The chromatographic method used for quantification of montelukast was a modification of the method by Raju et al. (22). Drug quantification was performed with HPLC with ultraviolet (UV) detection (Agilent HPLC system 1100/1200 series; Agilent, USA), using a C18 column (RP Agilent Eclipse XDB, 250 mm × 4.6 mm, 5 μm particle size), and ammonium acetate buffer pH 5.5 (A) and methanol (B) as mobile phase, delivered 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, flow rate was 1 mL min−1, run time was 12.30 min, detection wavelength was 284 nm and column temperature was 20°C.