A patient is hospitalized with a central nervous system infection that needs to be treated with water-soluble antibiotics. The medications will be instilled into the subarachnoid space via an epidural catheter

Question

Why is this the best route of administration for this patient? a. Intravenous water-soluble antibiotics cannot pass through the blood-brain barrier.
b. Only water-soluble medications can pass into the brain and cerebrospinal fluid.
c. Older patients better tolerate lipid soluble medications than younger patients.
d. Lipid soluble medications are safer for patients who are pregnant.

Answer 1

A
To be distributed to an organ, a medication needs to pass through all the biological membranes of that organ. Some membranes serve as barriers to the passage of medications. For example, the blood-brain barrier allows only lipid-soluble medications to pass into the brain and cerebrospinal fluid. Therefore central nervous system (CNS) infections sometimes require treatment with antibiotics injected directly into the subarachnoid space in the spinal cord. Older patients often experience adverse effects (e.g., confusion) because they experience a change in the permeability of the blood-brain barrier, which enhances the passage of fat-soluble medications into the brain. Lipid-soluble, nonionized drugs easily cross the placenta and can cause serious harm to the fetus.