Effect of the Subcutaneous Environment on Phase-Sensitive In Situ-Forming Implant Drug Release, Degradation, and Microstructure

In vitro and in vivo evaluation of in situ forming polyester implants for the extended release of carvedilol

Polyester based in situ forming implants (ISFIs) are injectable long-acting drug delivery systems that offer a wide range of unique advantages. As a result of these advantages, two relatively high molecular weight, ester terminated grades of poly (D,L-lactide-co-glycolide) (PLGA) and poly(D,L-lactide) (PLA) were evaluated for their ability (i) to form ISFIs loaded with carvedilol, and (ii) to control its release both in vitro and in vivo. At a polymeric concentration of 40% w/w, implant solutions were syringeable, injectable, and able to encapsulate carvedilol to a high degree (encapsulated drug% > 97%). When visualized using scanning electron microscopy (SEM), implants were found to have a dense thin surface atop porous sublayers. As for their in vitro evaluation, PLGA and PLA implants were able to maintain drug release over the course of 49 and 84 days, respectively. On the other hand, in vivo drug release from both implants was almost identical and lasted for only 42 days. This may be due to the overriding effect of the similar host environment at the injection site that diminished the effect of polymeric physiochemistry on phase inversion and drug release. Lastly, while the polymer-free drug/NMP solution completely released its drug content within the initial half hour in vitro, the formulation extended drug release in vivo. This could be due to a yet to be investigated interaction between carvedilol and NMP under in vivo conditions. These results cement the significance of formulating carvedilol loaded ISFIs for the management of chronic conditions.

Towards in vitro - In vivo correlation models for in situ forming drug implants

In vitro-In vivo correlation (IVIVC) is a main focus of the pharmaceutical industry, academia and the regulatory sectors, as this is an effective modelling tool to predict drug product in vivo performance based on in vitro release data and serve as a surrogate for bioequivalence studies, significantly reducing the need for clinical studies. Till now, IVIVCs have not been successfully developed for in situ forming implants due to the significantly different in vitro and in vivo drug release profiles that are typically achieved for these dosage forms. This is not unexpected considering the unique complexity of the drug release mechanisms of these products. Using risperidone in situ forming implants as a model, the current work focuses on: 1) identification of critical attributes of in vitro release testing methods that may contribute to differences in in vitro and in vivo drug release from in situ forming implants; and 2) optimization of the in vitro release method, with the aim of developing Level A IVIVCs for risperidone implants. Dissolution methods based on a novel Teflon shape controlling adapter along with a water non-dissolvable glass fiber membrane (GF/F) instead of a water dissolvable PVA film (named as GF/F-Teflon adapter and PVA-Teflon adapter, respectively), and an in-house fabricated Glass slide adapter were used to investigate the impact of: the surface-to-volume ratio, water uptake ratio, phase separation rate (measured by NMP release in 24 h post injection in vitro or in vivo), and mechanical pressure on the drug release patterns. The surface-to-volume ratio and water uptake were shown to be more critical in vitro release testing method attributes compared to the phase separation rate and mechanical pressure. The Glass slide adapter-based dissolution method, which allowed for the formation of depots with bio-mimicking surface-to-volume ratios and sufficient water uptake, has the ability to generate bio-relevant degradation profiles as well as in vitro release profiles for risperidone implants. For the first time, a Level A IVIVC (rabbit model) has been successfully developed for in situ forming implants. Release data for implant formulations with slightly different PLGA molecular weights (MWs) were used to develop the IVIVC. The predictability of the model passed external validation using the reference listed drug (RLD), Perseris®. IVIVC could not be developed when formulations with different PLGA molar ratios of lactic acid to glycolic acid (L/G) were included. The present work provides a comprehensive understanding of the impact of the testing method attributes on drug release from in situ forming implants, which is a valuable practice for level A IVIVC development.

In-situ forming PLGA implants: Towards less toxic solvents

In-situ forming poly(lactic-co-glycolic acid) (PLGA) implants offer a great potential for controlled drug delivery for a variety of applications, e.g. periodontitis treatment. The polymer is dissolved in a water-miscible solvent. The drug is dissolved or dispersed in this solution. Upon contact with aqueous body fluids, the solvent diffuses into the surrounding tissue and water penetrates into the formulation. Consequently, PLGA precipitates, trapping the drug. Often, N-methyl-2-pyrrolidine (NMP) is used as a water-miscible solvent. However, parenteral administration of NMP raises toxicity concerns. The aim of this study was to identify less toxic alternative solvent systems for in-situ forming PLGA implants. Various blends of polyethylene glycol 400 (PEG 400), triethyl citrate (TEC) and ethanol were used to prepare liquid formulations containing PLGA, ibuprofen (as an anti-inflammatory drug) and/or chlorhexidine dihydrochloride (as an antiseptic agent). Implant formation and drug release kinetics were monitored upon exposure to phosphate buffer pH 6.8 at 37 °C. Furthermore, the syringeability of the liquids, antimicrobial activity of the implants, and dynamic changes in the latter's wet mass and pH of the release medium were studied. Importantly, 85:10:5 and 60:30:10 PEG 400:TEC:ethanol blends provided good syringeability and allowed for rapid implant formation. The latter controlled ibuprofen and chlorhexidine release over several weeks and assured efficient antimicrobial activity. Interestingly, fundamental differences were observed concerning the underlying release mechanisms of the two drugs: Ibuprofen was dissolved in the solvent mixtures and partially leached out together with the solvents during implant formation, resulting in relatively pronounced burst effects. In contrast, chlorhexidine dihydrochloride was dispersed in the liquids in the form of tiny particles, which were effectively trapped by precipitating PLGA during implant formation, leading to initial lag-phases for drug release.

Mechanistic Computational Modeling of Implantable, Bioresorbable Drug Release Systems

Implantable, bioresorbable drug delivery systems offer an alternative to current drug administration techniques; allowing for patient-tailored drug dosage, while also increasing patient compliance. Mechanistic mathematical modeling allows for the acceleration of the design of the release systems, and for prediction of physical anomalies that are not intuitive and may otherwise elude discovery. This study investigates short-term drug release as a function of water-mediated polymer phase inversion into a solid depot within hours to days, as well as long-term hydrolysis-mediated degradation and erosion of the implant over the next few weeks. Finite difference methods are used to model spatial and temporal changes in polymer phase inversion, solidification, and hydrolysis. Modeling reveals the impact of non-uniform drug distribution, production and transport of H+ ions, and localized polymer degradation on the diffusion of water, drug, and hydrolyzed polymer byproducts. Compared to experimental data, the computational model accurately predicts the drug release during the solidification of implants over days and drug release profiles over weeks from microspheres and implants. This work offers new insight into the impact of various parameters on drug release profiles, and is a new tool to accelerate the design process for release systems to meet a patient specific clinical need.

In situ forming risperidone implants: Effect of PLGA attributes on product performance

Despite the unique advantages of injectable, long-acting in situ forming implant formulations based on poly(lactide-co-glycolide) (PLGA) and N-Methyl-2-Pyrrolidone (NMP), only six products are commercially available. A better understanding of PLGA will aid in the development of more in situ forming implant innovator and generic products. This article investigates the impact of slight changes in PLGA attributes, i.e., molecular weight (MW), lactide:glycolide (L/G) ratio, blockiness, and end group, on the in vitro and in vivo performance of PLGA-based in situ forming implant formulations. Perseris (risperidone) for extended-release injectable suspension was selected as the reference listed drug (RLD). A previously developed adapter-based USP 2 method was used for the in vitro release testing of various risperidone implant formulations. A rabbit model was used to determine the in vivo pharmacokinetic profiles of the formulations (subcutaneous administration) and deconvolution (Loo-Riegelman method) was conducted to obtain the in vivo release profiles. The results showed that a 5 KDa difference in the MW (19.2, 24.2, 29.2 KDa), a 5% variation in the L/G ratio (85/15, 80/20, 75/25) and the end-cap (acid vs ester) all significantly impacted the formulation behavior both in vitro and in vivo. Higher MW, higher L/G ratio and ester end-cap PLGA all resulted in longer release durations. The formulations prepared with polymers with different blockiness values (within the blockiness range tested) did not show differences in in vitro and in vivo release. An in vitro-in vivo correlation (IVIVC) was not developed due to the different in vitro and in vivo phase separation rates, swelling tendencies and consequent significantly different release profiles. This is the first report evaluating the impact of PLGA property variation (over a narrow range) on the performance of in situ forming implants. The knowledge gained will provide a better understanding of the mechanisms underlying risperidone in situ forming implant performance and will aid the development of future products.

In Vivo Characterization of Perseris and Compositionally Equivalent Formulations

Perseris is asubcutaneous extended-release risperidone in situ forming implant (suspension) indicated for the treatment of adult schizophrenia. Owing to the release rate controlling polymer poly(lactide-co-glycolide) (PLGA), one injection of Perseris can deliver risperidone for one month, which significantly reduces the administration frequency and improves patient compliance. The PLGA and drug used in Perseris was previously identified through reverse engineering and two compositionally equivalent formulations (F-1 and F-2) showing similar in vitro drug release were developed. The current work focuses on in vivo exploration of Perseris and the developed compositionally equivalent formulations using a rabbit model and further evaluate the sameness of the developed formulations compared to Perseris. The in vivo pharmacokinetic (PK) profiles, drug absorption rate, phase separation rate, macro appearance, weight loss as well as the water uptake of the solidified drug depots at different time points were investigated and compared with the in vitro release data as well as with dog and human in vivo data available in literature. Results show that the rabbit PK profile of Perseris was relevant with those obtained from both the dog model and the clinical data, indicating that the rabbit model is appropriate for investigation of the in vivo performance of risperidone implants. Consistent with their similar in vitro drug release, the two compositionally equivalent formulations demonstrated similar PK profiles, drug absorption rates, weight loss and swelling in vivo compared to Perseris. Although the erosion mechanism appeared to be similar between in vitro and in vivo, there were in vitro-in vivo differences concerning the drug release kinetics, phase separation rates and swelling behavior. This work provides a comprehensive in vitro/in vivo understanding of Perseris and the developed compositionally equivalent formulations, which will be beneficial for future development of generic as well as novel PLGA in situ forming implant products.

Reaching new lights: a review on photo-controlled nanomedicines and their in vivo evaluation

The selective and efficient delivery of bioactive molecules to sites of interest remains a formidable challenge in medicine. In recent years, it has been shown that stimuli-responsive drug delivery systems display several advantages over traditional drug administration such as an improved pharmacokinetic profile and the desirable ability to gain control over release. Light emerged as one of the most powerful stimuli due to its high biocompatibility, spatio-temporal control, and non-invasiveness. On the road to clinical translation, various chemical systems of high complexity have been reported with the aim to improve efficacy, safety, and versatility of drug delivery under complex biological conditions. For future research on the chemical design of such photo-controlled nanomedicines, it is essential to gain an understanding of their in vivo translation and efficiency. Here, we discuss photo-controlled nanomedicines that have been evaluated in vivo and provide an overview of the state-of-the-art that should guide future research design.

Long-acting injectable PLGA/PLA depots for leuprolide acetate: successful translation from bench to clinic

The excellent properties of polyesters combined with their ease of synthesis and modification enabled their wide use in the pharmaceutical industry. This has been translated into the approval of several injectable depots for clinical use. Long-acting depots for leuprolide acetate were among the first and most successful examples including Lupron Depot^® and ELIGARD^®. Studying these products is of great interest for researchers in both industry and academia. This will undoubtedly pave the road for the development of new as well as generic long-acting depots for a variety of drugs.

Basic Salt Additives Modulate the Acidic Microenvironment Around In Situ Forming Implants

There is a growing number of protein drugs, yet their limited oral bioavailability requires that patients receive frequent, high dose injections. In situ forming implants (ISFIs) for controlled release of biotherapeutics have the potential to greatly reduce the injection frequency and improve patient compliance. However, protein release from ISFIs is a challenge due to their proclivity for instability. Specifically, factors such as the acidic microclimate within ISFIs can lead to protein aggregation and denaturation. Basic salts have been shown in PLGA microparticle and microcylinder formulations to significantly reduce protein instability by neutralizing this acidic environment. The overall objective of the study was to demonstrate that basic salts can be used with an ISFI system to neutralize the implant acidification. To this end, the basic salts MgCO3 and Mg(OH)2 were added to a protein-releasing ISFI and the effect on drug release, pH, implant swelling, implant diffusivity, and implant erosion were evaluated. Either salt added at 3 wt% neutralized the acidic environment surrounding the implants, keeping the pH at 6.64 ± 0.03 (MgCO₃) and 6.46 ± 0.11 (Mg(OH)₂) after 28 day compared to 3.72 ± 0.05 with no salts added. The salts initially increased solution uptake into the implants but delayed implant degradation and erosion. The 3 wt% Mg(OH)₂ formulation also showed slightly improved drug release with a lower burst and increased slope. We showed that salt additives can be an effective way to modulate the pH in the ISFI environment, which can improve protein stability and ultimately improve the capacity of ISFIs for delivering pH-sensitive biomolecules. Such a platform represents a low-cost method of improving overall patient compliance and reducing the overall healthcare burden.

Effects of Drug Physicochemical Properties on In-Situ Forming Implant Polymer Degradation and Drug Release Kinetics

In-situ forming implants (ISFIs) represent a simple, tunable, and biodegradable polymer-based platform for long-acting drug delivery. However, drugs with different physicochemical properties and physical states in the polymer-solvent system exhibit different drug release kinetics. Although a few limited studies have been performed attempting to elucidate these effects, a large, systematic study has not been performed until now. The purpose of this study was to characterize the in vitro drug release of 12 different small molecule drugs with differing logP and pKa values from ISFIs. Drug release was compared with polymer degradation as measured by lactic acid (LA) release and change in poly(DL-lactide-co-glycolide) (PLGA) molecular weight (MW) measured by size exclusion chromatography with multi-angle laser light scattering (SEC-MALS). Drug physical state and morphology were also measured using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Together, these results demonstrated that hydrophilic drugs have higher burst release at 24 h (22.8–68.4%) and complete drug release within 60 days, while hydrophobic drugs have lower burst release at 24 h (1.8–18.9%) and can sustain drug release over 60–285 days. Overall, drug logP and drug physical state in the polymer–solvent system are the most important factors when predicting the drug release rate in an ISFI for small-molecule drugs. Hydrophilic drugs exhibit high initial burst and less sustained release due to their miscibility with the aqueous phase, while hydrophobic drugs have lower initial burst and more sustained release due to their affinity for the hydrophobic PLGA. Additionally, while hydrophilic drugs seem to accelerate the degradation of PLGA, hydrophobic drugs on the other hand seem to slow down the PLGA degradation process compared with placebo ISFIs. Furthermore, drugs that were in a crystalline state within the ISFI drugs exhibited more sustained release compared with amorphous drugs.

An Injectable In Situ Depot-Forming Lipidic Lyotropic Liquid Crystal System for Localized Intratumoral Drug Delivery

To address the need for localized chemotherapy against unresectable solid tumors, an injectable in situ depot-forming lipidic lyotropic liquid crystal system (L3CS) is explored that can provide spatiotemporal control over drug delivery. Although liquid crystals have been studied extensively before but their application as an injectable intratumoral depot system for locoregional chemotherapy has not been explored yet. The developed L3CS in the present study is a low-viscosity injectable fluid having a lamellar phase, which transforms into a hexagonal mesophase depot system on subcutaneous or intratumoral injection. The transformed depot system can be preprogrammed to provide tailored drug release intratumorally, over a period of one week to one month. To establish the efficacy of the developed L3CS, doxorubicin is used as a model drug. The drug release mechanism is studied in detail both in vitro and in vivo, and the efficacy of the developed system is investigated in the murine 4T1 tumor model. The direct intratumoral injection of the L3CS provided localized delivery of doxorubicin inside the tumor and restricted its access within the tumor only for a sustained period of time. This led to an over 10-fold reduction in tumor burden, reduced cardiotoxicity, and a significant increase in the median survival rate, compared to the control group. The developed L3CS thus provides an efficient strategy for localized chemotherapy against unresectable solid tumors with a great degree of spatial and temporal control over drug delivery.

How agarose gels surrounding PLGA implants limit swelling and slow down drug release

The aim of this study was to better understand to which extent and in which way the presence of an agarose gel (mimicking living tissue) around a PLGA [poly(lactic-co-glycolic acid)] implant affects the resulting drug release kinetics. Ibuprofen-loaded implants were prepared by hot melt extrusion. Drug release was measured upon exposure to phosphate buffer pH 7.4 in Eppendorf tubes, as well as upon inclusion into an agarose gel which was exposed to phosphate buffer pH 7.4 in an Eppendorf tube or in a transwell plate. Dynamic changes in the implants' dry & wet mass and dimensions were monitored gravimetrically and by optical macroscopy. Implant erosion and polymer degradation were observed by SEM and GPC. Different pH indicators were used to measure pH changes in the bulk fluids, gels and within the implants during drug release. Ibuprofen release was bi-phasic in all cases: A zero order release phase (~20% of the dose) was followed by a more rapid, final drug release phase. Interestingly, the presence of the hydrogel delayed the onset of the 2nd release phase. This could be attributed to the sterical hindrance of implant swelling: After a certain lag time, the degrading PLGA matrix becomes sufficiently hydrophilic and mechanically instable to allow for the penetration of substantial amounts of water into the system. This fundamentally changes the conditions for drug release: The latter becomes much more mobile and is more rapidly released. A gel surrounding the implant mechanically hinders system swelling and, thus, slows down drug release. These observations also strengthen the hypothesis of the "orchestrating" role of PLGA swelling for the control of drug release and can help developing more realistic in vitro release set-ups.

Drug release from in situ forming implants and advances in release testing

In situ forming implants, defined as liquid formulations that generate solid or semisolid depots following administration, have shown a range of advantages in drug delivery. This drug delivery strategy allows localized delivery, sustained drug release over periods of days to months, and is a less invasive option compared to traditional solid implants which typically require surgical implantation. Unfortunately, there are a number of quality control challenges in terms of drug release testing of these delivery systems which is likely to have contributed to the relatively few commercially available in situ forming implant products. This article reviews current marketed in situ forming implant products, FDA guidance on in vitro release testing, and formulation and environmental parameters influencing drug release from in situ forming implants. Formulation considerations for development of biological agents loaded in situ forming implants are also discussed. The advantages and limitations of typically used in vitro release testing methods are summarized. Difficulties in the development of in vitro-in vivo correlations (IVIVCs) for in situ forming implant are discussed. The knowledge presented will be helpful for the development of in situ forming implants, as well as for the development of appropriate in vitro testing methods and IVIVCs.

In Vitro Evaluation of Poly(lactide-co-glycolide) In Situ Forming Gels for Bedaquiline Fumarate Salt and Pharmacokinetics Following Subcutaneous Injection in Rats

This study evaluated in vitro and in vivo drug release of bedaquiline from in situ forming gels (ISGs) containing 200 mg eq./g bedaquiline fumarate salt prepared with four different grades of poly(d,l-lactide) (PDLLA) or poly(d,l-lactide-co-glycolide) (PLGA) with a lactide/glycolide ratio of 50/50 or 75/25 and acid (A) or ester (E) end-capping in N-methyl-2-pyrrolidone at a polymer/solvent ratio of 20/80% (w/w). Mean in vitro drug release in 0.05 M phosphate buffer pH 7.4 with 1% (w/v) sodium lauryl sulphate was 37.3, 47.1, 53.3, and 62.3% within 28 days for ISGs containing PLGA5050A, PDLLA, PLGA7525A, and PLGA7525E, respectively. The data suggested that drug release was primarily controlled by precipitated drug redissolving, rather than polymer erosion. In vivo pharmacokinetic profiles after subcutaneous injections in rats were comparable for all ISGs (mean half-lives (t_1/2) ranged from 1411 to 1695 h) and indicated a sustained drug release when compared to a solution of bedaquiline fumarate salt in polyethylene glycol 400/water 50/50% (v/v) (mean t_1/2 of 895 h). In conclusion, PLGA or PDLLA-based ISGs have shown potential for parenteral sustained delivery of bedaquiline, suggesting further preclinical and clinical studies. From a formulation point of view, this case example highlights the importance of the interplay between drug solubility in biological media and dissolution of drug precipitates, which, in addition to the incorporation of diffusion controlling polymers, governs the release of the active drug.

Fabrication of PLGA in situ forming implants and study on their correlation of in vitro release profiles with in vivo performances

In this study, a novel PLGA in situ forming implants (ISFIs) were fabricated and methods for testing the in vitro release profiles were also developed. The correlations between in vitro release profiles and in vivo performances (in vitro-in vivo correlation, IVIVC) were also studied. PLGA with different molecular weights were selected as the polymeric matrix. Biocompatible N-methy1-2-pyrrolidone (NMP) or glyceryl triacetate (GTA) were used as the solvents with the ratios of NMP/GTA from 60/40 (vol/vol) to 20/80 (vol/vol). Eprinomectin (EPR) was chosen as the model therapeutic. In vitro release profiles of the EPR-loaded PLGA ISFIs were investigated using various methods (i.e. 'tubule' sample-and-separate and dialysis method). Sprague-Dawley rats were used to study the in vivo pharmacokinetics of EPR-loaded PLGA ISFIs. The release data obtained via 'tubule' sample-separate method had a good IVIVC (Level A, R² > 0.99). These results showed that the 'tubule' sample-separate method was capable of discriminating the EPR-loaded ISFIs which were equivalent in formulation composition with manufacturing differences. Meanwhile, this method could be used to predict the in vivo performances of ISFIs in the investigated animal model.

Evolution of drug-eluting biomedical implants for sustained drug delivery

In the field of drug delivery, the most commonly used treatments have traditionally been systemically delivered using oral or intravenous administration. The problems associated with this type of delivery is that the drug concentration is controlled by first pass metabolism, and therefore may not always remain within the therapeutic window. Implantable drug delivery systems (IDDSs) are an excellent alternative to traditional delivery because they offer the ability to precisely control the drug release, deliver drugs locally to the target tissue, and avoid the toxic side effects often experienced with systemic administration. Since the creation of the first FDA-approved IDDS in 1990, there has been a surge in research devoted to fabricating and testing novel IDDS formulations. The versatility of these systems is evident when looking at the various biomedical applications that utilize IDDSs. This review provides an overview of the history of IDDSs, with examples of the different types of IDDS formulations, as well as looking at current and future biomedical applications for such systems. Though there are still obstacles that need to be overcome, ever-emerging new technologies are making the manufacturing of IDDSs a rewarding therapeutic endeavor with potential for further improvements.

In Vitro Tests of FDM 3D-Printed Diclofenac Sodium-Containing Implants

One of the most promising emerging innovations in personalized medication is based on 3D printing technology. For use as authorized medications, 3D-printed products require different in vitro tests, including dissolution and biocompatibility investigations. Our objective was to manufacture implantable drug delivery systems using fused deposition modeling, and in vitro tests were performed for the assessment of these products. Polylactic acid, antibacterial polylactic acid, polyethylene terephthalate glycol, and poly(methyl methacrylate) filaments were selected, and samples with 16, 19, or 22 mm diameters and 0%, 5%, 10%, or 15% infill percentages were produced. The dissolution test was performed by a USP dissolution apparatus 1. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide dye (MTT)-based prolonged cytotoxicity test was performed on Caco-2 cells to certify the cytocompatibility properties. The implantable drug delivery systems were characterized by thermogravimetric and heatflow assay, contact angle measurement, scanning electron microscopy, microcomputed tomography, and Raman spectroscopy. Based on our results, it can be stated that the samples are considered nontoxic. The dissolution profiles are influenced by the material properties of the polymers, the diameter, and the infill percentage. Our results confirm the potential of fused deposition modeling (FDM) 3D printing for the manufacturing of different implantable drug delivery systems in personalized medicine and may be applied during surgical interventions.

A candidate drug administered subcutaneously to rodents as drug particles showing hepatic recirculation which influenced the sustained release process

The aim of the present study was to evaluate and interpret the pharmacokinetic profiles after subcutaneous (s.c.) administration of crystalline AZ'72 nano- and microsuspensions to rodents. Both formulations were injected at 1.5 and 150 mg/kg to rats. For the lower dose, the profiles were similar after s.c. injection but extended as compared to oral administration. The overall exposure was higher for nanoparticles compared with microparticles during the investigated period. For the higher dose, injection of both suspensions resulted in maintained plateaus caused by the drug depots but, unexpectedly, at similar exposure levels. After addition of a further stabilizer, pluronic F127, nanosuspensions showed improved exposure with dose and higher exposure compared to larger particles in mice. Obviously, a stabilizer mixture that suits one delivery route is not necessarily optimal for another one. The differences in peak concentration (C_max) between nano- and microparticles were mainly ascribed to differences in dissolution rate. Plasma profiles in mice showed curves with secondary absorption peaks after intravenous and oral administration, suggesting hepatic recirculation following both administration routes. This process, together with the depot formulation, complicates the analysis of absorption from s.c. administration, i.e. multiple processes were driving the plasma profile of AZ'72.

Towards in vitro in vivo correlation for modified release subcutaneously administered insulins

Therapeutic proteins and peptides are mainly administrated by subcutaneous injection. In vitro release testing of subcutaneous injectables performed using methods that take the structure and environment of the subcutaneous tissue into account may improve predictability of the in vivo behavior and thereby facilitate establishment of in vitro in vivo correlations. The aim of the study was to develop a biopredictive flow-through in vitro release method with a gel-type matrix for subcutaneously administered formulations and to explore the possibility of establishing a level A in vitro in vivo correlation for selected insulin products. A novel gel-based flow-through method with the incorporation of an injection step was used to assess selected commercial insulin formulations with different duration of action (Actrapid®, Mixtard® 30, Insulatard®, Lantus®). The in vitro release method provided the correct rank ordering in relation to the in vivo performance. For the modified release insulins Insulatard® and Lantus®, an in vitro in vivo correlation using non-linear time scaling was established based on the in vitro release data and in vivo subcutaneous absorption data of the ¹²⁵I-labeled insulins taken from literature. Predicted absorption profiles were constructed using the in vitro in vivo correlation and subsequently converted into simulated plasma profiles. The approach taken may be of wider utility in characterizing injectables for subcutaneous administration.

Ultra-long-acting tunable biodegradable and removable controlled release implants for drug delivery

Here we report an ultra-long-acting tunable, biodegradable, and removable polymer-based delivery system that offers sustained drug delivery for up to one year for HIV treatment or prophylaxis. This robust formulation offers the ability to integrate multiple drugs in a single injection, which is particularly important to address the potential for drug resistance with monotherapy. Six antiretroviral drugs were selected based on their solubility in N-methyl-2-pyrrolidone and relevance as a combination therapy for HIV treatment or prevention. All drugs released with concentrations above their protein-adjusted inhibitory concentration and retained their physical and chemical properties within the formulation and upon release. The versatility of this formulation to integrate multiple drugs and provide sustained plasma concentrations from several weeks to up to one year, combined with its ability to be removed to terminate the treatment if necessary, makes it attractive as a drug delivery platform technology for a wide range of applications.

Sucrose Acetate Isobutyrate as an In situ Forming Implant for Sustained Release of Local Anesthetics

OBJECTIVE

In this study, an injectable Sucrose Acetate Isobutyrate (SAIB) drug delivery system (SADS) was designed and fabricated for the sustained release of Ropivacaine (RP) to prolong the duration of local anesthesia.

METHODS

By mixing SAIB, RP, and N-methyl-2-pyrrolidone, the SADS was prepared in a sol state with low viscosity before injection. After subcutaneous injection, the pre-gel solution underwent gelation in situ to form a drug-released depot.

RESULT

The in vitro release profiles and in vivo pharmacokinetic analysis indicated that RP-SADS had suitable controlled release properties. Particularly, the RP-SADS significantly reduced the initial burst release after subcutaneous injection in rats.

CONCLUSION

In a pharmacodynamic analysis of rats, the duration of nerve blockade was prolonged by over 3-fold for the RP-SADS formulation compared to RP solution. Additionally, RP-SADS showed good biocompatibility in vitro and in vivo. Thus, the SADS-based depot technology is a safe drug delivery strategy for the sustained release of local anesthetics with long-term analgesia effects.

Noninvasive characterization of in situ forming implant diffusivity using diffusion-weighted MRI

In situ forming implants (ISFIs) form a solid drug-eluting depot, releasing drug for an extended period of time after a minimally-invasive injection. Clinical use of ISFIs has been limited because many factors affect drug release kinetics. The aim of this study was to use diffusion-weighted MRI (DWI) to noninvasively quantify spatial-temporal changes in implant diffusivity in situ. ISFIs were formed using poly(lactic-co-glycolic) acid, with a molecular weight of either 15 kDa or 52 kDa, and fluorescein as the mock drug. Drug release, polymer erosion, polymer degradation, and implant diffusivity were analyzed in vitro over 21 days. DWI was also performed in vivo over 5 days. Spatial diffusivity maps of the implant were generated using DWI data. Results showed constant diffusivity at the implant shell ((1.17 ± 0.13) × 10^-3 mm²/s) and increasing diffusivity within the interior over time (from (0.268 ± 0.081) × 10^-3 mm²/s during day 1 to (1.88 ± 0.04) × 10^-3 mm²/s at 14 d), which correlated with increasing porosity of the implant microstructure. Implants formed in vivo followed the same diffusivity trend as those in vitro. This study validates the use of DWI to provide novel functional information about implant behavior through its ability to noninvasively characterize transport properties within the implant both in vitro and in vivo.

Increasing Distribution of Drugs Released from In Situ Forming PLGA Implants Using Therapeutic Ultrasound

One of the challenges in developing sustained-release local drug delivery systems is the limited treatment volume that can be achieved. In this work, we examine the effectiveness of using low frequency, high intensity ultrasound to promote the spatial penetration of drug molecules away from the implant/injection site boundary upon release from injectable, phase inverting poly(lactic acid-co-glycolic acid) (PLGA) implants. Fluorescein-loaded PLGA solutions were injected into poly(acrylamide) phantoms, and the constructs were treated daily for 14 days with ultrasound at 2.2 W/cm2 for 10 min. The 2D distribution of fluorescein within the phantoms was quantified using fluorescence imaging. Implants receiving ultrasound irradiation showed a 1.7-5.6 fold increase (p < 0.05) in fluorescence intensity and penetration distance, with the maximum increase observed 5 days post-implantation. However, this evidence was not seen when the same experiment was also carried out in phosphate buffer saline (pH 7.4). Results suggest an active role of ultrasound in local molecular transport in the phantom. An increase of fluorescein release and penetration depth in phantoms can be accomplished through brief application of ultrasound. This simple technique offers an opportunity to eventually enhance the therapeutic efficacy and broaden the application of local drug delivery systems.

The in vivo transformation and pharmacokinetic properties of a liquid crystalline drug delivery system

A liquid crystalline (LC) system, composed of phosphatidylcholine, sorbitan monoleate, and tocopherol acetate, was investigated to understand the in vivo transformation after subcutaneous injection, coupled with the physicochemical and pharmacokinetic properties of the formulation. The rat model was utilized to monitor a pseudo-time course transformation from a precursor LC formulation to the LC matrix, coupled with the blood concentration profiles of the formulations containing leuprolide acetate. Three formulations that result in the H_II phase, demonstrating dissimilar in vitro release profiles, were used. The formulation showing the highest AUC, C_max and T_max, also displayed the greatest release rate in vitro, the lowest viscosity (LC matrix), and an earlier transformation (LC precursor to matrix) in vivo. A potential link between viscosity, phase transformation, and drug release properties of a liquid crystalline system is described.

Sustained-Release Delivery System of a Slow Hydrogen Sulfide Donor, GYY 4137, for Potential Application in Glaucoma

Hydrogen sulfide (H₂S) targets both underlying factors in glaucoma pathogenesis by reducing elevated intraocular pressure (IOP) and providing retinal neuroprotection, whereas the current clinical approaches targets only reducing IOP. Therefore, H₂S could be a potential superior candidate for glaucoma pharmacotherapy. However, H₂S could be toxic in a concentration greater than 200 μM and its donors are unstable in water. Therefore, this study investigated the preparation and characterization of a non-aqueous in situ gelling sustained-release delivery system for H₂S donors. The delivery system was prepared by dissolving GYY 4137, a H₂S donor, in poly lactide-co-glycolide polymer (PLGA) (Resomer® RG 502H) solution prepared by dissolving polymer in a mixture of benzyl alcohol and benzyl benzoate in a ratio of 7:3, respectively. The GYY 4137 formulation was characterized for syringeability/injectability, change in pH and tonicity, moisture content, GYY 4137 degradation, and toxicity using rheometer, pH and osmometer, Karl Fisher titrimeter, NMR spectrometer, and Y79 retinoblastoma cells, respectively. The formulation was easily syringeable and injectable as evidenced by rheological data (plastic flow pattern with 43.89 ± 3.21 cP viscosity and 1.12 ± 0.15 Pa yield value). The pH, tonicity, and moisture content values were within acceptable range. NMR spectroscopy indicated presence of 4-methoxyphenylphosphonic acid (GYY 4137 degradation product). The GYY 4137 formulation did not show any significant (p < 0.05) toxicity except the solvent mixture. A sustained release of H₂S was observed up to 72 h. The in situ gel forming PLGA-based system can be manipulated to achieve sustained release of H₂S from its donor GYY 4137.

Hydrophobic mixed solvent induced PLGA-based in situ forming systems for smooth long-lasting delivery of Radix Ophiopogonis polysaccharide in rats

To obtain a sustained in vivo release of Radix Ophiopogonis polysaccharide, hydrophobic solvent-induced in situ forming systems were investigated, including the factors affecting drug release and anti-myocardial ischemic activity of a formulation.

Macroporous acrylamide phantoms improve prediction of in vivo performance of in situ forming implants

In situ forming implants (ISFIs) have shown promise as a sustained, local drug delivery system for therapeutics in a variety of applications. However, development of ISFIs has been hindered by poor correlation between in vitro study results and in vivo performance. In contrast to oral dosage forms, there is currently no clear consensus on a standard for in vitro drug dissolution studies for parenteral formulations. Recent studies have suggested that the disparity between in vivo and in vitro behavior of phase-inverting ISFIs may be, in part, due to differences in injection site stiffness. Accordingly, this study aimed to create acrylamide-based hydrogel phantoms of varying porosity and stiffness, which we hypothesized would better predict in vivo performance. Implant microstructure and shape were found to be dependent on the stiffness of the phantoms, while drug release was found to be dependent on both phantom porosity and stiffness. Specifically, SEM analysis revealed that implant porosity and interconnectivity decreased with increasing phantom stiffness and better mimicked the microstructure seen in vivo. Burst release of drug increased from 31% to 43% when in standard acrylamide phantoms vs macroporous phantoms (10kPa), improving the correlation to the burst release seen in vivo. Implants in 30kPa macroporous phantoms had the best correlation with in vivo burst release, significantly improving (p<0.05) the burst release relative to in vivo from 64%, using a standard PBS dissolution method, to 92%. These findings confirm that implant behavior is affected by injection site stiffness. Importantly, with appropriate optimization and validation, hydrogel phantoms such as the one investigated here could be used to improve the in vitro-in vivo correlation of in situ forming implant formulations and potentially augment their advancement to clinical use.