Toxicology USMLE Step 1 Practice Question

A 25-year-old man with a history of intravenous drug use is found unresponsive with shallow breathing (RR 8/min), bradycardia (HR 52/min), and pinpoint pupils. Vital signs show BP 88/56 mmHg, temperature 35.2°C, and SpO2 78% on room air. Physical examination reveals track marks on both forearms and fresh needle puncture wounds. Arterial blood gas shows respiratory acidosis with pH 7.22 and PaCO2 68 mmHg. No evidence of trauma or focal neurological deficits is noted. Which medication most appropriately reverses the life-threatening effects of his suspected overdose?