Theophylline and dyphylline levels in serum by liquid chromatography.

The widespread use of theophylline and dyphylline as bronchodilators in the treatment of acute and chronic obstructive airway disease, and recognition of the need to control the therapeutic drug level has created a demand for fast accurate measurement techniques. Measurement of theophylline levels by ultraviolet spectrophotometric techniques is hindered by interferences from barbiturates and caffeine, and thermal lability of the drug necessitates derivatization if gas chromatography is to be used. Because of these factors, a liquid chromatographic method has been developed which allows separation of the underviatized drug from interfering compounds, and quantitation of the theophylline in a single operation. In addition, the drug-containing fraction can be readily collected and subjected to mass spectral examination if there is any question as to its identify. The latter feature has particular significance in medico-legal cases.