Which drug is known to inhibit topoisomerase II (also known as DNA gyrase)?

Enrofloxacin is a fluoroquinolone antibiotic that exerts its effects by targeting bacterial topoisomerase II, also known as DNA gyrase. This enzyme is crucial for bacterial DNA replication, as it introduces negative supercoils into DNA, allowing for the unwinding necessary for replication and transcription. By inhibiting topoisomerase II, enrofloxacin disrupts this process, leading to cell death due to the inability of the bacteria to properly replicate their DNA.

Ciprofloxacin, while also targeting topoisomerase II, is not the best choice for the question given; the question specifies which drug is known to inhibit the enzyme, and enrofloxacin is often referenced in this context, particularly in veterinary medicine. Doxycycline, on the other hand, is a tetracycline antibiotic that works by inhibiting protein synthesis and does not target topoisomerases. Ampicillin is a penicillin antibiotic that primarily works by inhibiting bacterial cell wall synthesis, which is a different mechanism of action entirely. Thus, enrofloxacin stands out as the correct answer for its specific inhibition of topoisomerase II.