Which chemotherapeutic agent has good penetrability into the cerebrospinal fluid?

• A. Streptomycin
• B. Gentamicin
• C. Tobramycin
• D. Chloramphenicol

Answer: (D)

The main idea here is how well a drug can cross the blood–brain barrier to reach cerebrospinal fluid. Chloramphenicol is highly lipophilic and relatively small, so it penetrates the CSF readily and achieves therapeutic levels even when meninges aren’t inflamed. That makes it capable of treating CNS infections effectively.

In contrast, the aminoglycosides—streptomycin, gentamicin, and tobramycin—are hydrophilic and bulky, so they don’t cross into the CSF well. Their CSF concentrations are poor unless meningitis inflames the meninges, and even then they don’t reach levels as reliably as drugs that cross more easily.

So chloramphenicol’s chemical properties give it superior CSF penetration, which is why it’s the correct choice. (Note: its use is limited by toxicity, but that doesn’t change the reason for its CSF penetration.)