**Core Concept**
Digoxin is a cardiac glycoside used to treat heart failure and atrial fibrillation. Its toxicity can be influenced by several factors, including electrolyte imbalances, renal function, and magnesium levels.

**Why the Correct Answer is Right**
Digoxin toxicity is primarily related to its interaction with potassium, sodium, and calcium levels in the body. Hyperkalemia, or elevated potassium levels, actually protects against digoxin toxicity by competing with digoxin for binding sites on the sodium-potassium ATPase pump. This reduces the amount of digoxin available to bind to the cardiac sodium-potassium pump, thus reducing its toxic effects. Therefore, hyperkalemia is not a risk factor for digoxin toxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** Renal impairment can increase digoxin toxicity because digoxin is primarily excreted by the kidneys. Reduced renal function leads to decreased clearance of digoxin, resulting in higher plasma concentrations and increased risk of toxicity.
**Option C:** Hypomagnesemia, not hypermagnesemia, is associated with increased digoxin toxicity. Magnesium plays a crucial role in maintaining the stability of cardiac membranes, and its deficiency can predispose to digitalis-induced arrhythmias.
**Option D:** Hypercalcemia can increase digoxin toxicity by increasing the sensitivity of the heart to digoxin. Elevated calcium levels can enhance the binding of digoxin to the cardiac sodium-potassium pump, increasing its toxic effects.

**Clinical Pearl / High-Yield Fact**
When managing patients on digoxin therapy, it's essential to monitor their electrolyte levels regularly, particularly potassium, magnesium, and calcium. A simple mnemonic to remember the factors that increase digoxin toxicity is "KISS": Kidney problems (renal impairment), low Magnesium, and high Sodium (hypernatremia) all contribute to increased risk of toxicity.

✓ Correct Answer: B. Hyperkalemia