Purpose: Naloxone, an opioid antagonist, primarily available as injectable and was recently introduced as intranasal (IN) formulations (solutions) to easily treat opioid overdose victims. Due to the change of administration route, excipients used to formulate the intranasal formulations could affect permeation and systemic absorption of naloxone. To understand how the excipients and other formulation variables such as solution pH could affect the performance and stability of IN naloxone, the nasal permeation and stability of various naloxone IN formulations prepared in-house were investigated in this study using an in vitro nasal permeation model and a systematic stability study.
Methods: A full factorial design of experiment (DOE) with eighteen IN formulations was used to study the effect of the above-mentioned excipients on the nasal permeability and stability of naloxone at three naloxone concentrations (4, 22 and 40 mg/mL). In addition to the original set of DOE formulations, permeation and stability of naloxone IN formulations with adjusted pH values (between pH 4.0 and 6.0) was 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.) (Figure 1). 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 the stability study, the eighteen IN formulations prepared per DOE were stored at 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. Naloxone solution 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 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 our 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, and 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 strong 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 the excipients could be considered 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 needs to be stored in solutions with low pH for better product stability. Thus it is critical to keep the buffering capacity of naloxone IN formulations at the minimum, so that the IN formulations is stable during shelf-storage , but pH could be easily equilibrated to the pH of the nasal cavity facilitating naloxone permeation for rapid onset of the opioid antagonist action.
DISCLAIMER: this manuscript reflects the views of the authors and should not be construed to represent FDA’s views or policies.
Yang Yang– US FOOD AND DRUG ADMINISTRATION
Venkateswara Pavuluri– US Food and Drug Administration
Ciby Abraham– US Food and Drug Administration
Suresh Naraharisetti– US Food and Drug Administration
Muhammad Ashraf– Supervisory Chemist, US Food and Drug Administration, Silver Spring, Maryland
Manar Al-Ghabeish– US Food and Drug Administration