Final answer:
Atropine is the correct medication to administer for a client experiencing sinus bradycardia with hypotension and dizziness as it increases the heart rate by blocking acetylcholine receptors.
Step-by-step explanation:
If a client is experiencing sinus bradycardia with hypotension and dizzy spells, the medication commonly administered is atropine. Atropine works as an anticholinergic and counteracts the effects of excess acetylcholine that can slow the heart rate, effectively treating bradycardia by increasing the heart rate. It is the antidote to muscarinic acetylcholine receptor agonists and can be life-saving in instances where vagal stimulation has excessively reduced the heart rate.
The other medications listed serve different purposes: Digoxin is primarily a cardiac glycoside used to treat heart failure and atrial fibrillation by increasing the force of myocardial contraction; Lidocaine is an antiarrhythmic used for the treatment of ventricular arrhythmias; and Metoprolol is a beta blocker used to treat hypertension and prevent angina but could exacerbate bradycardia and hypotension. Therefore, atropine is the best choice for immediate treatment in this scenario.