Final answer:
Glucagon is the antidote administered in cases of β-blocker toxicity. It helps reverse the toxic effects of β-blockers by increasing myocardial contractility and heart rate.
Step-by-step explanation:
The antidote administered in cases of β-blocker toxicity is glucagon. Glucagon helps reverse the toxic effects of β-blockers by increasing myocardial contractility and heart rate through its action on the adenylyl cyclase pathway.