In reply:

Our team thanks Santos et al1 for their commentary in regard to the management of emergency department patients with presumed fentanyl overdose. They raise the important point that, because of the low postoverdose mortality risk, any observation window for such patients may be questionable. Boyer2 suggested a 4- to 6-hour observation period after naloxone resuscitation, but this is not supported by clear evidence in patients with fentanyl overdose. In therapeutic doses, fentanyl has a short duration of action because it is quickly redistributed out of the central nervous system into peripheral tissues before being quickly eliminated.

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