Oral bioavailability improvement of felodipine using tailored microemulsion: Surface science, ex vivo and in vivo studies

Intranasal delivery of doxepin: enhancing brain targeting efficiency utilizing nanostructured lipid carriers for a biopharmaceutics drug disposition classification system class-I drug

Doxepin, a Class-I Biopharmaceutics Drug Disposition Classification System (BDDCS) drug, exhibits poor bioavailability due to extensive first-pass metabolism. This research focuses on enhancing the delivery of doxepin by formulating nanostructured lipid carriers (NLCs) through the utilization of the Box-Behnken Design methodology. These optimized NLCs are intended for intranasal administration, with the ultimate goal of improving nose-to-brain drug delivery. NLCs were formulated using a high-speed homogenization technique. The optimized batch had a small particle size (75.80 ± 5.48 nm, PDI = 0.286), high entrapment efficiency (94.10 ± 0.16%), and sustained ex vivo release (82.25 ± 4.61% at 24 h). Characterization studies confirmed the conversion of doxepin from a crystalline to an amorphous state with uniform distribution in the lipid matrix. In vivo pharmacokinetic studies in rats showed significantly higher doxepin concentration in the brain tissue (Cmax = 16.77 µg/g, tmax = 30 min) after intranasal administration compared to intravenous administration (Cmax = 2.53 µg/g, tmax = 6 h). High-drug targeting efficiency (DTE = 284.3%) and direct transport percentage (DTP = 64.8%) suggested direct penetration of NLCs in the brain via olfactory and trigeminal pathways. In conclusion, the study highlights the potential of NLCs to improve the bioavailability of doxepin through nose-to-brain delivery and thereby potentially enable the treatment of neurological disorders.

Design, optimization, and evaluation for a long-time-released transdermal microneedle delivery system containing estradiol

Transdermal drug delivery systems (TDDS) have drawbacks such as poor absorption, low blood concentration, and delayed effects. Dissolving microneedle has sharp tips and short length, which overcome patients' pain and improve transdermal efficiency but has low mechanical strength and drug loading capacity. This study thereby proposes a microemulsion-encapsulated and long-time-released transdermal microneedle (MN) delivery system with estradiol (Es) as the model drug. The microemulsion (ME) was optimized by utilizing the pseudo-ternary phase diagram and D-optimal mixture design. The estradiol microemulsion-encapsulated microneedle (Es-ME-MN) was optimized by Box-Behnken design and prepared by freeze-thaw method. The Es-ME-MN obtained was characterized and evaluated through a large variety of studies. Es-ME-MN had sufficient mechanical strength to pierce skin and was safe enough, the length of which was 600 μm, and the Es content was 177.12 ± 0.72 μg/patch without drug-excipient chemical interaction. In vitro permeation study showed that Es-ME-MN has a higher transdermal efficiency and lower retention capacity than commercial estradiol patch and conventional MN. Es plasma concentration began to increase at 3 h and remained at 12.98-23.52 ng/mL until 72 h by pharmacokinetic experiments in the Es-ME-MN group. Es-ME-MN rapidly achieves effective blood concentrations through needle puncture and microemulsion delivery and maintains blood concentrations through the baseplate long-time release. Microemulsion-encapsulated, organic solvent-free, and long-time-released transdermal microneedle will make progress and provide a new idea for transdermal delivery of lipophilic drugs.

Water in nigella oil microemulsion for enhanced oral bioavailability of linagliptin

Linagliptin is hydrophilic antidiabetic with poor oral bioavailability due to poor permeability and pre-systemic metabolism. The objective was to assess w/o microemulsion for enhanced oral bioavailability of linagliptin. Nigella oil was used as oily phase based on its reported antidiabetic effect. Isopropyl myristate (IPM) or capryol were combined with nigella oil to impart intestinal membrane permeabilizing abilities. Pseudoternary phase diagrams were constructed utilizing nigella oil in presence and absence of isopropyl myristate or capryol as oily phase using Tween 60 as surfactant. W/O microemulsion formulations were selected from the constructed phase diagrams and linagliptin was loaded in the internal aqueous phase at a concentration of 0.5 mg/ml. The prepared formulations were physically evaluated and linagliptin in vitro release was monitored. Eventually, the in vivo hypoglycemic effect was assessed using diabetic rats. The developed microemulsions were of w/o type and exhibited Newtonian flow behavior with nigella/capryol microemulsion recording the lowest viscosity. The recorded droplet size values were 104.9, 121.2 and 86.4 nm for nigella, nigella/IPM and nigella/capryol microemulsions, respectively. All microemulsion formulations showed slower drug release rate compared with aqueous suspension with nigella/capryol microemulsion showing the highest release rate compared to other microemulsions. Release data from microemulsion best fitted to Higuchi model. In vivo oral hypoglycemic activity measurement reflected a more intensified hypoglycemic effect with rapid onset after oral ingestion of microemulsion compared to linagliptin dispersion. Nigella oil/IPM-based microemulsion was ranked as the most effective. The investigation highlighted the feasibility of w/o microemulsion for enhanced oral bioavailability of hydrophilic drugs like linagliptin.

Clozapine-laden carbon dots delivered to the brain via an intranasal pathway: Synthesis, characterization, ex vivo, and in vivo studies

Clozapine, which is widely used to treat schizophrenia, shows low bioavailability due to poor solubility and high first-pass metabolism. The study aimed to design clozapine-loaded carbon dots (CDs) to enhance availability of the clozapine to the brain via intranasal pathway. The CDs were synthesized by pyrolysis of citric acid and urea at 200 °C by hydrothermal technique and characterized by photoluminescence, transmission electron microscopy (TEM), X-ray Photoelectron Spectrometer (XPS), and Fourier transform infrared spectrum (FTIR). The optimized clozapine-loaded CDs (CLZ-CDs-1:3-200) showed a quasi-spherical shape (9-12 nm) with stable blue fluorescence. The CDs showed high drug solubilization capacity (1.5 mg drug in 1 mg/ml CDs) with strong electrostatic interaction with clozapine (drug loading efficiency = 94.74%). The ex vivo release study performed using nasal goat mucosa showed sustained release of clozapine (43.89%) from CLZ-CDs-1:3-200 for 30 h. The ciliotoxicity study (histopathology) confirmed no toxicity to the nasal mucosal tissues using CDs. In the rat model (in vivo pharmacokinetic study), when CDs were administrated by the intranasal route, a significantly higher concentration of clozapine in the brain tissue (Cmax = 58.07 ± 5.36 μg/g and AUCt (µg/h*g) = 105.76 ± 12.31) was noted within a short time (tmax = 1 h) compared to clozapine suspension administered by intravenous route (Cmax = 20.99 ± 3.91 μg/g, AUC t (µg/h*g) = 56.89 ± 12.31, and tmax = 4 h). The high value of drug targeting efficiency (DTE, 486%) index and direct transport percentage (DTP, 58%) indicates the direct entry of clozapine-CDs in the brain via the olfactory route. In conclusion, designed CDs demonstrated a promising dosage form for targeted nose-to-brain delivery of clozapine for the effective treatment of schizophrenia.

Preparation, characterization, and toxicity evaluation of microemulsion formulation containing prunetin for potential oral applications

Phytochemicals as therapeutic alternatives can have a fundamental impact on the various stages of inflammation and its resolution. Prunetin is a naturally occurring isoflavone and has been claimed to have numerous therapeutic potentials. The objective of this study is preparation, characterization, and toxicity evaluation of microemulsion formulation containing prunetin (PMF) for potential oral applications. With this research, it was targeted to emphasize the way of improving the therapeutic efficacy of natural biomolecules with a nontoxic and effective formulation. In the study, the pseudo-ternary phase diagram was developed and PMF was characterized by conductivity, droplet size, viscosity and pH. Effects against to cytokines (IL-1β and IL-6) and TNF-α levels of the PMF were determined by ELISA technique. Genotoxicity and acute oral toxicity tests were carried out according to OECD guidelines. The results showed that PMF is a colloid system that reduced proinflammatory cytokine levels in LPS-induced macrophage cells compared to the control group. PMF demonstrated no mutagenic activity against TA98, TA100, TA1535, and TA1537 Salmonella strains. The in vivo oral acute toxicity test results indicated that PMF did not show mortality or significant side effects even at 2000 mg/kg bw. This study represents PMF showed a good safety profile in animal study. It is thought that this formulation may have anti-inflammatory potential with further in vivo testing.

Nanosizing of Lavender, Basil, and Clove Essential Oils into Microemulsions for Enhanced Antioxidant Potential and Antibacterial and Antibiofilm Activities

Plant essential oils (EOs) possess significant bioactivities (antibacterial and antioxidant) and can be substituted for potentially harmful synthetic preservatives in the food industry. However, limited water solubility, bioavailability, volatility, and stability limit their use. Therefore, the goal of this research was nanosizing lavender essential oil (LEO), basil essential oil (BEO), and clove essential oil (CEO) in a microemulsion (ME) to improve their physicochemical attributes and bioefficacy. Tween 80 and Transcutol P were utilized for construction of pseudoternary phase diagrams. It was observed that the concentration of EOs had a great impact on the physicochemical and biological properties of MEs. A spherical droplet of MEs with a diameter of less than 20 nm with a narrower size distribution (polydispersity index (PDI) = 0.10-0.27) and a ζ potential of -0.27 to -9.03 was observed. ME formulations were also evaluated for viscosity, conductivity, and the refractive index. Moreover, the impact of delivery systems on the antibacterial property of EOs was assessed by determining the zone of inhibition and minimum inhibitory concentration against two distinct pathogen classes (S. aureus and E. coli). Crystal violet assay was used to measure the growth and development of biofilms. According to bioefficacy assays, ME demonstrated more efficient antibacterial activity against microorganisms at concentrations lower than pure EOs. CEO ME had superior activity againstS. aureus and E. coli. Similarly, dose-dependent antioxidant capacity was noted for MEs. Consequently, nanosized EO formulations with improved physicochemical properties and enhanced bioactivities can be employed in the food processing sector as a preservation agent.

Topical Microemulsions: Skin Irritation Potential and Anti-Inflammatory Effects of Herbal Substances

Microemulsions (MEs) have gained prominence as effective drug delivery systems owing to their optical transparency, low viscosity, and thermodynamic stability. MEs, when stabilized with surfactants and/or co-surfactants, exhibit enhanced drug solubilization, prolonged shelf life, and simple preparation methods. This review examines the various types of MEs, explores different preparation techniques, and investigates characterization approaches. Plant extracts and bioactive compounds are well established for their utilization as active ingredients in the pharmaceutical and cosmetic industries. Being derived from natural sources, they serve as preferable alternatives to synthetic chemicals. Furthermore, they have demonstrated a wide range of therapeutic effects, including anti-inflammatory, antimicrobial, and antioxidant activities. However, the topical application of plant extracts and bioactive compounds has certain limitations, such as low skin absorption and stability. To overcome these challenges, the utilization of MEs enables enhanced skin absorption, thereby making them a valuable mode of administration. However, considering the significant surfactant content in MEs, this review evaluates the potential skin irritation caused by MEs containing herbal substances. Additionally, the review explores the topical application of MEs specifically for herbal substances, with an emphasis on their anti-inflammatory properties.

An emerging era in manufacturing of drug delivery systems: Nanofabrication techniques

Nanotechnology has the capability of making significant contributions to healthcare. Nanofabrication of multifunctional nano- or micro-character systems is becoming incredibly influential in various sectors like electronics, photonics, energy, and biomedical gadgets worldwide. The invention of such items led to the merger of moderate cost and excellent quality nano or micro-characters into 3D structures. Nanofabrication techniques have many benefits as the primary technology for manipulating cellular surroundings to research signaling processes. The inherent nanoscale mechanisms of cyto-reactions include the existence and death of cells, stem cell segmentation, multiplication, cellular relocation, etc. Nanofabrication is essential in developing various nano-formulations like solid lipid nanoparticles, nanostructured lipid carriers, liposomes, niosomes, nanoemulsions, microemulsions etc. Despite the initial development cost in designing the nanofabrication-based products, it has also reduced the total cost of the healthcare system by considering the added benefits compared to the other standard formulations. Thus, the current review mainly focuses on nanofabrication techniques, advantages, disadvantages, applications in developing various nanocarrier systems, challenges and future perspectives.

Application of Design of Experiments in the Development of Self-Microemulsifying Drug Delivery Systems

Oral delivery has become the route of choice among all other types of drug administrations. However, typical chronic disease drugs are often poorly water-soluble, have low dissolution rates, and undergo first-pass metabolism, ultimately leading to low bioavailability and lack of efficacy. The lipid-based formulation offers tremendous benefits of using versatile excipients and has great compatibility with all types of dosage forms. Self-microemulsifying drug delivery system (SMEDDS) promotes drug self-emulsification in a combination of oil, surfactant, and co-surfactant, thereby facilitating better drug solubility and absorption. The feasible preparation of SMEDDS creates a promising strategy to improve the drawbacks of lipophilic drugs administered orally. Selecting a decent mixing among these components is, therefore, of importance for successful SMEDDS. Quality by Design (QbD) brings a systematic approach to drug development, and it offers promise to significantly improve the manufacturing quality performance of SMEDDS. Furthermore, it could be benefited efficiently by conducting pre-formulation studies integrated with the statistical design of experiment (DoE). In this review, we highlight the recent findings for the development of microemulsions and SMEDDS by using DoE methods to optimize the formulations for drugs in different excipients with controllable ratios. A brief overview of DoE concepts is discussed, along with its technical benefits in improving SMEDDS formulations.

Liquid antisolvent crystallization of pharmaceutical compounds: current status and future perspectives

The present work reviews the liquid antisolvent crystallization (LASC) to prepare the nanoparticle of pharmaceutical compounds to enhance their solubility, dissolution rate, and bioavailability. The application of ultrasound and additives is discussed to prepare the particles with narrow size distribution. The use of ionic liquid as an alternative to conventional organic solvent is presented. Herbal compounds, also known for low aqueous solubility and limited clinical application, have been crystalized by LASC and discussed here. The particle characteristics such as particle size and particle size distribution are interpreted in terms of supersaturation, nucleation, and growth phenomena. To overcome the disadvantage of batch crystallization, the scientific literature on continuous flow reactors is also reviewed. LASC in a microfluidic device is emerging as a promising technique. The different design of the microfluidic device and their application in LASC are discussed. The combination of the LASC technique with traditional techniques such as high-pressure homogenization and spray drying is presented. A comparison of product characteristics prepared by LASC and the supercritical CO₂ antisolvent method is discussed to show that LASC is an attractive and inexpensive alternative for nanoparticle preparation. One of the major strengths of this paper is a discussion on less-explored applications of LASC in pharmaceutical research to attract the attention of future researchers.

Nano-strategies as Oral Drug Delivery Platforms for Treatment of Cancer: Challenges and Future Perspectives

Oral drug administration is the oldest and widely used method for drug administration. The objectives behind developing an oral drug delivery for the treatment of cancer are to achieve low cost treatment by utilizing novel techniques to target cancer through gut-associated lymphoid tissue (GALT) and to enhance patient comfort and compliance through a hospital-free treatment leading to "Chemotherapy at Home." Unfortunately, due to the physiological environment of the GIT and physicochemical properties of drug candidate, the efficacy of oral drug delivery methods is limited in the treatment of cancer. Due to their low hydrophilicity, high P-gp efflux and restricted intestinal permeability most of the anti-cancer drugs fail to achieve oral bioavailability. The review focuses on the efforts, challenges, opportunities and studies conducted by scientists worldwide on the oral administration of anticancer medications via nanocarriers such as liposomes, SLNs and dendrimers, because of their potential to overcome the epithelial barrier associated with GALT, as well as the applications of different polymers in targeting the cancer. The oral delivery can set newer horizons in cancer therapy to make it more patient friendly.

In vitro and in vivo evaluation of brimonidine loaded silica nanoparticles-laden silicone contact lenses to manage glaucoma

Glaucoma is treated by frequent instillation of 0.2% w/v brimonidine tartrate eye drop solution, which showed poor ocular bioavailability of 1-3%. Medicated contact lenses can be used to improve the ocular drug bioavailability. However, drug loading in the contact lens matrix showed high burst release and changes the optophysical properties of the contact lens material. In this paper, a novel brimonidine loaded silica nanoparticles-laden silicone contact lenses (Bri-Si) were designed to achieve controlled drug delivery without altering the optophysical properties of the contact lens. Silica nanoparticles were prepared by polymerizing octadecyltrimethoxysilane (OTMS) molecules at the oil/water interface of microemulsion. Traditional soaking method (Bri-SM), direct brimonidine-loading method (Bri-DL) and microemulsion-laden contact lens (Bri-ME) were developed for comparison. The Bri-Si lens showed improved swelling, transmittance, oxygen permeability and lysozyme adherence compared to Bri-SM, Bri-DL and Bri-ME lenses. The Bri-DL lens showed high brimonidine leaching during extraction and sterilization steps, with low cumulative drug release. While, Bri-Si lens show controlled brimonidine release for 144 h. In a rabbit tear fluid model, the Bri-Si lens showed high brimonidine concentration for 96 h compared to Bri-ME lens and eye drop therapy. Based on histopathological studies of cornea, the Bri-Si lens was found to be safe for human applications. The data demonstrated the novel application of silica nanoparticles to control brimonidine release from the contact lens without altering the optophysical properties of the contact lens.

In vitro and in vivo evaluation of a novel lidocaine-loaded cubosomal gel for prolonged local anesthesia

Marketed lidocaine dosage forms (such as ointment, gels, and injections) used to manage acute and chronic pain showed a short duration of action (<2 h). In this study, a lidocaine-loaded cubosomal gel was prepared to sustain the release of lidocaine to prolong the local anesthetic effect (high drug retention in the skin). Lidocaine-loaded cubosomal gels were prepared by melt emulsification and sonication using Pluronic F127 and DL-α-monoolein (at different levels). The cubosomal gels were characterized by morphology, size, zeta potential, entrapment efficacy, assay, viscosity, pH, and texture profiles. Ex vivo lidocaine permeation and retention studies were performed using Sprague–Dawley rat skin. Transmission electron microscopy images confirmed the bi-continuous liquid crystalline phase with a honeycomb cubosome structure. The cubosomal particle size (103–227 nm), viscosity (13,524–15,627cp), and entrapment efficacy (78.4–94.7%) increase with the level of monoolein. The ex-vivo permeation study showed a biphasic release pattern, with lidocaine cleared from ointment within 4 h (97.9% cumulative release), while cubosomal gels showed sustained release up to 24 h (53.33–98.86% cumulative release). A skin retention study demonstrated that cubosomes can increase (up to 28-fold) the lidocaine content in the skin (4.56 mg) compared to ointment (0.19 mg). A rabbit skin irritation study showed no sign of irritation after the application of cubosomal gel. In the radiant heat tail-flick study, the local anesthetic effect of lidocaine from the cubosomal gel was sustained for up to 16 h with 1.43-fold higher efficacy than marketed ointment. In conclusion, the study demonstrated the potential of cubosomal nanoparticle-laden gel to sustain the release of lidocaine for prolonging local anesthetic effects for pain management.

Microemulsion Delivery System Improves Cellular Uptake of Genipin and Its Protective Effect against Aβ1-42-Induced PC12 Cell Cytotoxicity

Genipin has attracted much attention for its hepatoprotective, anti-inflammatory, and neuroprotection activities. However, poor water solubility and active chemical properties limit its application in food and pharmaceutical industries. This article aimed to develop a lipid-based microemulsion delivery system to improve the stability and bioavailability of genipin. The excipients for a genipin microemulsion (GME) preparation were screened and a pseudo-ternary phase diagram was established. The droplet size (DS), zeta potential (ZP), polydispersity index (PDI), physical and simulated gastrointestinal digestion stability, and in vitro drug release properties were characterized. Finally, the effect of the microemulsion on its cellular uptake by Caco-2 cells and the protective effect on PC12 cells were investigated. The prepared GME had a transparent appearance with a DS of 16.17 ± 0.27 nm, ZP of −8.11 ± 0.77 mV, and PDI of 0.183 ± 0.013. It exhibited good temperature, pH, ionic strength, and simulated gastrointestinal digestion stability. The in vitro release and cellular uptake data showed that the GME had a lower release rate and better bioavailability compared with that of free genipin. Interestingly, the GME showed a significantly better protective effect against amyloid-β (Aβ1-42)-induced PC12 cell cytotoxicity than that of the unencapsulated genipin. These findings suggest that the lipid-based microemulsion delivery system could serve as a promising approach to improve the application of genipin.

Multi-directionally evaluating the formation mechanism of 1,4-dihydropyridine drug nanosuspensions through experimental validation and computer-aided drug design

The poor aqueous solubility of 1,4-dihydropyridine drugs needs to be solved urgently to improve the bioavailability. Nanotechnology can improve drug solubility and dissolution by reducing particle size, but usually a specific polymer or surfactant is required for stabilization. In this study, Poloxamer-407(P-407) was screened as the optimal stabilize through energy simulation, molecular docking and particle size. morphological study, X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, Raman, in vitro dissolution test and molecular simulation of interactions were utilized to explore the formation mechanisms of four 1,4-dihydropyridine drugs/P-407 nanosuspensions. The result shows that the optimized nanosuspensions had the particle size in the nano-size range and maintained the original crystal state. The in vitro dissolution rate of the nanosuspension was 3-4 times higher than the corresponding API and could reduce the restriction of drug dissolution in different pH environments. Raman spectroscopy, FTIR and molecular docking simulations provided strong supporting evidence for the formation mechanism of 1,4-dihydropyridine drugs/P-407 nanosuspensions at the molecular level, which confirmed that the stable intermolecular hydrogen bond adsorption and hydrophobic interaction were formed between the drug and P-407. This research will provide practical concepts and technologies, which are helpful to develop nanosuspensions for the same class of drugs.

Bimatoprost-Loaded Silica Shell-Coated Nanoparticles-Laden Soft Contact Lenses to Manage Glaucoma: In Vitro and In Vivo Studies

Currently, glaucoma is managed by frequent instillation of bimatoprost eye drop therapy, which showed very poor ocular bioavailability. Contact lens is widely used as medical device to improve the drug retention on the ocular tissues. However, the traditional methods of drug loading in the contact lens matrix showed high burst release and changes the optophysical properties of the contact lens material. In this paper, a novel bimatoprost-loaded silica shell nanoparticles-laden soft contact lenses were developed to achieve sustain drug delivery without altering the optophysical properties of the contact lens. Silica-shell nanoparticles were prepared using octyltrimethoxysilane (OTMS) and microemulsion. Traditional soaking method (SM-BT), direct bimatoprost loading method (DL-BT), and microemulsion-laden contact lens (ME-BT) were developed for comparison. The silica shell-coated nanoparticles-laden soft contact lenses (SiS-BT) showed improved swelling, transmittance, oxygen permeability, and lysozyme adherence compared to SM-BT, DL-BT, and ME-BT lenses. The DL-BT and ME-BT batch showed high bimatoprost lost/leaching during extraction and sterilization steps, with low cumulative drug release. Also, SiS-BT lens showed sustain bimatoprost release for 96 h. In a rabbit tear fluid model, the SiS-BT lens showed high bimatoprost concentration for 72 h compared to ME-BT lens and eye drop therapy. Based on histopathological studies of cornea, the SiS-BT lens was found to be safe for human applications. The data demonstrated the novel application of silica shell nanoparticles to deliver bimatoprost from the contact lens for extended period of time without altering the optophysical properties of the contact lens.

Advances and challenges in the nanoparticles-laden contact lenses for ocular drug delivery

The delivery of drugs that target ocular tissues is challenging due to the physiological barriers of the eye like tear dilution, nasolacrimal drainage, blinking, tear turnover rate and low residence time Drug-laden contact lenses can be a possible solution to overcome some of these challenges. Nanoparticles are being extensively studied as novel systems for loading drugs into therapeutic contact lenses. The versatile features of the organic and inorganic nanoparticles and their diverse physicochemical properties make it possible to load and sustain drug release from the contact lenses. Nevertheless, several issues remains to be solved before its clinical application and commercialization such as changes in contact lens swelling (water content), transmittance, protein adherence, surface roughness, tensile strength, ion and oxygen permeability and drug leaching during contact lens manufacture. However, clinical studies demonstrated the potential of therapeutic contact lenses to manage the scientific, commercial and regulatory challenges to make its place in the market. This review highlights the different methodologies used to fabricate nanoparticle-laden contact lenses and highlights the major advances and challenges to commercialization.

Recent advances in ophthalmic preparations: Ocular barriers, dosage forms and routes of administration

The human eye is a complex organ with unique anatomy and physiology that restricts the delivery of drugs to target ocular tissues/sites. Recent advances in the field of pharmacy, biotechnology and material science have led to development of novel ophthalmic dosage forms which can provide sustained drug delivery, reduce dosing frequency and improve the ocular bioavailability of drugs. This review highlights the different anatomical and physiological factors which affect ocular bioavailability of drugs and explores advancements from 2016 to 2020 in various ophthalmic preparations. Different routes of drug administration such as topical, intravitreal, intraocular, juxtascleral, subconjunctival, intracameral and retrobulbar are discussed with their advances and limitations.

Development of a novel cannabinoid-loaded microemulsion towards an improved stability and transdermal delivery

The aim of this study was to develop a stable microemulsion (ME) for transdermal delivery of tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA). The lipid-based vehicles were selected by screening cannabinoid solubility and the emulsifying ability of surfactants. Pseudo-ternary phase diagrams were constructed by formulation of cannabinoids with Capryol® 90 as oil phase, Tween® 80, Solutol® HS15, Procetyl® AWS, and Cremophor® RH40 as surfactants, ethanol as cosurfactant, and distilled water as the aqueous phase. A significant improvement in transmembrane flux (J_ss), permeability coefficient (K_p), and enhancement ratio (E_R) was found in one system compared to other formulations. This ME consisted of 1.0% (w/w) of cannabinoids, 5% (w/w) of Capryol® 90, 44% (w/w) S_mix (2:1, Procetyl® AWS and Ethanol) and 50.0% (w/w) of distilled water. Additionally, the effects of pH on the permeation of the cannabinoids were investigated. Based on the pH value THCA and CBDA-loaded ME exhibited the highest permeation at pH 5.17 and pH 5.25. After storing the pH-adjusted P2 ME and the optimized P2 ME for 180 days at 4℃ and 25℃, the content of cannabinoids was over 95%. Consequently, the cannabinoid-loaded ME system is a promising option for solubilizing and stabilizing lipophilic drugs like cannabinoids and utilize them for transdermal delivery.

Nose to brain delivery of tailored clozapine nanosuspension stabilized using (+)-alpha-tocopherol polyethylene glycol 1000 succinate: Optimization and in vivo pharmacokinetic studies

Clozapine is widely used to treat schizophrenia as an atypical antipsychotic. Low solubility, poor dissolution rate, degradation in the gastrointestinal tract, high hepatic first-pass metabolism, and eventually less drug transfer in the brain are all issues with oral clozapine administration. On account of this poor pharmacokinetic parameters, the authors aimed to develop clozapine nanosuspension using (+)-alpha-tocopherol polyethylene glycol 1000 succinate (TPGS) and polyvinylpyrrolidone K-30 (PVP K-30) and deliver it through the intranasal route. The nanosuspension was prepared by the high-speed homogenization method with 3² full factorial design for optimization of the product. Quality Target Product Profile (QTPP) was enlisted before the product development. The amount of TPGS and speed of homogenizer were selected as independent variables whereas, particle size and drug permeation profile after 24 h (Y₂, %) were selected as dependent variables. As per the results of optimization, amount of TPGS and speed of homogenizer were chosen as 0.1% and 7000 rpm, respectively. The particle size of the optimized nanosuspension of clozapine was found to be 281 nm. The conversion of clozapine crystals to an amorphous form was verified by characterization studies (XRD and DSC). The drug permeability study showed 96.15% and 41.12% clozapine release after 24 h from nanosuspension and conventional suspension, respectively. The study of nasal cilio-toxicity (histopathological studies) demonstrated the appropriateness of nanosuspension for intranasal purposes. The single-dose in vivo pharmacokinetic analysis in the rat model showed a substantial increase in the therapeutic concentration of clozapine in the brain tissue in the case of intranasal nanosuspension (dose = 0.05 mg drug/0.1 mL, C_max = 8.62 ± 0.45 μg/g, t_max = 1 h) compared to conventional oral clozapine suspension (dose = 26.43 mg drug/0.158 mL, C_max = 1.14 ± 0.12 μg/g, t_max = 1 h).Ultimately, in the case of an intranasal route, a 3.56-fold increase in brain drug concentration was observed with a 528-fold lower drug dose compared with oral administration. The results suggest that clozapine nanosuspension may be used for successful nose-to-brain delivery.