A Validated Stability-Indicating HPLC Method for the Simultaneous Estimation of Tioconazole and Diflucortolone Valerate

1. 1. Overview of Dermatomycoses

Dermatomycoses represent highly prevalent superficial fungal infections restricted to keratinized layers of skin, hair, and nails. These infections are a major global public health concern with escalating incidence influenced by aging demographics and increasing immunocompromised populations.[1]

1. 2. Drug Profile I: Tioconazole (TCZ)

Classification: Synthetic, broad-spectrum imidazole derivative; topical antifungal agent

Chemical Properties:

• IUPAC Name: 1-[2-[(2-chloro-3-thienyl)methoxy]-2-(2,4-dichlorophenyl)ethyl]imidazole
• Molecular Formula: C₁₆H₁₃Cl₃N₂OS
• Molecular Weight: 387.70 g/mol
• Log P: 5.53 (highly lipophilic)
• pKa: ~6.5 (imidazole nitrogen) [2,3]

1. 3. Drug Profile II: Diflucortolone Valerate (DFV)

Classification: Synthetic, highly potent glucocorticoid for topical dermatological applications

Chemical Properties:

• IUPAC Name: [2-(6,9-difluoro-11-hydroxy-10,13-dimethyl-3-oxo-6,7,8,11,12,14,15,16-octahydrocyclopenta[a]phenanthren-17-yl)-2-oxoethyl] pentanoate
• Molecular Formula: C₂₇H₃₆F₂O₅
• Molecular Weight: 494.57 g/mol
• Log P: 3.6–4.1 (highly lipophilic)
• Stability: Highly sensitive to alkaline hydrolysis[2,3]

• 4. Rationale for TCZ + DFV Combination Therapeutic Justification:
• Addresses both root cause (mycological pathogen) and clinical symptoms (host immune reaction)
• Breaks the "scratch-infection" cycle
• Modified dermal pharmacokinetics through DFV-mediated vasoconstriction
• Accelerated patient compliance with visible relief within 24-48 hours
  5. Analytical Challenges

• Extreme concentration disparities (10:1 ratio)
• Overlapping chromophores with similar aromatic ring systems
• Complex matrices with emulsifiers, surfactants, fatty alcohols, and preservatives
  6. Aims and Objectives

Primary Aim:

To develop and validate a precise, accurate, and stability-indicating HPLC method for simultaneous estimation of TCZ and DFV in combined pharmaceutical formulations.

Specific Objectives:

1. Literature survey on physicochemical properties and existing analytical methods
2. Develop simple, rapid, precise RP-HPLC method for simultaneous estimation
3. Optimize chromatographic conditions (mobile phase, pH, flow rate, column, detection wavelength)
4. Validate method per ICH Q2(R1) guidelines
5. Establish stability-indicating nature through forced degradation studies
6. Assess peak purity using PDA detection
7. Apply validated method for quantitative assay of marketed formulation
8. Develop efficient sample preparation procedure for cream matrix extraction

2. MATERIALS AND METHODS
   1. Materials

Drugs and Reference Standards:

• Tioconazole: Yarrow Chem Products, Mumbai; Purity ≥98.0%; CAS: 65899-73-2
• Diflucortolone Valerate: Yarrow Chem Products, Mumbai; Purity ≥97.0%; CAS: 59198-70-8

Reagents and Chemicals:

• Orthophosphoric Acid, Potassium Dihydrogen Phosphate, Sodium Hydroxide, Hydrochloric Acid, Hydrogen Peroxide, Methanol and Acetonitrile

Instruments:

• HPLC System with PDA: Shimadzu LC-2010 / Agilent 1200, Analytical Balance: Shimadzu AUX220, pH Meter: Systronics μ pH System 361, Ultrasonicator: Enertech, UV-Visible Spectrophotometer: Shimadzu UV-1800, Hot Air Oven: Narang Scientific
  2. Methods
     1. Preparation of Mobile Phase Finalized Composition:

Buffer Preparation:

• 1. 1. 1. Weighed 6.805 g KH₂PO₄, transferred to 1000 mL beaker
        2. Added 900 mL HPLC-grade water, stirred until dissolution
        3. Adjusted pH to 3.5 ± 0.05 using orthophosphoric acid
        4. Made up to 1000 mL with HPLC-grade water
        5. Filtered through 0.45 μm nylon membrane filter
        6. Degassed by ultrasonication for 15-20 minutes[4,6]
     2. Preparation of Standard Stock Solutions
• Primary Stock (1000 μg/mL each): 10.0 mg standard in 10 mL methanol
• Combined Intermediate Stock (100 μg/mL each): 1.0 mL each primary stock diluted to 10 mL[5]
  1. 3. Sample Extraction from Topical Cream
        1. Weighed 1.0 g cream (containing 10 mg TCZ and 1 mg DFV)
        2. Added 15 mL HPLC-grade methanol (pre-warmed to 50°C)
        3. Ultrasonicated at 50°C for 15 minutes with intermittent swirling
        4. Transferred to 25 mL volumetric flask, made up with methanol
        5. Centrifuged at 3000 rpm for 10 minutes
        6. Filtered through 0.45 μm nylon syringe filter (discard first 0.5 mL)
        7. Diluted 0.5 mL filtrate to 10 mL with mobile phase
        8. Final concentrations: TCZ 20 μg/mL, DFV 2 μg/mL[,7,8]

2.2.4 Forced Degradation Studies

3.2 Method Development and Optimization

Optimized Chromatographic Conditions:

Alkaline Hydrolysis (0.1 N NaOH, 60°C, 2 hours):

Oxidative Stress (3% H₂O₂, Ambient, 24 hours):

Thermal Degradation (80°C, 24 hours):

Photolytic Degradation (UV/Visible Light, 24 hours):

Peak Purity Analysis (PDA):

           

3.5.3 Accuracy (Recovery Studies)

1. 7. Method Development Rationale

A C18 column was selected due to the lipophilic nature of both drugs (Log P: 5.53 for TCZ, 3.6–4.1 for DFV), ensuring adequate hydrophobic retention. Acetonitrile was preferred over methanol for its lower viscosity (0.37 vs 0.55 cP), reduced backpressure, and superior UV transparency at 254 nm; the optimized 70:30 acetonitrile:buffer ratio delivered optimal resolution (Rs = 2.6) with reasonable retention times. Buffer pH 3.5 was critical for peak symmetry—TCZ's imidazole nitrogen (pKa ~6.5) became fully protonated, suppressing silanol interactions and tailing, while DFV as a neutral steroid ester exhibited excellent symmetry.

1. 8. Extraction Procedure Optimization

Heated methanol extraction at 50°C with ultrasonication proved optimal by effectively dissolving both drugs while leaving lipid excipients insoluble, reducing cream viscosity, enhancing mass transfer, and disrupting drug-excipient associations via cavitation. Centrifugation yielded clear supernatant with minimal matrix interference, and 0.45 μm nylon filters showed no significant drug adsorption; discarding the first 0.5 mL filtrate prevented adsorptive losses, achieving >99% extraction efficiency..

3.9 Forced Degradation Interpretation

Alkaline hydrolysis was most severe—DFV showed 17.6% degradation (valerate ester saponification at C-21) and TCZ 12.4% (imidazole ring opening or benzyl ether cleavage). Acid hydrolysis caused 10.5% DFV and 7.2% TCZ degradation, consistent with ester hydrolysis. Oxidative stress affected TCZ more (11.1%) than DFV (6.6%) due to thioether sulfur oxidation to sulfoxide/sulfone derivatives. Thermal degradation was minimal (4.2–5.3%), confirming stability at normal manufacturing/storage temperatures (25–40°C), while photolytic degradation (6.2–8.5%) confirmed light sensitivity, necessitating amber packaging.

4. CONCLUSION

The present research successfully developed and validated a simple, precise, accurate, and stability-indicating RP-HPLC method for the simultaneous estimation of Tioconazole and Diflucortolone Valerate in combined topical cream formulations, employing a Phenomenex Luna C18 column (250 × 4.6 mm, 5 μm) with an isocratic mobile phase of acetonitrile and 0.05 M KH₂PO₄ buffer pH 3.5 (70:30 v/v) at 1.0 mL/min, detection at 254 nm, and 20 μL injection volume, achieving baseline resolution of DFV at ~6.5 min and TCZ at ~9.8 min (Rs >2.5). The method was validated per ICH Q2(R1) guidelines, meeting all acceptance criteria for specificity, linearity (R² ≥0.9997), accuracy (98-102% recovery), precision (%RSD ≤2.0%), LOD/LOQ, robustness, and solution stability; forced degradation studies confirmed its stability-indicating capability with degradation products well-resolved from parent peaks and PDA-confirmed spectral homogeneity (purity index ≥0.999), revealing alkaline hydrolysis as the most severe degradation pathway for both drugs (DFV: 17.6%, TCZ: 12.4%). The heated methanol extraction procedure (50°C) with ultrasonication yielded high recoveries (98-100%) with minimal matrix interference, and successful application to commercial topical cream demonstrated drug content of 99.1% of label claim for TCZ (9.91 mg/g) and 99.0% for DFV (0.99 mg/g), meeting pharmacopoeial specifications. Thus, this robust, reproducible, and regulatory-compliant method is highly suitable for routine quality control analysis, stability studies, and batch release testing of TCZ and DFV fixed-dose combination products in pharmaceutical industries.

REFERENCES

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