Characterization of the rotating dialysis cell as an in vitro model potentially useful for simulation of the pharmacokinetic fate of intra-articularly administered drugs

Assessment of joint pharmacokinetics and consequences for the intraarticular delivery of biologics

Intraarticular (IA) injections provide the opportunity to deliver biologics directly to their site of action for a local and efficient treatment of osteoarthritis. However, the synovial joint is a challenging site of administration since the drug is rapidly eliminated across the synovial membrane and has limited distribution into cartilage, resulting in unsatisfactory therapeutic efficacy. In order to rationally develop appropriate drug delivery systems, it is essential to thoroughly understand the unique biopharmaceutical environments and kinetics in the joint to adequately simulate them in relevant experimental models. This review presents a detailed view on articular kinetics and drug-tissue interplay of IA administered drugs and summarizes how these can be translated into reasonable formulation strategies by identification of key factors through which the joint residence time can be prolonged and specific structures can be targeted. In this way, pros and cons of the delivery approaches for biologics will be evaluated and the extent to which biorelevant models are applicable to gain mechanistic insights and ameliorate formulation design is discussed.

An ex-vivo model for transsynovial drug permeation of intraarticular injectables in naive and arthritic synovium

Estimation of joint residence time of a drug is a key requirement for rational development of intraarticular therapeutics. There is a great need for a predictive model to reduce the high number of animal experiments in early stage development. Here, a Franz-cell based porcine ex-vivo permeation model is proposed, and transsynovial permeation of fluorescently-labeled dextrans in the range of potential drug candidates (10-150 kDa), as well as a small molecule (fluorescein sodium) and charged dextran derivates, have been determined. In addition, a lipopolysaccharide (LPS) -induced synovitis model was assessed for inflammatory biomarker levels and its effect on permeation of the solutes. Size-dependent permeability was observed for the analytes, which distinctly differed from findings with an artificial polycarbonate membrane, which is a widely used model. LPS was found to successfully stimulate an inflammatory response and led to a reduced size selectivity of the synovial membrane. 150 kDa dextran flux was accelerated approximately 2.5-fold in the inflamed state, whereas the permeation of smaller molecules was little affected. Moreover, by varying the LPS concentrations, the ex-vivo model was shown to produce varying degrees of synovitis-like inflammation. A simple and highly relevant ex-vivo tool for investigation of transsynovial permeation was developed, offering the further advantage of mimicking synovitis-induced permeability changes. Thus, this model provides a promising method for formulation screening, while reducing the need for animal experiments.

Advanced in silico modeling explains pharmacokinetics and biodistribution of temoporfin nanocrystals in humans

Foscan®, a formulation comprising temoporfin dissolved in a mixture of ethanol and propylene glycol, has been approved in Europe for palliative photodynamic therapy of squamous cell carcinoma of the head and neck. During clinical and preclinical studies it was observed that considering the administration route, the drug presents a rather atypical plasma profile as plasma concentration peaks delayed. Possible explanations, as for example the formation of a drug depot or aggregation after intravenous administration, are discussed in current literature. In the present study an advanced in silico model was developed and evaluated for the detailed description of Foscan® pharmacokinetics. Therefore, in vitro release data obtained from experiments with the dispersion releaser technology investigating dissolution pressures of various release media on the drug as well as in vivo data obtained from a clinical study were included into the in silico models. Furthermore, precipitation experiments were performed in presence of biorelevant media and precipitates were analyzed by nanoparticle tracking analysis. Size analysis and particle fraction were also incorporated in this model and a sensitivity analysis was performed. An optimal description of the in vivo situation based on in vitro release and particle characterization data was achieved, as demonstrated by an absolute average fold error of 1.21. This in vitro-in vivo correlation provides an explanation for the pharmacokinetics of Foscan® in humans.

Drug-fortified liposomes as carriers for sustained release of NSAIDs: The concept and its validation in the animal model for the treatment of arthritis

Drug-fortified cationic liposomes of 6‑methoxy‑2‑naphthylacetic acid (6‑MNA) were prepared and characterized by various techniques. The residence time of drug-fortified liposomes in joint cavity was evaluated by intra-articular (IA) administration of the radio-labeled (^99mTc) liposomal formulation in the inflamed joints in rats. The cationic liposomal formulation composed of 6‑MNA (3) as an active agent, its double salt (4) with the lipid 1,2‑distearoyl‑sn‑glycero‑3‑phosphoethanolamine (DSPE), and pharmaceutically acceptable excipients such as hydrogenated soyabean phospatidylcholine (HSPC) and 1,2‑dioleyloxy‑3‑trimethylammoniumpropane chloride (DOTAP) were developed using thin film hydration technique. The cryo-TEM analysis confirmed that the prepared optimized liposomal formulation (DFL-2) was a mixture of small unilamellar vesicles (SUVs), large unilamellar vesicles (LUVs) and multilamellar vesicles (MLVs). In addition, the TEM analysis confirmed that the prepared liposomes were of spherical in shape having liposome size in the range of 500-900 nm and zeta potential of about +30 mV. The developed cationic liposomes exhibited sustained release profile of payload of 6‑MNA for over >12 h and about five times higher retention in the inflamed animal joints after 24 h (by scintigraphy of the joints) as compared to the plain 6‑MNA solution when administered by IA route. The anti-inflammatory activity of prepared liposomal composition is evaluated by Freund's adjuvant induced arthritic model in rats. The liposomal formulation was well tolerated by all animals indicating good biocompatibility. Further, the cationic liposomal formulation treated group showed decreased erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) level in comparison to the control and the standard groups in the in vivo study. The improved efficacy of the drug-fortified liposomal formulation was due to the coupled effect of longer retention and sustained release of the active drug 6‑MNA in the joints. From the obtained results it could be concluded that the combined effect of the cationic charge on the drug-fortified liposomes and the inherent affinity of the active agent towards the synovial joint tissues, coupled with slow release of the active drug due to double salt approach at the site of administration could potentially decrease the frequency of IA drug administration. Hence such a formulation could prove to be a therapeutic boon for the management of late stage arthritis.

A New Level A Type IVIVC for the Rational Design of Clinical Trials Toward Regulatory Approval of Generic Polymeric Long-Acting Injectables

Chronic neuropsychiatric disorders and diabetes mellitus affect millions of patients and require long-term supervision and expensive medical care. Although repeated drug administration can help manage these diseases, relapses and re-hospitalization owing to patient non-adherence and reduced therapeutic efficacy remain challenging. In response, long-acting injectables, which provide sustained drug release over longer periods at concentrations close to therapeutic ranges, have been proposed. Recent advancements include polymeric long-acting injectables (pLAIs), in which the active pharmaceutical ingredient (API) is encapsulated within U.S. Food and Drug Administration (FDA)-approved biocompatible polymers, such as poly(lactic-co-glycolic acid), or PLGA. Despite significant progress and development in the global pLAI market, FDA guidance for the approval of complex drug products, such as generic pLAIs, is not clearly defined. Although in vitro to in vivo correlation (IVIVC) can facilitate the identification of critical quality attributes (CQAs), drug formulations, and in vitro test platforms for evaluating drug performance in vivo, the application of IVIVC in order to shortlist time- and resource-intensive clinical trials for generic pLAIs has not been reported. Here, we propose a new Level A Type IVIVC that directly correlates the in vitro outcomes, such as drug dissolution, of candidate generic formulations with the clinical characteristics, such as drug absorption, of a reference listed drug (RLD), to help identify the specific generic pLAI formulations with clinical absorptions that are likely to be similar to that of the RLD, thereby reducing the number of clinical trials required for evaluation of clinical bioequivalence (BE). Therefore, the scope of the proposed method is intended only for the rational design of clinical trials, i.e., to shortlist the specific pLAI generic formulations for clinical BE evaluation, and not necessarily to analyze drug performances (i.e., drug safety and effectiveness) in the shortlisted clinical trials or post-approval. Once validated, this method will be of great value to developers of generic pLAIs and regulatory bodies to accelerate their approval of these generic pLAIs.

Crystal suspensions of poorly soluble peptides for intra-articular application: a novel approach for biorelevant assessment of their in vitro release

Crystal suspensions of 3 poorly soluble peptides (MSC1, 2 and 3), intended for intra-articular administration were prepared and in vitro release was tested by a modified USP IV apparatus, combined with a dialysis system. Half-lives of release profiles were ∼5 days for MSC1 and ∼0.5 days for MSC2 and MSC3, showing the potential to achieve sustained exposure from crystal suspensions after intra-articular administration. The in vitro release setup discriminated between (i) different formulations, (ii) different concentrations of API and (iii) different APIs. In addition it was shown that this method allows the modification of release conditions in order to gain more biorelevance for in vitro release testing in the field of intra-articular application: the influence of synovial fluid components hyaluronic acid and albumin was demonstrated, showing prolonged half-lives for suspensions containing 2.5% bovine serum albumin (5 days) and accelerated release rates for suspensions containing 1% sodium hyaluronate (2.5 days) in comparison to a suspension in phosphate buffered saline (4 days). Furthermore, it was demonstrated that release rates of a suspension containing an artificial synovial fluid were in accordance with suspensions containing bovine synovial fluid (t1/2∼4 days).

Accelerated in-vitro release testing methods for extended-release parenteral dosage forms

OBJECTIVES

This review highlights current methods and strategies for accelerated in-vitro drug release testing of extended-release parenteral dosage forms such as polymeric microparticulate systems, lipid microparticulate systems, in-situ depot-forming systems and implants.

KEY FINDINGS

Extended-release parenteral dosage forms are typically designed to maintain the effective drug concentration over periods of weeks, months or even years. Consequently, 'real-time' in-vitro release tests for these dosage forms are often run over a long time period. Accelerated in-vitro release methods can provide rapid evaluation and therefore are desirable for quality control purposes. To this end, different accelerated in-vitro release methods using United States Pharmacopeia (USP) apparatus have been developed. Different mechanisms of accelerating drug release from extended-release parenteral dosage forms, along with the accelerated in-vitro release testing methods currently employed are discussed.

SUMMARY

Accelerated in-vitro release testing methods with good discriminatory ability are critical for quality control of extended-release parenteral products. Methods that can be used in the development of in-vitro-in-vivo correlation (IVIVC) are desirable; however, for complex parenteral products this may not always be achievable.

In-vitro dissolution methods for controlled release parenterals and their applicability to drug-eluting stent testing

Objectives

Dissolution testing is a powerful tool for the characterization of dosage form performance in vitro under standardized conditions. In spite of the increasing number of parenterally administered medicinal products, currently there are no compendial dissolution test methods designed especially for these types of dosage forms. In addition to classical drug delivery systems, drug/device combination products, such as drug-eluting stents, are being used increasingly.

Key findings

This review describes the current methods that are used most often for in-vitro dissolution testing of parenteral dosage forms, i.e. the ‘sample and separate’ methods, the ‘dialysis’ methods, and the ‘flow-through’ methods, with a special emphasis on whether these methods can be used for drug-eluting stent testing. In the light of current regulatory requirements and with the exploding costs of preclinical and clinical development, test systems that include biorelevant parameters and are predictive of in-vivo performance are increasingly important. Published attempts to take biorelevant conditions into consideration in the design of dissolution test apparatus developed for parenteral dosage forms, including a method that was designed to emulate the embedding and flow-conditions at the site of stent implantation, have been outlined in this review.

Summary

In spite of the large quantity of highly potent controlled release parenteral products marketed today, there is still a lack of suitable methods for in vitro dissolution testing for these dosage forms especially with regard to biorelevant testing conditions. For dosage forms implanted into tissues it seems of major importance to reproduce the transport forces which are predominant in vivo (diffusive versus convective) in the in-vitro experimental setup.

Characterization of bupivacaine-loaded formulations based on liquid crystalline phases and microemulsions: the effect of lipid composition

This report details the structural characterization and the in vitro drug-release properties of different local anesthetic bupivacaine (BUP)-loaded inverted-type liquid crystalline phases and microemulsions. The effects of variations in the lipid composition and/or BUP concentration on the self-assembled nanostructures were investigated in the presence of the commercial distilled glycerol monooleate Myverol 18-99K (GMO) and medium-chain triglycerides (MCT). Synchrotron small-angle X-ray scattering (SAXS) and rotating dialysis cell model were used to characterize the BUP formulations and to investigate the in vitro BUP release profiles, respectively. The evaluation of SAXS data for the BUP-loaded GMO/MCT formulations indicates the structural transition of inverted-type bicontinuous cubic phase of the symmetry Pn3m → inverted-type hexagonal (H(2)) phase → inverted-type microemulsion (L(2)) with increasing MCT content (0-40 wt %). In the absence of MCT, the solubilization of BUP induces the transition of Pn3m → H(2) at pH 7.4; whereas a transition of Pn3m → (Pn3m + H(2)) is detected as the hydration is achieved at pH 6.0. To mimic the drug release and transport from in situ formed self-assembled systems after subcutaneous administration, the release experiments were performed by injecting low viscous stimulus-responsive precursors to a buffer in the dialysis cell leaving the surface area between the self-assembled system and the release medium variable. Our results suggest that the pH-dependent variations in the lipidic partition coefficient, K(l/w), between the liquid crystalline nanostructures and the surrounding buffer solution are significantly affecting BUP release rates. Thus, a first step toward understanding of the drug-release mechanism of this drug-delivery class has been undertaken tackling the influence of drug ionization as well as the type of the self-assembled nanostructure and its release kinetics under pharmaceutically relevant conditions.

Physicochemical characteristics and in vitro release from oil-based vehicles of peptidomimetics: parenteral depots for intra-articular administration

RESULTS

Basic physicochemical properties including their apparent solubility in aqueous buffer and vegetable oils of a series of 11 peptidomimetics varying with respect to chain length and degree of N-methylation were estimated. It was observed that the compounds in contact with water transformed into sticky, slowly dissolving semisolid materials. Based on these observations, the in vitro release behavior of selected peptide derivatives from oil solutions and in situ formed precipitates was investigated using a validated in vitro release model.

CONCLUSION

The results of this investigation suggest that both types of oil-based drug delivery systems might constitute alternative sustained release formulation principles of such amorphous peptide derivatives for the intra-articular route of administration.

On the search for in vitro in vivo correlations in the field of intra-articular drug delivery: administration of sodium diatrizoate to the horse

Development of suitable in vitro release models for formulation development as well as quality control purposes has to be initiated in the early design phase of injectable depots. Optimally, construction of an in vitro release model may lead to the establishment of in vitro in vivo correlations. By using a model compound (sodium diatrizoate, DTZ), the purpose of this study was to investigate the possibility of establishing in vitro in vivo relations between the DTZ disappearance profile obtained from the donor compartment of the rotating dialysis cell model and the joint disappearance profile following intra-articular administration. In vitro experiments were conducted by applying solutions of DTZ to the donor compartment. In the in vivo experiments, five horses were subjected to both intravenous and intra-articular administration of an aqueous solution of 3.9 mg DTZ/kg. A strong relation (R(2)=0.99) was obtained between the disappearance data from the donor compartment of the in vitro model and the disappearance data from the synovial fluid after intra-articular administration of DTZ. Furthermore, a relation (R(2)=0.91) between the appearance data obtained from the acceptor compartment and the deconvolved appearance serum data upon intra-articular administration of DTZ was obtained. The correlations obtained in this study hold promise that the rotating dialysis cell model has a role in the prediction of the intra-articular fate of drugs injected as solutions.

Role of in vitro release models in formulation development and quality control of parenteral depots

This review article provides an assessment of advantages/limitations of the use of current in vitro release models to predict in vivo performance of parenteral sustained release products (injectable depots). As highlighted, key characteristics influencing the in vivo drug fate may vary with the route of administration and the type of sustained release formulation. To this end, an account is given on three representative injection sites (intramuscular, subcutaneous and intra-articular) as well as on in vitro release mechanism(s) of drugs from five commonly investigated depot principles (suspensions, microspheres, hydrogels, lipophilic solutions, and liposomes/other nano-size formulations). Current in vitro release models are, to a different extent, able to mimic the rate, transport and equilibrium processes that the drug substance may experience in the environment of the administration site. Their utility for the purpose of quality control including in vitro-in vivo correlations and formulation design is discussed.

Intra-articular depot formulation principles: role in the management of postoperative pain and arthritic disorders

The joint cavity constitutes a discrete anatomical compartment that allows for local drug action after intra-articular injection. Drug delivery systems providing local prolonged drug action are warranted in the management of postoperative pain and not least arthritic disorders such as osteoarthritis. The present review surveys various themes related to the accomplishment of the correct timing of the events leading to optimal drug action in the joint space over a desired time period. This includes a brief account on (patho)physiological conditions and novel potential drug targets (and their location within the synovial space). Particular emphasis is paid to (i) the potential feasibility of various depot formulation principles for the intra-articular route of administration including their manufacture, drug release characteristics and in vivo fate, and (ii) how release, mass transfer and equilibrium processes may affect the intra-articular residence time and concentration of the active species at the ultimate receptor site.

Diflunisal salts of bupivacaine, lidocaine and morphine

The present work describes the characterization of diflunisal salts of the analgesic agents bupivacaine, lidocaine, and morphine including their solubility behaviour and release characteristics from solutions and selected salt suspensions in vitro using the rotating dialysis cell model. The solubility of the 1:1 salts at pH 7.4 differed by a factor of 9 with the bupivacaine and lidocaine salts representing the poorest and most soluble salt (0.73 and 6.6mM, respectively). Common ion effects were observed for the diflunisal salts of bupivacaine and morphine when various concentrations of the lidocaine-diflunisal salt were present in aqueous buffer (pH 7.4). The most pronounced salting-out effect was observed for the poorest soluble salt. From Setschenow type plots apparent salting-out constants of 265 M(-1) (bupivacaine) and 54.7 M(-1) (morphine) were calculated. After instillation of mixed salt suspensions comprising the diflunisal salts of bupivacaine and lidocaine into the donor cell of the release model, lidocaine appeared rapidly in the acceptor phase. After clearance of lidocaine from the donor cell, equal and constant fluxes of bupivacaine and diflunisal were observed. The residence times of bupivacaine within the donor compartment was prolonged with increasing lidocaine-diflunisal salt load in the mixed suspensions whereas the slopes of the linear part of the bupivacaine release profiles were affected to a minor extent only. The obtained data indicate that local multimodal analgesia, characterized by rapid onset and extended duration of action, can be achieved upon injection of mixed suspensions of salts differing with respect to aqueous solubility comprising a common ion into a small body compartment (such as the joint cavity).

In vitro assessment of drug release rates from oil depot formulations intended for intra-articular administration

In vitro drug release rates from oil depot formulations intended for intra-articular injection have been investigated by using the rotating dialysis cell. The rate of drug appearance in the acceptor phase after instillation of sesame oil solutions of naproxen and lidocaine into the small aqueous donor compartment applied to first-order kinetics. In the present three-compartment model oil-aqueous phase distribution equilibrium was maintained at all times in the donor phase and thus drug efflux from the donor compartment was dictated by the distribution coefficient. A mathematical description of the rate of drug release into the acceptor phase and the interdependence of the observed apparent first-order rate constants and the drug oil-water distribution coefficients is provided. The in vitro model may constitute a valuable tool in formulation design and development allowing comparison of drug release rates originating from alteration of the oil vehicle composition, the drug compound or the composition of the release media to be performed.

The "inverted cup" -- a novel in vitro release technique for drugs in lipid formulations

The aim of this study was to develop a membrane-free in vitro release method for drugs in lipid formulations. It was intended to be applicable to as wide a range as possible of preparations, independently of their polarity and viscosity. The principle of the novel technique is to keep the sample suspended in the release medium in an inverted glass cup, allowing a possible phase transition or swelling. Thirteen formulations containing bupivacaine, lidocaine and/or prilocaine in lipid vehicles with different physical properties were prepared and examined. When possible, in vitro release profiles obtained by the new method were compared to profiles obtained by earlier techniques. For three formulations of either bupivacaine or lidocaine in polar lipid formulations, in vitro release profiles were evaluated in relation to in vivo data, from nerve block and pharmacokinetic studies in rats. Preparations that could be investigated both by the "inverted cup" and by the earlier published "single drop" technique generally showed good agreement between the two release profiles. In the case of the polar lipid formulations, arterial blood concentration curves in rats could reasonably be predicted from the in vitro release profiles. In conclusion, the "inverted cup" technique should potentially be applicable to a wide range of lipid formulations of drugs, both for physico-chemical characterisation and for obtaining in vitro -- in vivo correlations.

Bupivacaine salts of diflunisal and other aromatic hydroxycarboxylic acids: aqueous solubility and release characteristics from solutions and suspensions using a rotating dialysis cell model

In the search for poorly soluble bupivacaine salts potentially enabling prolonged postoperative pain relief after local joint administration in the form of suspensions the solubility of bupivacaine salts of diflunisal and other aromatic hydroxycarboxylic acids were investigated together with the release characteristics of selected 1:1 salts from solutions and suspensions using a rotating dialysis cell model. The poorest soluble bupivacaine salts were obtained from the aromatic ortho-hydroxycarboxylic acids diflunisal, 5-iodosalicylic acid, and salicylic acid (aqueous solubilities: 0.6-1.9 mM at 37 degrees C). Diffusant appearance rates in the acceptor phase upon instillation of solutions of various salts in the donor cell applied to first-order kinetics. Calculated permeability coefficients for bupivacaine and the counterions diflunisal, 5-iodosalicylic acid, and mandelic acid were found to be correlated with the molecular size of the diffusants. Release experiments at physiological pH involving suspensions of the bupivacaine-diflunisal salt revealed that at each sampling point the diflunisal concentration exceeded that of bupivacaine in the acceptor phase. However, after an initial lag period, a steady state situation was attained resulting in equal and constant fluxes of the two diffusants controlled by the permeability coefficients in combination with the solubility product of the salt. Due to the fact that the saturation solubility of the bupivacaine-salicylic acid salt in water exceeded that of bupivacaine at pH 7.4, suspensions of the latter salt were unable to provide simultaneous release of the cationic and anionic species at pH 7.4. The release profiles were characterised by a rapid release of salicylate accompanied by a much slower appearance of bupivacaine in the acceptor phase caused by precipitation of bupivacaine base from the solution upon dissolution of the salt in the donor cell.