Pharmacokinetic analysis of antiviral drug ritonavir across the blood - brain barrier and its interaction with Scutellaria baicalensis using multisite microdialysis in rats

Ritonavir, an excellent inhibitor of CYP3A4, has recently been combined with nirmatrelvir to form Paxlovid for the treatment of severe acute respiratory syndrome coronavirus 2 infections. The root of Scutellaria baicalensis Georgi (S. baicalensis), a traditional Chinese medicinal (TCM) herb commonly used to treat heat/inflammation in the lung and digestive tracts, which are major organs targeted by viral infections, contains flavones that can influence the CYP3A metabolism pathway. To investigate the ability of ritonavir to cross the blood-brain barrier (BBB) and its potential herb-drug interactions with an equivalent TCM clinical dose of S. baicalensis, multisite microdialysis coupled with an LC-MS/MS system was developed using rat model. Pretreatment with S. baicalensis extract for 5 days, which contains less flavones than those used in previous studies, had a significant influence on ritonavir, resulting in a 2-fold increase in the total concentration of flavones in the blood and brain. Treatment also boosted the maximum blood concentration of flavones by 1.5-fold and the maximum brain concentration of flavones by 2-fold, all the while exerting no noticeable influence on the transfer ratio across the blood-brain barrier. These experimental results demonstrated that the use of a typical traditional Chinese medicinal dose of S. baicalensis is sufficient to influence the metabolic pathway and synergistically increase the concentration of ritonavir in rats.