The Effects of Arginine Vasopressin and Acetazolamide on CNS Clearance of Acetaminophen and Ibuprofen in Rats

Objective: The convective flow of CSF plays a crucial role for CNS to clear endogenous and xenobiotic substances. The objective of this study is to investigate the impact of modifying CSF flow with acetazolamide and arginine vasopressin (AVP) on the CNS clearance of ibuprofen and acetaminophen. Results: Microdialysis studies indicated that acetaminophen AUC ratio (Kp,uu) between brain ISF and unbound plasma increased from 0.40 ± 0.14 in the vehicle control group to 0.60 ± 0.27 in the acetazolamide treated group (P < 0.05). Conversely, acetaminophen’s steady-state ISFC to unbound_plasmaC ratio (Kp,uu) decreased from 0.44 ± 0.08 to 0.36 ± 0.07 upon IV infusion of 0.3 µg/hr AVP (P < 0.05). Using CSF concentration as a surrogate of unbound brain drug concentration, AVP treatment reduced the CSFAUC0-5hr/unbound_plasmaAUC0-5hr ratio from 1.63 to 0.85 for acetaminophen, and the CSFC4hr / unbound_plasmaC4hr ratio decreased from 0.91 ± 0.27 to 0.54 ± 0.12 for ibuprofen (P < 0.05). Conclusion: We have demonstrated that acetazolamide decreases the CNS clearance of acetaminophen, while AVP increases the CNS clearance of both acetaminophen and ibuprofen. Such changes are caused by altering the CSF production rates.