The client is demonstrating signs and symptoms of digoxin toxicity. The antidote for cardiac digitalis glycoside toxicity is:

A) Naloxone (Narcan):
Naloxone is the antidote for opioid overdose, not for digoxin toxicity. It works by reversing the effects of opioid drugs such as morphine, heroin, and oxycodone by binding to opioid receptors in the brain. While Naloxone is vital in opioid toxicity, it has no effect on the toxicity of digoxin.

B) Digoxin immune FAB (Digibind):
Digoxin immune FAB (Digibind) is the antidote for digoxin toxicity. It works by binding to the digoxin molecules in the bloodstream, thereby inactivating them and preventing them from exerting their toxic effects on the heart. This treatment is critical in cases of severe digoxin toxicity, particularly when the patient exhibits symptoms such as life-threatening arrhythmias, severe bradycardia, or altered mental status. 

C) Vitamin K:
Vitamin K is the antidote for warfarin (Coumadin) toxicity, not digoxin toxicity. It promotes the synthesis of clotting factors in the liver and is used to reverse excessive anticoagulation in cases of bleeding due to warfarin. It has no effect on digoxin toxicity, which requires specific treatment with digoxin immune FAB.

D) Inamrinone (Inocor):
Inamrinone is an inotropic medication used to treat severe heart failure by improving heart contractility. However, it is not used as an antidote for digoxin toxicity. In fact, inamrinone and other inotropic agents may be used cautiously in patients with digoxin toxicity, as they could potentially exacerbate arrhythmias, a known complication of digoxin toxicity.