Fed State Simulated Intestinal Fluid Research Articles

Biomimetic PVPA in vitro model for estimation of the intestinal drug permeability using fasted and fed state simulated intestinal fluids

A prerequisite for successful oral drug therapy is the drug’s ability to cross the gastrointestinal barrier. Considering the increasing number of new chemical entities in modern drug discovery, reliable and fast in vitro models are required for early and efficient prediction of intestinal permeability. To mimic the intestinal environment, use of biorelevant media may provide valuable information on in vivo drug permeation. The present study aims at improving the novel biomimetic phospholipid vesicle-based permeation assay’s (PVPAbiomimetic) biorelevance by investigating the applicability of the biorelevant media; fasted state simulated intestinal fluid (FaSSIF) and fed state simulated intestinal fluid (FeSSIF). The FaSSIF and FeSSIF’s influence on the permeability of the model drugs acyclovir, indomethacin, griseofulvin and nadolol was then assessed. The barriers’ robustness in terms of storage stability was also evaluated. The barriers were found to maintain their integrity in presence of FaSSIF and FeSSIF. The model drugs showed changes in permeability in presence of the different simulated intestinal fluids that were in agreement with previous reports. Moreover, the barrier showed improved storage stability by maintaining its integrity for 6months. Altogether, this study moves the PVPAbiomimetic an important step towards a better in vitro permeability model for use in drug development.

Biorelevant media resistant co-culture model mimicking permeability of human intestine

Cell culture models are currently used to predict absorption pattern of new compounds and formulations in the human gastro-intestinal tract (GIT). One major drawback is the lack of relevant apical incubation fluids allowing mimicking luminal conditions in the GIT. Here, we suggest a culture model compatible with biorelevant media, namely Fasted State Simulated Intestinal Fluid (FaSSIF) and Fed State Simulated Intestinal Fluid (FeSSIF). Co-culture was set up from Caco-2 and mucus-secreting HT29-MTX cells using an original seeding procedure. Viability and cytotoxicity assays were performed following incubation of FeSSIF and FaSSIF with co-culture. Influence of biorelevant fluids on paracellular permeability or transporter proteins were also evaluated. Results were compared with Caco-2 and HT29-MTX monocultures. While Caco-2 viability was strongly affected with FeSSIF, no toxic effect was detected for the co-cultures in terms of viability and lactate dehydrogenase release. The addition of FeSSIF to the basolateral compartment of the co-culture induced cytotoxic effects which suggested the apical mucus barrier being cell protective. In contrast to FeSSIF, FaSSIF induced a slight increase of the paracellular transport and both tested media inhibited partially the P-gp-mediated efflux in the co-culture. Additionally, the absorptive transport of propranolol hydrochloride, a lipophilic β-blocker, was strongly affected by biorelevant fluids. This study demonstrated the compatibility of the Caco-2/HT29-MTX model with some of the current biorelevant media. Combining biorelevant intestinal fluids with features such as mucus secretion, adjustable paracellular and P-gp mediated transports, is a step forward to more realistic in-vitro models of the human intestine.

A study on the inhibitory mechanism for cholesterol absorption by α-cyclodextrin administration.

Background: Micelle formation of cholesterol with lecithin and bile salts is a key process for intestinal absorption of lipids. Some dietary fibers commonly used to reduce the lipid content in the body are thought to inhibit lipid absorption by binding to bile salts and decreasing the lipid solubility. Amongst these, α-cyclodextrin (α-CD) is reportedly one of the most powerful dietary fibers for decreasing blood cholesterol. However, it is difficult to believe that α-CD directly removes cholesterol because it has a very low affinity for cholesterol and its mechanism of action is less well understood than those of other dietary fibers. To identify this mechanism, we investigated the interaction of α-CD with lecithin and bile salts, which are essential components for the dissolution of cholesterol in the small intestine, and the effect of α-CD on micellar solubility of cholesterol.Results: α-CD was added to Fed-State Simulated Intestinal Fluid (FeSSIF), and precipitation of a white solid was observed. Analytical data showed that the precipitate was a lecithin and α-CD complex with a molar ratio of 1:4 or 1:5. The micellar solubility of cholesterol in the mixture of FeSSIF and α-CD was investigated, and found to decrease through lecithin precipitation caused by the addition of α-CD, in a dose-dependent manner. Furthermore, each of several other water-soluble dietary fibers was added to the FeSSIF, and no precipitate was generated.Conclusion: This study suggests that α-CD decreases the micellar solubility of cholesterol in the lumen of the small intestine via the precipitation of lecithin from bile salt micelles by complex formation with α-CD. It further indicates that the lecithin precipitation effect on the bile salt micelles by α-CD addition clearly differs from addition of other water-soluble dietary fibers. The decrease in micellar cholesterol solubility in the FeSSIF was the strongest with α-CD addition.

Mechanism of Chemical Degradation and Determination of Solubility by Kinetic Modeling of the Highly Unstable Sesquiterpene Lactone Nobilin in Different Media

The objective of this work was first to investigate the chemical degradation of the sesquiterpene lactone nobilin and determine its solubility under conditions of concurrent degradation for partially amorphous starting material; second, to determine the effect of biorelevant media used in the in vitro measurement of intestinal absorption on degradation and solubility of nobilin. Purely aqueous medium (aq-TMCaco ), fasted and fed state simulated intestinal fluid (FaSSIF-TMCaco and FeSSIF-TMCaco ), and two liposomal formulations (LiposomesFaSSIF and LiposomesFeSSIF ) with the same lipid concentration as FaSSIF-TMCaco and FeSSIF-TMCaco were used. Degradation products were identified by nuclear magnetic resonance and X-ray crystallography and the order of reaction kinetics was determined. Solubility was deduced with a mathematical model encompassing dissolution, degradation, and reprecipitation kinetics that took into account particle size distribution of the solid material. Degradation mechanism of nobilin involved water-catalyzed opening of the lactone ring and transannular cyclization resulting in five degradation products. Degradation followed first-order kinetics in aq-TMCaco and FaSSIF-TMCaco , and higher-order kinetics in FeSSIF-TMCaco and the two liposomal formulations, whereas degradation in the latter media was diminished. Solubility of nobilin increased in the order: aq-TMCaco < FaSSIF-TMCaco , < LiposomesFaSSIF < FeSSIF-TMCaco < LiposomesFeSSIF . Improvement of stability and solubility was consistent with the incorporation of the nobilin molecule into colloidal lipid particles. The developed kinetic model is proposed to be a useful tool for deducing solubility under dynamic conditions.

Use of biorelevant media for assessment of a poorly soluble weakly basic drug in the form of liquisolid compacts: in vitro and in vivo study

The purpose of this work is to use biorelevant media to evaluate the robustness of a poorly water soluble weakly basic drug to variations along the gastrointestinal tract (GIT) after incorporation in liquisolid compacts and to assess the success of these models in predicting the in vivo performance. Liquisolid tablets were prepared using mosapride citrate as a model drug. A factorial design experiment was used to study the effect of three factors, namely: drug concentration at two levels (5% and 10%), carriers at three levels (avicel, mannitol and lactose) and powder excipients ratio (R) of the coating material at two levels (25 and 30). The in vitro dissolution media utilized were 0.1 N HCl, hypoacidic stomach model and a transfer model simulating the transfer from the stomach to the intestine. All compacts released above 95% of drug after 10 min in 0.1 N HCl. In the hypoacidic model, the compacts with R 30 were superior compared to R 25, where they released >90% of drug after 10 min compared to 80% for R 25. After the transfer of the optimum compacts from Simulated gastric fluid fast (SGFfast) to fasted state simulated intestinal fluid, slight turbidity appeared after 30 min, and the amount of drug dissolved slightly decreased from 96.91% to 90.59%. However, after the transfer from SGFfast to fed state simulated intestinal fluid, no turbidity or precipitation occurred throughout time of the test (60 min). In vivo pharmacokinetic study in human volunteers proved the success of the in vitro models with enhancement of the oral bioavailability (121.20%) compared to the commercial product.

Lecithin-linker formulations for self-emulsifying delivery of nutraceuticals.

Lecithin-linker microemulsions are formulations produced with soybean lecithin in combination with a highly lipophilic (lipophilic linker) and highly hydrophilic (hydrophilic linkers) surfactant-like additives. In this work, lecithin-linker systems were formulated to produce self-emulsifying delivery systems for β-carotene and β-sitosterol. The concentration of the lipophilic linker, sorbitan monooleate, was adjusted to minimize the formation of liquid crystals. The concentration of hydrophilic linkers, decaglyceryl caprylate/caprate and PEG-6-caprylic/capric glycerides, was gradually increased (scanned) until single phase clear microemulsions were obtained. For these scans, the oil (ethyl caprate) to water ratio was set to 1. The single phase, clear microemulsions were diluted with fed-state simulated intestinal fluid (FeSSIF) and produced stable emulsions, with drop sizes close to 200 nm. Using pseudo-ternary phase diagrams to evaluate the process of dilution of microemulsion preconcentrates (mixtures of oil, lecithin and linkers with little or no water) with FeSSIF, it was determined that self-emulsifying systems are obtained when the early stages of the dilution produce single phase microemulsions. If liquid crystals or multiple phase systems are obtained during those early stages, then the emulsification yields unstable emulsions with large drop sizes. An in vitro permeability study conducted using a Flow-Thru Dialyzer revealed that stable emulsions with drop sizes of 150-300 nm produce large and irreversible permeation of β-carotene to sheep intestine. On the other hand, unstable emulsions produced without the linker combination separated in the dialyzer chamber.

In Vitro and In Situ Evaluation of pH-Dependence of Atazanavir Intestinal Permeability and Interactions with Acid-Reducing Agents

The objectives of this study were to evaluate the effects of intestinal lumen pH, food intake, and acid-reducing agents on the intestinal permeability of atazanavir, an HIV-1 protease inhibitor. Atazanavir permeability across Caco-2 cell monolayers (P app) and in situ steady-state permeability across rat jejunum and ileum (P eff) were evaluated in buffers of varied pH (4.5-8.5), in fasted- or fed-state simulated intestinal fluid, or in presence of acid-reducing drugs (e.g., omeprazole). In vitro accumulation and apical-to-basolateral P app of atazanavir increased with decreasing pH. This effect appeared to be associated with lower atazanavir efflux by P-glycoprotein at acidic pH (5.5) compared to neutral pH. In situ atazanavir P eff across rat jejunum and ileum also decreased 2.7 and 2.3-fold, respectively, when pH was increased from 4.5 to 8.5. Several acid-reducing agents (e.g., omeprazole) moderately inhibited atazanavir efflux in Caco-2 monolayers; however, this effect was not observed in situ. Fed-state buffer significantly increased atazanavir apical-to-basolateral P app (p < 0.001) and in situ P eff (p < 0.05) compared to fasted-state buffer. Atazanavir permeability is sensitive to changes in intestinal lumen pH. This pH-sensitivity may contribute to atazanavir clinical interactions with acid-reducing agents and variable oral bioavailability.

A simplified method to screen for in-vivo performance of oral lipid formulations

To develop a simplified in-vitro screening method for oral lipid-based formulations using intestinal biorelevant media including lipolysis, as an alternative to pH-stat lipolysis models. Fasting state simulated intestinal fluid version 2 (FaSSIF-V2) and early fed state simulated intestinal fluid (FeSSIF) were modified for use in a simplified lipolysis screening method. This screening method consists of the following steps: dispersion of the lipid formulation in biorelevant media; incubation of dispersions on an orbital shaker for 60 min at 37°C; ultracentrifugation of dispersions and drug assay of supernatants. This method was evaluated using four lipid-based formulations containing danazol, which had previously been assessed by in-vitro pH-stat lipolysis and compared in an in-vivo study in dogs. Biorelevant media were modified under consideration of both physiological and practical aspects, including adjustment of the pH to 6.5, the addition of calcium ions and the addition of 100 U/ml porcine pancreatin to enable lipolysis of a test formulation. Using a modified FaSSIF-V2, the same rank order in performance of four danazol formulations as previously observed in a pH-stat model was observed, and these results also reflected the in-vivo study results. The results in modified early FeSSIF suggested that there would be a change in the rank order of formulation performance in the fed state compared with the fasted state. By comparing the formulation behaviour in the presence and absence of pancreatin, it was concluded that dispersion is more important than lipolysis for precipitation from the formulation in the fasted state, but that lipolysis is predicted to increase in relevance in the fed state. The new, simplified method for lipolysis enables a more efficient screening for the in-vivo performance of lipid formulations in the fasted state and enables a prediction of formulation behaviour in both the fed and fasted states. An additional advantage of the method is that the relative influence of lipolysis and dispersion on drug release can be directly compared.

Solubility Profiling of HIV Protease Inhibitors in Human Intestinal Fluids

The present study pursued to profile the intestinal solubility of nine HIV protease inhibitors (PIs) in fasted- and fed-state human intestinal fluids (FaHIF, FeHIF) aspirated from four volunteers. In addition, the ability of fasted- and fed-state simulated intestinal fluids (FaSSIF, FeSSIF) to predict the intestinal solubility was evaluated. All PIs were poorly soluble in FaHIF (from 7 μM for ritonavir to 327 μM for darunavir) and FeHIF (from 15 μM for atazanavir to 409μM for darunavir). For four of nine PIs, food intake significantly enhanced the solubilizing capacity of intestinal fluids (up to 18.4-fold increase for ritonavir). The intersubject variability (average coefficient of variance CVfed = 60.6%, CVfasted = 40.4%) was higher as compared with the intrasubject variability (CVfed = 41.3%, CVfasted = 20.5%). PI solubilities correlated reasonably well between FaSSIF and FaHIF (R = 0.817), but not between FeSSIF and FeHIF (R = 0.617). To conclude, postprandial conditions increased the inter- and intrasubject variability of the PIs. The inability of FeSSIF to accurately predict the FeHIF solubility emphasizes the need for a multivariate approach to determine solubility profiles, taking into account solid-state characteristics, pH, mixed bile acid/phospholipid micelles, and digestive products.

Solubilization thermodynamics of ibuprofen in modified and classical FeSSIF biorelevant media

Abstract Some thermodynamic information related to the transfer of ibuprofen (IBP) between aqueous systems at pH 5.0 and micellar systems, in some biorelevant media, is reported. For this purpose, the apparent solubility of IBP at different temperatures, in the modified and classical Fed State Simulated Intestinal Fluid (FeSSIF) media, at different concentrations of sodium taurocholate and phosphatidylcholine, was studied. It is observed that temperature and surfactant concentration affected the apparent solubility of this drug in these aqueous media. The solubility results were used to determine the micelle partition coefficients expressed in mole fraction ( K m/w X ) in both media. For modified FeSSIF, K m/w X values varied from 8102 at 293.15 to 5987 at 313.15 K, whereas for classical FeSSIF, this property varied from 11,551 to 8540, considering the same temperatures. The temperature dependence of solubility and micelle partition coefficient allowed the calculation of the respective thermodynamic quantities of transfer of IBP from the aqueous media to the micellar pseudo-phases. Gibbs energies and enthalpies were negative, whereas entropies were positive, in a different way to the IBP solubilization behavior in the modified and classical Fasted State Simulated Intestinal Fluid (FaSSIF) biorelevant media. These results indicate spontaneous processes of transfer, and driven by enthalpy and entropy in both FeSSIF media. The thermodynamic quantities were interpreted in terms of solute–micellar interactions, especially hydrogen bonding and electrostatics interactions. Also, the critical micelle concentrations (CMC) of surfactants in each medium were determined, obtaining values of 6.7 and 3.4 mmol L − 1 , for modified and classical FeSSIF at 293.15 K, respectively.

Preparation and Comparative Release Characteristics of Three Anthocyanin Encapsulation Systems

Bilberries (Vaccinium myrtillus L.) and their major polyphenolic constituents, anthocyanins, have preventive activities inter alia against colon cancer and inflammatory bowel diseases. However, anthocyanins are sensitive to environmental conditions; thus their bioavailability in the gastrointestinal tract is an important determinant of their in vivo activity. In the study reported here, the potential benefits of encapsulating an anthocyanin rich bilberry extract (BE) on anthocyanin stability were investigated. Nonencapsulated BE and three different BE loaded microcapsule systems were incubated in simulated gastric fluid (SGF) and fed state simulated intestinal fluid (FeSSIF). After exposure to these media, released anthocyanins were identified and quantified by HPLC with UV/Vis detection. Although a rapid release of anthocyanins was observed within the first 20 min, encapsulation of anthocyanins doubled the amount of available anthocyanins after 150 min of incubation. These results illustrate the ability of encapsulation to inhibit early degradation of anthocyanins in the intestinal system.

Comparison of Particle Size and Dispersion State among Commercial Cyclosporine Formulations and Their Effects on Pharmacokinetics in Rats

Generic versions of Neoral, a microemulsion capsule formulation of cyclosporine, have been approved worldwide. However, there are concerns about the quality and efficacy of the generics due to the formulation specificity and differences in inactive ingredients among products. In this study, we measured the physicochemical properties of both the innovator and the generic formulations, and compared their bioavailability in rats. When the capsule contents were dispersed in water, the absorbance (600 nm wavelength) of generic products was higher than that of the innovator. Whereas the dispersion solution of the innovator in Fed State Simulated Intestinal Fluid was nearly clear, that of all the generics became white and turbid. The mean diameter of the microemulsion (or emulsion) formed in water by the generics was 39.7, 57.7, 64.5, and 74.8 nm, all of which were larger than that of the innovator (26.4 nm). Although the T(max) of the generics tended to be long relative to that of the innovator, there were no significant differences between the innovator and generics with regard to maximum blood concentration (C(max)) or area under the curve (AUC). These results suggest that the physicochemical differences between the innovator and the generics will not have a significant effect on C(max) or AUC, which is necessary to ensure bioequivalence.

The conflict between in vitro release studies in human biorelevant media and the in vivo exposure in rats of the lipophilic compound fenofibrate

The performance of four different lipid-based (Tween 80–Captex 200P, Tween 80–Capmul MCM, Tween 80–Caprol 3GO and Tween 80–soybean oil) and one commercially available micronized formulation (Lipanthyl Micronized ®) of the lipophilic compound fenofibrate was compared in vitro in various biorelevant media and in vivo in rats. In simulated gastric fluid without pepsin (SGF sp) and fasted state simulated intestinal fluid (FaSSIF), only Tween 80–Captex 200P system resulted in a stable fenofibrate concentration, but no supersaturation was obtained. The other three lipid based systems created fenofibrate supersaturation; however they did not maintain it. In fed state simulated intestinal fluid (FeSSIF), all lipid-based formulations resulted in complete dissolution of fenofibrate during the experiment, which represented a supersaturated state for Tween 80–Capmul MCM and Tween 80–Caprol 3GO systems. In both FaSSIF and FeSSIF, all lipid-based formulations yielded a higher fenofibrate concentration than the micronized formulation. Contrary to the in vitro results, no significant difference in the in vivo performance was observed among the four tested lipid-based formulations both in the fasted and the fed states. The in vivo performance of all lipid-based formulations was better than that of Lipanthyl Micronized ®, in the fasted as well as in the fed state. The fact that for the lipid based systems the in vitro differences in pharmaceutical performance were not translated into in vivo differences can be attributed to the continuous excretion of bile in the gastrointestinal tract of rats, causing enhanced solubilizing capacity for lipophilic drugs. This study clearly points to the conflicting situation that might arise during the preclinical phase of the development of lipid based formulations of lipophilic drugs as the performance of such systems is very often evaluated by both in vitro release studies in human biorelevant media as well as in vivo studies in rats. Care must be taken to select a relevant animal model.

Intestinal drug solubility estimation based on simulated intestinal fluids: Comparison with solubility in human intestinal fluids

The purpose of this study was to validate both existing fasted and fed state simulated intestinal fluids (FaSSIF and FeSSIF), and simpler, alternative media for predicting intraluminal drug solubility during drug discovery and early drug development. For 17 model drugs, the solubilizing capacity of FaSSIF c and FeSSIF c (subscript indicates the use of crude taurocholate) and different concentrations of d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) in phosphate buffer were correlated with the solubilizing capacity of human intestinal fluids (HIF) in the fasted and the early postprandial state. A good correlation between solubility in fasted HIF and FaSSIF c and between solubility in fed HIF and FeSSIF c was obtained, indicated by R 2 values of 0.91 and 0.86, respectively. Comparable values were obtained for 0.1% TPGS for the fasted state ( R 2 = 0.84) and 2% TPGS for the fed state ( R 2 = 0.84). Direct estimation of intestinal drug solubility by the measured solubilities in FaSSIF c and FeSSIF c was acceptable. However, better estimates were obtained by calculating solubilities based on the equations describing the relationship between solubilities in FaSSIF c and FeSSIF c as function of observed solubilities in HIF. Using this approach, the predictive value of the TPGS-based solvent system was also acceptable and comparable to that of FaSSIF c and FeSSIF c. In conclusion, FaSSIF c and FeSSIF c can be considered biorelevant media for intestinal solubility estimation. A simpler TPGS-based system may be a valuable alternative with improved stability and lower cost.

Simulated Biological Fluids with Possible Application in Dissolution Testing

This literature review is a compilation of the composition and, in most cases, the preparation instructions for simulated biological fluids that may be used as dissolution media in the evaluation of dissolution profiles and amount of drug released from pharmaceutical dosage forms. The use of simulated biological fluids can give a better understanding of the release mechanisms and possible in vivo behavior of a product and enhance the predictive capability of the dissolution testing. A summary of the major characteristics of the most used routes of administration that may affect dissolution and absorption of drug substances is presented. The routes and simulated biological fluids covered by this review are: • Parenteral: simulated body fluid and simulated synovial fluid. • Oral: fasted-state simulated gastric fluid, fed-state simulated gastric fluid, fasted-state simulated intestinal fluid, fed-state simulated intestinal fluid, simulated colonic fluid, fasted-state simulated colonic fluid, and fed-state simulated colonic fluid. • Buccal and sublingual: simulated saliva. • Pulmonary: simulated lung fluid. • Vaginal: simulated vaginal fluid and simulated semen. • Ophthalmic: simulated tears. Simulated sweat is also included. Some examples of how these simulated biological fluids are used to evaluate dosage forms are included in each route of administration. INTRODUCTION Until some decades ago, most of the conventional pharmaceutical dosage forms were essentially injections, oral formulations (solutions, suspensions, tablets, and capsules), topical creams, and ointments. With the progress of drug delivery technology, novel dosage forms have been developed to overcome the problems associated with conventional drug delivery. Research has been directed toward the use of alternatives to the parenteral route for drugs that cannot be delivered orally. Potential alternative portals of drug entry to the systemic circulation include buccal, sublingual, nasal, pulmonary, and vaginal routes, among others. These routes of administration are also used for the local delivery of drugs directly to the site of action, with consequent reduction in the dose needed to produce a pharmacological effect, eliminating problems related to first-pass metabolism and possibly minimizing systemic side effects (1). An important application of dissolution testing is the prediction of in vivo performance of pharmaceutical dosage forms. The media typically used for quality control dissolution testing do not represent all aspects of the physiological conditions of the most used routes of administration and do not allow correlation with in vivo data. Prediction of dosage form performance in the site where most of the absorption occurs requires adequate simulation of the in vivo conditions. This paper describes some characteristics of the parenteral, oral, buccal and sublingual, pulmonary, ophthalmic, and vaginal routes that are important to consider when developing simulated media. A compilation of the composition and preparation of several simulated biological fluids, including simulated sweat, with potential use as dissolution media is presented. PARENTERAL ROUTE The most used routes of injection are intramuscular, intravenous, and subcutaneous and are normally associated with short-term effects. Novel implant devices that can adequately control drug release and provide a prolonged duration of effect have been developed (1). To evaluate the in vitro drug release from these dosage forms, the dissolution medium should have ion concentrations almost equal to those of the human plasma. Table 1 describes the ionic composition of simulated body fluid (SBF) and human blood plasma. Simulated body fluid was developed initially to evaluate the surface structural changes of glass-ceramics used to manufacture artificial vertebrae, ileum, tooth roots (2), and bioactive material used to repair hard tissues such as artificial middle-ear bone and maxillofacial implants (3). This simulated body fluid was prepared using the reagents listed in Table 2. These reagents were added to 700 mL of water in the order given in Table 2, one by one, after each reagent was completely dissolved. The pH was adjusted to 7.4 with 1 M *Corresponding author. diss-18-03-03.indd 15 8/31/2011 3:22:15 PM dx.doi.org/10.14227/DT180311P15

Online monitoring of dissolution tests using dedicated potentiometric sensors in biorelevant media

The performance of the Ion-Selective Electrode (ISE) for in vitro dissolution testing using biorelevant media was evaluated in this study. In vitro dissolution was carried out using USP apparatus 2 (paddle method) with classical and with updated biorelevant media to simulate the pre- and postprandial states. The ISE was used as an analytical stand-alone system and in combination with a single-point HPLC–UV measurement. A modified method enabling the use of the ISE for very poorly soluble substances is also proposed. In terms of f 2-factor, the results acquired using the ISE for the drug diphenhydramine-HCl were found to be very similar to the results obtained by manual sampling followed by HPLC–UV analysis. In Fed State Simulated Gastric Fluid (FeSSGF), a medium containing 50% milk, the ISE is more practical since the need to separate proteins from the analyte prior to HPLC–UV analysis is eliminated. Further work will be needed to establish ISE methodology for Fed State Simulated Intestinal Fluid (FeSSIF) media. In summary, the ISE has promise as an analytical tool for research and development applications.

Drug Supersaturation in Simulated Human Intestinal Fluids Representing Different Nutritional States

It was the purpose of this study to explore supersaturation of poorly soluble drugs in human intestinal fluids (HIF), and to assess potential food effects on the creation and maintenance of supersaturation. Duodenal fluids were collected from healthy volunteers and pooled according to three nutritional states (fasted-, fed-, and fat-enriched fed state). Supersaturation was created at a fixed degree of supersaturation (DS=20) using the solvent-shift method. Fasted- and fed-state simulated intestinal fluids (FaSSIF and FeSSIF) were used as intestinal simulation media. Supersaturation in HIF showed to be stable up to a certain degree for different poorly soluble drugs. In HIF as well as in FaSSIF and FeSSIF, supersaturation appeared to be compound and medium specific. Supersaturation stability was found to be inversely proportional to the solubility in the corresponding media. Food intake affected itraconazole supersaturation positively. On the contrary, etravirine and loviride supersaturation decreased upon food intake. Supersaturation experiments in FaSSIF and FeSSIF showed similar results as in HIF for etravirine and loviride, whereas itraconazole supersaturation behaved differently in HIF versus simulation media. The present study illustrates, for the first time, that supersaturation can be created and maintained in HIF, even in the absence of excipients.

A Modified Physiological BCS for Prediction of Intestinal Absorption in Drug Discovery

In this study, the influence of physiologically relevant media on the compound position in a biopharmaceutical classification system (BCS) which resembled the intestinal absorption was investigated. Both solubility and permeability limited compounds (n = 22) were included to analyze the importance of each of these on the final absorption. Solubility was determined in three different dissolution media, phosphate buffer pH 6.5 (PhB 6.5), fasted state simulated intestinal fluid (FaSSIF), and fed state simulated intestinal fluid (FeSSIF) at 37 °C, and permeability values were determined using the 2/4/A1 cell line. The solubility data and membrane permeability values were used for sorting the compounds into a BCS modified to reflect the fasted and fed state. Three of the seven compounds sorted as BCS II in PhB 6.5 (high permeability, low solubility) changed their position to BCS I when dissolved in FaSSIF and/or FeSSIF (high permeability, high solubility). These were low dosed (20 mg or less) lipophilic molecules displaying solvation limited solubility. In contrast, compounds having solid-state limited solubility had a minor increase in solubility when dissolved in FaSSIF and/or FeSSIF. Although further studies are needed to enable general cutoff values, our study indicates that low dosed BCS Class II compounds which have solubility normally restricted by poor solvation may behave as BCS Class I compounds in vivo. The large series of compounds investigated herein reveals the importance of investigating solubility and dissolution under physiologically relevant conditions in all stages of the drug discovery process to push suitable compounds forward, to select proper formulations, and to reduce the risk of food effects.

The apparent solubilizing capacity of simulated intestinal fluids for poorly water-soluble drugs

Drug solubility testing in biorelevant media has become an indispensable tool in pharmaceutical development. Despite this importance, there is still an incomplete understanding of how poorly soluble compounds interact with these media. The aim of this study was to apply the concept of the apparent solubilization capacity to fasted and fed state simulated intestinal fluid (FaSSIF and FeSSIF, respectively). A set of non-ionized poorly soluble compounds was studied in biorelevant media prepared from an instantly dissolving complex (SIF™ Powder) at 37°C. The values of the solubilization capacity were different between FaSSIF and FeSSIF but correlated. Drug inclusion into the mixed micelles was highly specific for a given compound. The ratio of the FeSSIF to FaSSIF solubility was in particular considered and discussed in terms of the apparent solubilizing capacity. The apparent solubilization concept appears to be useful for the interpretation of biorelevant solubility tests. Further studies are needed to explore acidic and basic drugs.

Dissolution media simulating the intralumenal composition of the small intestine: physiological issues and practical aspects.

The objective of this study was to test various aspects of dissolution media simulating the intralumenal composition of the small intestine, including the suitability of the osmolality-adjusting agents and of the buffers, the substitution of crude sodium taurocholate (from ox bile) for pure sodium taurocholate and the substitution of partially hydrolysed soybean phosphatidylcholine for egg phosphatidylcholine. It was concluded that biorelevant media should contain sodium as the major cation species to better reflect the physiology. However, the use of non-physiologically relevant buffers is inevitable, especially for simulation of the fed state in the small intestine. The buffers used may affect the solubility product of weakly basic compounds with pK(a)(s) higher than about 5, the solubility of extremely highly lipophilic compounds due to salting in/out properties of the anion of the buffer and the stability of the dissolving compound. It is prudent in relevant situations to run an additional dissolution test in a modified fed state simulated intestinal fluid (FeSSIF) (or fasted state simulated intestinal fluid (FaSSIF), where applicable) containing alternative buffer species. Although a mixture of bile salts is physiologically more relevant than pure sodium taurocholate, this issue seems to be of practical importance in only a few cases. Adequate simulations in these cases will probably require the use of a number of pure substances and could substantially increase the cost of the test. Finally, unless the drug is extremely lipophilic (ca. logP> 5), egg phosphatidylcholine can be substituted by partially hydrolysed soybean phosphatidylcholine.