In Reply.—The slower, initial first-order elimination half-life values are similar in the patient of Kadlec et al1 and in our much younger patients and seem to indicate saturation of the predominant metabolic pathway. We attributed the slow first-order elimination of methylation, whereas Kadlec et al suggested that first-order renal clearance was apparent. This may not be so, however, since their patient was anuric for ten hours, and there is significant positive correlation between the renal clearance of theophylline and urine flow rate.2
Kadlec et al suggest that no caffeine was found in their patient because of her age. However, Hartemann et al3 have found caffeine in the serum of an 18-month-old infant who ingested 204 mg/kg theophylline, achieving a peak serum concentration of 86 μg/mL. We have shown in our laboratory4 that during analysis of caffeine by high-performance liquid chromatography, excessive heating of samples during
SIMONS KJ, SIMONS FER. Theophylline Pharmacokinetics-Reply. Am J Dis Child. 1981;135(1):83. doi:10.1001/archpedi.1981.02130250068026
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