Flucytosine is particularly toxic to which type of cells?

Flucytosine is particularly toxic to rapidly proliferating tissues due to its mechanism of action. Flucytosine is an antimetabolite that gets converted inside the fungal cell into 5-fluorouracil, which then interferes with nucleic acid synthesis by inhibiting thymidylate synthase. This inhibition affects cells that are rapidly dividing, including those found in various tissues, such as bone marrow and the gastrointestinal tract.

Rapidly proliferating cells are more susceptible to the effects of flucytosine because they are continuously undergoing the processes of DNA and RNA synthesis, which flucytosine disrupts. As a result, tissues with high turnover rates, such as those involved in immune response or tissue regeneration, experience significant toxicity. This makes the answer particularly fitting in recognizing the target of flucytosine's cytotoxic effects compared to other cell types, which might not be as affected due to slower rates of proliferation.