Effect of administration method, animal weight and age on the intranasal delivery of drugs to the brain

Background: The intranasal route of administration has proven to be an effective method for bypassing the blood brain barrier and avoiding first pass hepatic metabolism when targeting drugs to the brain. Most small molecules gain rapid access to CNS parenchyma when administered intranasally. However, bioavailability is affected by various factors ranging from the molecular weight of the drug to the mode of intranasal delivery. Comparison with existing methods: We examined the effects of animal posture, intranasal application method and animal weight and age on the delivery of radiolabeled pralidoxime (H-3-2-PAM) to the brain of rats. Results: We found that using upright vs. supine posture did not significantly affect H-3-2-PAM concentrations in different brain regions. Older animals with higher weights required increased doses to achieve the same drug concentration throughout the brain when compared to young animals with lower body weights. The use of an intranasal aerosol propelled delivery device mainly increased bioavailability in the olfactory bulbs, but did not reliably increase delivery of the drug to various other brain regions, and in some regions of the brain delivered less of the drug than simple pipette administration. Conclusion: In view of the emerging interest in the use of intranasal delivery of drugs to combat cognitive decline in old age, we tested effectiveness in very old rats and found the method to be as effective in older rats. (C) 2017 Elsevier B.V. All rights reserved.