Modification of in vitro drug release rate from oily parenteral depots using a formulation approach

Long-acting intramuscular injections of ELQ-331, an antimalarial agent

The overarching premise of this investigation is that injectable, long-acting antimalarial medication would encourage adherence to a dosage regimen for populations at risk of contracting the disease. To advance support for this goal, we have developed oil-based formulations of ELQ-331 (a prodrug of ELQ-300) that perform as long-acting, injectable chemoprophylactics with drug loading as high as 160 mg/ml of ELQ-331. In a pharmacokinetic study performed with rats, a single intramuscular injection of 12.14 mg/kg maintained higher plasma levels than the previously established minimum fully protective plasma concentration (33.25 ng/ml) of ELQ-300 for more than 4 weeks. The formulations were well tolerated by the rats and the tested dose produced no adverse reactions. We believe that by extending the length of time between subsequent injections, these injectable oil-based solutions of ELQ-331 can offer a more accessible, low-cost option for long-acting disease prevention and reduced transmission in malaria-endemic regions and may also be of use to travelers.

Enhancing Oil Solubility of BCS Class II Drug Phenytoin Through Hydrophobic Ion Pairing to Enable High Drug Load in Injectable Nanoemulsion to Prevent Precipitation at Physiological pH With a Potential to Prevent Phlebitis

This work investigates the micellar titration of phenytoin (a weakly acidic drug) with cetyltrimethylammonium hydroxide (CTAH) to form a hydrophobic ion-pair to enhance oil solubility of phenytoin, followed by an effort to formulate nanoemulsion that could potentially prevent precipitation of phenytoin at physiological pH. The ion-pair formulated in nanoemulsion was evaluated for in vitro precipitation during serial dilution at physiological pH. The formation of ion-pair during titration was explained in context of pH-solubility data. The mathematical model successfully integrated ionization and micellization equilibria to reflect on dominant mechanisms for solubilization. The micellar phenomenon during titration was confirmed using Dynamic Light Scattering (DLS). The phase changes of the excess undissolved solids during titration were evident from X-Ray Powder Diffraction (XRPD) and Fourier Transform Infrared Spectroscopy (FTIR). This analysis confirmed the conversion of phenytoin into ionized state and its subsequent ionic interaction with CTAH forming hydrophobic ion-pair complex (HIP). The complete ion pair formation was evident at pHmax (8.8 to 9.2), and its 1:1 stoichiometry was confirmed using HPLC (Phenytoin and CTAH) and H1 NMR, hence could also be called as a lipophilic salt. The ion-pair (salt) was insoluble in water and showed remarkably high partition coefficient (log P) in octanol/water. As characterized by Hot Stage Microscopy (HSM), the melting point of the ion-pair complex was lowered to 150.8⁰C compared to the free acid (> 300οC), this was even further lowered to 81.1 °C when evaluated in castor oil. This led to approximately eight-fold higher solubility of hydrophobic ion pair (HIP) in castor oil compared to the free acid form. The high miscibility in castor oil was suitable to formulate a high drug load injectable dispersed system. This was successfully achieved with lecithin and polysorbate as emulsifiers without leaching drug into continuous phase at pH 7.4. This nanoemulsion (<300 nm, and > +30 mV zeta potential) remain stable when evaluated over a period of one month. A serial dilution study of the nanoemulsion was performed in PBS buffer, microscopic observations suggested no birefringence despite incubation at 25°C for several hours. This result indicated that Phenytoin remained strongly partitioned within dispersed oily phase with a higher drug loading when ion-paired phenytoin was used. The higher drug load could enable a small volume slow bolus injection to meet 50 mg/min or lower delivery rate criteria for Phenytoin in the clinical set up. This provided a pathway to further explore potential injectable nano-emulsion formulations that could alleviate typical phlebitis issue associated with the injectable phenytoin solution administration at physiological pH.

Assessment of glyceride-structured oleogels as an injectable extended-release delivery system of bupivacaine

This manuscript systematically assesses three different glycerides (tripalmitin, glyceryl monostearate, and a blend of mono-, di- and triesters of palmitic and stearic acids (Geleol™)) as potential gelator structuring agents of medium-chain triglyceride oil to form an oleogel-based injectable long-acting local anesthetic formulation for postoperative pain management. Drug release testing, oil-binding capacity, injection forces, x-ray diffraction, differential scanning calorimetry, and rheological testing were serially performed to characterize the functional properties of each oleogel. After benchtop assessment, the superior bupivacaine-loaded oleogel formulation was compared to bupivacaine HCl, liposomal bupivacaine, and bupivacaine-loaded medium-chain triglyceride oil in a rat sciatic nerve block model to assess in vivo long-acting local anesthetic performance. In vitro drug release kinetics were similar for all formulations, indicating that drug release rate is primarily dependent on the drug's affinity to the base oil. Glyceryl monostearate-based formulations had superior shelf-life and thermal stability. The glyceryl monostearate oleogel formulation was selected for in vivo evaluation. It was found to have a significantly longer duration of anesthetic effect than liposomal bupivacaine and was able to provide anesthesia twice as long as the equipotent bupivacaine-loaded medium-chain triglyceride oil, indicating that the increased viscosity of the oleogel provided enhanced controlled release over the drug-loaded oil alone.

Preparation of an oil suspension containing ondansetron hydrochloride as a sustained release parenteral formulation

Ondansetron hydrochloride (ODS) is a selective 5-hydroxytryptamine type 3 antagonist for nausea and emesis prevention in neoplastic patients. To reduce dosing frequency and side effects and improve patient compliance, a sustained release parenteral formulation of ODS was developed. Microparticles of methylcellulose (MC) and ODS were prepared using the spray-drying method and suspended in oils to form oil suspensions. The formulations were evaluated for residual moisture, drug content, size distribution, DSC, XRD, FTIR, SEM, drug release, and pharmacokinetic studies. The effects of polymers and oils on the drug release were evaluated. MC showed the most prominent sustained release effect among various polymers examined with the optimum MC/ODS ratio of 2:1 (w/w). The particle size of the produced microparticles was in the mean diameter of approximately 3 μm. Physicochemical characterization suggested that ODS existed in an amorphous matrix within the microparticles and interacted with MC via hydrogen bonds. Corn oil was selected as the appropriate oil for suspension due to the sustained release of ODS and the appropriate viscosity. The optimized sustained release formulation of ODS was the corn oil suspension of spray-dried microparticles containing MC and ODS (2:1, w/w). It showed an in vitro drug sustained release up to 120 h, while the oil suspension of ODS without any polymer released the drug within 2 h. Following subcutaneous administration in rats, the optimized formulation could prolong the drug release until 72 h with the enhanced bioavailability in comparison with the ODS solution. The oil suspension of spray-dried microparticles might be an efficient approach for prolongation of the drug effect in the management of nausea and emesis. Graphical abstract.

Strengths, weaknesses, opportunities and challenges for long acting injectable therapies: Insights for applications in HIV therapy

Advances in solid drug nanoparticle technologies have resulted in a number of long-acting (LA) formulations with the potential for once monthly or longer administration. Such formulations offer great utility for chronic diseases, particularly when a lack of medication compliance may be detrimental to treatment response. Two such formulations are in clinical development for HIV but the concept of LA delivery has its origins in indications such as schizophrenia and contraception. Many terms have been utilised to describe the LA approach and standardisation would be beneficial. Ultimately, definitions will depend upon specific indications and routes of delivery, but for HIV we propose benchmarks that reflect perceived clinical benefits and available data on patient attitudes. Specifically, we propose dosing intervals of ≥1week, ≥1month or ≥6months, for oral, injectable or implantable strategies, respectively. This review focuses upon the critical importance of potency in achieving the LA outcome for injectable formulations and explores established and emerging technologies that have been employed across indications. Key technological challenges such as the need for consistency and ease of administration for drug combinations, are also discussed. Finally, the review explores the gaps in knowledge regarding the pharmacology of drug release from particulate-based LA injectable suspensions. A number of hypotheses are discussed based upon available data relating to local drug metabolism, active transport systems, the lymphatics, macrophages and patient-specific factors. Greater knowledge of the mechanisms that underpin drug release and protracted exposure will help facilitate further development of this strategy to achieve the promising clinical benefits.

From micro- to nanostructured implantable device for local anesthetic delivery

Local anesthetics block the transmission of painful stimuli to the brain by acting on ion channels of nociceptor fibers, and find application in the management of acute and chronic pain. Despite the key role they play in modern medicine, their cardio and neurotoxicity (together with their short half-life) stress the need for developing implantable devices for tailored local drug release, with the aim of counterbalancing their side effects and prolonging their pharmacological activity. This review discusses the evolution of the physical forms of local anesthetic delivery systems during the past decades. Depending on the use of different biocompatible materials (degradable polyesters, thermosensitive hydrogels, and liposomes and hydrogels from natural polymers) and manufacturing processes, these systems can be classified as films or micro- or nanostructured devices. We analyze and summarize the production techniques according to this classification, focusing on their relative advantages and disadvantages. The most relevant trend reported in this work highlights the effort of moving from microstructured to nanostructured systems, with the aim of reaching a scale comparable to the biological environment. Improved intracellular penetration compared to microstructured systems, indeed, provides specific drug absorption into the targeted tissue and can lead to an enhancement of its bioavailability and retention time. Nanostructured systems are realized by the modification of existing manufacturing processes (interfacial deposition and nanoprecipitation for degradable polyester particles and high- or low-temperature homogenization for liposomes) or development of novel strategies (electrospun matrices and nanogels). The high surface-to-volume ratio that characterizes nanostructured devices often leads to a burst drug release. This drawback needs to be addressed to fully exploit the advantage of the interaction between the target tissues and the drug: possible strategies could involve specific binding between the drug and the material chosen for the device, and a multiscale approach to reach a tailored, prolonged drug release.

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.

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.

Critical factors influencing the in vivo performance of long-acting lipophilic solutions--impact on in vitro release method design

Parenteral long-acting lipophilic solutions have been used for decades and might in the future be used in the design of depots with tailored delivery characteristics. The present review highlights major factors influencing the in vivo performance of lipophilic solutions. Furthermore, an account is given of the characteristics of employed in vitro release methods with a focus on the "state" of sink condition, the stirring conditions, and the oil-water interfacial area. Finally, the capability of in vitro release data to predict the in vivo performance of drug substances administrated in the form of lipophilic solutions is discussed. It is suggested that as long as the major rate-limiting in vivo release mechanism is governed by the drug partitioning between the oil vehicle and the tissue fluid, the use of in vitro release testing in quality control appears to be realistic. With increasing lipophilicity of the drug substances and longer duration of action, the in vivo drug release process may become more complex. As discussed, practical analytical problems together with the inability of release methods to mimic two or more concomitant in vivo events may constitute severe impediments for establishment of in vitro in vivo correlations.

Extraction and analysis of chemical modification patterns in drug development

Most drugs have been continuously modified from prototypic compounds in the drug development process. Such chemical modifications in the history of drug development are expected to contain a wealth of medicinal chemists' knowledge, and the KEGG DRUG structure maps have been compiled to capture this knowledge. Here we attempted to extract the information on the chemical modification patterns from 3745 approved drugs in the KEGG DRUG database and 255 drug pairs in the KEGG DRUG structure maps. We first identified 236 core structures and 506 peripheral fragments from the KEGG DRUG database using bit-represented fingerprints and hierarchical clustering of similar structures. We then examined position-dependent relationships between core structures and peripheral fragments, which revealed the tendency of specific fragments connected to specific modification sites on the core structures. Next we converted the drug pairs into 204 peripheral fragment changes at the modification sites. Each change was represented by the transformation profile defined as a difference of fingerprint bit patterns, and the hierarchical clustering of similar transformation profiles was performed. We thus identified 125 chemical modification patterns that characterize the KEGG DRUG structure maps. These patterns were further applied to the reconstruction of a new structure map. The approach presented here may be applicable to systematic in silico drug modifications.

In silico prediction of drug permeability across buccal mucosa

PURPOSE

To develop and validate a computational model capable of predicting buccal permeability based on various structural and physicochemical descriptors.

METHODS

Apparent permeability coefficients (K(p)) of 15 different drugs across porcine buccal mucosa were determined. Multiple linear regression (MLR) and maximum likelihood estimations (MLE) were used to develop the model based on a training set of 15 drugs with permeability as the response variable and the various descriptors as the predictor variables. The final model was validated with an external data set consisting of permeability values obtained from the literature.

RESULTS

Drug permeabilities ranged from 30 x 10(-6) (nimesulide) to 3.3 x 10(-9) cm/s (furosemide). Regression analysis showed that 95% of the variability in permeability data can be explained by a model that includes molecular volume, distribution coefficient at pH 6.8, number of hydrogen bond donors, and number of rotatable bonds. Smaller molecular size, high lipophilicity, lower hydrogen bond capability and greater flexibility were important for permeability. The buccal model was found to have a good predictive capability.

CONCLUSION

A simple model was developed and validated for predicting the buccal drug permeability. This model will be useful in assessing the feasibility of drugs for transbuccal delivery.

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.

In Situ-Forming Oleogel Implant for Rivastigmine Delivery

PURPOSE

To provide a simplified dosing schedule and potentially reduce side effects associated to peak plasma concentrations, an in situ-forming oleogel implant was studied for the sustained-release of rivastigmine.

MATERIALS AND METHODS

The gel was prepared by dissolving 5-10% (w/w) N-stearoyl L: -alanine methyl ester (SAM) organogelator in safflower oil containing either dissolved rivastigmine or its dispersed hydrogen tartrate salt. Rheological analysis, differential scanning calorimetry, and infrared spectroscopy were carried out to assess the impact of drug incorporation on the oleogel; this was followed by in vitro and in vivo release studies.

RESULTS

A weakening of intermolecular interactions was suggested by gel-sol transition temperature drops of 10-15 degrees C upon incorporation of dissolved drug. Meanwhile, the dispersed drug salt induced minimal or no changes in transition temperature. Gels containing dispersed rivastigmine had the lowest burst in vitro (<15% in 24 h). In vivo, the 10% SAM formulation containing dispersed rivastigmine provided prolonged drug release within the therapeutic range for 11 days, with peak plasma levels well below the toxic threshold and up to five times lower than for the control formulation.

CONCLUSIONS

This study established SAM gels to be a promising option for sustained-release formulations in the treatment of Alzheimer's Disease.

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.

In vivo release of bupivacaine from subcutaneously administered oily solution. Comparison with in vitro release

A non-randomized cross-over study was performed with bupivacaine HCl (5 mg x ml(-1)) aqueous solution and bupivacaine free base (4.44 mg x ml(-1)) in Viscoleo/castor oil 2:1 (v/v) administered s.c. to male Wistar rats. Plasma levels were analyzed by LC-MS. Plasma profiles obtained after administration of oily solution showed a prolonged bupivacaine release with lower peak plasma levels as compared to administration of an aqueous formulation applied in the same compartment. t(1/2), t(max), C(max) and AUC(0-infinity) for the aqueous solution were 63+/-8 min, 19+/-16 min, 194+/-46 ng x ml(-1) and 25,000+/-3000 ng min x ml(-1), respectively, while the corresponding data for the oil solution were 368+/-89 min, 334+/-186 min, 36+/-25 ng x ml(-1) and 25,000+/-6000 ng x min x ml(-1). The present data indicate the potential of designing an oil formulation of bupivacaine with a prolonged local analgetic effect exhibiting a minimum of systemic toxicity. In vivo release of bupivacaine from the oil solution was evaluated by a numerical deconvolution method. In vivo release kinetics was found to be first-order and corresponded well with in vitro release kinetics found using a rotating dialysis cell. This led to establishment of an in vitro/in vivo correlation for this particular formulation.

Characteristics of drug substances in oily solutions. Drug release rate, partitioning and solubility

In vitro rate of drug release from oil solutions was investigated in a rotating dialysis cell. A log linear correlation was established between the rate constant (k(obs)) for attainment of equilibrium and apparent partition coefficient (P(app)) between oil vehicle and release media using various weak acids and bases and non-electrolytes. Collander like linear free energy relationships were observed allowing various oil-aqueous buffer partition coefficients to be calculated from known octanol-aqueous buffer partition coefficients. Solubility of the various drug substances in oil vehicles were investigated. A linear correlation was observed between log molar solubility and melting point of the solutes. Release profiles obtained for release of two local anaesthetics dissolved in the same oil vehicle exhibited an unexpected behavior involving an initial delayed release of the most lipophilic local anaesthetic.

Determination of the disappearance rate of iodine-125 labelled oils from the injection site after intramuscular and subcutaneous administration to pigs

The rate of disappearance of clinically used vegetable oils, Viscoleo, sesame oil, castor oil and isopropyl myristate, from the injection site after intramuscular (i.m.) or subcutaneous (s.c.) administration to pigs were determined by using a non-invasive gamma-scintigraphy method. All the oil vehicles were spiked with 2.5% (v/v) (125)I-triolein and six injections of 1.9 ml were given to each of 12 pigs. No significant difference (ANOVA) in disappearance rate of each individual oil vehicle from the different injection sites was observed after administration of the oils: i.m. in the lower back, s.c. in the neck and s.c. in the mid-back. Likewise, no inter-individual difference between the pigs was observed. The half-life of 14 days for Viscoleo was significantly smaller than those of the other oil vehicles (P<0.0001), i.e. 23,20,20 days for sesame oil, castor oil and isopropyl myristate, respectively. Due to the spreading effect of the oils and reflux of the oils through the injection canal, the half-lives were calculated omitting the data for the first sampling day.

Addition of hydrogen bond donating excipients to oil solution: effect on in vitro drug release rate and viscosity

In oily vehicles containing different hydrogen bond donating excipients rates of transfer of the weak electrolytes naproxen and lidocaine from the oil phase to the aqueous medium were measured by using the rotating dialysis cell. A logarithmic linear correlation was established between the apparent partition coefficient, P(app), and the first-order rate constant related to attainment of equilibrium between the two phases, k(obs), which fitted well with results from former publications. Further, release data for the non-electrolyte testosterone were found to fit into this linear correlation. Apparent partition coefficients were determined between oil vehicles containing various amounts of hydrogen bond donating excipients and phosphate buffer, pH 6.00, revealing a rise in log P(app) with increasing concentration of excipient. Viscosity was measured for castor oil containing vehicles showing a linear relationship between percentage (v/v) castor oil and log viscosity (mPas) of the mixed vehicle.

Actions of ricinoleic acid and structurally related fatty acids on the gastrointestinal tract. II. Effects on water and electrolyte absorption in vitro

Ricinoleic acid, the active component of castor oil, and related fatty acids were studied to determine their relative inhibitory effects on water and electrolyte absorption using everted hamster jejunal and ileal segments. Differences were found between hydroxylated and nonhydroxylated congeners as well as between cis and trans geometric isomers. At a mucosal concentration of 2.0 mM, the unsaturated fatty acids had the following rank order of potency on inhibition of water absorption: ricionoleate greater than or equal to ricinelaidate- greater than equal to linoleate greater than oleate greater than linelaidate greater than elaidate. Ricinoleyl alcohol was effective at 2.0 mM but the methyl ester of ricinoleic acid was ineffective at this concentration. Among a series of saturated fatty acids including palmitate, stearate, a mixture of 9- and 10-hydroxystearate, and 12-hydroxystearate, only the last compound had any inhibitory effect on water absorption. The results define those portions of the ricinoleic acid molecule required for its effect on water and electrolyte absorption and suggest that classification of this cathartic as an "irritant" or "stimulant" should be re-evlauated.