is to confirm the identity, purity, potency, and physical properties of drugs, including factors like bioavailability and stability. This process ensures that analytical methods are suitable for evaluating drugs, particularly the active pharmaceutical ingredient (API).

1.3 Validation:

Validation is the documented process of demonstrating that a procedure, process, equipment, material, activity, or system consistently produces the intended outcome. According to ISO, validation involves verifying through examination and objective evidence that specific requirements for an intended use have been met. The FDA defines validation as the process of generating documented proof that provides strong assurance a particular process will consistently yield a product that meets its predetermined specifications and quality standards.

2.1 Spectroscopy:

2.1 UV Spectroscopy:

Ultraviolet (UV) spectroscopy is an analytical technique used to study the absorption of ultraviolet and visible light by chemical substances. It is based on the principle that molecules can absorb light in the UV-visible region of the electromagnetic spectrum, which causes electrons to transition from lower to higher energy molecular orbitals. These transitions include σ to σ*, n to σ*, π to π*, and n to π*, depending on the structure and functional groups present in the molecule. The resulting UV spectrum is typically a plot of absorbance versus wavelength, with the most important feature being the wavelength of maximum absorbance (λmax), which provides valuable information about the compound’s electronic structure. One of the main applications of UV spectroscopy is in quantitative analysis, guided by the Beer-Lambert Law, which relates absorbance to concentration, path length, and molar absorptivity. This makes it a useful tool for determining the concentration of a compound in solution. Qualitatively, UV spectroscopy can help identify functional groups, assess the degree of conjugation, and analyze the structure of organic and inorganic molecules. It is widely used in fields such as pharmaceutical analysis, where it helps in identifying and quantifying drugs, as well as in biochemistry, where it is employed to study nucleic acids and proteins—DNA typically absorbs UV light at 260 nm, while proteins show maximum absorbance around 280 nm due to aromatic amino acids. Several factors can influence UV absorption, including the presence of conjugated systems (which usually shift λmax to longer wavelengths), solvent effects, pH, and the nature of substituents on the molecule. Overall, UV spectroscopy is a powerful and versatile method for understanding molecular structure and composition through electronic transitions.

2.2 High Performance Liquid Chromatography:

High Performance Liquid Chromatography (HPLC) is a powerful and widely used analytical technique for separating, identifying, and quantifying components in a chemical mixture. It operates based on the principle of differential partitioning between a mobile phase and a stationary phase. In HPLC, the sample mixture is dissolved in a liquid (the mobile phase) and passed through a column packed with a solid material (the stationary phase) under high pressure. As the sample moves through the column, different components interact differently with the stationary phase, causing them to elute at different times. These differences in retention times allow for effective separation of the mixture’s components. HPLC is capable of analyzing compounds that are not volatile or that decompose at high temperatures, which makes it suitable for a wide range of substances including pharmaceuticals, food products, environmental samples, and biological fluids. The system typically consists of a solvent reservoir, pump, injector, column, detector, and data processor. Detectors such as UV-Vis, fluorescence, refractive index, or mass spectrometry are commonly used to identify and quantify the eluted compounds. There are different types of HPLC depending on the nature of the stationary and mobile phases, including reverse phase, normal phase, ion exchange, and size exclusion chromatography. Among these, reverse phase HPLC (RP-HPLC) is the most commonly used, especially for organic and biological samples. HPLC provides high resolution, speed, sensitivity, and reproducibility, making it an essential tool in pharmaceutical analysis, clinical research, and industrial quality control. Reverse Phase-High Performance Liquid Chromatography (RP-HPLC) is a widely used analytical technique in chemistry and biochemistry for separating, identifying, and quantifying components in a mixture. It is a type of High-Performance Liquid Chromatography (HPLC) where the stationary phase is non-polar (hydrophobic) and the mobile phase is relatively polar. The most commonly used stationary phase in RP-HPLC consists of silica particles bonded with long-chain alkyl groups, typically C18 (octadecyl), making it hydrophobic. The mobile phase usually consists of water mixed with an organic solvent such as methanol or acetonitrile, often with an added buffer to control pH. The separation in RP-HPLC is based on the hydrophobic interactions between the analytes and the stationary phase. Compounds with greater hydrophobicity will interact more strongly with the non-polar stationary phase and therefore elute more slowly, while more polar compounds elute faster due to weaker interactions. The retention time of each component helps in its identification, while the area under the peak in the chromatogram is used for quantification. RP-HPLC is particularly useful for analyzing non-volatile, thermally unstable, or polar compounds such as pharmaceuticals, peptides, proteins, and plant extracts. It offers high resolution, sensitivity, and reproducibility, making it a preferred method in pharmaceutical quality control and bioanalytical studies. Various detectors can be coupled with RP-HPLC, such as UV-Vis, fluorescence, or mass spectrometry, to enhance detection and identification of analytes. Overall, RP-HPLC is a powerful and reliable technique for precise chemical analysis and compound separation.

2.3 High Performance Thin Layer Chromatography:

High Performance Thin Layer Chromatography (HPTLC) is an advanced form of traditional Thin Layer Chromatography (TLC) that offers improved resolution, sensitivity, and reproducibility for the separation and analysis of chemical substances. Like TLC, HPTLC is a planar chromatography technique where samples are applied as small spots or bands on a flat stationary phase—usually a glass, plastic, or aluminum plate coated with a thin layer of adsorbent material such as silica gel, alumina, or cellulose. The mobile phase (solvent or solvent mixture) moves through the stationary phase by capillary action, and different compounds in the sample travel at different rates, allowing for their separation. What distinguishes HPTLC from conventional TLC is the use of finer particle size in the stationary phase, automated sample application, more precise development chambers, and densitometric scanning for detection and quantification. These enhancements allow for better separation, faster analysis, and higher sensitivity. The method is especially useful for the analysis of complex mixtures such as plant extracts, pharmaceuticals, food products, and cosmetic formulations. After development, the chromatographic plate is typically visualized using UV light, iodine vapors, or specific chemical reagents, and the separated compounds appear as spots or bands at different locations (Rf values). Quantitative analysis in HPTLC is achieved using a densitometer, which measures the intensity of each spot, correlating it with the amount of compound present. HPTLC is valued for its simplicity, low cost, high throughput, and the ability to analyze multiple samples simultaneously. It is particularly useful in quality control, herbal drug standardization, forensic analysis, and environmental monitoring, making it a reliable and efficient analytical tool in modern laboratories.

2.4 Ultra Performance Liquid Chromatography:

Ultra Performance Liquid Chromatography (UPLC) is an advanced chromatographic technique that builds upon the principles of High Performance Liquid Chromatography (HPLC), offering significantly improved speed, resolution, and sensitivity. The key difference between UPLC and HPLC lies in the use of stationary phase particles that are smaller than 2 micrometers in diameter (typically around 1.7 µm), compared to the 3–5 µm particles used in conventional HPLC. These smaller particles allow for greater surface area, more efficient separation, and faster analysis times. In UPLC, higher operating pressures—up to 15,000 psi (compared to 6,000 psi in HPLC)—are used to push the mobile phase through the tightly packed column. As a result, UPLC can achieve sharper peaks, better resolution, and reduced run times, making it particularly suitable for high-throughput environments. This is especially beneficial in pharmaceutical development, where quick and precise analysis of drug compounds is essential. UPLC systems are equipped with highly sensitive detectors, such as UV, PDA (photodiode array), fluorescence, or mass spectrometry, allowing for the detection of very low concentrations of analytes. Despite its advantages, UPLC requires specialized equipment and columns capable of withstanding high pressures, which can increase operational costs. Overall, UPLC represents a significant advancement in liquid chromatography. It is widely used in pharmaceutical research, clinical testing, food safety, environmental monitoring, and metabolomics, where speed, sensitivity, and efficiency are critical.

3. Drug Profile:

3.1 Tofacitinib:

Tofacitinib is an oral medication that belongs to a class of drugs known as Janus kinase (JAK) inhibitors. It is primarily used to treat autoimmune diseases by interfering with the JAK-STAT signaling pathway, which is involved in the body’s inflammatory response. Tofacitinib is commonly prescribed for conditions such as rheumatoid arthritis, psoriatic arthritis, ulcerative colitis, and, in some cases, ankylosing spondylitis and juvenile idiopathic arthritis. Marketed under the brand name Xeljanz, it is available in both immediate-release and extended-release tablet forms. While tofacitinib can be effective in controlling inflammation and managing symptoms of autoimmune diseases, it carries several significant risks. These include an increased likelihood of serious infections such as tuberculosis, higher chances of developing certain types of cancer, blood clots, and major cardiovascular events. Because of these risks, the medication includes a black box warning and requires close monitoring. Doctors often recommend routine blood tests, liver function tests, and screening for tuberculosis and hepatitis before and during treatment. Common side effects include headache, diarrhea, and upper respiratory infections, while more serious side effects may involve liver enzyme elevations and gastrointestinal perforations. Tofacitinib should be used cautiously in older adults, individuals with a history of heart disease or cancer, and those prone to infections. It is also not typically recommended for use during pregnancy or breastfeeding without medical supervision.

Fig: 8 Chemical Structure of Tofacitinib

3.2 Physio-Chemical Properties:

• Chemical Name: 3-((3R,4R)-4-methyl-3-(methyl(7H-pyrrolo[2,3-d] pyrimidin-4- yl)
• amino) piperidin-1-yl)-3-oxopropanenitrile
• Brand Name: XELJANZ
• Molecular Formula: C₂₂H₂₈N₆O₈
• Melting Point: 212°C (413.6°F)
• Boiling Point: 585.8 °C
• Bioavailability: 74%
• Half-Life: 3 hours

3.3 Mechanism of Action:

As an inhibitor of Janus kinase (JAK), tofacitinib functions by preventing the intracellular enzymes known as Janus kinases from participating in the signaling cascades that cause inflammation. By inhibiting these enzymes, tofacitinib reduces the inflammatory response associated with conditions like rheumatoid arthritis and psoriatic arthritis. Specifically, it inhibits JAK1 and JAK3, which are crucial for lymphocyte activation, function, and  proliferation. This, in turn, affects the JAK-STAT signaling pathway, which plays a role in hematopoiesis and immune cell function.

Fig: 9 Mechanism action Of Tofacitinib

3.4 Pharmacokinetics:

Tofacitinib is rapidly absorbed after oral administration, with peak plasma concentrations (C_max) typically occurring within 0.5 to 1 hour for immediate-release formulations and around 4 hours for extended-release formulations. It has an absolute oral bioavailability of approximately 74%. The drug is moderately bound to plasma proteins (about 40%) and has a steady-state volume of distribution of roughly 87 L, indicating extensive tissue distribution. Tofacitinib is primarily metabolized in the liver by the cytochrome P450 enzymes, mainly CYP3A4, with minor involvement from CYP2C19. It has a terminal elimination half-life of approximately 3 hours for immediate-release and about 6 hours for extended-release formulations. The drug is eliminated through both renal and hepatic pathways: about 30% of the dose is excreted unchanged in urine, while the remainder is eliminated as metabolites via urine and feces. Pharmacokinetics may be altered in patients with hepatic or renal impairment, requiring dose adjustments in such populations.

4. Literature Review:

4.1 UV Specctroscopy:

4.2 Reverse Phase-High Performance Liquid Chromatography:

4.3 High Performance Liquid Chromatography:

Table: 3 Review Of HPLC

4.4 High Performance Thin Layer Chromatography:

Table: 4 Review Of HPTLC

4.5 Ultra Performance Liquid Chromatography:

Table: 5 Review Of UPLC