In vivo N7 methylation of theophylline to caffeine in premature infants. Studies with use of stable isotopes.

We studied the metabolism of theophylline in premature neonates by the use of molecules labelled with stable isotopes. 2 prematures received from birth up to 8th day of life 3 mg/kg/8 h of a mixed solution containing 46% of labelled and 54% of unlabelled theophylline. Plasma levels of caffeine and theophylline, measured by gas chromatographic mass spectrometric analysis, demonstrated the in vivo biotransformation of theophylline to caffeine in prematures.