Category: Preclinical Development
Purpose: Naloxone, an opioid antagonist, was primarily available as an injectable drug product but recently has been introduced as an intranasal (IN) solution to facilitate quick treatment of opioid overdose victims. The intranasal formulation of naloxone contains various excipients which could affect permeation and systemic absorption of naloxone as compared to the naloxone injection. In fact, one patented formulation reported substantially lower relative bioavailability compared to intramuscular naloxone injection, implying that the composition of IN formulations may play a critical role in determining the rate and extent of nasal absorption of naloxone. To evaluate the effect of these excipients and other formulation variables such as solution pH on the performance and stability of IN naloxone, in-house naloxone IN formulations were investigated in this study using an in vitro nasal permeation model and a comprehensive stability study.
Methods: A full factorial design of experiment (DOE) with eighteen IN formulations was used to study the effect of the excipients on the nasal permeability and stability of naloxone at three naloxone concentrations (4, 22 and 40 mg/mL). In addition, permeation and stability of naloxone IN formulations with pH ranging between pH 4.0 and 6.0 were also evaluated. The apparent permeability (Papp) of naloxone across human epithelia from various IN formulations was studied employing Ussing chambers (Physiologic instruments, Inc) mounted with EpiAirwayTM culture inserts (membrane supported human upper airway epithelia, MetTak, Inc.). Trans epithelial electrical resistance (TEER) was also recorded throughout the experiment to assess the impact of excipients or solution pH on the integrity of the epithelial cells. For stability evaluation, the eighteen IN formulations prepared per DOE were stored under accelerated (40°C/75%RH), inter-mediate (30°C/75%RH) and long-term (25°C/60%RH) storage conditions for up to one year. Also, naloxone solutions of various pH (4.0 to 6.0) were stored at 60°C for 7 days or 25°C for 30 days. The samples were analyzed using a stability-indicating chromatographic method, adopted from compendia with modifications, using Waters ACQUITY H-class UPLC system.
Results: Benzalkonium chloride (BC) and benzyl alcohol (BA) were found to increase the Papp of naloxone and decrease TEER of the treated epithelia. These results suggest that both preservatives can enhance the permeability of naloxone probably through disrupting the integrity of epithelia. BC at a concentration of 0.003% (w/v) produced permeability enhancement similar to that of BA at a concentration of 0.5% (w/v). Thus, BC is a more efficient permeability enhancer. On the other hand, ethylenediaminetetraacetic acid (EDTA) caused around 80% reduction in the permeability of naloxone mainly by lowering the pH of the IN formulations. Based on this finding, the impact of solution pH on the permeation of naloxone was further investigated. The results show that the Papp of naloxone increased around 51 times when the pH of IN formulations increased from 4.0 to 6.0, indicating the epithelial permeation of naloxone is higher at pH 6.0. Nevertheless, the results of the stability study show that naloxone is less stable in solutions at pH > 5.0. After being stored at 60°C for 7 days, the amount of an unknown degradant with RRT 0.40 was found to be 0.27 ± 0.01 % at pH 4.0, while it increased to 0.49 ± 0.02% and 1.16% ± 0.06% at pH 5.0 and 6.0, respectively. A similar trend was observed when comparing the amount of total impurities in stability samples with different pH (4.0 – 6.0). As naloxone needs to be stored at low pH, our findings suggest that excess buffering agents should be avoided in naloxone IN formulations
Conclusion: In this study, two key factors affecting permeation of naloxone IN were identified. Use of BC or BA was found to enhance the permeation of naloxone and thus formulators could consider using a suitable permeation enhancer for naloxone IN formulations. The permeation of naloxone was also found to be highly pH dependent. The Papp of naloxone increased significantly as the pH of IN formulations increased. However, the results of our stability study indicate that naloxone solution has longer shelf life when stored with low pH. Thus, it is critical to keep the buffering capacity of naloxone IN formulations at the minimum, so that the IN formulations remains stable during shelf-life, and the pH could be easily equilibrated to the pH of nasal cavity facilitating naloxone permeation for rapid onset of the opioid agonist action.
Disclaimer: This work reflects the views of the authors and should not be construed to represent FDA’s views or policies.
Hao-jui Hsu– ORISE Research Fellow, US Food and Drug Administration, Silver Spring, Maryland
Yang Yang– Chemist, FDA, Silver Spring, Maryland
Venkateswara Pavuluri– US Food and Drug Administration, Silver Spring, Maryland
Suresh Naraharisetti– US Food and Drug Administration, Silver Spring, Maryland
Muhammad Ashraf– Supervisory Chemist, US Food and Drug Administration, Silver Spring, Maryland