The chromatographic methods used for drug analysis were modifications of published methods (31,32). Drug quantification was performed with HPLC with ultraviolet (UV) detection (Agilent HPLC system 1100/1200 series; Agilent, USA). A RP Agilent Eclipse XDB C18 column (250 mm × 4.6 mm, 5-μm particle size) was used for both drugs. For montelukast, the mobile phase was composed of ammonium acetate buffer pH 5.5 and methanol (solvents A and B, respectively) delivered at a flow rate of 1 mL min−1, on a linear gradient. The selected gradient started with 10% of solvent B, which was increased to 50% within 2 min, and 90% within 4 min; at 11.30 min, the initial conditions of analysis were re-established. Injection volume was 100 μL. Analysis was performed at 20°C and the detection wavelength was 284 nm. Elution time for montelukast was 8.9 min. For analysis of mesalazine, the mobile phase was composed of 0.05% TFA/water and methanol (95:5), delivered at a flow rate of 1 mL min−1. Injection volume was 20 μL. Analysis was performed at 40°C and the detection wavelength was 304 nm. Elution time for mesalazine was 4.6 min.