Letter to the Editor: Response to letter on randomized controlled study on the use of multiple-dose activated charcoal in patients with supratherapeutic phenytoin levels

To the Editor

As noted, one of the biggest limiting factors in our study¹ was the low sample size of eligible patients. An increase in patient enrollment may have had the benefit of including females in the study, perhaps including some with higher phenytoin levels greater than 40 mg/L, which may have improved the power of the study. Our low enrollment was due to the relatively few presentations of severe phenytoin toxicity and lack of resources. It is uncertain whether critically ill patients would also benefit from MDAC any more than non-critically ill patients. These patients may have other coingestions and therapeutic requirements. Also, it is unlikely that a retroactive consent would have increased our number of critically ill patients as our consultation service was very active in consulting such patients and their presentation was limited if non-existent in our hospital system. We agree that for such a study on multi-dose activated charcoal (MDAC), looking at the more critically ill would be of benefit.

There may be a theoretical risk to increasing seizures by lowering phenytoin levels more rapidly. None of our patients experienced breakthrough seizures associated with subtherapeutic levels including those that dropped below 20 mg/L during the study period, and we are unaware of any reports of patients having seizures from use of MDAC. In addition, we intended to stop using MDAC in each patient when their serum phenytoin levels reached 25 mg/L to avoid a decrease below a therapeutic level.

There are several transcription errors in Table 1. Under the Time to study completion, the following are the corrected times for the Control Group: patient 1–172 hours, patient 2–35.6 hours, patient 5–11.6 hours, patient 6–196 hours, and patient 8–113 hours. The following are the corrected times for the MDAC Group: patient 1–19.3 hours, patient 2–13.0 hours and patient 3–32.7 hours. Under Last measured concentration the corrected level for the control group patient 5 was 24.0 mg/L. For the MDAC group, the corrected level for patient 1 was 23.9 mg/L and for patient 2 the level was 22.4 mg/L.