Sir.—Although our article is not cited by Simons et al (Journal 1980;134:39-41), we first reported the phenomenon of biphasic theophylline elimination in 1978.1 Although our case involved an older child (7 months), the elimination curves are surprisingly similar. It should be noted that our patient did not receive phenobarbital. As a result, we speculate that phenobarbital has nothing to do with the shorter half-life reported in the second phase. If case 1 of Simons et al had been followed up long enough, it is likely that a similar phenomenon could have been observed. In our case report, the time at which the kinetic change took place was approximately the same. There were no caffeine metabolites present in our patient, and we attribute this to the age differential. The ratio of CSF theophylline to serum theophylline is approximately the same level in both their case and our case. We
KADLEC GJ, JARBOE CH, POLLARD SJ. Theophylline Pharmacokinetics. Am J Dis Child. 1981;135(1):82–83. doi:10.1001/archpedi.1981.02130250068025
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