Development and Validation of an Assay Method for Levothyroxine Soft Gelatin Capsules Utilizing the RP-HPLC Technique

Area of Science:

• Analytical Chemistry
• Pharmaceutical Analysis

Background:

• Levothyroxine sodium is a critical medication for treating hypothyroidism.
• Accurate quantification of levothyroxine sodium in dosage forms is essential for patient safety and therapeutic efficacy.
• Existing analytical methods may lack the specificity or sensitivity required for comprehensive quality control.

Purpose of the Study:

• To develop and validate a robust, precise, and stability-indicating reversed-phase high-performance liquid chromatography (RP-HPLC) method for levothyroxine sodium.
• To ensure the method's specificity towards all known impurities listed in the levothyroxine drug substance monograph.
• To establish a single, sensitive method for assay across a wide range of levothyroxine sodium capsule strengths.

Main Methods:

• RP-HPLC using an InertSustain AQ C18 column (250 × 4.6 mm, 5 μm) at 60°C.
• A gradient mobile phase consisting of phosphate buffer and acetonitrile, with detection at 225 nm.
• Method validation encompassing linearity, precision, LOD, LOQ, specificity, robustness, and stability-indicating capability.

Main Results:

• The method demonstrated excellent linearity (r² > 0.999) across the validated range.
• High precision was observed with %RSD values of 0.2% for standards and 0.8% for samples.
• The method proved specific for all 14 known impurities, with LOD at 0.05 ppm and LOQ at 0.1 ppm.

Conclusions:

• A validated, stability-indicating RP-HPLC method for levothyroxine sodium in soft gelatin capsules was successfully developed.
• The method is accurate, precise, specific, and robust, suitable for routine quality control and regulatory submissions.
• This analytical approach ensures the quality and safety of levothyroxine sodium capsules across all marketed strengths.