Development and Validation of Stability-Indicating RP-HPLC Method for the Simultaneous Determination of Tizanidine HCl and Meloxicam in Rabbit's Plasma

High-performance liquid chromatography (HPLC) is a widely used technique for the simultaneous detection and quantification of different drugs. The purpose of the current study was to develop a simple and cost-effective reversed-phase high-performance liquid chromatography (RP-HPLC) method for the simultaneous determination of tizanidine (TZN) HCl and meloxicam (MLX) in rabbit's plasma. Assay of TZN and MLX was performed after extraction of drug from plasma by liquid-liquid extraction technique using methanol and diethyl ether as protein precipitants. Isocratic elution was performed in a Kromasil (R) C18 column (dimension, 250 x 4.60 mm; particle size, 5 mu m) with mobile phase consisting of methanol-water (8: 2). Orthophosphoric acid was used to adjust the pH of the mobile phase 3.0, and detection was done at 228 nm. Flow rate was 0.8 mL/min with ambient temperature and average operating pressure of 1400 psig. Retention time of TZN was 2.612 min and that of MLX was 6.960 min with a resolution of 3.18. Both drugs showed satisfactory linearity in the range of 10 to 50 ng/mL with correlation coefficients (R-2) of 0.9989 and 0.9972 for TZN and MLX, respectively. The developed method was validated successfully for linearity, system suitability, intra-day and inter-day accuracy, and precision, robustness, and specificity following International Conference on Harmonization (ICH) guidelines. Conclusively, a precise, stable, reproducible, economical, and suitable method for estimation of pharmacokinetic evaluation was developed and validated.