## **Core Concept**
The question tests the understanding of drug interactions, specifically the risk of cardiac arrhythmias due to QT interval prolongation. Sparfloxacin is a fluoroquinolone antibiotic, and terfenadine is an antihistamine. Both classes of drugs are known to affect cardiac electrophysiology.

## **Why the Correct Answer is Right**
The combination of sparfloxacin and terfenadine can cause **QT interval prolongation**, leading to a potentially life-threatening arrhythmia known as Torsades de Pointes. Sparfloxacin, like other fluoroquinolones, can prolong the QT interval by blocking potassium channels in the heart. Terfenadine, a second-generation antihistamine, is also known to prolong the QT interval through a similar mechanism. When used together, their effects on the QT interval are additive or even synergistic, significantly increasing the risk of serious cardiac arrhythmias.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although drug interactions can lead to various adverse effects, the specific combination of sparfloxacin and terfenadine is particularly noted for its risk of cardiac arrhythmias rather than a general effect like hypotension.
- **Option B:** This option does not directly relate to the well-documented interaction between fluoroquinolones like sparfloxacin and antihistamines like terfenadine.
- **Option C:** While seizures are a potential side effect of some fluoroquinolones, especially at high doses or in susceptible individuals, the combination of sparfloxacin and terfenadine is specifically concerning for cardiac effects rather than seizures.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **QT interval prolongation** can lead to Torsades de Pointes, a potentially fatal arrhythmia. Drugs that prolong the QT interval are often listed together on medication interaction checkers, and caution is advised when combining such agents. Specifically, the concomitant use of certain fluoroquinolones (like sparfloxacin) with antihistamines (like terfenadine) should be avoided due to this risk.

## **Correct Answer:** D. Torsades de Pointes.