Poly(ethyleneglycol) 500 Dimethylether as Novel Solvent for Injectable In Situ Forming Depots

Ocular Drug Delivery: Emerging Approaches and Advances

Complex anatomical and physiological barriers make the eye a challenging organ to treat from a drug delivery perspective. Currently available treatment methods (topical eyedrops) for anterior segment diseases pose several limitations in terms of bioavailability and patient compliance. Conventional drug delivery methods to treat posterior segment ocular diseases are primarily intravitreal injection (IVT) of solutions. IVT is highly invasive and leads to retinal toxicity, endophthalmitis, and intraocular inflammation, frequently requiring professional administration and frequent clinical visits. Advanced drug delivery treatment strategies could improve patient compliance and convenience. Long-acting drug delivery platforms (biodegradable or nonbiodegradable) provide sustained/controlled release of drugs for at least four to six months. Smart drug delivery alternatives, for instance, in situ forming implants, are injectable formulations that form semisolid-to-solid implants in response to the various stimuli of pH, light, osmolarity, and temperature. Additionally, nanoparticulate drug delivery systems, contact lenses, electrospun patches, and microneedle-based drug delivery systems provide minimally invasive treatment options for ocular disorders. This comprehensive review focuses on advanced drug delivery options for the management of ocular disorders.

An in vitro gel-based system for characterizing and predicting the long-term performance of PLGA in situ forming implants

In situ forming implants are exposed to an extracellular matrix resembling a gel rather than aqueous solution upon subcutaneous administration. The aim of study was to develop a gel-based release testing system for characterizing the long-term in vitro behavior of in situ forming implants. The gel-based system consisted of an agarose gel mimicking the subcutaneous injection site and a receiver layer comprising phosphate buffer. Poly(D,L-lactide-co-glycolide) in situ forming implants containing leuprolide acetate as the model peptide and N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO) or triacetin as co-solvent were investigated. The gel-based release testing system discriminated between the formulations. Accelerated release data obtained at elevated temperatures were able to predict real-time release applying the Arrhenius equation. Monitoring of the microenvironmental pH of the implants was performed by UV-Vis imaging in the gel-based system at 50 °C. A pH drop (from pH 7.4 to 6.7 for the NMP and DMSO implants, to pH 5.5 for the triacetin implants) within the first day was observed, followed by an increase to pH ∼7.4. The gel-based system coupled with UV imaging offered opportunity for detailed evaluation and prediction of the in vitro performance of long-acting injectables, facilitating future development of in situ depot forming delivery systems.

Self-assembled drug delivery system based on low-molecular-weight bis-amide organogelator: synthesis, properties and in vivo evaluation

CONTEXT

Orgnaogels based on amino acid derivatives have been widely used in the area of drug delivery.

OBJECTIVE

An organogel system based on l-lysine derivatives was designed and prepared to induce a thermal sensitive implant with higher transition temperature, better mechanical strength, and shorter gelation time.

MATERIALS AND METHODS

The organogel was prepared by injectable soybean oil and methyl (S)-2,5-ditetradecanamidopentanoate (MDP), which was synthesized for the first time. Candesartan cilexetil (CC) was chosen as model drug. Different formulations were designed and optimized by response surface method. Thermal, rheology properties, and gelation kinetics of the optimized formulation had been characterized. The release behaviors in vitro, as well as in vivo were evaluated in comparison with the oily solution of drugs. Finally, the local inflammation response of in situ organogel was assessed by histological analysis.

RESULTS AND DISCUSSION

Results showed that the synthesized gelator, MDP, had a good gelation ability and the organogels obtained via the self-assembly of gelators in vegetable oils exhibited great thermal and rheology properties, which guaranteed their state in body. In vivo pharmacokinetic demonstrated that the organogel formulation could extend the drug release and maintain a therapeutically effective plasma concentration at least 10 d. In addition, this implant showed acceptable moderate inflammation.

CONCLUSION

The in situ forming l-lysine-derivative-based organogel could be a promising matrix for sustained drug delivery of the drugs with low solubility.

In situ polyethylene sebacate particulate carriers as an alternative to Freund's adjuvant for delivery of a contraceptive peptide vaccine--A feasibility study

The present study evaluates the feasibility of particulate carriers of a biodegradable polymer polyethylene sebacate (PES) as an alternative to Freund's adjuvant in the design of a peptide vaccine formulation. The vaccine formulation comprised of PES and the antigen KLH conjugated 80kDa HSA peptide-1 dissolved in N-methyl-2-pyrrolidone (NMP)/NMP-water as solvent. The antigen revealed good stability and the formulations were readily syringeable. Intradermal injection of the formulations resulted in the formation of PES particulates in situ at the site of injection. The NMP formulations revealed larger particulates which elicited no immunogenic response when injected in rabbits. On the other hand the NMP-water formulation revealed formation of microparticles which were significantly smaller in size, in combination with a small fraction of nanoparticles. It elicited an antibody titer up to 1:3200 in rabbits following intradermal injection. Western blot confirmed generation of antibodies specific to the peptide. Contraceptive efficacy was confirmed by loss of sperm motility and head-to-head agglutination of sperms in the treatment group. Unlike the severe reactions observed with administration of Freund's adjuvant, only mild hypersensitivity reaction was observed with the PES formulations. The mild reaction coupled with the contraceptive efficacy observed suggested PES particulates as a viable alternative to Freund's adjuvant.

The anti-melanoma efficiency of the intratumoral injection of cucurbitacin-loaded sustained release carriers: in situ-forming implants

Our previous studies revealed that the PLGA-based particulate systems loaded with cucurbitacin showed limited anti-melanoma efficiency in xenograft animal models after intratumoral injection, which was due to the undesirable initial burst release and the leakage of the particulate carriers from the injection site through the pinhole. In this paper, two categories of in situ-forming implants (ISFIs) for intratumoral injection, PLGA ISFIs and SAIB ISFIs, were systemically evaluated for their potentials for on solid tumor treatment via intratumoral injection. The in vitro drug release profiles of these two ISFIs were different due to the different sol-gel transition properties. The pharmacodynamics results revealed that SAIB ISFIs displayed obvious therapeutic efficiencies to melanoma, and multi-points injection of SASIB ISFIs displayed better efficiency than single-point injection. The different sol-gel transition properties and mechanism for PLGA ISFIs and SAIB ISFIs affected both the drug release and strongly impacted the pharmacokinetic parameters and pharmacodynamic effectiveness. Also, the adhesive property of SAIB to the local tissue could extend the retention and inhibit the leakage of the SAIB ISFIs, thus enhanced the anticancer effectiveness. Comparison of the various intratumoral injection systems, appropriate drug release profiles (lower initial burst and steady release) and good retention (minimum leakage from the injection site) would benefit to the antitumor effects of the intratumoral depots.

Long-term delivery of protein therapeutics

INTRODUCTION

Proteins are effective biotherapeutics with applications in diverse ailments. Despite being specific and potent, their full clinical potential has not yet been realized. This can be attributed to short half-lives, complex structures, poor in vivo stability, low permeability, frequent parenteral administrations and poor adherence to treatment in chronic diseases. A sustained release system, providing controlled release of proteins, may overcome many of these limitations.

AREAS COVERED

This review focuses on recent development in approaches, especially polymer-based formulations, which can provide therapeutic levels of proteins over extended periods. Advances in particulate, gel-based formulations and novel approaches for extended protein delivery are discussed. Emphasis is placed on dosage form, method of preparation, mechanism of release and stability of biotherapeutics.

EXPERT OPINION

Substantial advancements have been made in the field of extended protein delivery via various polymer-based formulations over last decade despite the unique delivery-related challenges posed by protein biologics. A number of injectable sustained-release formulations have reached market. However, therapeutic application of proteins is still hampered by delivery-related issues. A large number of protein molecules are under clinical trials, and hence, there is an urgent need to develop new methods to deliver these highly potent biologics.

Chitosan/glucose 1-phosphate as new stable in situ forming depot system for controlled drug delivery

Chitosan (CS)-based thermosensitive solutions that turn into semi-solid hydrogels upon injection at body temperature have increasingly drawn attention over the last decades as an attractive new type of in situ forming depot (ISFD) drug delivery system. Despite the great potential of the standard CS/β-glycerophosphate (β-GP) thermogelling solutions, their lack of stability over time at room temperature as well as at refrigerated conditions renders them unsuitable as ready-to-use drug product. In the present study, we investigated Glucose-1-Phosphate (G1-P) as an alternative gelling agent for improving the stability of CS-based ISFD solutions. The in vitro release performance of CS/G1-P formulations was assessed using several model compounds. Furthermore, the local tolerance of subcutaneously implanted CS/G1-P hydrogels was investigated by histological examination over three weeks. The thermogelling potential of CS/G1-P solutions, determined by rheology, is dependent on the polymer molecular weight (Mw) and concentration as well as on the G1-P concentration. Differential scanning calorimetry (DSC) measurements confirmed that sol/gel transition takes place at around body temperature and is not fully thermo-reversible. The long term storage stability was evaluated through the appearance, pH, viscosity and gelation time at 37°C of the solution. The results emphasized an enhanced stability of the CS/G1-P system compared to the standard CS/β-GP. CS solution with 0.40 mmol/g G1-P is stable for at least 9 months at 2-8°C, versus less than 1 month when using β-GP as gelling agent. Furthermore, the solution is easy to inject, as evidenced from injectability evaluation using 23-30 G needles. In vitro release experiments showed a sustained release over days to weeks for hydrophilic model compounds, demonstrating thereby that CS/G1-P may be suitable for the prolonged delivery of drugs. The inflammatory reaction observed in the tissue surrounding the hydrogel in rats was a typical foreign body reaction, similar to the one observed for CS/β-GP hydrogels. These features confirm the potential of CS/G1-P solutions as an injectable ready-to-use in situ forming hydrogel.

In situ forming parenteral depot systems based on poly(ethylene carbonate): effect of polymer molecular weight on model protein release

The objective of this study was to investigate the effect of molecular weight (MW) on the drug release from poly(ethylene carbonate) (PEC) based surface-eroding in situ forming depots (ISFD). In phosphate buffered saline (PBS) pH 7.4, 63.7% of bovine serum albumin BSA was released from high MW PEC of 200 kDa (PEC200) in DMSO (15%, w/w) in 2 days, while during the same time period, the release of BSA from PEC41 samples was only 22.5%. At higher concentrations of PEC41 (25%, w/w), the initial burst was further reduced, and even after 6 days, only 16.3% was released. Compared to depots based on PEC200, there was lower rate of solvent release, slower phase inversion, and a denser surface in PEC41 samples. An expansion in size of PEC41 depots suggested that the polymer barrier of PEC41 impeded the diffusion of solvent out of the samples effectively. In conclusion, the initial burst of protein from ISFD of PEC41 was significantly reduced, which would be a promising candidate as polymeric carrier.

Formulation strategies for sustained release of proteins

Proteins constitute an increasing proportion of the drugs in development. The barriers to their entry into the blood stream and rapid clearance means that they often have to be injected several times a day, affecting patient compliance. This paper reviews the major technologies enabling the development of injectable sustained-release products and formulation strategies to maintain protein integrity and modify release rates. Whilst many injectable sustained-release products are on the market, these are all delivering small molecular weight drugs and peptides. This is due to the manufacturing processes that denature and degrade the proteins upon encapsulation and release into the body. Formulation strategies are discussed and a number of new technologies reviewed that are able to overcome the issues with conventional manufacturing processes. The reliance of many processes on organic solvents has prevented their application to the development of injectable sustained release protein products. The development of entirely solvent free and aqueous methods of manufacture of these products has meant that numerous sustained-release protein products are close to reaching the market.

Formulation and evaluation of in situ forming PLA implant containing tinidazole for the treatment of periodontitis

Periodontitis is caused by periodontopathic bacteria and antibacterial agents are placed in a periodontal pocket with the intention of enhancing the local effect. To maximize the therapeutic effects while reducing the adverse effects, tinidazole was delivered by in situ forming system. One approach for reducing burst release rate was to testify in situ forming effect. The effect of 0%-10% (w/w) polyethylene glycol 400 and 3% (w/w) glycerol on the tinidazole release from a poly(DL-lactide) (PLA) injectable implant was evaluated. The results showed that the in vitro initial burst release rate was decreased in the presence of poly(ethyleneglycol) PEG 400 and glycerol. A formulation containing 30% (w/w) PLA (M(w) 7300) dissolved in 62% (w/w) N-methyl-2-pyrrolidone, 5% (w/w) PEG 400, and 3%(w/w) glycerol with 5% (w/w) tinidazole was shown to be optimum. Twelve adult beagle dogs were used in the periodontitis model. The treatment group I, II, and positive control group was administrated with gel containing 5%(w/w) tinidazole, 2.5%(w/w) tinidazole, and periocline, respectively. Dog studies revealed that periocline and the developed formulation could significantly decrease symptoms of periodontitis, and they were better than gel containing 2.5% (w/w) tinidazole. The developed formulation could sustain the release of tinidazole for local delivery over 7 days. These findings suggested that the developed formulation was a viable alternative to conventional drug to cure periodontitis.

A novel risperidone-loaded SAIB-PLGA mixture matrix depot with a reduced burst release: effects of solvents and PLGA on drug release behaviors in vitro/in vivo

The purpose of this study was to develop an in situ forming SAIB (sucrose acetate isobutyrate)-PLGA (poly (d, lactide-co-glycolide)) mixture matrix depot for sustained release of risperidone. The factors affecting the risperidone release kinetics were investigated to obtain further insight into the drug release mechanisms. The burst release in vitro was significantly reduced (4.95%) by using DMSO as solvent. And, increasing the PLGA content from 2 to 10% w/w decreased the initial release from 6.95 to 1.05%. The initial release in vivo decreased with increasing PLGA content (2.0% w/w PLGA, C(max) = 1161.7 ± 550.2 ng ml(-1); 10% w/w PLGA, C(max) = 280.3 ± 98.5 ng ml(-1)). The persistence (AUC(4-20 days)) over 20 days increased from 76.8 ± 20.7 to 362.8 ± 75.0 ng d ml(-1) by inclusion of 10% PLGA compared with the PLGA-free depot. These results demonstrate that the SAIB-PLGA mixture matrix depot could be useful as a sustained delivery system for risperidone.

Characterization of polyoxyethylenes according to the number of hydroxy end groups by hydrophilic interaction chromatography at critical conditions for polyethylene glycol

Polyoxyethylenes with different functionality and architecture can be separated according to the number of terminal hydroxy groups on polar stationary phases in acetone water mobile phases containing 90-97% acetone. The best results were obtained on a HILIC column. Typical samples, which can be analyzed by this technique, are polyethylene glycols, their mono- and dialkyl ethers, macromonomers, the fatty esters of PEG, and ethoxylated glycerol.