Abstract
A method for the quantitation of theophylline (13DMX) and the three metabolites, 1-methyluric acid (1MU), 3-methylxanthine (3MX) and 1,3-dimethyluric acid (13DMU) in human plasma and urine has been developed. The method is based on a simple one-step liquid-liquid extraction with ethylacetate-2 propanol followed by isocratic, reversed-phase high-performance liquid chromatography with UV detection (detection wavelength: 273 nm). The overall mean recoveries ranged from 86 to 95% for the four compounds. The detection limit was 1 μm for 1MU, 3MX and 13DMU and 2 μ M for 13DMX in urine, and 0.1 μ M for 1MU, 3MX and 13DMU and 0.2 μ M for 13DMX in plasma. The intra-day and inter-day coefficient of variation was <6% and <9%, respectively, and the accuracy was within ±10% in both urine and plasma. The simple but sensitive method is highly suitable for the development of theophylline as a probe drug for assessing CYP1A2 activity in man.
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