Nasal powder formulation employing microenvironmental pH-modifier for rapid absorption of mirtazapine

Antidepressant mirtazapine (MRZ) has been drawing attention in the management of delirium. However, oral use of MRZ could have drawbacks in onset of actions and ease of administration by caregivers. This study was the first attempt to develop nasal powder formulation (NP), an easily-administered formulation, of MRZ containing a microenvironmental pH-modifier for rapid dissolution and absorption. Ten mixtures of MRZ and counterions were tested in terms of the supersaturation level and stability to select a favorable pH-modifier. NP of MRZ (NP/MRZ) with the selected counterion was prepared by jet milling and characterized regarding physicochemical properties and pharmacokinetic (PK) behaviors after intranasal administration to rabbits. In phosphate buffer solution (PBS, pH5.6), glutamic acid (Glu) showed 10.7-fold supersaturation of MRZ, with the value being the highest among the ten counterions tested. The addition of Glu led to no significant change in the photostability or chemical stability of MRZ compared with crystalline MRZ. NP/MRZ with Glu (NP/MRZ-E) consisted of microcrystals of MRZ and Glu attached to lactose carriers, and over 93% of MRZ was emitted from a capsule in Jetlizer™. Both NP/MRZ-E and NP/MRZ exhibited enhanced dissolution in PBS compared with crystalline MRZ, and more rapid dissolution was observed for NP/MRZ-E. In rabbits, a crushed MRZ tablet (3 ​mg-MRZ/kg, p.o.) exhibited a time to maximum plasma concentration (T _max) and bioavailability (BA) of 72 ​min and 10%, respectively. NP/MRZ-E (0.3 ​mg-MRZ/kg, i.n.) showed T _max of <5 ​min with BA of 93%, and this result might be due to rapid dissolution/permeation in nasal mucosa and avoidance of the hepatic first-pass effect. In conclusion, NP employing a microenvironmental pH-modifier would be a promising dosage form of MRZ to offer rapid nasal absorption.