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Summary
A quantitative method for the simultaneous determination of theophylline (THP) and its metabolites, 1,3-dimethyluric acid (1,3-DMU), 1-methyluric acid (1-MU) and 3-methylxanthine (3-MX), in urine is described, using a preliminary extraction step with ‘Extreluf column and high pressure liquid chromatographic separation. Urinary excretion data of theophylline and its metabolites from 2 healthy male volunteers on a regular diet demonstrated high background values of 1-MU, to a lesser degree for 3-MXandTHP, and virtually none for 1,3-DMU, when the subjects were not receiving theophylline. Observed increments {above background values) following single-dose (375 mg) administrations of theophylline, orally and rectally, demonstrated 1,3-DMU as the predominant urinary excretory product together with 3-MX as an additional urinary metabolite, while the virtual absence of any increments in the 1-MU metabolite would indicate that biotransformation of theophylline to the 1-MU pathway is minimal or insignificant after theophylline administration to subjects on a regular diet (possibly due to enzyme saturation associated with dietary methyl-xanthines). Similar excretion patterns of THP and its metabolites in urine after theophylline administrations, orally and rectally, suggest hepatic metabolism of theophylline after the two different routes of administration to be similar.