Department of Pharmaceutics, University of Minnesota, Minneapolis, MN 55414, USA.
Department of Experimental and Clinical Pharmacology, University of Minnesota, Minneapolis, MN 55414, USA; Center for Orphan Drug Research, University of Minnesota, Minneapolis, MN 55414, USA.
J Control Release. 2018 Nov 10;289:1-9. doi: 10.1016/j.jconrel.2018.09.013. Epub 2018 Sep 15.
The low aqueous solubility of diazepam (DZP) presents a challenge in formulating nasal sprays without the use of organic solvents. One approach to overcome this challenge involves co-administration of a soluble prodrug, avizafone (AVF), with a converting enzyme to produce supersaturated DZP at the site of administration. In addition to overcoming solubility issues, the supersaturated state of DZP provides an increased driving force for enhanced permeation across nasal mucosa. However, supersaturated solutions are metastable, and there is a limit to the degree of supersaturation (S) that can be reached without causing spontaneous phase separation of the solute. The aim of this article was to determine how formulation parameters affect the rate of DZP supersaturation, maximum degree of supersaturation, and phase separation kinetics. A model enzyme, Aspergillus oryzae protease (AOP), was used to convert AVF to DZP, via an open ring intermediate (ORI). A second derivative UV spectroscopic method was developed to simultaneously monitor DZP solution concentration and the time course of DZP phase separation. Fitting a kinetic model, with prior knowledge of the enzyme kinetic parameters, the rate constant for conversion of ORI to DZP was found to be 0.470 ± 0.012 min. Kinetics and supersaturated solution stability were studied as a function of formulation parameters, including temperature, pH, buffering agent, AVF concentration, and enzyme concentration. The maximum aqueous solution concentration for DZP at 32 °C was determined to be 1.22 ± 0.03 mM DZP (S = 9.38) and was insensitive to changes in formulation parameters, excepting temperature. Supersaturated solutions of DZP could be maintained at the maximum concentration for >24 h, even in the presence of phase separated DZP. Polarized light microscopy, PXRD, and DSC analysis indicated that the phase separated DZP was amorphous upon formation and remained so for >24 h. Our findings suggest that co-administration of AVF with a suitable human converting enzyme will provide a viable mechanism for IN delivery of DZP and result in very rapid and complete absorption to quickly terminate seizure emergencies.
地西泮（DZP）的水溶性低，在不使用有机溶剂的情况下制备鼻喷雾剂时会带来挑战。一种克服此挑战的方法是将可溶性前药阿维扎芬（AVF）与转化酶一起给药，以在给药部位产生过饱和的 DZP。除了克服溶解度问题外，DZP 的过饱和状态为穿过鼻黏膜的增强渗透提供了更大的驱动力。然而，过饱和溶液是亚稳的，并且在不引起溶质自发相分离的情况下，达到的过饱和度（S）程度存在限制。本文的目的是确定配方参数如何影响 DZP 过饱和度的速率、最大过饱和度和相分离动力学。使用模型酶米曲霉蛋白酶（AOP）通过开环中间体（ORI）将 AVF 转化为 DZP。开发了二阶导数紫外光谱法来同时监测 DZP 溶液浓度和 DZP 相分离的时间过程。通过拟合动力学模型，并利用酶动力学参数的先验知识，发现 ORI 转化为 DZP 的速率常数为 0.470±0.012 min。研究了动力学和过饱和溶液稳定性作为配方参数（包括温度、pH 值、缓冲剂、AVF 浓度和酶浓度）的函数。在 32°C 时，DZP 的最大水溶液浓度确定为 1.22±0.03 mM DZP（S=9.38），并且对除温度以外的配方参数变化不敏感。DZP 的过饱和溶液在最大浓度下可维持>24 h，即使存在分离的 DZP 也是如此。偏光显微镜、PXRD 和 DSC 分析表明，形成的分离的 DZP 是无定形的，并且在>24 h 内仍然如此。我们的研究结果表明，AVF 与合适的人转化酶一起给药将为 DZP 的 IN 给药提供可行的机制，并导致非常快速和完全的吸收，以迅速终止癫痫发作紧急情况。
