Optimised NLC: a nanotechnological approach to improve the anaesthetic effect of bupivacaine

Enantiomeric Excess Bupivacaine in a Lavender Oil NLC Tested in a Melanoma Model: Prolonged Release and Anticancer Effect

Recent studies have highlighted the potential of local anesthetics (LA) as adjuvants in cancer treatment, specifically by increasing survival rates when used in surgical excisions. However, the clinical use of LA is restricted due to their systemic toxicity. The development of drug delivery systems could address this issue and advance the utilization of these molecules. In this research, we explored the pharmacokinetics (using microdialysis probes) and antitumor properties of a nanostructured lipid carrier (NLC) formulation containing the commercially available enantiomeric excess form of bupivacaine (BVCS75). This NLC was prepared with lavender oil (NLC-L-BVC), an excipient with inherent antitumor properties. We compared this formulation to a control (NLC-BVC) using synthetic lipids. Pharmacokinetic assessments of the NLCs confirmed the sustained release of BVCS75 within the tumor, characterized by a reduced elimination rate constant and longer half-life (∼6×). The encapsulation of BVCS75 within nanoparticles (whether natural or synthetic) enhanced its effectiveness in treating the primary tumor, resulting in the inhibition of tumor growth (70% with NLC-L-BVC and 72% with NLC-BVC), outperforming free BVC (17% inhibition). However, the association of lavender oil with BVCS75 in an NLC did not yield synergistic properties. Furthermore, all BVCS75 treatments (whether free or encapsulated) improved animal survival rates. These findings confirm that encapsulation of bupivacaine in NLC can prolong drug action at the local site, contributing to improved local antitumor therapy while mitigating systemic effects.

The Application and Pharmaceutical Development of Etomidate: Challenges and Strategies

Etomidate is a synthetic imidazole anesthetic that exerts hypnotic effects by potentiating the action of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) or directly activating the anionic GABA (GABAA) receptor. It stands out among many anesthetics because of its multiple advantages, such as good hemodynamic stability and minimal inhibition of spontaneous respiration. However, its low water solubility and side effects, such as adrenal cortex inhibition and myoclonus, have limited the clinical application of this drug. To address these issues, extensive research has been conducted on the drug delivery of etomidate in recent decades, which has led to the emergence of different etomidate preparations. Despite so many etomidate preparations, so far some of the toxic side effects have not yet been effectively addressed. Herein we discuss the pharmaceutical design of etomidate that may resolve the above problem. We also propose targeted strategies for future research on etomidate preparations and discuss the feasibility of different administration routes and dosage forms to expand the application of this drug. Through this review, we hope to draw more attention to the potential of etomidate and its application challenges and provide valuable insights into the development of new etomidate preparations.

Construction of bupivacaine-loaded gelatin-based hydrogel delivery system for sciatic nerve block in mice

Peripheral nerve blockade (PNB) is a common treatment to relieve postoperative pain. However, local anesthetics alone have a short duration of action and severe side effects during postoperative analgesia. In order to overcome these limitations, the present study reported an injectable hydrogel with a drug slow-release profile for regional nerve blockade. The injectable hydrogel was prepared by crosslinking with gelatin and NHS-PEG-NHS, which was degradable in the physiological environment and displayed sustainable release of anesthetics locally, thus improving the disadvantage of the high toxicity of local anesthetics. In this regard, we conducted a series of in vitro characterizations and proved that the hydrogel has a porous three-dimensional mesh structure with high drug loading capability, and sustainable drug release profile. And cytotoxicity experiments confirmed the good biocompatibility of the hydrogel. It was shown that using the animal sciatic nerve block model, the analgesic effect was greatly improved in vivo, and there was no obvious evidence of permanent inflammation or nerve damage in the block site's sections. This locally slow-release platform, combined with local anesthetics, is therefore a promising contender for long-acting analgesia.

Fresh Carrier for an Old Topical Local Anesthetic: Benzocaine in Nanostructured Lipid Carriers

Nanostructured lipid carriers (NLC) have emerged as innovative drug delivery systems, offering distinct advantages over other lipid-based carriers, such as liposomes and solid lipid nanoparticles. Benzocaine (BZC), the oldest topical local anesthetic in use, undergoes metabolism by pseudocholinesterase, leading to the formation of p-aminobenzoic acid, a causative agent for allergic reactions associated with prolonged BZC usage. In order to mitigate adverse effects and enhance bioavailability, BZC was encapsulated within NLC. Utilizing a 23 factorial design, formulations comprising cetyl palmitate (solid lipid), propylene glycol monocaprylate (liquid lipid), and Pluronic F68 as surfactants were systematically prepared, with variations in the solid/liquid lipid mass ratios (60:40-80:20%), total lipid contents (15-25%), and BZC concentrations (1-3%). The optimized formulation underwent characterization by dynamic light scattering, differential scanning calorimetry, Raman imaging, X-ray diffraction, small-angle neutron scattering, nanotracking analysis, and transmission electron microscopy (TEM)/cryo-TEM, providing insights into the nanoparticle structure and the incorporation of BZC into its lipid matrix. NLCBZC exhibited a noteworthy encapsulation efficiency (%EE = 96%) and a 1 year stability when stored at 25 °C. In vitro kinetic studies and in vivo antinociceptive tests conducted in mice revealed that NLCBZC effectively sustained drug release for over 20 h and prolonged the anesthetic effect of BZC for up to 18 h. We therefore propose the use of NLCBZC to diminish the effective anesthetic concentration of benzocaine (from 20 to 3% or less), thus minimizing allergic reactions that follow the topical administration of this anesthetic and, potentially, paving the way for new routes of BZC administration in pain management.

Quality-by-Design-Driven Nanostructured Lipid Scaffold of Apixaban: Optimization, Characterization, and Pharmacokinetic Evaluation

Apixaban, an anticoagulant, is limited in its efficacy due to poor solubility, low bioavailability, and extensive metabolism. This study investigates the application of nanostructured lipid carriers (NLCs) to enhance the bioavailability of Apixaban. NLCs were prepared using the high-pressure homogenization method. The influence of independent variables, viz., the amount of Tween 80, HPH pressure, and the number of HPH cycles, were studied using a 23 factorial design. The average particle size, PDI, zeta potential, and entrapment efficiency of the optimized NLCs were found to be 232 ± 23 nm, with 0.514 ± 0.13 PDI and zeta potential of about -21.9 ± 2.1 mV, respectively. Additionally, concerning the thermal and crystallographic properties of the drug, the NLCs showed drug entrapment without altering its potency. The in-vitro drug release studies revealed an immediate release pattern, followed by sustained release for up to 48 h. In-vivo pharmacokinetic experiments demonstrated that Apixaban-loaded NLCs exhibited higher values of t1/2 (27.76 ± 1.18 h), AUC0-∞ (19,568.7 ± 1067.6 ng·h/mL), and Cmax (585.3 ± 87.6 ng/mL) compared to free drugs, indicating improved bioavailability. Moreover, a decrease in the elimination rate constant (Kel) reflected the sustained effect of Apixaban with NLCs. NLCs offer improved oral absorption rates and enhanced therapeutic impact compared to free drugs, potentially reducing dose frequency and improving patient outcomes.

Local anesthetic delivery systems for the management of postoperative pain

Postoperative pain (POP) is a major clinical challenge. Local anesthetics (LAs), including amide-type LAs, ester-type LAs, and other potential ion-channel blockers, are emerging as drugs for POP management because of their effectiveness and affordability. However, LAs typically exhibit short durations of action and prolonging the duration by increasing their dosage or concentration may increase the risk of motor block or systemic local anesthetic toxicity. In addition, techniques using LAs, such as intrathecal infusion, require professional operation and are prone to catheter displacement, dislodgement, infection, and nerve damage. With the development of materials science and nanotechnology, various LAs delivery systems have been developed to compensate for these disadvantages. Numerous delivery systems have been designed to continuously release a safe dose in a single administration to ensure minimal systemic toxicity and prolong pain relief. LAs delivery systems can also be designed to control the duration and intensity of analgesia according to changes in the external trigger conditions, achieve on-demand analgesia, and significantly improve pain relief and patient satisfaction. In this review, we summarize POP pathways, animal models and methods for POP testing, and highlight LAs delivery systems for POP management. STATEMENT OF SIGNIFICANCE: Postoperative pain (POP) is a major clinical challenge. Local anesthetics (LAs) are emerging as drugs for POP management because of their effectiveness and affordability. However, they exhibit short durations and toxicity. Various LAs delivery systems have been developed to compensate for these disadvantages. They have been designed to continuously release a safe dose in a single administration to ensure minimal toxicity and prolong pain relief. LAs delivery systems can also be designed to control the duration and intensity of analgesia to achieve on-demand analgesia, and significantly improve pain relief and patient satisfaction. In this paper, we summarize POP pathways, animal models, and methods for POP testing and highlight LAs delivery systems for POP management.

Recent Research Advances in Nano-Based Drug Delivery Systems for Local Anesthetics

From a clinical perspective, local anesthetics have rather widespread application in regional blockade for surgery, postoperative analgesia, acute/chronic pain control, and even cancer treatments. However, a number of disadvantages are associated with traditional local anesthetic agents as well as routine drug delivery administration ways, such as neurotoxicity, short half-time, and non-sustained release, thereby limiting their application in clinical practice. Successful characterization of drug delivery systems (DDSs) for individual local anesthetic agents can support to achieve more efficient drug release and prolonged duration of action with reduced systemic toxicity. Different types of DDSs involving various carriers have been examined, including micromaterials, nanomaterials, and cyclodextrin. Among them, nanotechnology-based delivery approaches have significantly developed in the last decade due to the low systemic toxicity and the greater efficacy of non-conventional local anesthetics. Multiple nanosized materials, including polymeric, lipid (solid lipid nanoparticles, nanostructured lipid carriers, and nanoemulsions), metallic, inorganic non-metallic, and hybrid nanoparticles, offer a safe, localized, and long-acting solution for pain management and tumor therapy. This review provides a brief synopsis of different nano-based DDSs for local anesthetics with variable sizes and structural morphology, such as nanocapsules and nanospheres. Recent original research utilizing nanotechnology-based delivery systems is particularly discussed, and the progress and strengths of these DDSs are highlighted. A specific focus of this review is the comparison of various nano-based DDSs for local anesthetics, which can offer additional indications for their further improvement. All in all, nano-based DDSs with unique advantages provide a novel direction for the development of safer and more effective local anesthetic formulations.

Improved Local Anesthesia at Inflamed Tissue Using the Association of Articaine and Copaiba Oil in Avocado Butter Nanostructured Lipid Carriers

Unsuccessful anesthesia often occurs under an inflammatory tissue environment, making dentistry treatment extremely painful and challenging. Articaine (ATC) is a local anesthetic used at high (4%) concentrations. Since nanopharmaceutical formulations may improve the pharmacokinetics and pharmacodynamics of drugs, we encapsulated ATC in nanostructured lipid carriers (NLCs) aiming to increase the anesthetic effect on the inflamed tissue. Moreover, the lipid nanoparticles were prepared with natural lipids (copaiba (Copaifera langsdorffii) oil and avocado (Persia gratissima) butter) that added functional activity to the nanosystem. NLC-CO-A particles (~217 nm) showed an amorphous lipid core structure according to DSC and XDR. In an inflammatory pain model induced by λ-carrageenan in rats, NLC-CO-A improved (30%) the anesthetic efficacy and prolonged anesthesia (3 h) in relation to free ATC. In a PGE2-induced pain model, the natural lipid formulation significantly reduced (~20%) the mechanical pain when compared to synthetic lipid NLC. Opioid receptors were involved in the detected analgesia effect since their blockage resulted in pain restoration. The pharmacokinetic evaluation of the inflamed tissue showed that NLC-CO-A decreased tissue ATC elimination rate (ke) by half and doubled ATC’s half-life. These results present NLC-CO-A as an innovative system to break the impasse of anesthesia failure in inflamed tissue by preventing ATC accelerated systemic removal by the inflammatory process and improving anesthesia by its association with copaiba oil.

Preparation of Ropivacaine Encapsulated by Zeolite Imidazole Framework Microspheres as Sustained-Release System and Efficacy Evaluation

The management of persistent postoperative pain still remains a clinical challenge currently. Although ropivacaine (RVC) is widely used for postoperative analgesia as a local anesthetic, the short half-life makes it difficult to achieve the desired duration of analgesia. Herein, a RVC sustained-release microspheres encapsulated by zeolite imidazole framework-8 (RVC@ZIF-8) was synthesized for the first time, which prolonged the sustained-release of RVC and decreased the resulting drug toxicity. RVC can continuously release in vitro for at least 96 h with high drug loading of 30.6 % and RVC@ZIF-8 had excellent biocompatibility and low cytotoxicity. In sciatic nerve block model, the sensory block time of RVC@ZIF-8 was significantly prolonged compared with RVC, achieving more than 72 h post injection and no inflammation or lesion were found. Based on high drug loading, ideal sustained-release and superior biological safety, RVC@ZIF-8 will be a novel delivery material for local anesthetic with potential application.

Docetaxel Loaded in Copaiba Oil-Nanostructured Lipid Carriers as a Promising DDS for Breast Cancer Treatment

Breast cancer is the neoplasia of highest incidence in women worldwide. Docetaxel (DTX), a taxoid used to treat breast cancer, is a BCS-class-IV compound (low oral bioavailability, solubility and intestinal permeability). Nanotechnological strategies can improve chemotherapy effectiveness by promoting sustained release and reducing systemic toxicity. Nanostructured lipid carriers (NLC) encapsulate hydrophobic drugs in their blend-of-lipids matrix, and imperfections prevent drug expulsion during storage. This work describes the preparation, by design of experiments (2³ factorial design) of a novel NLC formulation containing copaiba oil (CO) as a functional excipient. The optimized formulation (NLC_DTX) showed approximately 100% DTX encapsulation efficiency and was characterized by different techniques (DLS, NTA, TEM/FE-SEM, DSC and XRD) and was stable for 12 months of storage, at 25 °C. Incorporation into the NLC prolonged drug release for 54 h, compared to commercial DTX (10 h). In vitro cytotoxicity tests revealed the antiproliferative effect of CO and NLC_DTX, by reducing the cell viability of breast cancer (4T1/MCF-7) and healthy (NIH-3T3) cells more than commercial DTX. NLC_DTX thus emerges as a promising drug delivery system of remarkable anticancer effect, (strengthened by CO) and sustained release that, in clinics, may decrease systemic toxicity at lower DTX doses.

Evaluation of the Miscibility of Novel Cocoa Butter Equivalents by Raman Mapping and Multivariate Curve Resolution-Alternating Least Squares

Cocoa butter (CB) is an ingredient traditionally used in the manufacturing of chocolates, but its availability is decreasing due to its scarcity and high cost. For this reason, other vegetable oils, known as cocoa butter equivalents (CBE), are used to replace CB partially or wholly. In the present work, two Peruvian vegetable oils, coconut oil (CNO) and sacha inchi oil (SIO), are proposed as novel CBEs. Confocal Raman microscopy (CRM) was used for the chemical differentiation and polymorphism of these oils with CB based on their Raman spectra. To analyze their miscibility, two types of blends were prepared: CB with CNO, and CB with SIO. Both were prepared at 5 different concentrations (5%, 15%, 25%, 35%, and 45%). Raman mapping was used to obtain the chemical maps of the blends and analyze their miscibility through distribution maps, histograms and relative standard deviation (RSD). These values were obtained with multivariate curve resolution-alternating least squares. The results show that both vegetable oils are miscible with CB at high concentrations: 45% for CNO and 35% for SIO. At low concentrations, their miscibility decreases. This shows that it is possible to consider these vegetable oils as novel CBEs in the manufacturing of chocolates.

A pre-formulation study of tetracaine loaded in optimized nanostructured lipid carriers

Tetracaine (TTC) is a local anesthetic broadly used for topical and spinal blockade, despite its systemic toxicity. Encapsulation in nanostructured lipid carriers (NLC) may prolong TTC delivery at the site of injection, reducing such toxicity. This work reports the development of NLC loading 4% TTC. Structural properties and encapsulation efficiency (%EE > 63%) guided the selection of three pre-formulations of different lipid composition, through a 2³ factorial design of experiments (DOE). DLS and TEM analyses revealed average sizes (193-220 nm), polydispersity (< 0.2), zeta potential |- 21.8 to - 30.1 mV| and spherical shape of the nanoparticles, while FTIR-ATR, NTA, DSC, XRD and SANS provided details on their structure and physicochemical stability over time. Interestingly, one optimized pre-formulation (CP-TRANS/TTC) showed phase-separation after 4 months, as predicted by Raman imaging that detected lack of miscibility between its solid (cetyl palmitate) and liquid (Transcutol) lipids. SANS analyses identified lamellar arrangements inside such nanoparticles, the thickness of the lamellae been decreased by TTC. As a result of this combined approach (DOE and biophysical techniques) two optimized pre-formulations were rationally selected, both with great potential as drug delivery systems, extending the release of the anesthetic (> 48 h) and reducing TTC cytotoxicity against Balb/c 3T3 cells.

Prolonged anesthesia and decreased toxicity of enantiomeric-excess bupivacaine loaded in ionic gradient liposomes

Bupivacaine is the most employed local anesthetic in surgical procedures, worldwide. Its systemic toxicity has directed the synthesis of the less toxic, S(-) enantiomer. This work describes a formulation of ionic gradient liposomes (IGL) containing _S75BVC, an enantiomeric excess mixture of 75% S(-) and 25% R(+) bupivacaine. IGL prepared with 250 mM (NH₄)₂SO₄ in the inner aqueous core of phosphatidylcholine and cholesterol (3:2 mol%) vesicles plus 0.5% _S75BVC showed average sizes of 312.5 ± 4.5 nm, low polydispersity (PDI < 0.18), negative zeta potentials (-14.2 ± 0.2 mV) and were stable for 360 days. The encapsulation efficiency achieved with IGL_S75BVC (%EE = 38.6%) was higher than with IGL prepared with racemic bupivacaine (IGL_RBVC, %EE = 28.3%). TEM images revealed spherical vesicles and µDSC analysis provided evidence on the interaction of the anesthetic with the lipid bilayer. Then, in vitro - release kinetics and cytotoxicity- and in vivo - toxic effects in Zebrafish and biochemical/histopathological analysis plus analgesia in Wistar rats - tests were performed. IGL_S75BVC exhibited negligible toxicity against Schwann cells and Zebrafish larvae, and it did not affect biochemical markers or the morphology of rat tissues (heart, brain, cerebellum, sciatic nerve). The in vitro release of _S75BVC from IGL was extended from 4 to 24 h, justifying the prolonged anesthetic effect measured in rats (~9 h). The advantages of IGL_S75BVC formulation over IGL_RBVC and plain bupivacaine formulations (prolonged anesthesia, preferential sensorial blockade, and no toxicity) confirm its potential for clinical use in surgical anesthesia.

Lipid nanoparticles loaded with butamben and designed to improve anesthesia at inflamed tissues

The most frequently used local anesthetics (LA) for local infiltration have an ionizable amine in the range of pH 7.6-8.9. Effective anesthesia of inflamed tissues is a great challenge, especially because the induced local acidosis decreases the fraction of the neutral (more potent) LA species in situ. To solve this limitation, the butyl-substituted benzocaine analogue butamben (BTB) - that has no ionizable amine group close to the physiological pH - could be useful if it was not for its low solubility. To overcome the solubility problem, an optimized formulation for BTB using nanostructured lipid carriers (NLC) was developed by a factorial design and characterized using DLS, XRD, DSC and cryo-EM. The release kinetics and cytotoxicity of the new formulation were measured in vitro, while the in vivo tests assessed its effectiveness on healthy and inflamed tissues, in rats. The optimized NLCBTB formulation showed desirable physicochemical properties (size = 235.6 ± 3.9 nm, polydispersity = 0.182 ± 0.006 and zeta potential = -23.6 ± 0.5 mV), high (99.5%) encapsulation efficiency and stability during 360 days of storage at room temperature. NLCBTB prolonged the release of butamben and decreased its in vitro cytotoxicity without inducing any in vivo toxic alteration. In the inflammatory hyperalgesia model, the NLCBTB formulation showed potential for the management of inflammatory pain, displaying greater analgesic effectiveness (40%) and a prolonged effect.

Nanocarriers From Natural Lipids With In Vitro Activity Against Campylobacter jejuni

Campylobacter jejuni (CJ) is the most prevalent zoonotic pathogen of chicken meat and related products, which may lead to gastroenteritis and autoimmune diseases in humans. Although controlling this bacterium is important, CJ strains resistance against traditional antibiotic therapy has been increased. Vegetable oils and fats are natural biomaterials explored since the Ancient times, due to their therapeutic properties. Nanotechnology has promoted the miniaturization of materials, improving bioavailability and efficacy, while reducing the toxicity of loaded active molecules. In this work, a screening of 28 vegetable oils was firstly performed, in order to select anti-CJ candidates by the disc diffusion test. Thus, the selected liquid lipids were used as active molecules in nanostructured lipid carriers (NLC) formulations. The three resultant systems were characterized in terms of particle size (~200 nm), polydispersity index (~0.15), and zeta potential (~-35mV), and its physicochemical stability was confirmed for a year, at 25°C. The structural properties of NLC were assessed by infrared (FTIR-ATR) and differential scanning calorimetry (DSC) analyses. The spherical nanoparticle morphology and narrow size distribution was observed by transmission electron microscopy (TEM) and field emission scanning electron (FE-SEM) analyses, respectively. Then, the in vitro antimicrobial activity test determined the minimum inhibitory concentration (MIC) of each formulation against CJ strains, in both free (1-3 mg/ml^-1) and sessile (0.78 mg/ml^-1) forms. Finally, the in vitro biocompatibility of NLC was demonstrated through cell viability using VERO cell line, in which F6 was found twice less cytotoxic than pure olibanum oil. Considering the abovementioned achieved, F6 formulation is able to be evaluated in the in vivo anti-CJ efficacy assays.

Porous Core/Dense Shell PLA Microspheres Embedded with High Drug Loading of Bupivacaine Crystals for Injectable Prolonged Release

Objective of the study was to design an injectable microsphere preparation with high drug loading of bupivacaine for prolonged release and local anesthetic. PLA or PLGA was used as the biodegradable matrix material to fabricate microspheres with the o/w emulsification-solvent evaporation method. The characterization of bupivacaine microspheres was observed by SEM, DSC, and XRPD. The microsphere preparation and extended drug release, as well as the plasma drug concentration and sciatic nerve blockade after injection of the microsphere formulation to rats were investigated. High drug-loading microspheres of more than 70% were successfully obtained with extended drug release over 5 days in vitro depending on the type of matrix and the feed ratio of drug to polymer. SEM, DSC, and XRPD results verified a novel microsphere structure characterized as the porous core composed of PLA material and form II bupivacaine crystals and dense shell formed of PLA layer. The mechanism that bupivacaine was dissolved inside the microsphere and diffused across the dense shell was suggested for drug release in vitro. The optimized PLA microsphere formulation showed low and steady plasma drug concentration over 5 days and prolonged duration of sensory and motor blockade of sciatic nerve lasted more than 3 days. Results indicated that the porous core-shell structure of PLA microsphere formulation would provide enormous potential as an injectable depot for locally prolonged delivery of bupivacaine and control of postoperative pain.

Articaine in functional NLC show improved anesthesia and anti-inflammatory activity in zebrafish

Anesthetic failure is common in dental inflammation processes, even when modern agents, such as articaine, are used. Nanostructured lipid carriers (NLC) are systems with the potential to improve anesthetic efficacy, in which active excipients can provide desirable properties, such as anti-inflammatory. Coupling factorial design (FD) for in vitro formulation development with in vivo zebrafish tests, six different NLC formulations, composed of synthetic (cetyl palmitate/triglycerides) or natural (avocado butter/olive oil/copaiba oil) lipids were evaluated for loading articaine. The formulations selected by FD were physicochemically characterized, tested for shelf stability and in vitro release kinetics and had their in vivo effect (anti-inflammatory and anesthetic effect) screened in zebrafish. The optimized NLC formulation composed of avocado butter, copaiba oil, Tween 80 and 2% articaine showed adequate physicochemical properties (size = 217.7 ± 0.8 nm, PDI = 0.174 ± 0.004, zeta potential = - 40.2 ± 1.1 mV, %EE = 70.6 ± 1.8) and exhibited anti-inflammatory activity. The anesthetic effect on touch reaction and heart rate of zebrafish was improved to 100 and 60%, respectively, in comparison to free articaine. The combined FD/zebrafish approach was very effective to reveal the best articaine-in-NLC formulation, aiming the control of pain at inflamed tissues.

Pessaries containing nanostructured lipid carriers (NLC) for prolonged vaginal delivery of progesterone

Progesterone (PRG) plays a crucial role in the female reproductive system, being the vaginal route the most adequate for its administration, as this drug has an extensive hepatic first pass effect. Nonetheless, vaginal PRG dosage forms originate immediate drug release and requires repeated administrations, which is unpleasant. Thereby, it is necessary to develop alternative delivery systems for prolonged vaginal release of PRG. The objective of this work was the development of pessaries for the prolonged vaginal delivery of PRG. Studies began with the preparation of an aqueous dispersion of PRG-loaded NLC (NLC_PRG), followed by the evaluation of its biocompatibility in human immortalized keratinocytes (HaCat cells), using three different methods (neutral red uptake, resazurin reduction and sulforhodamine B assays). Finally, the NLC_PRG was incorporated into pessaries, which were further characterized according to the European Pharmacopoeia to assess their suitability to prolong PRG release through the vaginal route. The results showed that, after preparation, 90% of the NLC_PRG had sizes equal or lower than 315.60 ± 0.01 nm, and an EE of 96.42 ± 0.00%. All the assays used to assess the biocompatibility of NLC_PRG showed the absence of cytotoxicity towards HaCaT cells for concentrations up to 10 μg/mL. In all cytotoxicity assays, a cytotoxic effect was only observed for concentrations equal or higher than 25 μg/mL, which provides high confidence in the obtained results. The outcomes of this study suggest the suitability of using pessaries containing PRG-loaded NLC for sustained drug release, which is an innovative therapeutic strategy and constitutes a promising alternative for the vaginal use of PRG. However, further ex vivo and in vivo studies are needed to fully clarify the pharmacokinetic and toxicological profile before reaching the clinical use.

Injectable in situ forming nanogel: A hybrid Alginate-NLC formulation extends bupivacaine anesthetic effect

Finding an ideal anesthetic agent for postoperative pain control, with long action and low side effects, is still a challenge. Local anesthetics have potential for such application if their time of action is improved. This work introduces a new hybrid formulation formed by the association of a nanostructured lipid carrier with a biopolymeric system to encapsulate bupivacaine (BVC). The hybrid formulation was physicochemical and structurally characterized by DLS, TEM, DSC, XRD and FTIR-ATR, and it remained stable for 12 months at room temperature. In vivo analgesia and imaging tests showed that the hybrid system was able to modulate the release, and to increase the concentration of BVC at the site of action, by forming a nanogel in situ. Such nanogel improved over 5 times (>24 h) the anesthesia duration, when compared to free BVC at clinical (0.5%) doses. Therefore, this novel in situ-forming nanogel shows great potential to be used in postsurgical pain control, improving the action of BVC, without losing its versatility of (infiltrative) application.

Improved efficacy of naproxen-loaded NLC for temporomandibular joint administration

Inflammatory conditions of the temporomandibular joint (TMJ) and peripheral tissues affect many people around the world and are commonly treated with non-steroidal anti-inflammatory drugs (NSAIDs). However, in order to get desirable results, treatments with NSAIDs may take weeks, causing undesirable side effects and requiring repeated administration. In this sense, this work describes the development of an optimized nanostructured lipid carrier (NLC) formulation for intra-articular administration of naproxen (NPX). An experimental design (2³) selected the best formulation in terms of its physicochemical and structural properties, elucidated by different methods (DLS, NTA, TEM, DSC, and ATR-FTIR). The chosen formulation (NLC-NPX) was tested on acute inflammatory TMJ nociception, in a rat model. The optimized excipients composition provided higher NPX encapsulation efficiency (99.8%) and the nanoparticles were found stable during 1 year of storage at 25 °C. In vivo results demonstrated that the sustained delivery of NPX directly in the TMJ significantly reduced leukocytes migration and levels of pro-inflammatory cytokines (IL-1β and TNF-α), for more than a week. These results point out the NLC-NPX formulation as a promising candidate for the safe treatment of inflammatory pain conditions of TMJ or other joints.

Excipient-excipient interactions in the development of nanocarriers: an innovative statistical approach for formulation decisions

Excipient interaction has become essential knowledge for rational formulation design of nanoparticles. Nanostructured lipid carriers (NLCs) include at least three types of excipient, which enhance excipient interaction possibilities and relevance. The present article introduces an alternative approach for evaluating a great number of excipients with few samples, using NLC as a model delivery system. This approach is based on two sequential experiments using Hall-2 experimental design and analysis of excipient interactions in respect to their physicochemical properties by multilevel statistics. NLCs were prepared using a hot emulsification-ultrasonication method with lidocaine and nine excipients (solid lipids, oils and surfactants). The evaluated parameters were z-average size (DLS), dispersity (DLS), zeta potential (electrophoretic mobility) and entrapment efficiency (HPLC). Cetyl palmitate, beeswax, castor oil, capric/caprylic acid and polysorbate 80 all presented larger effects amongst the studied factors as well as a clear pattern of synergistic interactions. Following the verified trends, we produced an optimized NLC that exhibited all desirable physicochemical characteristics and a modified drug release profile. Our results demonstrate the methodology’s robustness, which can be applied to other nanoparticles and establish a cost-effective excipient evaluation.

Lipid-based carriers for the delivery of local anesthetics

INTRODUCTION

There is a clinical need for pharmaceutical dosage forms devised to prolong the acting time of local anesthetic (LA) agents or to reduce their toxicity. Encapsulation of LA in drug delivery systems (DDSs) can provide long-term anesthesia for inpatients (e.g. in immediate postsurgical pain control, avoiding the side effects from systemic analgesia) and diminished systemic toxicity for outpatients (in ambulatory/dentistry procedures). The lipid-based formulations described here, such as liposomes, microemulsions, and lipid nanoparticles, have provided several nanotechnological advances and therapeutic alternatives despite some inherent limitations associated with the fabrication processes, costs, and preclinical evaluation models.

AREAS COVERED

A description of the currently promising lipid-based carriers, including liposomes, microemulsions, and nanostructured lipid carriers, followed by a systematic review of the existing lipid-based formulations proposed for LA. Trends in the research of these LA-in-DDS are then exposed, from the point of view of administration route and alternatives for non-traditionally administered LA molecules.

EXPERT OPINION

Considering the current state and potential future developments in the field, we discuss the reasons for why dozens of formulations published every year fail to reach clinical trials; only one lipid-based formulation for the delivery of local anesthetic (Exparel®) has been approved so far.

Evaluation of miscibility and polymorphism of synthetic and natural lipids for nanostructured lipid carrier (NLC) formulations by Raman mapping and multivariate curve resolution (MCR)

Nanostructured lipid carriers (NLC) belong to youngest lipid-based nanocarrier class and they have gained increasing attention over the last ten years. NLCs are composed of a mixture of solid and liquid lipids, which solubilizes the active pharmaceutical ingredient, stabilized by a surfactant. The miscibility of the lipid excipients and structural changes (polymorphism) play an important role in the stability of the formulation and are not easily predicted in the early pharmaceutical development. Even when the excipients are macroscopically miscible, microscopic heterogeneities can result in phase separation during storage, which is only detected after several months of stability studies. In this sense, this work aimed to evaluate the miscibility and the presence of polymorphism in lipid mixtures containing synthetic (cetyl palmitate, Capryol 90®, Dhaykol 6040 LW®, Precirol ATO5® and myristyl myristate) and natural (beeswax, cocoa and shea butters, copaiba, sweet almond, sesame and coconut oils) excipients using Raman mapping and multivariate curve resolution - alternating least squares (MCR-ALS) method. The results were correlated to the macroscopic stability of the formulations. Chemical maps constructed for each excipient allowed the direct comparison among formulations, using standard deviation of the histograms and the Distributional Homogeneity Index (DHI). Lipid mixtures of cetyl palmitate/Capryol®; cetyl palmitate/Dhaykol®; myristyl myristate/Dhaykol® and myristyl myristate/coconut oil presented a single histogram distribution and were stable. The sample with Precirol®/Capryol® was not stable, although the histogram distribution was narrower than the samples with cetyl palmitate, indicating that miscibility was not the factor responsible for the instability. Structural changes before and after melting were identified for cocoa butter and shea butter, but not in the beeswax. Beeswax + copaiba oil sample was very homogenous, without polymorphism and stable over 6 months. Shea butter was also homogeneous and, in spite of the polymorphism, was stable. Formulations with cocoa butter presented a wider histogram distribution and were unstable. This paper showed that, besides the miscibility evaluation, Raman imaging could also identify the polymorphism of the lipids, two major issues in lipid-based formulation development that could help guide the developer understand the stability of the NLC formulations.

On local anesthetic action of some dimethylacetamide compounds

The study aim was to explore local anesthetic properties of some tertiary and quaternary derivatives of dimethylacetamide.

Materials and methods. The study was performed on white laboratory mice and rats of both sexes, male Agouti guinea pigs, and isolated sciatic nerves of lake frog. In the focus of the study there were two quaternary and eight tertiary compounds of dimethylacetamide with substituted anion with some amino and carbonic acids residue. A local anesthetic property was predicted by computational analysis. Acute toxicity of the most promising substances was studied in mice through subcutaneous route. Local anesthetic activity of tertiary compounds LKhT-3-00, LKhT-4-00 and quaternary LKhT-12-02 was studied on models of terminal, infiltration and conduction anesthesia. The influence of substances on mixed nerve conduction was investigated on lake frog’s isolated sciatic nerves.

Results and discussion. The greatest probability of the local anesthetic activity during computational analysis was estimated for the tertiary derivatives of dimethylacetamide LKhT-3-00 and LKhT-4-00 and for the quaternary compound LKhT-12-02. According to their toxicological profile, the compounds belong to moderately toxic substances (class 3). On the model of terminal and infiltration anesthesia, substances LKhT-3-00 and LKhT-4-00 at concentrations of 0.5-1% rapidly cause deep and prolonged anesthesia. On the models of conduction anesthesia, the quaternary derivative of dimethylacetamide LKhT-12-02 has the greatest analgesic effect. The duration of the effect of the substance is over 3 hours. All the investigated compounds block sciatic nerve conduction. The longest effect is registered for LKhT-12-02.

Conclusions. Dimethylacetamide derivatives at concentrations of 0.5-1.0% exhibit a local anesthetic activity, and are effective for terminal, conduction and infiltration anesthesia. Their effect is due to blockade of nerve conduction.

Solid Lipid Nanoparticles for Dibucaine Sustained Release

Dibucaine (DBC) is among the more potent long-acting local anesthetics (LA), and it is also one of the most toxic. Over the last decades, solid lipid nanoparticles (SLN) have been developed as promising carriers for drug delivery. In this study, SLN formulations were prepared with the aim of prolonging DBC release and reducing its toxicity. To this end, SLN composed of two different lipid matrices and prepared by two different hot-emulsion techniques (high-pressure procedure and sonication) were compared. The colloidal stability of the SLN formulations was tracked in terms of particle size (nm), polydispersity index (PDI), and zeta potential (mV) for 240 days at 4 °C; the DBC encapsulation efficiency was determined by the ultrafiltration/centrifugation method. The formulations were characterized by differential scanning calorimetry (DSC), electron paramagnetic resonance (EPR), and release kinetic experiments. Finally, the in vitro cytotoxicity against 3T3 fibroblast and HaCaT cells was determined, and the in vivo analgesic action was assessed using the tail flick test in rats. Both of the homogenization procedures were found suitable to produce particles in the 200 nm range, with good shelf stability (240 days) and high DBC encapsulation efficiency (~72⁻89%). DSC results disclosed structural information on the nanoparticles, such as the lower crystallinity of the lipid core vs. the bulk lipid. EPR measurements provided evidence of DBC partitioning in both SLNs. In vitro (cytotoxicity) and in vivo (tail flick) experiments revealed that the encapsulation of DBC into nanoparticles reduces its intrinsic cytotoxicity and prolongs the anesthetic effect, respectively. These results show that the SLNs produced are safe and have great potential to extend the applications of dibucaine by enhancing its bioavailability.

Nanohybrid hydrogels designed for transbuccal anesthesia

BACKGROUND

Local anesthesia in dentistry is by far the most terrifying procedure for patients, causing treatment interruption. None of the commercially available topical formulations is effective in eliminating the pain and phobia associated to the needle insertion and injection.

MATERIALS AND METHODS

In this work we prepared a nanostructured lipid-biopolymer hydrogel for the sustained delivery of lidocaine-prilocaine (LDC-PLC) for transbuccal pre-anesthesia. The lipid was composed of optimized nanostructured lipid carriers (NLC) loaded with 5% LDC-PLC (NLC/LDC-PLC). The biopolymer counterpart was selected among alginate, xanthan (XAN), and chitosan matrices. The XAN-NLC hydrogel presented the most uniform aspect and pseudoplastic rheological profile, as required for topical use; therefore, it was selected for subsequent analyses. Accelerated stability tests under critical conditions (40°C; 75% relative humidity) were conducted for 6 months, in terms of drug content (mg/g), weight loss (%), and pH.

RESULTS

In vitro LDC-PLC release profile through Franz diffusion cells revealed a bimodal kinetics with a burst effect followed by the sustained release of both anesthetics, for 24 hours. Structural analyses (fourier transform infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy) gave details on the molecular organization of the hybrid hydrogel, confirming the synergic interaction between the components. Safety and efficacy were evaluated through in vitro cell viability (3T3, HaCat, and VERO cells) and in vivo antinociceptive (tail-flick, in mice) tests, respectively. In comparison to a control hydrogel and the eutectic mixture of 5% LDC-PLC cream (EMLA®), the XAN-NLC/LDC-PLC hybrid hydrogel doubled and quadrupled the anesthetic effect (8 hours), respectively.

CONCLUSION

Considering such exciting results, this multifaceted nanohybrid system is now ready to be further tested in clinical trials.

Comparison of different chemometric methods to extract chemical and physical information from Raman images of homogeneous and heterogeneous semi-solid pharmaceutical formulations

In formulations of nanostructured lipid carriers, lipid solid dispersions and self-emulsifying drug delivery systems, it is common that a solid or semi-solid lipid excipient is mixed with a liquid solvent or liquid lipid. Even when the excipients are visually miscible upon melting, they might have microscopic non-homogeneities which could lead to instability over time and future phase separation. Raman mapping associated with chemometric methods can be useful to evaluate spatial distribution of compounds, however it has not been extensively applied to the formulations mentioned above. The aim of this work was to compare the outcomes of three different chemometric methods - principal components analysis (PCA), multivariate curve resolution with alternating least squares (MCR-ALS) and independent components analysis (ICA) - to study two systems of very different degrees of microscopic miscibility: cetyl palmitate + Transcutol^© (heterogeneous) and polyethylene glycol 6000 (PEG 6000) + Tween 80^© (homogeneous). These two samples were chosen due to large differences in spatial distribution of the compounds over the pixels which could require different approaches for data treatment. The three methods were compared regarding recovered concentrations (or scores), signals (or loadings) and the need for matrix augmentation to obtain reliable results. Results showed that PCA loadings were the mathematical differences of the spectra of pure compounds for both samples, and therefore only 'contrast images' could be generated. MCR and ICA provided signals that could be related to the chemical components, however MCR presented rotational ambiguities even for the very heterogeneous sample, a situation in which ICA performed better as a blind search method. For the homogeneous sample, both methods showed rank deficiency and therefore the use of a matrix augmentation was necessary. ICA and PCA allowed identifying physical modifications in the homogeneous semi-solid PEG 6000/Tween 80^® sample over the time, probably due to the folding/unfolding of the crystalline chains of PEG 6000. Therefore, this work discusses the ability of the three chemometrics methods to extract information from Raman spectra in order to characterize the chemical, spatial and even physical aspects of semi-solid pharmaceutical formulations, which could be of much use for stability studies of different drug delivery systems.

Levobupivacaine Thermogel for Long-acting Analgesia

The adequate management of analgesia, by pharmacological methods or not, is a great challenge. Local anesthetics are used for pain relief, mainly by parenteral, intramuscular, catheter, and other routes of administration. The use of in situ forming systems becomes an alternative for the control of pain. The present research investigates development of thermogels containing poloxamer and levobupivacaine. All formulations were prepared by the cold method; the compatibilities of the excipients were evaluated by DSC, rheology and viscosities, transition temperature, syringeability, release kinetics, and permeation. The compatibility of the tested excipients with the drug was initially observed; all formulations had a viscosity increase at 37°C. Different delivery rates were observed in both the release and permeation studies. The developed systems maintained the in vitro release of the drug for a long period, likely decreasing side effects in vivo and avoiding the need for supplementary analgesia by other routes.

Precision-guided long-acting analgesia by Gel-immobilized bupivacaine-loaded microsphere

Peripheral nerve blockade (PNB) is a conventional strategy for the management of acute postoperative pain. However, the short duration of the associated analgesia and the potential systemic toxicity due to the low molecular weights of local anesthetics limit their application. Methods: An in situ forming injectable Gel-microsphere (Gel-MS) system consisting of PLGA-PEG-PLGA Gel (Gel) and Gel-immobilized bupivacaine-loaded microsphere (MS/BUP) was prepared for precision-guided long-acting analgesia. A series of in vitro characterizations, such as scanning electron microscopy, rheology analysis, confocal laser scanning microscopy, drug release, and erosion and degradation, were carried out. After that, the in vivo analgesia effect of the Gel-MS system, the immobilization effect of Gel on the MS, and biocompatibility of the system were evaluated using a sciatic nerve block model. Results: The BUP release from the Gel-MS system was regulated by both the inner MS and the outer Gel matrix, demonstrating sustained BUP release in vitro for several days without an initial burst release. More importantly, incorporation of the Gel immobilized the MS and hindered the diffusion of MS from the injection site because of its in situ property, which contributed to a high local drug concentration and prevented systemic side effects. In vivo, a single injection of Gel-MS/BUP allowed rats to maintain sensory and motor blockade significantly longer than treatment with MS/BUP (P < 0.01) or BUP-loaded Gel (Gel-BUP, P < 0.01). Histopathological results demonstrated the excellent biodegradability and biocompatibility of the Gel-MS system without neurotoxicity. Conclusion: This precision-guided long-acting analgesia, which provides an in situ and sustained release of BUP, is a promising strategy for long-acting analgesia, and could represent a potential alternative for clinical pain management.

Use of nanoparticle concentration as a tool to understand the structural properties of colloids

Elucidation of the structural properties of colloids is paramount for a successful formulation. However, the intrinsic dynamism of colloidal systems makes their characterization a difficult task and, in particular, there is a lack of physicochemical techniques that can be correlated to their biological performance. Nanoparticle tracking analysis (NTA) allows measurements of size distribution and nanoparticle concentration in real time. Its analysis over time also enables the early detection of physical instability in the systems not assessed by subtle changes in size distribution. Nanoparticle concentration is a parameter with the potential to bridge the gap between in vitro characterization and biological performance of colloids, and therefore should be monitored in stability studies of formulations. To demonstrate this, we have followed two systems: extruded liposomes exposed to increasing CHCl₃ concentrations, and solid lipid nanoparticles prepared with decreasing amounts of poloxamer 188. NTA and dynamic light scattering (DLS) were used to monitor changes in nanoparticle number and size, and to estimate the number of lipid components per particle. The results revealed a strong negative correlation between particle size (determined by DLS) and concentration (assessed by NTA) in diluted samples, which should be adopted to monitor nanocolloidal stability, especially in drug delivery.