Direct Delivery of Caffeine from Nose to Brain: The Effect of Anesthesia on Caffeine Pharmacokinetics and Brain Distribution D. Inoue1, M. Hirao1, A. Tanaka2, K. Kusamori2, H. Katsumi2, A. Yamamoto2, T. Sakane3, T. Furubayashi1 1Shujitsu University, 2Kyoto Pharmaceutical University, 3Kobe Pharmaceutical University Purpose The intranasal drug delivery has drawn much attention for drug delivery to the brain. The nasal cavity is connected anatomically with CNS and the drug applied intranasally can gain a quick and easy access to the brain through the pathways along the olfactory and trigeminal nerves. Therefore, intranasal drug delivery can be utilized as a means of preferential drug delivery to the brain. The purpose of the present study is to assess the pharmacokinetics of a drug administrated intranasally to rats, and to investigate the effect of anesthesia on drug pharmacokinetics in the brain. Methods Caffeine was used as a model drug to investigate the plasma and brain pharmacokinetics of drugs in rats. The animal experiments were conducted using adult male rats which received 2 mg/mL caffeine solution under urethane anesthesia or under conscious condition. For intranasal (IN) administration, 20 μL of caffeine solution was instilled into one side of the nasal cavity by a microliter syringe through 10 mm polyethylene tube. Total 40 μL of drug solution was administrated bilaterally to the rat nasal cavity. For intravenous (IV) administration, caffeine solution (1 mL/kg of 0.4 mg/mL) was injected into the right femoral vein of rats. After an appropriate time interval, rats were anesthetized and cerebrospinal fluid (CSF) was collected by the technique of cisternal puncture. After blood sampling blood was removed by transcardial perfusion of ice-cold phosphate-buffered solution from abdominal vein, and then the whole brain was obtained. Olfactory bulb (OB), cerebrum (CR), cerebellum (CL) and hippocampus (HI) were dissected and the caffeine concentration of each sample was measured. Plasma pharmacokinetics and distribution of caffeine in CSF and the brain was estimated. The effect of anesthesia on the pharmacokinetics and brain distribution of caffeine was investigated, comparing the data under anesthesia with those under conscious condition. Results After intravenous dosing, caffeine appeared in CSF and the brain at initial sampling time (5 min) and concentrations reached a peak 5-15 min following IV administration, indicating that caffeine is distributed quickly from systemic circulation through blood-brain barrier (BBB) to the brain. AUC ratios (brain or CSF/plasma) under anesthesia and conscious condition were similar, suggesting that the distribution of caffeine into the brain and CSF after IV administration may be unaffected by the urethane anesthesia. In contrast, AUC ratios under anesthesia after IN administration were increased by 45% (brain) and 38% (CSF), as compared with the conscious condition. Additionally, under conscious condition, the drug targeting index (DTI) and the direct transport percentage to the brain (DTPbrain) were 1.03 and 2.5% and DTPCSF was 18.6%, while, DTI, DTPbrain and DTPCSF under anesthesia were 1.20, 16.2% and 42.3%, respectively. Since these parameters represent the index of efficacy of nasal drug delivery to CSF and the brain, it was suggested that caffeine was directly transported from nose to the brain after IN administration, and the transport of caffeine to the brain and CSF was enhanced under anesthesia. Recently, it has been reported that natural sleep or anesthesia drive the rate of clearance of beta-amyloid and inulin injected frontal cortex (Xie L, et al., Science, 342, 6156, 2013). The secretion of CSF may be changed by sleep. Our results show that caffeine distribution in the brain was facilitated under anesthesia. The mechanism of this finding is not clear at present. We are now trying to clarify the detail of this finding, assuming some contribution of the change in the secretion of CSF. Conclusion Caffeine was distributed in brain and CSF quickly and easily from systemic circulation. From the results, caffeine transport to the brain and CSF was unaffected by anesthesia after IV administration, while the increase of caffeine distribution in the brain and CSF was observed after IN administration under anesthesia. These findings suggest that the nose to brain direct delivery and caffeine transport may be affected by the change in CSF secretion under anesthesia.