Theophylline was assayed with a high performance liquid chromatography equipped with a reverse-phase column (Hypersil BDS C18, 250 × 4.6 mm, 5 µm) and a UV spectrophotometer at 272 nm (Shimadzu SPD-6AV). The mobile phase of acetonitrile and 0.2 M acetate buffer solution (pH 4.5) in the volume ratio of 6.5 : 93.5 (%, v/v) was applied at a flow rate of 1.0 mL/min. The intra- and inter-day precision and accuracy of the HPLC analytical method were validated before sample analysis.