In vitro performance of composition-equivalent PLGA microspheres encapsulating exenatide acetate by solvent evaporation.

The once-weekly Bydureon® (Bdn) PLGA microsphere formulation encapsulating the GLP-1 receptor agonist, exenatide acetate, is an important complex injectable product prepared by coacervation for the treatment of type 2 diabetic patients. Encapsulation by coacervation is useful to minimize an undesirable initial burst of exenatide, but it suffers from manufacturing difficulties such as process scale-up and batch-to-batch variations. Herein we prepared exenatide acetate-PLGA formulations of similar compositions using the desirable alternative double emulsion-solvent evaporation technique. After screening several process variables, we varied the PLGA concentration, the hardening temperature, and the collected particle size range, and determined the resulting drug and sucrose loading, initial burst release, in vitro retention kinetics, and peptide degradation profiles using Bdn as a positive control. All formulations exhibited a triphasic release profile with a burst, lag, and rapid release phase, although the burst release was greatly decreased to <5% for some. Marked differences were observed in the peptide degradation profiles, particularly the oxidized and acylated fractions, when the polymer concentration was varied. For one optimal formulation, the release and peptide degradation profiles were similar to Bdn microspheres, albeit with an induction time shift of one week, likely due to the slightly higher Mw of PLGA in Bdn. These results highlight the effects of key manufacturing variables on drug release and stability in composition-equivalent microspheres encapsulating exenatide acetate and indicate the potential of manufacturing the microsphere component of Bdn by solvent evaporation.

Efficient aqueous remote loading of peptides in poly(lactic-co-glycolic acid).

Poly(lactic-co-glycolic acid) (PLGA) long-acting release depots are effective for extending the duration of action of peptide drugs. We describe efficient organic-solvent-free remote encapsulation based on the capacity of common uncapped PLGA to bind and absorb into the polymer phase net positively charged peptides from aqueous solution after short exposure at modest temperature. Leuprolide encapsulated by this approach in low-molecular-weight PLGA 75/25 microspheres slowly and continuously released peptide for over 56 days in vitro and suppressed testosterone production in rats in an equivalent manner as the 1-month Lupron Depot®. The technique is generalizable to encapsulate a number of net cationic peptides of various size, including octreotide, with competitive loading and encapsulation efficiencies to traditional methods. In certain cases, in vitro and in vivo performance of remote-loaded PLGA microspheres exceeded that relative to marketed products. Remote absorption encapsulation further removes the need for a critical organic solvent removal step after encapsulation, allowing for simple and cost-effective sterilization of the drug-free microspheres before encapsulation of the peptide.

Minimizing the initial burst of octreotide acetate from glucose star PLGA microspheres prepared by the solvent evaporation method.

Sandostatin long-acting release (SLAR) depot for 1-month controlled release of octreotide is a somatostatin analogue product that has been used extensively in the pharmacological treatment of acromegaly. The complexities in the SLAR coacervation manufacturing processes and the use of a unique glucose-starpoly(lactic-co-glycolic acid) (PLGA-glu) may have contributed to the lack of US FDA-approved generic products referencing SLAR in the USA. To address this challenge, we encapsulated octreotide acetate by the commonly used solvent evaporation method in microspheres of a similar composition to SLAR, including the use of a comparable PLGA-glu. Based on our previous study that identified key formulation variables to prepare octreotide acetate/PLGA-glu microspheres, including lowering initial peptide pH and introducing an annealing step post loading, here we added NaCl to the external water phase to further improve the formulation. The resulting microspheres exhibited highly similar release and stability performance in vitro to SLAR, including an exceptionally low initial burst. The very low initial burst was also confirmed by pharmacokinetics in rats. Full erosion behavior analysis (polymer MW, water uptake and mass loss) revealed a slightly faster degradation of SLAR than the solvent evaporation formulations. Analysis of kinetics of dry Tg of the formulations reflected (a) the elevated residual solvent in SLAR and was not duplicated in the solvent evaporation formulations, and (b) the slightly higher Tg of peptide loaded formulations relative to than blank microspheres, consistent with the interaction of the acetate salt of octreotide with linear PLGA chains in the PLGA-glu. These data indicate that it is possible to prepare peptide loaded microspheres by the solvent evaporation method with extraordinarily similar performance to microspheres, such as those in SLAR, that are prepared by the low-burst release coacervation method.

Development and characterization of composition-equivalent formulations to the Sandostatin LAR® by the solvent evaporation method.

Sandostatin long-acting release® (SLAR) is a long-acting injectable somatostatin analogue formulation composed of octreotide encapsulated in glucose-initiated poly(lactic-co-glycolic acid) (PLGA) microspheres. Despite the end of patent protection, SLAR remains resistant to generic competition likely due to complexity of production process, the uniqueness of the glucose star polymer, and the instability of octreotide in the formulation. Here, we describe development of glucose-PLGA-based composition-equivalent to SLAR formulations prepared by double emulsion-solvent evaporation method and the effect of variations in encapsulation variables on release kinetics and other formulation characteristics. The following encapsulation variables were adjusted at constant theoretical loading of 7.0% peptide: PLGA concentration, pH of inner water phase, and stirring rate. After final drying, the microspheres were examined with and without annealing at 50 °C under vacuum for 3 days. The loading and encapsulation efficiency (EE) of octreotide acetate, manufacturing yield, and in vitro drug release kinetics in PBStc (10 mM phosphate-buffered saline (PBS) with 1% triethyl citrate and 0.02% sodium azide at pH 7.4) were determined by UPLC. The in vitro release and acylation kinetics of octreotide for the solvent evaporation formulations prepared were similar to SLAR although the initial burst was slightly higher. Key formulation steps identified to maximize microsphere yield and minimize residual solvent and initial burst release included (a) addition of acetic acid to the peptide before preparation and (b) annealing the microspheres under vacuum after drying. Controlled release octreotide formulations prepared and investigated in this study could provide a better understanding of the effect of production variables on release performance and supply information useful for making progress in manufacturing of SLAR generic equivalents.

Adequate formulation approach for oral chemotherapy: Etoposide solubility, permeability, and overall bioavailability from cosolvent- vs. vitamin E TPGS-based delivery systems.

Injectable-to-oral conversions for anticancer drugs represent an important trend. The goal of this research was to investigate the suitability of formulation approaches for anticancer oral drug delivery, aiming to reveal mechanistic insights that may guide oral chemotherapy development. TPGS vs. PEG-400 were studied as oral formulations for the anticancer drug etoposide, accounting for drug solubility, biorelevant dissolution, permeability, solubility-permeability interplay, and overall bioavailability. Increased etoposide solubility was demonstrated with both excipients. Biorelevant dissolution revealed that TPGS or PEG-400, but not aqueous suspension, allowed complete dissolution of the entire drug dose. Both TPGS and PEG-400 resulted in decreased in-vitro etoposide permeability across artificial membrane, i.e. solubility-permeability tradeoff. While PEG-400 resulted in the same solubility-permeability tradeoff also in-vivo, TPGS showed the opposite trend: the in-vivo permeability of etoposide was markedly increased in the presence of TPGS. This increased permeability was similar to the drug permeability under P-gp inhibition. Rat PK study demonstrated significantly higher etoposide bioavailability from TPGS vs. PEG-400 or suspension (AUC of 72, 41, and 26 µg·min/mL, respectively). All in all, TPGS-based delivery system allows overcoming the solubility-permeability tradeoff, increasing systemic etoposide exposure. Since poor solubility and strong efflux are common to many anticancer agents, this work can aid in the development of better oral delivery approach for chemotherapeutic drugs.

Characterization of attributes and in vitro performance of exenatide-loaded PLGA long-acting release microspheres.

Bydureon® (Bdn) is a once-weekly injectable long-acting release (LAR) product for adults with type 2 diabetes based on PLGA microspheres encapsulating the glucagon like peptide (GLP-1) analog, exenatide. Despite its widespread use in type 2 diabetes treatment, little information has been published concerning the physical-chemical aspects and exenatide stability in this product. Here, we developed and validated methods to evaluate attributes and performance of Bdn such as particle size/size distribution and residual levels of moisture and organic solvent(s). The reverse engineering of the exenatide LAR was also performed to identify and quantify principal components in the product. Stability-indicating UPLC and LC-MS methods were applied to characterize exenatide degradation (such as oxidation, deamidation and acylation products) during in vitro release evaluation. The 55-µm volume-median Bdn microspheres slowly released the exenatidein vitroover two months with a very low initial burst release to avoid unwanted side effects. Residual organic solvent levels (methylene chloride, ethanol, heptane, and silicon oil) also met the USP criteria. Peptide acylation was the most prominent peptide reaction during both encapsulation and in vitro release, and the acylated peptide steadily increased during release relative to parent exenatide, becoming the most abundant peptide species extracted from the microspheres at later release stages. The presence of peptide impurities during the release period, which are not extractable in the polymer and likely insoluble in water, might be one potential cause for immunogenicity. Further evaluation will be needed to confirm this hypothesis. Release of peptide was minimal over the first 2 weeks before the microspheres steadily released peptide for more than 28 days. The rigorous technical approach discussed in this paper may provide critical information for both companies and the FDA for developing generic exenatide-PLGA formulations and other important PLGA microsphere products.

Physical-Chemical Characterization of Octreotide Encapsulated in Commercial Glucose-Star PLGA Microspheres.

Sandostatin LAR (SLAR) is an injectable long-acting release (LAR) microsphere formulation for octreotide based on a biodegradeable glucose star copolymer of d,l-lactic and glycolic acids (PLGA-glu), which is primarily used for the treatment of patients with acromegaly. There currently is no generic SLAR approved in the United States despite expiration of patent coverage. To understand better this important formulation, SLAR was assessed for its composition and physical-chemical properties. Octreotide release kinetics was monitored under physiological conditions over 56 days together with several bioerosion parameters [mass loss, water uptake, pH of release media, polymer molecular weight (Mw), and confocal microscopy after BODIPY uptake]. A significant increase in the amount of released peptide occurred after day 14. After 1 day of incubation in PBST, octreotide was not extractable completely from SLAR during 2 h of the extraction process, but complete extraction was accomplished after 24 h, which suggested that strong and noncovalent PLGA-octreotide interactions occurred beginning in the initial release phase. Leuprolide is considered as a cationic peptide competitor for octreotide-PLGA interactions and its presence in the release medium resulted in more continuous octreotide release from SLAR, which was linearly correlated with the mass loss from the polymer (i.e., an indication of erosion-controlled release). These data strongly suggest that octreotide forms a salt with acid end groups of linear PLGA chains that are either present as impurities in, and/or produced by the degradation of, the PLGA-Glu. This salt is expected to catalyze octreotide acylation and extend peptide release beyond that driven by erosion control. The characterization studies of physicochemical properties of SLAR described here could be useful for the development and regulatory evaluation of generic octreotide microspheres as well as new polymer formulations, in which the polymer strongly interacts with encapsulated peptides.

The solubility, permeability and the dose as key factors in formulation development for oral lipophilic drugs: Maximizing the bioavailability of carbamazepine with a cosolvent-based formulation.

The purpose of this research was to investigate drug dose, solubility, permeability, and their interplay, as key factors in oral formulation development for lipophilic drugs. A PEG400-based formulation was studied for five doses of the lipophilic drug carbamazepine, accounting for biorelevant dissolution of the dose in the GIT, and in-vivo bioavailability in rats. With the three lower doses (10, 25 and 50 mg/kg), complete in-vitro dissolution was achieved and maintained throughout the experiment with this formulation, while significant precipitation was obtained with higher doses (100 and 200 mg/kg). Likewise, the studied formulation allowed complete bioavailability in-vivo with the three lower doses, while the same formulation allowed only 76% and 42% bioavailability for the 100 and 200 mg/kg doses, respectively. There was good correlation between the in-vitro and in-vivo results. In conclusion, this work demonstrates that the dose is a crucial factor in formulation development; while a given formulation may be optimal for a certain drug dose, it may no longer be optimal for higher doses of the same drug. Hence, the solubility, the permeability, and their interplay, have to be considered in light of the drug dose intended to be administered in order to achieve successful oral formulation development.

Segmental-Dependent Intestinal Drug Permeability: Development and Model Validation of In Silico Predictions Guided by In Vivo Permeability Values.

The goal of this work was to develop an in silico model that allows predicting segmental-dependent permeability throughout the small intestine (SI). In vivo permeability of 11 model drugs in 3 SI segments (jejunum, mid-SI, ileum) was studied in rats, creating a data set that reflects the conditions throughout the SI. Then, a predictive model was developed, combining physicochemical drug properties influencing the underlying mechanism of passive permeability: Log p, polar surface area, MW, H-bond count, and Log fu, with microenvironmental SI conditions. Excellent correlation was evident between the predicted and experimental data (R2 = 0.914), with similar predictability in each SI segment. Log p and Log fu were identified as the major determinants of permeability, with similar contribution. Total H-bond count was also a significant determinant, followed by polar surface area and MW. Leaving out any of the model parameters decreased its predictability. The model was validated against 5 external drugs, with excellent predictability. Notably, the model was able to predict the segmental-dependent permeability of all drugs showing this trend experimentally. Model predictability was better in the high-permeability versus low-permeability range. Overall, our approach of constructing a straightforward in silico model allowed reliable predictions of segmental-dependent intestinal permeability, providing new insights into relative effects of drug-related factors and gastrointestinal environment on permeability.

Concomitant solubility-permeability increase: Vitamin E TPGS vs. amorphous solid dispersion as oral delivery systems for etoposide.

Vitamin E TPGS (TPGS) has both surfactant and P-glycoprotein (P-gp) inhibitory effects. While surfactants were previously found to cause solubility-permeability tradeoff, TPGS P-gp inhibitory effects may change this unfavorable interplay. The purpose of this research was to investigate the solubility-permeability interplay when using TPGS vs. amorphous solid dispersions (ASD) as oral drug delivery systems for the anticancer, P-gp substrate, lipophilic drug etoposide. The concentration-dependent effects of TPGS (0-100mg/mL) vs. ASD on the solubility of etoposide, as well as the in-vitro (PAMPA) vs. in-vivo (intestinal rat perfusion) permeability of the drug were studied, and the resulting solubility-permeability interplay was analyzed. TPGS above CMC (0.3mg/mL) increased etoposide solubility linearly, and ASD allowed significant supersaturation. Etoposide in-vitro PAMPA permeability decreased markedly with increasing TPGS levels, similarly to the solubility-permeability tradeoff previously defined for surfactants. In contrast, the presence of TPGS significantly increased etoposide in-vivo rat permeability, attributable to P-gp inhibition, similarly to the effect of the potent P-gp inhibitor GF120918 (10µg/mL). High supersaturation achieved via ASD increased the drug's in-vivo permeability to the level obtained by TPGS or GF120918, supporting P-gp saturation. In conclusion, unique pattern of solubility-permeability interplay was found, involving concomitant increase of both the solubility and the permeability, as opposed to the previously reported tradeoff for solubilization methods and the unchanged permeability for supersaturation; P-gp inhibition/saturation by TPGS or by supersaturation allows simultaneous increase of both solubility and permeability, representing a significant advantage of such drug delivery approaches when suitable.

Toward Successful Cyclodextrin Based Solubility-Enabling Formulations for Oral Delivery of Lipophilic Drugs: Solubility-Permeability Trade-Off, Biorelevant Dissolution, and the Unstirred Water Layer.

The purpose of this work was to investigate key factors dictating the success/failure of cyclodextrin-based solubility-enabling formulations for oral delivery of low-solubility drugs. We have studied the solubility, the permeability, and the solubility-permeability interplay, of the highly lipophilic drug danazol, formulated with different levels (8.5, 10, 20, and 30%) of the commonly used hydroxypropyl-ß-cyclodextrin (HPßCD), accounting for the biorelevant solubilization of the drug along the gastrointestinal tract (GIT), the unstirred water layer (UWL) adjacent to the GI membrane, and the overall absorption. HPßCD significantly increased danazol solubility, and decreased the drugs' permeability, in a concentration-dependent manner. These Peff results were in good correlation (R2 = 0.977) to literature rat AUC data of the same formulations. Unlike vehicle without HPßCD, formulations containing 8.5% HPßCD and above were shown to successfully dissolve the drug dose during the entire biorelevant dissolution experiment. We conclude that CD-based solubility-enabling formulations should contain the minimal amount of CD sufficient to dissolve the drug dose throughout the GIT, and not more than that; excess CD does not provide solubility gain but causes further permeability loss, and the overall absorption is then impaired. Moreover, a significant UWL effect was revealed in danazol intestinal permeability, and accounting for this effect allowed an excellent prediction of the solubility-permeability trade-off vs % HPßCD. Overall, this work assessed the contribution of each individual step of the absorption cascade to the success/failure of HPßCD-based formulation, allowing a more mechanistic development process of better solubility-enabling formulations.

Advantageous Solubility-Permeability Interplay When Using Amorphous Solid Dispersion (ASD) Formulation for the BCS Class IV P-gp Substrate Rifaximin: Simultaneous Increase of Both the Solubility and the Permeability.

Rifaximin is a BCS class IV (low-solubility, low-permeability) drug and also a P-gp substrate. The aims of this work were to assess the efficiency of different rifaximin amorphous solid dispersion (ASDs) formulations in achieving and maintaining supersaturation and to investigate the consequent solubility-permeability interplay. Spray-dried rifaximin ASDs were prepared with different hydrophilic polymers and their ability to achieve and maintain supersaturation was assessed. Then, rifaximin's apparent intestinal permeability was investigated as a function of increasing supersaturation both in vitro using the parallel artificial membrane permeability assay (PAMPA) and in vivo using the single-pass rat intestinal perfusion (SPIP) model. The efficiency of the different ASDs to achieve and maintain supersaturation of rifaximin was found to be highly polymer dependent, and the copovidone/HPC-SL formulation was found to be superior to the other two, allowing supersaturation of 200× that of the crystalline solubility for 20 h. In vitro, rifaximin flux was increased and the apparent permeability was constant as a function of increasing supersaturation level. In vivo, on the other hand, absorption rate coefficient (k a) was first constant as a function of increasing supersaturation, but at 250×, the crystalline solubility k a was doubled, similar to the k a in the presence of the strong P-gp inhibitor GF120918. In conclusion, a new and favorable nature of solubility-permeability interplay was revealed in this work: delivering high supersaturation level of the BCS class IV drug rifaximin via ASD, thereby saturating the drugs' P-gp-mediated efflux transport, led to the favorable unique win-win situation, where both the solubility and the permeability increased simultaneously.

Striking the Optimal Solubility-Permeability Balance in Oral Formulation Development for Lipophilic Drugs: Maximizing Carbamazepine Blood Levels.

The purpose of this research was to investigate the performance of cosolvent based solubility-enabling formulations in oral delivery of lipophilic drugs, accounting for the gastrointestinal tract (GIT) luminal solubilization processes, the solubility-permeability interplay, and the overall in vivo systemic absorption. The poorly soluble antiepileptic agent carbamazepine was formulated in three cosolvent-based formulations: 20%, 60%, and 100% PEG-400, and the apparent solubility and rat permeability of the drug in these formulations were evaluated. The performance of the formulations in the dynamic GIT environment was assessed utilizing the biorelevant pH-dilution method. Then, the overall in vivo drug exposure was investigated following oral administration to rats. The three formulations showed dramatic solubility and permeability differences; the 100% PEG-400 provided the highest solubility enhancement and the 20% the poorest, while the exact opposite was evident from the permeability point of view. The dissolution results indicated that the 20% PEG-400 formulation crashes quickly following oral administration, but both the 60% and the 100% PEG-400 formulations allowed full solubilization of the dose throughout the entire GIT-like journey. The best in vivo performing formulation was the 60% PEG-400 (Fsys > 90%), followed by the 100% PEG-400 (Fsys = 76%), and the 20% PEG-400 formulation (Fsys ≈ 60%). In conclusion, this work demonstrates the in vivo solubility-permeability trade-off in oral delivery of lipophilic drugs; when a solubility-enabling formulation is developed, minimal threshold solubility should be targeted, that is just enough to allow solubilization of the drug dose throughout the GIT, while excess solubilizer should be avoided.

Hydrotropic Solubilization of Lipophilic Drugs for Oral Delivery: The Effects of Urea and Nicotinamide on Carbamazepine Solubility-Permeability Interplay.

Hydrotropy refers to increasing the water solubility of otherwise poorly soluble compound by the presence of small organic molecules. While it can certainly increase the apparent solubility of a lipophilic drug, the effect of hydrotropy on the drugs' permeation through the intestinal membrane has not been studied. The purpose of this work was to investigate the solubility-permeability interplay when using hydrotropic drug solubilization. The concentration-dependent effects of the commonly used hydrotropes urea and nicotinamide, on the solubility and the permeability of the lipophilic antiepileptic drug carbamazepine were studied. Then, the solubility-permeability interplay was mathematically modeled, and was compared to the experimental data. Both hydrotropes allowed significant concentration-dependent carbamazepine solubility increase (up to ∼30-fold). A concomitant permeability decrease was evident both in vitro and in vivo (∼17-fold for nicotinamide and ∼9-fold for urea), revealing a solubility-permeability tradeoff when using hydrotropic drug solubilization. A relatively simplified simulation approach based on proportional opposite correlation between the solubility increase and the permeability decrease at a given hydrotrope concentration allowed excellent prediction of the overall solubility-permeability tradeoff. In conclusion, when using hydrotropic drug solubilization it is prudent to not focus solely on solubility, but to account for the permeability as well; achieving optimal solubility-permeability balance may promote the overall goal of the formulation to maximize oral drug exposure.

Segmental-dependent permeability throughout the small intestine following oral drug administration: Single-pass vs. Doluisio approach to in-situ rat perfusion.

Intestinal drug permeability is position dependent and pertains to a specific point along the intestinal membrane, and the resulted segmental-dependent permeability phenomenon has been recognized as a critical factor in the overall absorption of drug following oral administration. The aim of this research was to compare segmental-dependent permeability data obtained from two different rat intestinal perfusion approaches: the single-pass intestinal perfusion (SPIP) model and the closed-loop (Doluisio) rat perfusion method. The rat intestinal permeability of 12 model drugs with different permeability characteristics (low, moderate, and high, as well as passively and actively absorbed) was assessed in three small intestinal regions: the upper jejunum, mid-small intestine, and the terminal ileum, using both the SPIP and the Doluisio experimental methods. Excellent correlation was evident between the two approaches, especially in the upper jejunum (R2=0.95). Significant regional-dependent permeability was found in half of drugs studied, illustrating the importance and relevance of segmental-dependent intestinal permeability. Despite the differences between the two methods, highly comparable results were obtained by both methods, especially in the medium-high Peff range. In conclusion, the SPIP and the Doluisio method are both equally useful in obtaining crucial segmental-dependent intestinal permeability data.

The solubility-permeability interplay and oral drug formulation design: Two heads are better than one.

Poor aqueous solubility is a major challenge in today's biopharmaceutics. While solubility-enabling formulations can significantly increase the apparent solubility of the drug, the concomitant effect on the drug's apparent permeability has been largely overlooked. The mathematical equation to describe the membrane permeability of a drug comprises the membrane/aqueous partition coefficient, which in turn is dependent on the drug's apparent solubility in the GI milieu, suggesting that the solubility and the permeability are closely related, exhibit a certain interplay between them, and treating the one irrespectively of the other may be insufficient. In this article, an overview of this solubility-permeability interplay is provided, and the available data is analyzed in the context of the effort to maximize the overall drug exposure. Overall, depending on the type of solubility-permeability interplay, the permeability may decrease, remain unchanged, and even increase, in a way that may critically affect the formulation capability to improve the overall absorption. Therefore, an intelligent design of solubility-enabling formulation needs to consider both the solubility afforded by the formulation and the permeability in the new luminal environment resulting from the formulation.

Head-To-Head Comparison of Different Solubility-Enabling Formulations of Etoposide and Their Consequent Solubility-Permeability Interplay.

The purpose of this study was to conduct a head-to-head comparison of different solubility-enabling formulations, and their consequent solubility-permeability interplay. The low-solubility anticancer drug etoposide was formulated in several strengths of four solubility-enabling formulations: hydroxypropyl-ß-cyclodextrin, the cosolvent polyethylene glycol 400 (PEG-400), the surfactant sodium lauryl sulfate, and an amorphous solid dispersion formulation. The ability of these formulations to increase the solubility of etoposide was investigated, followed by permeability studies using the parallel artificial membrane permeability assay (PAMPA) and examination of the consequent solubility-permeability interplay. All formulations significantly increased etoposide's apparent solubility. The cyclodextrin-, surfactant-, and cosolvent-based formulations resulted in a concomitant decreased permeability that could be modeled directly from the proportional increase in the apparent solubility. On the contrary, etoposide permeability remained constant when using the ASD formulation, irrespective of the increased apparent solubility provided by the formulation. In conclusion, supersaturation resulting from the amorphous form overcomes the solubility-permeability tradeoff associated with other formulation techniques. Accounting for the solubility-permeability interplay may allow to develop better solubility-enabling formulations, thereby maximizing the overall absorption of lipophilic orally administered drugs.

The use of captisol (SBE7-ß-CD) in oral solubility-enabling formulations: Comparison to HPßCD and the solubility-permeability interplay.

The aim of this research was to study the interaction of sulfobutyl ether7 ß-cyclodextrin (captisol) and 2-hydroxypropyl-ß-cyclodextrin (HPßCD) with the poorly soluble antiarrhythmic drug amiodarone, and to investigate the consequent solubility-permeability interplay. Phase-solubility studies of amiodarone with the two cyclodextrins, followed by PAMPA and rat intestinal permeability experiments, were carried out, and the solubility-permeability interplay was then illustrated as a function of increasing cyclodextrin content. Equimolar levels of captisol allowed ∼10-fold higher amiodarone solubility than HPßCD, as well as binding constant. With both captisol and HPßCD, decreased in vitro and in vivo amiodarone apparent permeability was evident with increasing CD levels and increased apparent solubility. A theoretical model assuming direct proportionality between the apparent solubility increase allowed by the CD and permeability decrease was able to accurately predict the solubility-permeability tradeoff as a function of CD levels. In conclusion, the addition of ionic interactions (e.g. amiodarone-captisol) to hydrophobic interactions of the inclusion complex formation may result in synergic effect on solubilization; however, it is not merely the solubility that should be examined when formulating an oral poorly soluble compound, but the solubility-permeability balance, in order to maximize the overall drug exposure.

In-situ intestinal rat perfusions for human Fabs prediction and BCS permeability class determination: Investigation of the single-pass vs. the Doluisio experimental approaches.

Intestinal drug permeability has been recognized as a critical determinant of the fraction dose absorbed, with direct influence on bioavailability, bioequivalence and biowaiver. The purpose of this research was to compare intestinal permeability values obtained by two different intestinal rat perfusion methods: the single-pass intestinal perfusion (SPIP) model and the Doluisio (closed-loop) rat perfusion method. A list of 15 model drugs with different permeability characteristics (low, moderate, and high, as well as passively and actively absorbed) was constructed. We assessed the rat intestinal permeability of these 15 model drugs in both SPIP and the Doluisio methods, and evaluated the correlation between them. We then evaluated the ability of each of these methods to predict the fraction dose absorbed (Fabs) in humans, and to assign the correct BCS permeability class membership. Excellent correlation was obtained between the two experimental methods (r(2)=0.93). An excellent correlation was also shown between literature Fabs values and the predictions made by both rat perfusion techniques. Similar BCS permeability class membership was designated by literature data and by both SPIP and Doluisio methods for all compounds. In conclusion, the SPIP model and the Doluisio (closed-loop) rat perfusion method are both equally useful for obtaining intestinal permeability values that can be used for Fabs prediction and BCS classification.

Quantification of carbamazepine and its 10,11-epoxide metabolite in rat plasma by UPLC-UV and application to pharmacokinetic study.

A rapid, selective and sensitive UPLC-UV method was developed and validated for the quantitative analysis of carbamazepine and its epoxide metabolite in rat plasma. A relatively small volume of plasma sample (200 µL) is required for the described analytical method. The method includes simple protein precipitation, liquid-liquid extraction, evaporation, and reconstitution steps. Samples were separated on a Waters Acquity UPLC BEH C18 column (1.7 µm, 2.1 × 100 mm) with a gradient mobile phase consisted of 60:40 going to 40:60 (v/v) water-acetonitrile at a flow rate of 0.5 mL/min. The total run time was as low as 6 min, representing a significant improvement in comparison to existing methods. Excellent linearity (r(2) > 0.999) was achieved over a wide concentration range. Close to complete recovery, short analysis time, high stability, accuracy, precision and reproducibility, and low limit of quantitation were demonstrated. Finally, we successfully applied this analytical method to a pre-clinical oral pharmacokinetic study, revealing the plasma profiles of both carbamazepine and carbamazepine-10,11-epoxide following oral administration of carbamazepine to rats. The advantages demonstrated in this work make this analytical method both time- and cost-efficient approach for drug and metabolite monitoring in the pre-clinical/clinical laboratory.