Which substance is used as an antidote for beta blocker overdose?

Glucagon is the correct antidote for beta blocker overdose due to its unique pharmacological properties. In cases of beta blocker toxicity, the normal response of the cardiovascular system is impaired due to the blockade of beta-adrenergic receptors, which can lead to bradycardia and hypotension. Glucagon works independently of the beta receptors and stimulates the production of cyclic AMP (cAMP) through glucagon receptors. This action increases heart rate and myocardial contractility, effectively counteracting the effects of the beta blocker overdose.

Other treatments may aim to enhance heart function or manage symptoms, but glucagon is specifically utilized in this scenario due to its effectiveness in reversing the cardiovascular effects caused by beta blockers. This is particularly beneficial in severe cases where cardiac support is crucial.

It is also important to understand that the other substances listed do not serve as effective antidotes for beta blocker overdose. For instance, ephedrine could potentially increase sympathetic output but does not directly address the underlying receptor blockade. Nitrites are used for cyanide poisoning but have no role in beta blocker toxicity. Penicillamine is a chelating agent used primarily in heavy metal poisoning and autoimmune diseases, making it irrelevant in the context of beta blocker overdose.