Intrathecal chemotherapy: brain tissue profiles after ventriculocisternal perfusion

Area of Science:

• Pharmacology
• Neuroscience
• Drug Delivery

Background:

• Understanding drug distribution in the brain is critical for effective intrathecal administration.
• Rhesus monkeys serve as a relevant model for studying drug penetration in primate brains.

Purpose of the Study:

• To quantify the diffusion and distribution of isotopically labeled drugs within the caudate nucleus of rhesus monkeys.
• To determine apparent diffusion constants and capillary permeability of selected drugs after ventriculocisternal perfusion.
• To evaluate the utility of these parameters in predicting drug concentrations following intrathecal administration.

Main Methods:

• Ventriculocisternal perfusions were conducted using five isotopically labeled drugs in rhesus monkeys.
• Tissue diffusion concentration profiles in the caudate nucleus were analyzed.
• Periventricular distribution space, apparent diffusion constants, and capillary permeability (extracellular fluid-transcapillary half-time) were measured.

Main Results:

• Significant variations in periventricular distribution space were observed, with cytosine arabinoside showing the highest ( > 170 µL/100 mg).
• Apparent diffusion constants were determined for hydroxyurea (2.0 x 10^-6 cm²/sec) and methotrexate (1.2 x 10^-6 cm²/sec).
• Capillary permeability varied, with rapid exchange for thiotepa (1.0 min) and BCNU (0.8 min), and low permeability suggested for cytosine arabinoside.

Conclusions:

• Apparent parenchymal diffusion constants and capillary permeability are key parameters for predicting intrathecal drug levels.
• Drug-specific diffusion and permeability characteristics influence their distribution and efficacy within the brain parenchyma.
• These findings support the development of optimized intrathecal drug delivery strategies.