A continuous flow method for estimation of drug release rates from emulsion formulations

Swelling kinetics of mixtures of soybean phosphatidylcholine and glycerol dioleate

Lipid-based drug delivery systems offer the potential to enhance bioavailability, reduce dosing frequency, and improve patient adherence. In aqueous environment, initially dry lipid depots take up water and form liquid crystalline phases. Variation of lipid composition, depot size and hydration-induced phase transitions will plausibly affect the diffusion in and out of the depot. Lipid depots of soybean phosphatidylcholine (SPC) and glycerol dioleate (GDO) mixtures were hydrated for varying time durations in a phosphate-buffered saline (PBS) buffer and then analyzed with Karl Fischer titration, magnetic resonance imaging (MRI) and gravimetrically. Mathematical modeling of the swelling process using diffusion equations, was used to estimate the parameters of diffusion. Both composition of lipid mixture and depot size affect swelling kinetics… The diffusion parameters obtained in Karl Fischer titration and MRI (with temporal and spatial resolution respectively) are in good agreement. Remarkably, the MRI results show a gradient of water content within the depot even after the end of diffusion process. Apparently contradicting the first Fick's law in its classical form, these results find an explanation using the generalized Fick's law that considers the gradient of chemical potential rather than concentration as the driving force of diffusion.

Lipid Emulsion to Treat Acute Poisonings: Mechanisms of Action, Indications, and Controversies

Biodetoxification using intravenous lipid emulsion (ILE) in acute poisoning is of growing interest. As well as for local anesthetics, ILE is currently used to reverse toxicity caused by a broad-spectrum of lipophilic drugs. Both pharmacokinetic and pharmacodynamic mechanisms have been postulated to explain its possible benefits, mainly combining a scavenging effect called "lipid sink" and cardiotonic activity. Additional mechanisms based on ILE-attributed vasoactive and cytoprotective properties are still under investigation. Here, we present a narrative review on lipid resuscitation, focusing on the recent literature with advances in understanding ILE-attributed mechanisms of action and evaluating the evidence supporting ILE administration that enabled the international recommendations. Many practical aspects are still controversial, including the optimal dose, the optimal administration timing, and the optimal duration of infusion for clinical efficacy, as well as the threshold dose for adverse effects. Present evidence supports the use of ILE as first-line therapy to reverse local anesthetic-related systemic toxicity and as adjunct therapy in lipophilic non-local anesthetic drug overdoses refractory to well-established antidotes and supportive care. However, the level of evidence is low to very low, as for most other commonly used antidotes. Our review presents the internationally accepted recommendations according to the clinical poisoning scenario and provides the precautions of use to optimize the expected efficacy of ILE and limit the inconveniences of its futile administration. Based on their absorptive properties, the next generation of scavenging agents is additionally presented. Although emerging research shows great potential, several challenges need to be overcome before parenteral detoxifying agents could be considered as an established treatment for severe poisonings.

Chemical Sensors Based on Molecularly Imprinted Polymers Can Determine Drug Release Kinetics from Nanocarriers without Filtration, Centrifugation, and Dialysis Steps

With the development of drug delivery systems, the use of nanomaterials for slow, targeted, and effective drug release has grown significantly. To ensure the quality of performance, it is essential to obtain drug release profiles from therapeutic nanoparticles prior to in vivo testing. Typically, the methods of monitoring the drug release profile from nanoparticle drug delivery systems include one or more filtration, separation, and sampling steps, with or without membrane, which cause several systematic errors and make the process time-consuming. Here, the release rate of doxorubicin as a model drug from liposome as a nanocarrier was determined via highly selective binding of released doxorubicin to the doxorubicin-imprinted electropolymerized polypyrrole as a molecularly imprinted polymer (MIP). Incubation of the MIP-modified substrate with imprinted cavities complementary to doxorubicin molecules in the releasing medium leads to the binding of released doxorubicin molecules to cavities. The drug trapped in the cavities is determined by one of the analytical methods depending on its signaling properties. In this work, due to the favorable electrochemical properties of doxorubicin, the voltammetry method was used for quantitative analysis of released doxorubicin. The voltammetric oxidation peak current intensity of doxorubicin on the surface of the electrode was enhanced by increasing the release time. This membranelle platform allows fast, reliable, and simple monitoring of drug release profiles without any sample preparation, filtration, and centrifugation in buffer and blood serum samples.

Development of an In Vitro Release Assay for Low-Density Cannabidiol Nanoparticles Prepared by Flash NanoPrecipitation

Nanoparticle encapsulation is an attractive approach to improve the oral bioavailability of hydrophobic therapeutics. The high specific surface area of nanoparticle formulations, combined with the thermodynamically driven increased solubility of an amorphous drug core, promotes rapid drug dissolution. However, the physicochemical properties of the hydrophobic therapeutic can present obstacles to in vitro characterization of nanoparticle formulations. Namely, drugs with low density and high membrane binding affinity frustrate traditional analytical methods to monitor release kinetics from nanoparticles. In this work, cannabidiol (CBD) was encapsulated into nanoparticles with low polydispersity and high drug loading via Flash NanoPrecipitation (FNP), a scalable self-assembly process. Hydroxypropyl methylcellulose acetate succinate (HPMCAS) and lecithin were employed as amphiphilic particle stabilizers during the FNP process. However, the low density and high membrane binding affinity of the amorphous CBD nanoparticle core prevented the characterization of in vitro release kinetics by conventional methods. Released CBD could not be separated from intact nanoparticles by filtration or centrifugation. To address this challenge, an alternative approach is described to coencapsulate 6 nm hydrophobic Fe₃O₄ colloids with CBD during FNP. The Fe₃O₄ colloids were added at 33% by mass (approximately 20% by volume) to increase the density of the nanoparticles, resulting in particles with an average diameter of 160 nm (CBD-lecithin-Fe₃O₄) or 280 nm (CBD-HPMCAS-Fe₃O₄). This densification enabled the centrifugal separation of dissolved (released) CBD from unreleased CBD during the in vitro assay while avoiding the losses associated with a filtration step. The resulting nanoparticle formulations provided more rapid and complete in vitro dissolution kinetics than bulk CBD, representing a 6-fold improvement in dissolution compared to crystalline CBD. The coencapsulation of high-density Fe₃O₄ colloids to enable the separation of nanoparticles from release media is a novel approach to measuring in vitro release kinetics of nanoencapsulated low-density, hydrophobic drug molecules.

Evaluation of Extended-Release of Piroxicam Loaded Pectin-Zein Hydrogel Microspheres: In Vitro, Ex Vivo, and In Vivo Studies

OBJECTIVE

This study evaluated drug delivery systems based on Pectin (P) and Zein (Z) hydrogel microspheres. Piroxicam (Px) loaded P/Z hydrogel microspheres (P/Z HM) were developed, and their extended-release pharmacokinetic properties were evaluated.

METHODS

Experiments were executed under three different conditions: in vitro, ex vivo, and in vivo. Then, the in vitro-in vivo correlations (IVIVC) and ex vivo - in vivo correlations (EVIVC) were examined.

RESULTS

Analysis of drug release mechanisms were evaluated by fitting the in vitro data into the Ritger-Peppas equation, showing the contribution of both polymers' relaxation and drug diffusion from the hydrogel microspheres. The fraction absorbed in vivo was determined by the deconvolution of plasma concentration data using the Loo-Riegelman method. After oral single-dose administration of the two formulations, their basic independent model parameters were calculated.

CONCLUSION

P/Z HM had different drug release behaviors in in vitro and in vivo conditions. However, the ex vivo and in vivo characteristics were similar (R² = 0.99). This seemed reasonable to use the ex vivo method to predict the in vivo drug absorption behavior during the polymeric drug delivery system developmental studies. The P/Z HM formulation maintained the drug dose at the colon site for a long duration and could be applied for delivery of active pharmaceutical and food ingredients to the colon site.

Reverse-dialysis can be misleading for drug release studies in emulsions as demonstrated by NMR dilution experiments

Emulsions are an important class of carriers for the delivery of hydrophobic drugs. While knowledge of drug release kinetics is critical to optimizing drug carrying emulsions, there remain many open questions about the validity of standard characterization methods such as the commonly used reverse-dialysis. In this paper, the kinetic parameters of isoflurane release in perfluorotributylamine emulsions determined from both reverse-dialysis and nuclear magnetic resonance (NMR) dilution experiments are compared. The NMR-determined kinetic parameters of isoflurane release were found to be approximately seven orders of magnitude larger than those determined from conventional reverse-dialysis and were also shown to be consistent with prior in vivo observations of the anesthetization of rats.

Transfer Investigations of Lipophilic Drugs from Lipid Nanoemulsions to Lipophilic Acceptors: Contributing Effects of Cholesteryl Esters and Albumin as Acceptor Structures

When studying the release of poorly water-soluble drugs from colloidal drug delivery systems designed for intravenous administration, the release media should preferentially contain lipophilic components that represent the physiological acceptors present in vivo. In this study, the effect of different acceptor structures was investigated by comparing the transfer of fenofibrate, retinyl acetate, and orlistat from trimyristin nanoemulsion droplets into lipid-containing hydrogel particles, as well as to bovine serum albumin (BSA). A nanodispersion based on trimyristin and cholesteryl nonanoate was incorporated into the hydrogel particles (mean diameter ~40 µm) in order to mimic the composition of lipoproteins. The course of transfer observed utilizing the lipid-containing hydrogel particles as an acceptor was in relation to the lipophilicity of the drugs: the higher the logP value, the slower the transfer. There was no detectable amount of the drugs transferred to BSA in liquid solution, demonstrating clearly that albumin alone does not contribute substantially as acceptor for the lipophilic drugs under investigation in this study. In contrast, cholesteryl nonanoate contributes to a much greater extent. However, in all cases, the partition equilibrium of the drugs under investigation was in favor of the trimyristin emulsion droplets.

Optimization, and in vitro and in vivo evaluation of etomidate intravenous lipid emulsion

The aim of this investigation was to develop an etomidate intravenous lipid emulsion (ETM-ILE) and evaluate its properties in vitro and in vivo. Etomidate (ETM) is a hydrophobic drug, and organic solvents must be added to an etomidate injectable solution (ETM-SOL) to aid dissolution, that causes various adverse reactions on injection. Lipid emulsions are a novel drug formulation that can improve drug loading and reduce adverse reactions. ETM-ILE was prepared using high-pressure homogenization. Univariate experiments were performed to select key conditions and variables. The proportion of oil, egg lecithin, and poloxamer 188 (F68) served as variables for the optimization of the ETM-ILE formulation by central composite design response surface methodology. The optimized formulation had the following characteristics: particle size, 168.0 ± 0.3 nm; polydispersity index, 0.108 ± 0.028; zeta potential, −36.4 ± 0.2 mV; drug loading, 2.00 ± 0.01 mg/mL; encapsulation efficiency, 97.65% ± 0.16%; osmotic pressure, 292 ± 2 mOsmol/kg and pH value, 7.63 ± 0.07. Transmission electron microscopy images showed that the particles were spherical or spheroidal, with a diameter of approximately 200 nm. The stability study suggested that ETM-ILE could store at 4 ± 2 °C or 25 ± 2 °C for 12 months. Safety tests showed that ETM-ILE did not cause hemolysis or serious vascular irritation. The results of the pharmacokinetic study found that ETM-ILE was bioequivalent to ETM-SOL. However, a higher concentration of ETM was attained in the liver, spleen, and lungs after administration of ETM-ILE than after administration of ETM-SOL. This study found that ETM-ILE had great potential for clinical applications.

Independent co-delivery of model actives with different degrees of hydrophilicity from oil-in-water and water-in-oil emulsions stabilised by solid lipid particles via a Pickering mechanism: a-proof-of-principle study

HYPOTHESIS

The development of vehicles for the co-encapsulation of actives with diverse characteristics and their subsequent controllable co-delivery is gaining increasing research interest. Predominantly centred around pharmaceutical applications, the majority of such co-delivery approaches have been focusing on solid formulations and less so on liquid-based systems. Simple emulsions can be designed to offer a liquid-based microstructural platform for the compartmentalised multi-delivery of actives.

EXPERIMENTS

In this work, solid lipid nanoparticle stabilised Pickering emulsions were used for the co-encapsulation/co-delivery of two model actives with different degrees of hydrophilicity. Lipid particles containing a model hydrophobic active were prepared in the presence of either Tween 20 or whey protein isolate, and were then used to stabilise water-in-oil or oil-in-water emulsions, containing a secondary model active within their dispersed phase.

FINDINGS

Solid lipid nanoparticles prepared with either type of emulsifier were able to provide stable emulsions. Release kinetic data fitting revealed that different co-delivery profiles can be achieved by controlling the surface properties of the lipid nanoparticles. The current proof-of-principle study presents preliminary data that confirm the potential of this approach to be utilised as a flexible liquid-based platform for the segregated co-encapsulation and independent co-release of different combinations of actives, either hydrophobic/hydrophilic or hydrophobic/hydrophobic, with diverse release profiles.

Investigation of Controlled Release Molecular Mechanism of Oil Phase in Spilanthol Emulsion: Development and In Vitro, In Vivo Characterization

The aim of the present study was to develop a spilanthol emulsion and investigate the effect of oil and drug physicochemical properties on drug release and skin retention at molecular level. Formulation factors including oil, emulsifier, and humectant were investigated by in vitro skin retention/permeation study and the optimized formulation was evaluated in vitro and in vivo. In addition, the controlled release effect of oil was characterized using drug emulsion distribution study, drug release study, FT-IR, and molecular modeling. The optimized emulsion (squalane as oil phase) obtained the maximum skin retention (118.71 ± 10.30 μg/g), which significantly restored skin hydroxyproline content (23.99 ± 2.21 μg/g), compared with the positive group (14.75 ± 1.84 μg/g) and the negative group (15.55 ± 2.03 μg/g). It was caused by high drug release of squalene and good drug-skin miscibility. FT-IR and molecular modeling showed that spilanthol (SPI) interacted with squalene through Van der Waals force, which was weaker than a hydrogen bond formed with other oils, thus exhibited good drug release properties. And the released drug was stored in the skin due to good drug-skin miscibility, which was proved by miscibility calculation and molecular modeling. In conclusion, an effective emulsion was developed and the controlled release effect of oil phase was proved through drug-excipient interaction.

Development of nanoemulsion for efficient brain parenteral delivery of cefuroxime: designs, characterizations, and pharmacokinetics

Background and aim

Drugs that are effective against diseases in the central nervous system and reach the brain via blood must pass through the blood-brain barrier (BBB), a unique interface that protects against potential harmful molecules. This presents a major challenge in neuro-drug delivery. This study attempts to fabricate the cefuroxime-loaded nanoemulsion (CLN) to increase drug penetration into the brain when parenterally administered.

Methods

The nanoemulsions were formulated using a high-pressure homogenization technique and were characterized for their physicochemical properties.

Results

The characterizations revealed a particle size of 100.32±0.75 nm, polydispersity index of 0.18±0.01, zeta potential of -46.9±1.39 mV, viscosity of 1.24±0.34 cps, and osmolality of 285.33±0.58 mOsm/kg, indicating that the nanoemulsion has compatibility for parenteral application. CLN was physicochemically stable within 6 months of storage at 4°C, and the transmission electron microscopy revealed that the CLN droplets were almost spherical in shape. The in vitro release of CLN profile followed a sustained release pattern. The pharmacokinetic profile of CLN showed a significantly higher C_max, area under the curve (AUC)_0-t , prolonged half-life, and lower total plasma clearance, indicating that the systemic concentration of cefuroxime was higher in CLN-treated rats as compared to cefuroxime-free treated rats. A similar profile was obtained for the biodistribution of cefuroxime in the brain, in which CLN showed a significantly higher C_max, AUC_0-t , prolonged half-life, and lower clearance as compared to free cefuroxime solution.

Conclusion

Overall, CLN showed excellent physicochemical properties, fulfilled the requirements for parenteral administration, and presented improved in vivo pharmacokinetic profile, which reflected its practical approach to enhance cefuroxime delivery to the brain.

Determining drug release rates of hydrophobic compounds from nanocarriers

Obtaining meaningful drug release profiles for drug formulations is essential prior to in vivo testing and for ensuring consistent quality. The release kinetics of hydrophobic drugs from nanocarriers (NCs) are not well understood because the standard protocols for maintaining sink conditions and sampling are not valid owing to mass transfer and solubility limitations. In this work, a new in vitroassay protocol based on 'lipid sinks' and magnetic separation produces release conditions that mimic the concentrations of lipid membranes and lipoproteins in vivo, facilitates separation, and thus allows determination of intrinsic release rates of drugs from NCs. The assay protocol is validated by (i) determining the magnetic separation efficiency, (ii) demonstrating that sink condition requirements are met, and (iii) accounting for drug by completing a mass balance. NCs of itraconazole and cyclosporine A (CsA) were prepared and the drug release profiles were determined. This release protocol has been used to compare the drug release from a polymer stabilized NC of CsA to a solid drug NP of CsA alone. These data have led to the finding that stabilizing block copolymer layers have a retarding effect on drug release from NCs, reducing the rate of CsA release fourfold compared with the nanoparticle without a polymer coating.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'.

Parenteral emulsions and liposomes to treat drug overdose

Drug overdoses from both pharmaceutical and recreational drugs are a major public health concern. Although some overdoses may be treated with specific antidotes, the most common treatment involves providing supportive care to allow the body to metabolize and excrete the toxicant. In many cases, supportive care is limiting, ineffective, and expensive. There is a clear medical need to improve the effectiveness of detoxification, in particular by developing more specific therapies or antidotes for these overdoses. Intravenous lipid emulsions (ILEs) have been investigated as a potential treatment for overdoses of local anesthetics and other hydrophobic drugs. While ILE therapy has been successful in several cases, its use beyond local anesthetic systemic toxicity is controversial and its mechanism of detoxification remains a subject of debate. ILEs were not originally developed to treat overdose, but clarifying the mechanisms of detoxification observed with ILE may allow us to design more effective future treatments. Liposomes are highly biocompatible and versatile formulations, thus it was a natural step to explore their use for drug overdose therapy as well. Several researchers have designed liposomes using a variety of approaches including surface charge, pH gradients, and inclusion of enzymes in the liposome core to optimize the formulations for detoxification of a specific drug or toxicant. The in vitro results for drug sequestration by liposomes are very promising and animal trials have in some cases shown comparable performance to ILE at reduced lipid dosing. This narrative review summarizes the current status and advances in the use of emulsions and liposomes for detoxification and also suggests several areas in which studies are needed for developing future therapies.