Opioid Overdose
Excess mu-opioid activation blunts the brainstem response to carbon dioxide, so ventilation fails first; naloxone displaces the opioid, but for less time than the opioid lasts.
Definition
Opioid overdose is opioid-induced respiratory depression: a respiratory rate of 8 breaths per minute or less in a person who is barely rousable, unconscious or cyanosed, usually with pinpoint pupils. That combination, rather than the drug history, is what makes naloxone indicated.
First principles
One receptor explains the whole toxidrome
Opioids activate mu-opioid receptors. In the brainstem this blunts the ventilatory response to rising carbon dioxide, so the person breathes slowly and shallowly. The same receptor family produces sedation and miosis. The threshold that matters is numerical: respiratory depression means a respiratory rate of 8 breaths per minute or less, in someone barely rousable, unconscious or cyanosed. That is the finding which makes naloxone indicated, not the drug history.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.