Final answer:
Atropine is the drug used as an antidote to treat bradycardia caused by beta blocker toxicity by increasing heart rate.
Step-by-step explanation:
The drug that can be used as an antidote to treat bradycardia associated with beta blocker toxicity is atropine. Beta blockers, such as metoprolol and propanolol, act by binding to the beta receptors on the heart and blocking them, leading to a decrease in heart rate. When too much of a beta blocker is given, it can result in bradycardia (abnormally slow heart rate) or even cardiac arrest. Atropine is an anticholinergic drug that can be used to counteract the effects of beta blockers on the heart by blocking the muscarinic acetylcholine receptors, thus increasing the heart rate.