What method is used for fast delivery of a drug to the cerebrospinal fluid?

• A. Oral
• B. Intraperitoneal
• C. Intravenous
• D. Topical

Answer: (B)

Delivering a drug to the cerebrospinal fluid quickly requires bypassing the blood-brain barrier and placing the drug directly into the CSF. The fastest way to do that is by direct administration into CSF spaces—intrathecal (into the spinal canal) or intraventricular (into the brain ventricles) injections.

Oral administration and topical application never provide rapid CSF exposure. Intraperitoneal absorption is slow and variable and ultimately relies on systemic circulation, which is not a fast or reliable route to CSF. Intravenous delivery is rapid systemically, but crossing into CSF still depends on the blood-brain barrier, so it is not as direct or fast as intrathecal or intraventricular administration.

In summary, the quickest route to CSF is direct CSF injection, which isn’t represented among the listed options. If choosing among systemic routes, intravenous is faster than oral or topical, but it does not achieve fast direct CSF delivery like a CSF-specific route would.