Where Is the Drug? Quantitative 3D Distribution Analyses of Confined Drug-Loaded Polymer Matrices

Sensing technologies and experimental platforms for the characterization of advanced oral drug delivery systems

Complex and miniaturized oral drug delivery systems are being developed rapidly for targeted, controlled drug release and improved bioavailability. Standard analytical techniques are widely used to characterize i) drug carrier and active pharmaceutical ingredients before loading into a delivery device (to ensure the solid form), and ii) the entire drug delivery system during the development process. However, in light of the complexity and the size of some of these systems, standard techniques as well as novel sensing technologies and experimental platforms need to be used in tandem. These technologies and platforms are discussed in this review, with a special focus on passive delivery systems in size range from a few 100 µm to a few mm. Challenges associated with characterizing these systems and evaluating their effect on oral drug delivery in the preclinical phase are also discussed.

How Molecular Mobility, Physical State, and Drug Distribution Influence the Naproxen Release Profile from Different Mesoporous Silica Matrices

Aiming to evaluate how the release profile of naproxen (nap) is influenced by its physical state, molecular mobility, and distribution in the host, this pharmaceutical drug was loaded in three different mesoporous silicas differing in their architecture and surface composition. Unmodified and partially silylated MCM-41 matrices, respectively MCM-41 and MCM-41_sil, and a biphenylene-bridged periodic mesoporous organic matrix, PMO_Bph, were synthetized and used as drug carriers, having comparable pore sizes (∼3 nm) and loading percentages (∼30% w/w). The loaded guest was investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dielectric relaxation spectroscopy (DRS). DSC and XRD confirmed amorphization of a nap fraction incorporated inside the pores. A narrower glass transition was detected for PMO_Bph_nap, taken as an indication of the impact of host ordering, which also hinders the guest molecular mobility inside the pores as probed by DRS. While the PMO_Bph matrix is highly hydrophobic, the unmodified MCM-41 readily adsorbs water, accelerating the nap relaxation rate in the respective composite. In the dehydrated state, the faster dynamics was found for the silylated matrix since guest-host hydrogen bond interactions were inhibited to some extent by methylation. Nevertheless, in all the prepared composites, bulk-like crystalline drug deposits outside pores in a greater extent in PMO_Bph_nap. The DRS measurements analyzed in terms of conductivity show that, upon melting, nap easily migrates into pores in MCM-41-based composites, while it stays in the outer surface in the ordered PMO_Bph, determining a faster nap delivery from the latter matrix. On the other side, the mobility enhancement in the hydrated state controls the drug delivery in the unmodified MCM-41 matrix vs the silylated one. Therefore, DRS proved to be a suitable technique to disclose the influence of the ordering of the host surface and its chemical modification on the guest behavior, and, through conductivity depletion, it provides a mean to monitor the guest entrance inside the pores, easily followed even by untrained spectroscopists.

Non-uniform drug distribution matrix system (NUDDMat) for zero-order release of drugs with different solubility

A decrease in the drug release rate over time typically affects the performance of hydrophilic matrices for oral prolonged release. To address such an issue, a Non-Uniform Drug Distribution Matrix (NUDDMat) based on hypromellose was proposed and demonstrated to yield zero-order release. The system consisted of 5 overlaid layers, applied by powder layering, having drug concentration decreasing from the inside towards the outside of the matrix according to a descending staircase function. In the present study, manufacturing and performance of the described delivery platform were evaluated using drug tracers having different water solubility. Lansoprazole, acetaminophen and losartan potassium were selected as slightly (SST), moderately (MST) and highly (HST) soluble tracers. By halving the thickness of the external layer, which contained no drug, linear release of HST and MST was obtained. The release behavior of the NUDDMat system loaded with a drug having pH-independent solubility was shown to be consistent in pH 1.2, 4.5 and 6.8 media. Based on these results, feasibility of the NUDDMat platform by powder layering was demonstrated using drugs having different physico-technological characteristics. Moreover, its ability to generate zero-order release was proved in the case of drugs with water solubility in a relatively wide range.