2.6. Evaluation of FDC tablets

Ten tablets were randomly selected for each of the 16 formulas of APX and CLOP batch to perform weight variation, thickness, and hardness test. The friability test of IR CLOP and ER APX formulated tablets were evaluated using the pharm-test friabilator. The disintegration times of the IR CLOP formulated tablets were evaluated using a pharm-test disintegrator that operated at 37 ± 2 °C. Six tablets of CLOP were placed into the six cells of the rack, one per cell, and then immersed in water. For all evaluations, the means and standard deviations were calculated.

Ten tablets of each formula were powdered in a mortar and a pestle. The weight of one tablet (75.75 mg and 150.05 mg of APX and CLOP, respectively) was dissolved in 100 ml ACN, leftover a night to ensure complete dissolution, 5 ml of solution was filtered in a 50 ml volumetric flask through a 0.45 μm syringe filter, and the volume was made up using purified water. The drug content assay was evaluated by chromatographic separation of the APIs on a BDS Hypersil C₁₈, (4.6*150 mm, 5 μm), with ACN and TFA in the ratio 48:52 (v/v) as a mobile phase, at a flow rate of 0.9 ml/ min., column temperature 45 °C, and injection volume of 5 μL. The calibration curve was developed for each API and the correlation coefficient R² was more than 0.999 (Al-Shami et al., 2024).

For CLOP, in vitro drug release studies were carried out in 750 ml of 0.1 N HCL for 2 hrs. For APX, in vitro, drug release studies were carried out in 900 ml of 0.05 M Sodium phosphate buffer with 0.05 % SLS for 24 hrs. A USP type II dissolution apparatus (paddle type) was used to test both at 75 rpm and 37 ± 0.5 °C. All dissolution studies were performed on three tablets of each formula.

The in vitro drug release study for the final FDC, two strengths, was carried out using the USP delayed release method A (United States Pharmacopeial Convention, 2011). The study was performed in 750 ml of 0.1 N HCL. Samples were withdrawn at (5, 10, 20, 30, 45, 60, and 120 min.). After 2 hrs., 250 ml of 0.2 M tribasic sodium phosphate equilibrate 37 ± 0.5 °C was added to the dissolution media, and the pH of the media was adjusted to (6.8 ± 0.05). The apparatus continued to run for 24 hrs. A sample of 5 ml was withdrawn from the dissolution media in a specified period (4, 8, 12, 16, 20, and 24 hrs.). All of the experiments were tested using a USP type II dissolution apparatus (paddle type) at 75 rpm and 37 ± 0.5 °C. All dissolution studies were performed on six tablets of each formula.

A sample of 5 ml was withdrawn from the dissolution media using an auto-sampler, and no volume correction was made. The samples were filtered using a 0.45 μm Clarify® syringe filter. The absorbance of the samples was measured using a spectrophotometric method at 210 nm using HPLC developed method(Al-Shami et al., 2024) and the % cumulative release (% CR) was plotted using calculated mean values of cumulative drug release versus time.

The release data were fitted to five kinetic models including; zero-order, first-order, Higuchi, Hixon-Crowell, and Korsmeyer-Peppas to determine the drug release mechanism with the aid of DD Solver add-in software. The drug release mechanism was considered according to the coefficient of determination; R² values (Grassi and Grassi, 2014).