Drug release from hydroxypropylcellulose gels cannot be statistically predicted from their viscometric and initial viscoelastic properties

This study questioned whether rheological properties can predict drug (metronidazole) release from Hydroxypropylcellulose (HPC) platforms. Viscometric and viscoelastic properties of aqueous, alcohols/diols and mixed solvent HPC solutions and gels were determined using viscometry and oscillatory analysis. Drug release was conducted at pH 7.4 under sink conditions. Relationships between rheological parameters and drug release were modelled using multiple linear stepwise regression. Viscometry identified ethanol and water as good solvents for HPC. Diol solvents were predicted to exhibit greater interactions with HPC (COSMO modelling) but possessed lowest intrinsic viscosities. Pentanediol or ethylene glycol prepared gels exhibited greatest elasticity. No relationships were observed between dilute solution properties and initial gel viscoelasticity. Drug release from HPC gels occurred via gel erosion and diffusion. No relationships were observed between initial gel viscoelasticity and drug release and thus, for gel platforms that undergo erosion in aqueous media, drug release cannot be predicted from initial gel viscoelasticity.

Mechanistic investigations into the encapsulation and release of small molecules and proteins from a supramolecular nucleoside gel in vitro and in vivo

Supramolecular gels have recently emerged as promising biomaterials for the delivery of a wide range of bioactive molecules, from small hydrophobic drugs to large biomolecules such as proteins. Although it has been demonstrated that each encapsulated molecule has a different release profile from the hydrogel, so far diffusion and steric impediment have been identified as the only mechanisms for the release of molecules from supramolecular gels. Erosion of a supramolecular gel has not yet been reported to contribute to the release profiles of encapsulated molecules. Here, we use a novel nucleoside-based supramolecular gel as a drug delivery system for proteins with different properties and a hydrophobic dye and describe for the first time how these materials interact, encapsulate and eventually release bioactive molecules through an erosion-based process. Through fluorescence microscopy and spectroscopy as well as small angle X-ray scattering, we show that the encapsulated molecules directly interact with the hydrogel fibres - rather than being physically entrapped in the gel network. The ability of these materials to protect proteins against enzymatic degradation is also demonstrated here for the first time. In addition, the released proteins were proven to be functional in vitro. Real-time fluorescence microscopy together with macroscopic release studies confirm that erosion is the key release mechanism. In vivo, the gel completely degrades after two weeks and no signs of inflammation are detected, demonstrating its in vivo safety. By establishing the contribution of erosion as a key driving force behind the release of bioactive molecules from supramolecular gels, this work provides mechanistic insight into the way molecules with different properties are encapsulated and released from a nucleoside-based supramolecular gel and sets the basis for the design of more tailored supramolecular gels for drug delivery applications.

In vitro evaluation of poloxamer in situ forming gels for bedaquiline fumarate salt and pharmacokinetics following intramuscular injection in rats

The objective of this study was to evaluate in vitro and in vivo drug release from in situ forming gels prepared with poloxamer 338 (P338) and/or 407 (P407) in N-methyl-2-pyrrolidone (NMP)/water mixtures for the model compound bedaquiline fumarate salt. The impact of total poloxamer concentration (20%–25% (w/w)), P338/P407 ratio (100/0%–0/100% (w/w)) and NMP/water ratio (0/100%–25/75% (v/v)) on gel point temperature (GPT) was investigated via a design of experiments (DoE), showing that GPT decreased mainly with increasing poloxamer concentration and decreasing P338/P407 ratio, while the relation with NMP/water ratio was more complex resulting in a flexion. Based on the DoE, four formulations with 10 mg/g bedaquiline fumarate salt, a fixed NMP/water ratio of 25/75% (v/v) and varying total poloxamer concentration and P338/P407 ratio were selected for evaluation of gel erosion in vitro. The fastest eroding formulation had the lowest total poloxamer concentration (20% (w/w)) and the lowest P338/P407 ratio (20.4/79.6% (w/w)), while the formulation with the highest total poloxamer concentration (23.5% (w/w)) and highest P338/P407 ratio (100/0% (w/w)) showed the lowest gel erosion rate. These fast and slow eroding formulations showed a similar trend for in vitro drug release and in vivo pharmacokinetics after intramuscular (IM) injection in rats. In vivo t_max of the IM administered poloxamer in situ forming gels was about 6 h and a short-term sustained drug release was observed in vivo in rats up to 24 h after dosing, similar to a solution of bedaquiline fumarate salt in polyethylene glycol (PEG400)/water. In conclusion, IM administration of the evaluated poloxamer in situ forming gels may be useful for drugs that require a short-term sustained release, but is not able to extend drug release rates up to weeks or months.