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The excretion of theophylline and its metabolites was studied in 8 premature infants treated for apnea. Changes and differences in metabolic patterns were sought. Theophylline and

metabolites were assayed in urine and serum by HPLC. Urine was passed through a Dowex-2 column for clean-up prior to injection. Recovery of compounds by this method was >95%. In 6 patients,

multiple 6 hour urine specimens were assayed.

Theophylline accounted for 62% of the total drug and metabolites excreted. The range was 54 to 95%. 1,3 dimethyluric acid (13DMU), the predominant metabolite in adults, accounted for 22% of

the excreted drug. 1-methyluric acid and 3-methylxanthine comprised the remainder, although caffeine was not quantitated.

In 3 patients, there was a shift to a larger percentage excretion of 13DMU during therapy suggesting a development of metabolizing capacity. Dosage change in one patient resulted in no

change in metabolite pattern.

Differences between patients may be the result of genetic variability or prenatal xenobiotics for which information was incomplete in this study.

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