Which of the following drugs works in the cytosol?

Nitroglycerin is the correct answer because it functions as a vasodilator primarily in the cytosol of vascular smooth muscle cells. Once administered, nitroglycerin is converted to nitric oxide (NO) in the body, a signaling molecule that diffuses into the smooth muscle cells where it activates guanylate cyclase. This leads to an increase in intracellular levels of cyclic GMP (cGMP), which ultimately causes relaxation of smooth muscle and dilation of blood vessels.

In contrast, vancomycin is an antibiotic that works by inhibiting cell wall synthesis in bacteria, requiring it to act outside the cytosol, specifically targeting the bacterial cell wall. Penicillin operates in a similar manner, preventing the formation of peptidoglycan layers in bacterial cell walls. Ciprofloxacin is a fluoroquinolone antibiotic that affects bacterial DNA replication and functions by inhibiting bacterial DNA gyrase and topoisomerase IV, which are located in the bacterial cytoplasm but not the cytosol of human cells.

Thus, nitroglycerin's role as a cytosolic agent highlights its mechanism of action related to vasodilation and the importance of intra-cellular signaling pathways.