Dissolution of hydrocortisone in human and simulated intestinal fluids

Development of 3D printed mini-waffle shapes containing hydrocortisone for children's personalized medicine

Hydrocortisone is mainly used in the substitution treatment of adrenal insufficiency which results in a dysregulation of cortisol. Compounding of hydrocortisone capsules remains the only low-dose oral treatment suitable for the pediatric population. However, capsules often show non-compliance in mass and content uniformity. Three-dimensional printing offers the prospect of practising personalized medicine for vulnerable patients like children. The goal of this work is to develop low-dose solid oral forms containing hydrocortisone by hot-melt extrusion coupled with fused deposition modeling for the pediatric population. Formulation, design and processes temperatures were optimized to produce printed forms with the desired characteristics. Red mini-waffle shapes containing drug loads of 2, 5 and 8 mg were successfully printed. This new 3D design allow to release more than 80% of the drug in 45 minutes indicating a conventional release like the one obtained with capsules. Mass and content uniformity, hardness and friability tests complied with European Pharmacopeia specifications, despite the considerable challenge of the small dimensions of the forms. This study demonstrates that FDM can be used to produce innovative pediatric-friendly printed shapes of an advanced pharmaceutical quality to practice personalize medicine.

Embedding a Sensitive Liquid-Core Waveguide UV Detector into an HPLC-UV System for Simultaneous Quantification of Differently Dosed Active Ingredients during Drug Release

Individual dosing of pharmaceutics and personalized medicine have become important with regard to therapeutic safety. Dose adjustments, biorelevant drug release and combination of multiple active substances in one dosage form for the reduction in polymedication are essential aspects that increase the safety and acceptance of the patient’s pharmacotherapy. Therefore, not only innovative drug products but also new analytical methods are needed during the drug development phase and for quality control that can simultaneously determine different active ingredients and cover wide concentration ranges. We investigated a liquid-core waveguide UV absorbance flow cell detector coupled to an existing HPLC-UV system. A Teflon AF 2400 capillary tubing of 20 cm length was connected in series to the HPLC flow line and enabled a lower limit of quantification of 1 ng/mL pramipexole (increase in sensitivity by 20 compared to common 0.9 cm flow cells). This allowed the low-concentration of pramipexole and the higher concentrations of levodopa and benserazide occurring during drug release to be determined in a single chromatographic run within 22.5 min.

Small scale in vitro method to determine a bioequivalent equilibrium solubility range for fasted human intestinal fluid

Drug solubility is a key parameter controlling oral absorption, but intestinal solubility is difficult to assess in vitro. Human intestinal fluid (HIF) aspirates can be applied but they are variable, difficult to obtain and expensive. Simulated intestinal fluids (SIF) are a useful surrogate but multiple recipes are available and the optimum is unknown. A recent study characterised fasted HIF aspirates using a multi-dimensional approach and determined nine bioequivalent SIF media recipes that represented over ninety percent of HIF compositional variability. In this study these recipes have been applied to determine the equilibrium solubility of twelve drugs (naproxen, indomethacin, phenytoin, piroxicam, aprepitant, carvedilol, zafirlukast, tadalafil, fenofibrate, griseofulvin, felodipine, probucol) previously investigated using a statistical design of experiment (DoE) approach. The bioequivalent solubility measurements are statistically equivalent to the previous DoE, enclose literature solubility values in both fasted HIF and SIF, and the solubility range is less than the previous DoE. These results indicate that the system is measuring the same solubility space as literature systems with the lower overall range suggesting improved equivalence to in vivo solubility, when compared to DoEs. Three drugs (phenytoin, tadalafil and griseofulvin) display a comparatively narrow solubility range, a behaviour that is consistent with previous studies and related to the drugs' molecular structure and properties. This solubility behaviour would not be evident with single point solubility measurements. The solubility results can be analysed using a custom DoE to determine the most statistically significant factor within the media influencing solubility. This approach has a lower statistical resolution than a formal DoE and is not appropriate if determination of media factor significance for solubilisation is required. This study demonstrates that it is possible to assess the fasted intestinal equilibrium solubility envelope using a small number of bioequivalent media recipes obtained from a multi-dimensional analysis of fasted HIF. The derivation of the nine bioequivalent SIF media coupled with the lower measured solubility range indicate that the solubility results are more likely to reflect the fasted intestinal solubility envelope than previous DoE studies and highlight that intestinal solubility is a range and not a single value.

Investigating the Impact of Crohn's Disease on the Bioaccessibility of a Lipid-Based Formulation with an In Vitro Dynamic Gastrointestinal Model

The aim of the study was to investigate the impact of Crohn's disease (CD) on the performance of a lipid-based formulation of ciprofloxacin in a complex gastrointestinal simulator (TIM-1, TNO) and to compare the luminal environment in terms of bile salt and lipid composition in CD and healthy conditions. CD conditions were simulated in the TIM-1 system with a reduced concentration of porcine pancreatin and porcine bile. The bioaccessibility of ciprofloxacin was similar in simulated CD and healthy conditions considering its extent as well as its time course in the jejunum and ileum filtrate. Differences were observed in terms of the luminal concentration of triglycerides, monoglycerides, and fatty acids in the different TIM-1 compartments, indicating a reduction and delay in the lipolysis of formulation excipients in CD. The quantitative analysis of bile salts revealed higher concentrations for healthy conditions (standard TIM-1 fasted-state protocol) in the duodenum and jejunum TIM-1 compartments compared to published data in human intestinal fluids of healthy subjects. The reduced concentrations of bile salts in simulated CD conditions correspond to the levels observed in human intestinal fluids of healthy subjects in the fasted state.A lipidomics approach with ultra performance liquid chromatography (UPLC)/mass spectrometry (MS) has proven to be a time-efficient method to semiquantitatively analyze differences in fatty acid and bile salt levels between healthy and CD conditions. The dynamic luminal environment in CD and healthy conditions after administration of a lipid-based formulation can be simulated using the TIM-1 system. For ciprofloxacin, an altered luminal lipid composition had no impact on its performance indicating a low risk of altered performance in CD patients.

Exploring the Impact of Intestinal Fluid Components on the Solubility and Supersaturation of Danazol

Eleven simulated intestinal fluids (SIF) were designed using a Design of Experiment (DoE) approach. The DoE SIF covered a range of compositions of fasted state human intestinal fluid (FaHIF) with regard to pH, bile salt (BS), and phospholipid (PL). Using the model compound danazol, the apparent crystalline solubility (aCS) and apparent amorphous solubility (aAS), as well as the supersaturation propensity was determined in the DoE SIF media. The aCS of danazol was dependent on the composition of the SIF, with PL as the main factor, and a small effect from BS and an interaction between BS and PL. From the DoE solubility data a model was derived, which could predict aCS in commercially available SIF (FaSSIF-V1 and -V2) and in a range of FaHIF. The aAS of danazol was differently affected by the SIF composition than the aCS; PL was again the main factor influencing the aAS, but interactions between BS and pH, as well as pH and PL were also important. The supersaturation propensities of danazol in the DoE SIF media were affected by the same factors as the aCS. Hence, the supersaturation behaviour and aCS of danazol, were found to be closely related.

Characterisation of fasted state gastric and intestinal fluids collected from children

Fundamental knowledge about the composition of intestinal fluids in paediatric populations is currently unavailable. This study aimed to characterise gastric and intestinal fluid from paediatric populations. Gastric and intestinal fluid samples were obtained during routine clinical endoscopy from paediatric patients at a large teaching hospital. These fluids were characterised to measure the pH; buffer capacity; osmolality; bile acid concentration and composition. A total of 55 children were recruited to the study aged from 11 months to 15 years of age where 53 gastric fluid samples and 40 intestinal fluid samples were obtained. pH values recorded ranged from pH 0.57 to 11.05 (median: 2.50) in gastric fluids and from 0.89 to 8.97 (median: 3.27) in intestinal fluids. The buffer capacity did not change significantly between gastric and intestinal fluids with median values of 12 mM/L/ΔpH for both fluids. Gastric fluid osmolality values ranged from 1 to 615 mOsm/kg, while intestinal fluid values ranged from 35 to 631 mOsm/kg. Gastric fluid bile acid concentrations ranged from 0.002 to 2.3 mM with a median value of 0.017 mM whilst intestinal fluid bile acid concentrations ranged from 0.0008 to 3.3 mM with a median value of 0.178 mM. Glycocholate; taurocholic acid; glycochenodeoxycholate and taurochenodeoxycholate were the most commonly identified bile acids within paediatric intestinal fluids. All compositional components were associated with large inter-individual variability. Further work is required to develop simulated paediatric media and to explore the impact of these media on drug solubility and dissolution.

A Biopredictive In Vitro Approach for Assessing Compatibility of a Novel Pediatric Hydrocortisone Drug Product within Common Pediatric Dosing Vehicles

Purpose

The objective of the present work was to screen whether a novel pediatric hydrocortisone granule formulation can be co-administered with common food matrices and liquids.

Methods

Pediatric hydrocortisone granules were studied using a biopredictive in vitro approach. Experiments included an in situ chemical compatibility study of active ingredient and drug product with liquid dosing vehicles and soft foods commonly ingested by infants, pre-school- and school children. Drug solubility and stability experiments in the different vehicle types and, drug release/dissolution experiments mimicking age-related pediatric gastric conditions after administering the hydrocortisone granules together with the dosing vehicles and after different exposure/mixing times were performed.

Results

In the simulated dosing scenarios applied in dissolution experiments, in vitro dissolution in gastric conditions was rapid and complete. Results of the chemical compatibility/stability studies indicated that mixing with the different dosing vehicles studied should not be an issue regarding drug degradation products.

Conclusions

A novel in vitro approach ensuring a proper risk assessment of the use of dosing vehicles in the administration of pediatric dosage forms was established and applied to a novel pediatric hydrocortisone drug product. The studied dosing vehicles were shown to not alter performance of the drug product and are thus considered suitable for administration with hydrocortisone granules.

Multidimensional analysis of human intestinal fluid composition

The oral administration of solid dosage forms is the commonest method to achieve systemic therapy and relies on the drug's solubility in human intestinal fluid (HIF), a key factor that influences bioavailability and biopharmaceutical classification. However, HIF is difficult to obtain and is known to be variable, which has led to the development of a range of simulated intestinal fluid (SIF) systems to determine drug solubility in vitro. In this study we have applied a novel multidimensional approach to analyse and characterise HIF composition using a published data set in both fasted and fed states with a view to refining the existing SIF approaches. The data set provided 152 and 172 measurements of five variables (total bile salt, phospholipid, total free fatty acid, cholesterol and pH) in time-dependent HIF samples from 20 volunteers in the fasted and fed state, respectively. The variable data sets for both fasted state and fed state are complex, do not follow normal distributions but the amphiphilic variable concentrations are correlated. When plotted 2-dimensionally a generally ellipsoid shaped data cloud with a positive slope is revealed with boundaries that enclose published fasted or fed HIF compositions. The data cloud also encloses the majority of fasted state and fed state SIF recipes and illustrates that the structured nature of design of experiment (DoE) approaches does not optimally cover the variable space and may examine media compositions that are not biorelevant. A principal component analysis in either fasted or fed state in combination with fitting an ellipsoid shape to enclose the data results in 8 points that capture over 95% of the compositional variability of HIF. The variable's average rate of concentration change in both fasted state and fed state over a short time scale (10 min) is zero and a Euclidean analysis highlights differences between the fasted and fed states and among individual volunteers. The results indicate that a 9-point DoE (8 + 1 central point) could be applied to investigate drug solubility in vitro and provide statistical solubility limits. In addition, a single point could provide a worst-case solubility measurement to define the lowest biopharmaceutical classification boundary or for use during drug development. This study has provided a novel description of HIF composition. The approach could be expanded in multiple ways by incorporation of further data sets to improve the statistical coverage or to cover specific patient groups (e.g., paediatric). Further development might also be possible to analyse information on the time dependent behaviour of HIF and to guide HIF sampling and analysis protocols.

Small scale design of experiment investigation of equilibrium solubility in simulated fasted and fed intestinal fluid

It is widely recognised that drug solubility within the gastrointestinal tract (GIT) differs from values determined in a simple aqueous buffer and to circumvent this problem measurement in biorelevant fluids is determined. Biorelevant fluids are complex mixtures of components (sodium taurocholate, lecithin, sodium phosphate, sodium chloride, pancreatin and sodium oleate) at various concentrations and pH levels to provide systems simulating fasted (FaSSIF) or fed (FeSSIF) intestinal media. Design of Experiment (DoE) studies have been applied to investigate FaSSIF and FeSSIF and indicate that a drug's equilibrium solubility varies over orders of magnitude, is influenced by the drug type and individual or combinations of media components, with some of these interactions being drug specific. Although providing great detail on the drug media interactions these studies are resource intensive requiring up to ninety individual experiments for FeSSIF. In this paper a low sample number or reduced DoE system has been investigated by restricting components with minimal solubility impact to a single value and only investigating variations in the concentrations of sodium taurocholate, lecithin, sodium oleate, pH and additionally in the case of fed media, monoglyceride. This reduces the experiments required to ten (FaSSIF) and nine (FeSSIF). Twelve poorly soluble drugs (Ibuprofen, Valsartan, Zafirlukast, Indomethacin, Fenofibrate, Felodipine, Probucol, Tadalafil, Carvedilol, Aprepitant, Bromocriptine and Itraconazole) were investigated and the results compared to published DoE studies and literature solubility values in human intestinal fluid (HIF), FaSSIF or FeSSIF. The solubility range determined by the reduced DoE is statistically equivalent to the larger scale published DoE results in over eighty five percent of the cases. The reduced DoE range also covers HIF, FaSSIF or FeSSIF literature solubility values. In addition the reduced DoE provides lowest measured solubility values that agree with the published DoE values in ninety percent of the cases. However, the reduced DoE only identified single and in some cases none of the major components influencing solubility in contrast to the larger published DoE studies which identified multiple individual components and component interactions. The identification of significant components within the reduced DoE was also dependent upon the drug and system under investigation. The study demonstrates that the lower experimental number reduces statistical power of the DoE to resolve the impact of media components on solubility. However, in a situation where only the solubility range is required the reduced DoE can provide the desired information, which will be of benefit during in vitro development studies. Further refinements are possible to extend the reduced DoE protocol to improve biorelevance and application into areas such as PBPK modelling.

Simulated, biorelevant, clinically relevant or physiologically relevant dissolution media: The hidden role of bicarbonate buffer

In-vitro dissolution testing of pharmaceutical formulations has been used as a quality control test for many years. At early drug product development, in vivo predictive dissolution testing can be used for guidance in the rational selection of candidate formulations that best fit the desired in vivo dissolution characteristics. At present, the most widely applied dissolution media are phosphate-based buffers and, in some cases, the result of dissolution tests performed in such media have demonstrated reasonable/acceptable IVIVCs. However, the presence of phosphates in human GI luminal fluids is insignificant, which makes the use of such media poorly representative of the in vivo environment. The gastrointestinal lumen has long been shown to be buffered by bicarbonate. Hence, much interest in the development of suitable biorelevant in vitro dissolution media based on bicarbonate buffer systems has evolved. However, there are inherent difficulties associated with these buffers, such as maintaining the pH throughout the dissolution test, as CO₂ tends to leave the system. Various mathematical models have been proposed to analyze bicarbonate buffers and they are discussed in this review. Approaches such as using simpler buffer systems instead of bicarbonate have been proposed as surrogate buffers to produce an equivalent buffer effect on drug dissolution on a case-by-case basis. There are many drawbacks related to simpler buffers systems including their poor in vivo predictability. Considerable discrepancies between phosphate and bicarbonate buffer dissolution results have been reported for certain dosage forms, e.g. enteric coated formulations. The role and need of bicarbonate-based buffers in quality control testing requires scientific analysis. This review also encompasses on the use of bicarbonate-based buffers as a potentially in vivo predictive dissolution medium for enteric coated dosage forms.

A quality by design approach to develop topical creams via hot-melt extrusion technology

The advantages of hot-melt extrusion technology (HME) over conventional techniques to develop topical semisolids have been established. However, this technique is not widely used for semisolid production. Therefore, the aim of this novel work was to develop creams using the melt extrusion technology while applying Quality by Design (QbD) principles to study the effects of the extrusion process parameters on the product characteristics. The model drug selected was hydrocortisone acetate. A 2³ factorial design was considered for the factor influence study, which resulted in eight formulations to be extruded. Of the process parameters considered, the temperature of zone 2 had a significant influence on the work of adhesion of the creams. A similar permeation profile was obtained for all the formulations with the formulations following a diffusion based drug release mechanism. The results from the size distribution graph indicated stable cream formulations. In conclusion, this technology coupled with a design of experiments approach could be utilized to study how the extrusion process parameters could be modified to develop consistent topical creams with ideal product characteristics.

Topography of Simulated Intestinal Equilibrium Solubility

Oral administration of a solid dosage form requires drug dissolution in the gastrointestinal tract before absorption. Solubility is a key factor controlling dissolution, and it is recognized that, within the intestinal tract, this is influenced by the luminal fluid pH, amphiphile content, and composition. Various simulated intestinal fluid recipes have been introduced to mimic this behavior and studied using a range of different experimental techniques. In this article, we have measured equilibrium solubility utilizing a novel four component mixture design (4CMD) with biorelevant amphiphiles (bile salt, phospholipid, oleate, and monoglyceride) within a matrix of three pH values (5, 6, and 7) and total amphiphile concentrations (11.7, 30.6, and 77.5 mM) to provide a topographical and statistical overview. Three poorly soluble drugs representing acidic (indomethacin), basic (carvedilol), and neutral (fenofibrate) categories have been studied. The macroscopic solubility behavior agrees with literature and exhibits an overall increasing solubility from low pH and total amphiphile concentration to high pH and total amphiphile concentration. Within the matrix, all three drugs display different topographies, which can be related to the statistical effect levels of the individual amphiphiles or amphiphile interactions on solubility. The study also identifies previously unreported three and four way factor interactions notably between bile salt, phospholipid, pH, and total amphiphile concentration. In addition, the results also reveal that solubility variability is linked to the number of amphiphiles and the respective ratios in the measurement fluid, with the minimum variation present in systems containing all four amphiphiles. The individual 4CMD experiments within the matrix can be linked to provide a possible intestinal solubility window for each drug that could be applied in PBPK modeling systems. Overall the approach provides a novel overview of intestinal solubility topography along with greater detail on the impact of the various factors studied; however, each matrix requires 351 individual solubility measurements. Further studies will be required to refine the experimental protocol in order the maximize information garnered while minimizing the number of measurements required.

Content uniformity of quartered hydrocortisone tablets in comparison with mini-tablets for paediatric dosing

OBJECTIVES

Children requiring cortisol replacement therapy are often prescribed hydrocortisone doses of 2.5 mg, but as this is commercially unavailable 10 mg tablets, with functional break lines, are split commonly in an attempt to deliver the correct dose. This study aimed to determine the dose variation obtained from quartered hydrocortisone tablets when different operators performed the splitting procedure and to ascertain whether better uniformity could be attained from mini-tablets as an alternative formulation.

METHODS

Hydrocortisone 10 mg tablets were quartered by four different operators using a standard pill splitter. Hydrocortisone 2.5 mg mini-tablets (3 mm diameter) were formulated using a wet granulation method and manufactured using a high-speed rotary press simulator. The weight and content uniformity of the quartered tablets and mini-tablets were assessed according to pharmacopoeial standards. The physical strength and dissolution profiles of the mini-tablets were also determined.

RESULTS

More than half of all quartered 10 mg tablets were outside of the ±10% of the stated US Pharmacopoeia hydrocortisone content (mean 2.34 mg, SD 0.36, coefficient of variation (CV) 15.18%) and more than 40% of the quartered tablets were outside the European Pharmacopoeia weight variation. Robust mini-tablets (tensile strengths of >4 MPa) were produced successfully. The mini-tablets passed the pharmacopoeial weight and content uniformity requirements (mean 2.54 mg, SD 0.04, CV 1.72%) and drug release criteria during in vitro dissolution testing.

CONCLUSION

This study confirmed that quartering 10 mg hydrocortisone tablets produces unacceptable dose variations and that it is feasible to produce 3 mm mini-tablets containing more accurate doses for paediatric patients.

Statistical investigation of the full concentration range of fasted and fed simulated intestinal fluid on the equilibrium solubility of oral drugs

Upon oral administration the solubility of a drug in intestinal fluid is a key property influencing bioavailability. It is also recognised that simple aqueous solubility does not reflect intestinal solubility and to optimise in vitro investigations simulated intestinal media systems have been developed. Simulated intestinal media which can mimic either the fasted or fed state consists of multiple components each of which either singly or in combination may influence drug solubility, a property that can be investigated by a statistical design of experiment technique. In this study a design of experiment covering the full range from the lower limit of fasted to the upper limit of fed parameters and using a small number of experiments has been performed. The measured equilibrium solubility values are comparable with literature values for simulated fasted and fed intestinal fluids as well as human fasted and fed intestinal fluids. The equilibrium solubility data range is statistically equivalent to a combination of published fasted and fed design of experiment data in six (indomethacin, phenytoin, zafirlukast, carvedilol, fenofibrate and probucol) drugs with three (aprepitant, tadalafil and felodipine) drugs not equivalent. In addition the measured equilibrium solubility data sets were not normally distributed. Further studies will be required to determine the reasons for these results however it implies that a single solubility measurement without knowledge of the solubility distribution will be of limited value. The statistically significant media factors which promote equilibrium solubility (pH, sodium oleate and bile salt) were in agreement with published results but the number of determined significant factors and factor interactions was fewer in this study, lecithin for example did not influence solubility. This may be due to the reduction in statistical sensitivity from the lower number of experimental data points or the fact that using the full range will examine media parameters ratios that are not biorelevant. Overall the approach will provide an estimate of the solubility range and the most important media factors but will not be equivalent to larger scale focussed studies. Further investigations will be required to determine why some drugs do not produce equivalent DoE solubility distributions, for example combined fasted and fed DoE, but this simply may be due to the complexity and individuality of the interactions between a drug and the media components.

Statistical investigation of simulated fed intestinal media composition on the equilibrium solubility of oral drugs

Gastrointestinal fluid is a complex milieu and it is recognised that gut drug solubility is different to that observed in simple aqueous buffers. Simulated gastrointestinal media have been developed covering fasted and fed states to facilitate in vitro prediction of gut solubility and product dissolution. However, the combination of bile salts, phospholipids, fatty acids and proteins in an aqueous buffered system creates multiple phases and drug solubility is therefore a complex interaction between these components, which may create unique environments for each API. The impact on solubility can be assessed through a statistical design of experiment (DoE) approach, to determine the influence and relationships between factors. In this paper DoE has been applied to fed simulated gastrointestinal media consisting of eight components (pH, bile salt, lecithin, sodium oleate, monoglyceride, buffer, salt and pancreatin) using a two level D-optimal design with forty-four duplicate measurements and four centre points. The equilibrium solubility of a range of poorly soluble acidic (indomethacin, ibuprofen, phenytoin, valsartan, zafirlukast), basic (aprepitant, carvedilol, tadalafil, bromocriptine) and neutral (fenofibrate, felodipine, probucol, itraconazole) drugs was investigated. Results indicate that the DoE provides equilibrium solubility values that are comparable to literature results for other simulated fed gastrointestinal media systems or human intestinal fluid samples. For acidic drugs the influence of pH predominates but other significant factors related to oleate and bile salt or interactions between them are present. For basic drugs pH, oleate and bile salt have equal significance along with interactions between pH and oleate and lecithin and oleate. Neutral drugs show diverse effects of the media components particularly with regard to oleate, bile salt, pH and lecithin but the presence of monoglyceride, pancreatin and buffer have significant but smaller effects on solubility. There are fourteen significant interactions between factors mainly related to the surfactant components and pH, indicating that the solubility of neutral drugs in fed simulated media is complex. The results also indicate that the equilibrium solubility of each drug can exhibit individualistic behaviour associated with the drug's chemical structure, physicochemical properties and interaction with media components. The utility of DoE for fed simulated media has been demonstrated providing equilibrium solubility values comparable with similar in vitro systems whilst also providing greater information on the influence of media factors and their interactions. The determination of a drug's gastrointestinal solubility envelope provides useful limits that can potentially be applied to in silico modelling and in vivo experiments.

Statistical investigation of simulated intestinal fluid composition on the equilibrium solubility of biopharmaceutics classification system class II drugs

A drug's solubility and dissolution behaviour within the gastrointestinal tract is a key property for successful administration by the oral route and one of the key factors in the biopharmaceutics classification system. This property can be determined by investigating drug solubility in human intestinal fluid (HIF) but this is difficult to obtain and highly variable, which has led to the development of multiple simulated intestinal fluid (SIF) recipes. Using a statistical design of experiment (DoE) technique this paper has investigated the effects and interactions on equilibrium drug solubility of seven typical SIF components (sodium taurocholate, lecithin, sodium phosphate, sodium chloride, pH, pancreatin and sodium oleate) within concentration ranges relevant to human intestinal fluid values. A range of poorly soluble drugs with acidic (naproxen, indomethacin, phenytoin, and piroxicam), basic (aprepitant, carvedilol, zafirlukast, tadalafil) or neutral (fenofibrate, griseofulvin, felodipine and probucol) properties have been investigated. The equilibrium solubility results determined are comparable with literature studies of the drugs in either HIF or SIF indicating that the DoE is operating in the correct space. With the exception of pancreatin, all of the factors individually had a statistically significant influence on equilibrium solubility with variations in magnitude of effect between the acidic and basic or neutral compounds and drug specific interactions were evident. Interestingly for the neutral compounds pH was the factor with the second largest solubility effect. Around one third of all the possible factor combinations showed a significant influence on equilibrium solubility with variations in interaction significance and magnitude of effect between the acidic and basic or neutral compounds. The least number of significant media component interactions were noted for the acidic compounds with three and the greatest for the neutral compounds at seven, with again drug specific effects evident. This indicates that a drug's equilibrium solubility in SIF is influenced depending upon drug type by between eight to fourteen individual or combinations of media components with some of these drug specific. This illustrates the complex nature of these fluids and provides for individual drugs a visualisation of the possible solubility envelope within the gastrointestinal tract, which may be of importance for modelling in vivo behaviour. In addition the results indicate that the design of experiment approach can be employed to provide greater detail of drug solubility behaviour, possible drug specific interactions and influence of variations in gastrointestinal media components due to disease. The approach is also feasible and amenable to adaptation for high throughput screening of drug candidates.

Evaluation of fasted and fed state simulated and human intestinal fluids as solvent system in the Ussing chambers model to explore food effects on intestinal permeability

The Ussing chambers model is almost exclusively used in the presence of plain aqueous phosphate buffers as solvent system. In an attempt to further elucidate the effect of luminal ingredients and postprandial conditions on intestinal permeability, pooled fasted and fed state human intestinal fluids (FaHIFpool, FeHIFpool) were used. In addition, simulated intestinal fluids of both nutritional states (FaSSIF, FeSSIF) were evaluated as possible surrogate media for HIF. The use of FaHIFpool generated a broad range of Papp values for a series of 16 model drugs, ranging from 0.03×10(-6)cm/s (carvedilol) to 33.8×10(-6)cm/s (naproxen). A linear correlation was observed between Papp values using FaSSIF and FaHIFpool as solvent system (R=0.990), justifying the use of FaSSIF as surrogate medium for FaHIF in the Ussing chambers. In exclusion of the outlier carvedilol, a strong sigmoidal relationship was found between Papp and fahuman of 15 model drugs, illustrated by correlation coefficients of 0.961 and 0.936 for FaHIFpool and FaSSIF, respectively. When addressing food effects on intestinal permeability, the use of FeHIFpool resulted in a significantly lower Papp value for nine out of sixteen compounds compared to fasting conditions. FeSSIF as solvent system significantly overestimated Papp values in FeHIFpool. To conclude, the optimized Ussing chambers model using biorelevant media as apical solvent system holds great potential to investigate food effects in a more integrative approach, taking into account drug solubilisation, supersaturation and formulation effects.

Composition and physicochemical properties of fasted-state human duodenal and jejunal fluid: a critical evaluation of the available data

Various methods of sampling and analyzing intestinal fluids have been applied over the years. In this report, data that have been published to date about the composition of fasted-state human intestinal fluid (HIF) and its physicochemical properties are summarized and the influence of the methods used to generate the data is discussed. Key physiological parameters summarized include pH, buffer capacity, osmolarity, and ionic strength in both the fasted duodenum and jejunum. Furthermore, the bile salts and phospholipids in the fasted small intestine are addressed in terms of both qualitative and quantitative composition with respect to the different types and degrees of hydroxylation of bile salts. Taurocholate, glycocholate, and glycochenodeoxycholate were identified as the main bile salts. Lysolecithin was identified as the predominant phospholipid species in fasted HIF because of the enzymatic degradation of lecithin. Together with other intestinal surfactants, such as cholesterol and free fatty acids, the influence of bile acids and phospholipids on the surface tension of fasted HIF was evaluated. A good working knowledge of all the above-mentioned parameters is important to optimize the composition of biorelevant media, with a view to improving the prediction of in vivo dissolution and release performance of drugs and dosage forms.

Improving outcomes in patients with adrenal insufficiency: a review of current and future treatments

INTRODUCTION

Adrenal insufficiency is a rare but life-threatening disease. Conventional therapy consists of glucocorticoid replacement using hydrocortisone administered two or three times daily. Although such therapy extends life expectancy, mortality is not normalized, and quality of life remains poor. This failure to restore normal health is thought to be due to the inability of conventional glucocorticoid replacement therapy to normalize total cortisol exposure and to respond to the increased need for glucocorticoids during illness and stress. Also, current management regimens do not restore or replicate the intrinsic circadian rhythm of cortisol secretion.

AREAS COVERED

This narrative review was based on a PubMed and Medline search of all English-language articles on the safety and efficacy of glucocorticoid replacement therapy in patients with adrenal insufficiency. Based on this search we discuss current treatment strategies in terms of the failure to maintain or normalize metabolism and quality of life in patients with adrenal insufficiency. The rationale for, and technology behind, the development of modified-release preparations of hydrocortisone are described, together with the evidence suggesting that hydrocortisone preparations that mimic the physiological circadian pattern of cortisol release are more effective than conventional glucocorticoid replacement therapies.

CONCLUSIONS

Modified-release hydrocortisone treatments for patients with adrenal insufficiency more closely mimic the physiological circadian pattern of cortisol secretion than conventional twice or thrice daily treatment. The available evidence suggests that these modified-release preparations should improve metabolic outcomes and quality of life.

Oral biopharmaceutics tools - time for a new initiative - an introduction to the IMI project OrBiTo

OrBiTo is a new European project within the IMI programme in the area of oral biopharmaceutics tools that includes world leading scientists from nine European universities, one regulatory agency, one non-profit research organization, four SMEs together with scientists from twelve pharmaceutical companies. The OrBiTo project will address key gaps in our knowledge of gastrointestinal (GI) drug absorption and deliver a framework for rational application of predictive biopharmaceutics tools for oral drug delivery. This will be achieved through novel prospective investigations to define new methodologies as well as refinement of existing tools. Extensive validation of novel and existing biopharmaceutics tools will be performed using active pharmaceutical ingredient (API), formulations and supporting datasets from industry partners. A combination of high quality in vitro or in silico characterizations of API and formulations will be integrated into physiologically based in silico biopharmaceutics models capturing the full complexity of GI drug absorption. This approach gives an unparalleled opportunity to initiate a transformational change in industrial research and development to achieve model-based pharmaceutical product development in accordance with the Quality by Design concept. Benefits include an accelerated and more efficient drug candidate selection, formulation development process, particularly for challenging projects such as low solubility molecules (BCS II and IV), enhanced and modified-release formulations, as well as allowing optimization of clinical product performance for patient benefit. In addition, the tools emerging from OrBiTo are expected to significantly reduce demand for animal experiments in the future as well as reducing the number of human bioequivalence studies required to bridge formulations after manufacturing or composition changes.

Regional intestinal drug permeation: biopharmaceutics and drug development

Over the last 25 years, profound changes have been seen in both the development and regulation of pharmaceutical dosage forms, due primarily to the extensive use of the biopharmaceutical classification system (BCS) in both academia and industry. The BCS and the FDA scale-up and post-approval change guidelines were both developed during the 1990s and both are currently widely used to claim biowaivers. The development of the BCS and its wide acceptance were important steps in pharmaceutical science that contributed to the more rational development of oral dosage forms. The effective permeation (Peff) of drugs through the intestine often depends on the combined outcomes of passive diffusion and multiple parallel transport processes. Site-specific jejunal Peff cannot reflect the permeability of the whole intestinal tract, since this varies along the length of the intestine, but is a useful approximation of the fraction of the oral dose that is absorbed. It appears that drugs with a jejunal Peff>1.5×10(-4)cm/s will be completely absorbed no matter which transport mechanisms are utilized. In this paper, historical clinical data originating from earlier open, single-pass perfusion studies have been used to calculate the Peff of different substances from sites in the jejunum and ileum. More exploratory in vivo studies are required in order to obtain reliable data on regional intestinal drug absorption. The development of experimental and theoretical methods of assessing drug absorption from both small intestine and various sites in the colon is encouraged. Some of the existing human in vivo data are discussed in relation to commonly used cell culture models. It is crucial to accurately determine the input parameters, such as the regional intestinal Peff, as these will form the basis for the expected increase in modeling and simulation of all the processes involved in GI drug absorption, thus facilitating successful pharmaceutical development in the future. It is suggested that it would be feasible to use open, single-pass perfusion studies for the in vivo estimation of regional intestinal Peff, but that care should be taken in the study design to optimize the absorption conditions.

Drug "supersaturation" states induced by polymeric micelles and liposomes: a mechanistic investigation into permeability enhancements

The objective of this study was to investigate if the increase in apparent solubility induced by liposomalization or micellization of the poorly soluble drug hydrocortisone (HC) would lead to an enhancement of its permeability through biological membranes. For this purpose phosphatidylcholine liposome formulations as well as d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) micelle dispersions and polyvinylpyrrolidone (PVP) supersaturated solutions were prepared in order to increase the apparent solubility of HC. Both the apparent solubility of hydrocortisone (i.e. amount of drug entrapped plus non-entrapped in the carriers) as well as the concentration of molecularly dissolved drug (i.e. fraction non-entrapped into carriers, truly molecularly dissolved fraction) were characterized. Subsequently, the permeability of hydrocortisone was assessed for each type of formulation using the in vitro sheep nasal mucosa permeability assay. In all formulations where solubilizing agents are present, an enhanced flux of HC (compared to the pure drug powder suspension) is observed. The expected linear correlation between apparent solubilities and fluxes was not found, whereas, the concentrations of molecularly dissolved HC were found to be directly proportional to the respective fluxes. This is an experimental proof for the hypothesis that, of all the strategies to increase the apparent solubility of poorly soluble drugs, enhancement of the molecularly dissolved drug concentration (induction of true supersaturation) would lead to better permeation though membranes.

Lipid digestion as a trigger for supersaturation: evaluation of the impact of supersaturation stabilization on the in vitro and in vivo performance of self-emulsifying drug delivery systems

The generation of supersaturation in the gastrointestinal (GI) tract is an increasingly popular means of promoting oral absorption for poorly water-soluble drugs. The current study examined the impact of changes to the quantities of medium-chain (MC) lipid (Captex 300:Capmul MCM), surfactant (Cremophor EL) and cosolvent (EtOH), and the addition of polymeric precipitation inhibitors (PPI), on supersaturation during the dispersion and digestion of MC self-emulsifying drug delivery systems (SEDDS) containing danazol. The data suggest that digestion acts as a "trigger" for enhanced supersaturation and that solubilization/precipitation behavior is correlated with the degree of supersaturation on dispersion (S(M)DISP) or digestion (S(M)DIGEST). The ability of the formulation to maintain solubilization in vitro decreased as the S(M) of the formulation increased. PPI significantly increased supersaturation stabilization and precipitation was inhibited where S(M)DISP < 3.5 and S(M)DIGEST < 4. In the presence of polymer, some degree of supersaturation was maintained up to S(M)DIGEST ∼ 8. Differentiation in the ability of SEDDS to maintain drug solubilization stems from the ability to stabilize supersaturation and for MC SEDDS, utilization of lower drug loads, higher surfactant levels (balanced against increases in S(M)DISP), lower cosolvent and the addition of PPI enhanced formulation performance. In vivo studies confirmed the ability of PPI to promote drug exposure at moderate drug loads (40% of saturated solubility in the formulation). At higher drug loads (80% saturation) and in lipid-free SEDDS, this effect was lost, suggesting that the ability of PPIs to stabilize supersaturation in vitro may, under some circumstances, overestimate utility in vivo.

Bile salt composition is secondary to bile salt concentration in determining hydrocortisone and progesterone solubility in intestinal mimetic fluids

Simulated intestinal fluids (SIFs) used to assay the solubility of orally administered drugs are typically based on a single bile salt; sodium taurocholate (STC). The aim of this study was to develop mimetic intestinal fluids with a closer similarity to physiological fluids than those reported to date by developing a mixed bile salt (MBS) system (STC, sodium glycodeoxycholate, sodium deoxycholate; 60:39:1) with different concentrations of lecithin, the preponderant intestinal phospholipid. Hydrocortisone and progesterone were used as model drugs to evaluate systematically the influence of SIF composition on solubility. Increasing total bile salt concentration from 0 to 30 mM increased hydrocortisone and progesterone solubility by 2- and ∼25-fold, respectively. Accordingly, higher solubilities were measured in the fed-state compared to the fasted-state SIFs. Progesterone showed the greatest increases in solubility in STC and MBS systems (2-7-fold) compared to hydrocortisone (no significant change; P>0.05) as lecithin concentration was increased. Overall, MBS systems gave similar solubility profiles to STC. In conclusion, the addenda of MBS and lecithin were found to be secondary to the influence of BS concentration. These data provide a foundation for the design of more bio-similar media for pivotal decision-guiding assays in drug development and quality control settings.

Simulating fasted human intestinal fluids: understanding the roles of lecithin and bile acids

The purpose of this work is to evaluate the roles of lecithin and bile salts in a new generation of fasted simulated small intestinal fluid (FaSSIF-II), thus enhancing the closer mimic of simulated fluids to the real human intestinal fluids (HIF) in drug discovery and drug product development. To assess the effects of lecithin in FaSSIF-II, solubility studies were conducted at 37 °C using four media including first generation simulated intestinal fluid (FaSSIF-I), FaSSIF-II, phosphate pH 6.5 buffer, and HIF. A total of 24 model compounds representing a wide range of biopharmaceutic properties were included. The drug solubility values measured in the FaSSIF-II were compared with those in FaSSIF-I, pH 6.5 buffer and HIF. To assess the effects of bile acids, solubility was measured for 4 compounds in the FaSSIF-I containing five different bile acids of various concentrations. The lecithin concentration in the FaSSIF-II is lowered from 0.75 mM to 0.2 mM. The results suggested that the FaSSIF-II is a better medium to reflect HIF, compared with pH 6.5 phosphate buffer and FaSSIF-I. Solubility of neutral compounds including atovaquone, carbamazepine, cyclosporine, danazol, diethylstilbestrol, felodipine, griseofulvin and probucol in FaSSIF-II showed improvement in predicting the in vivo solubility. The relative standard deviation (SD) of solubility measurement in FaSSIF-II is comparable with FaSSIF-I. For the acidic and basic tested compounds, the FaSSIF-II performs similarly to the FaSSIF-I. Experimental results showed that the level of bile salts typically is less than 5 mM under fasted state. Among the five studied bile acids, the conjugation (glycine or taurine) has no impact on the drug solubilization, while there may be a minimal effect of the degree of hydroxylation of the steroid ring system on solubilization. The lecithin concentration of 0.2 mM in FaSSIF-II has been demonstrated to closely represent HIF, for both neutral and ionizable compounds. In the composition of simulated intestinal fluids, the structure of bile acids has minimal effect, providing the flexibility of choosing one bile salt to represent complex in vivo bile acids.

Determination of intraluminal theophylline concentrations after oral intake of an immediate-and a slow-release dosage form

The purpose of this study was to evaluate a protocol which enables determining luminal drug concentrations after oral drug administration in man. Human intestinal fluids were aspirated from two sampling sites (duodenum and jejunum) at different time points after oral intake of theophylline; an immediate- and a slow-release dosage form were used to demonstrate the feasibility of discriminating between different formulations. Osmolarity and pH of the aspirates were measured and theophylline concentrations were determined by HPLC-UV. After intake of the immediate-release formulation of theophylline, duodenal maximum concentrations up to 3 mm were reached within 30 min. Theophylline appeared to be almost completely absorbed before it reached the second sampling site in the jejunum, as observed jejunal concentrations were lower than 10% of the maximal duodenal concentrations. These results are in agreement with fast dissolution and fast absorption through the intestinal mucosa, which could be expected as theophylline belongs to class I of the Biopharmaceutical Classification System. In contrast to the immediate-release formulation, administering the slow-release dosage form resulted in a gradual appearance of theophylline, reaching maximal intestinal concentrations below 300 μm. The proposed methodology can be used to assess luminal drug concentrations and to monitor the time- and site-dependent composition of intestinal fluids after intake of an oral dosage form. This approach may contribute to a better understanding of the behaviour of oral drug formulations in the gastrointestinal tract and may be exploited to further unravel the complexity of the gastrointestinal absorption process. In addition, knowledge of luminal drug concentrations may assist in the selection of drug concentrations applied in in-vitro permeability assays.

Toward an in vivo dissolution methodology: a comparison of phosphate and bicarbonate buffers

The purpose of this research was to evaluate the difference between the pharmaceutical phosphate buffers and the gastrointestinal bicarbonates in dissolution of ketoprofen and indomethacin, to illustrate the dependence of buffer differential on biopharmaceutical properties of BCS II weak acids, and to recommend phosphate buffers equivalent to bicarbonates. The intrinsic dissolution rates of ketoprofen and indomethacin were experimentally measured using a rotating disk method at 37 degrees C in USP SIF/FaSSIF and various concentrations of bicarbonates. Theoretical models including an improved reaction plane model and a film model were applied to estimate the surrogate phosphate buffers equivalent to the bicarbonates. Experimental results show that the intrinsic dissolution rates of ketoprofen and indomethacin in USP and FaSSIF phosphate buffers are 1.5-3.0 times that in the 15 mM bicarbonates. Theoretical analysis demonstrates that the buffer differential is largely dependent on the drug pK(a) and second on solubility, and weakly dependent on the drug diffusivity. Further, in accordance with the drug pK(a), solubility and diffusivity, a simple phosphate surrogate was proposed to match an average bicarbonate value (15 mM) of the upper gastrointestinal region. Specifically, phosphate buffers of 13-15 mM and 3-4 mM were recommended for ketoprofen and indomethacin, respectively. For both ketoprofen and indomethacin, the intrinsic dissolution using the phosphate surrogate buffers closely approximated the 15 mM bicarbonate buffer. This work demonstrates the substantial difference between pharmaceutical phosphates and physiological bicarbonates in determining the drug intrinsic dissolution rates of BCS II weak acids, such as ketoprofen and indomethacin. Surrogate phosphates were recommended in order to closely reflect the in vivo dissolution of ketoprofen and indomethacin in gastrointestinal bicarbonates, which has significant implications for defining buffer systems for BCS II weak acids in developing in vitro bioequivalence dissolution methodology.

Replacement therapy of oral hydrocortisone in adrenal insufficiency: the influence of gastrointestinal factors

BACKGROUND

Replacing glucocorticoids in primary adrenal insufficiency (AI) or Addison's disease (AD) is today based on oral replacement therapy with hydrocortisone in a conventional immediate-release tablet. It is recognised that physiological gastrointestinal factors may have a strong influence on the plasma concentration-time profile of hydrocortisone. Hydrocortisone has a sufficiently high permeability in both the small and large intestine, but in vivo dissolution from the available oral product is limited at higher doses. The short elimination half-life of hydrocortisone (approximately 1.5 h) when given in traditional immediate-release dosage forms requires two or more dose administrations per day, with high peaks and low trough values in between. The endogenous secretion of cortisol from the adrenal cortex follows a distinct diurnal pattern, with increasing and high plasma levels of cortisol early in the morning (approximately 05.00-08.00 h), intermediate levels in the afternoon, low levels in the evening and a cortisol-free interval at night. There is, therefore, a clinical need for an improved drug delivery product that more closely follows the circadian pattern of cortisol in plasma.

OBJECTIVE

The pharmaceutical and biopharmaceutical properties of the dosage form containing hydrocortisone will determine intestinal absorption rate and the plasma concentration-time profile of hydrocortisone (cortisol). Factors that cause or result in pharmacokinetic variability should be understood and avoided where possible.

METHODS

A literature search was performed with the aim of covering the field of gastrointestinal drug absorption of hydrocortisone in AD.

RESULTS/CONCLUSION

Novel oral drug delivery principles for facilitation of once-daily dosing and providing a safe and physiologically based plasma concentration-time profile of hydrocortisone in replacement therapy are discussed. Development of new drug formulations is ongoing and will certainly lead to an improved replacement therapy of AD with hydrocortisone. Of special interest is a therapy based on once-daily treatment and less fluctuating plasma concentrations of hydrocortisone (cortisol).

In vitro evaluation of the dissolution behaviour of itraconazole in bio-relevant media

Drugs in the gastrointestinal tract are exposed to a medium of partially digested food, comprising mixtures of fat, protein and carbohydrate. The dissolution behaviour of itraconazole was evaluated in bio-relevant media which were developed to take this into account. Media containing milk with different fat contents, protein (albumin, casein, gluten and gelatin), carbohydrates (glucose, lactose and starch) and amino acids (lysine, glycine, alanine and aspartic acid) to mimic a digested meal and bile components (sodium taurocholate and lecithin) to represent a key endogenous digestive material were investigated. The effect of medium composition on the intrinsic dissolution rate of itraconazole was evaluated as this drug has extremely poor solubility and its bioavailability is affected by food. Dissolution tests were carried out in simple compendial media based on dilute solutions of hydrochloric acid or neutral solutions of phosphate buffer and in more complex media containing the dietary components. The data obtained showed that most of the dietary components enhanced the solubility compared to simulated gastric fluid (SGF) but to differing extents. The greatest increase in dissolution was observed with the addition of milk and albumin although an increase was also seen with other proteins, amino acids and simulated gastrointestinal fluids.

Rapid throughput solubility screening method for BCS class II drugs in animal GI fluids and simulated human GI fluids using a 96-well format

A rapid solubility-screening assay was developed with a focus on Biopharmaceutic Classification Scheme (BCS) class II drug solubility in animal and simulated human gastrointestinal (GI) fluids. The assay enables biologically promising drug leads to be evaluated for solubility limitations earlier in the drug development process, minimizes GI fluid needs, and produces in vitro solubility information with potential in vivo implications. A number of BCS II drugs were dissolved in DMSO at approximately 40 mM, and robotically distributed to a 96-well plate. The DMSO was evaporated and drugs were equilibrated with selected GI fluids, both fed and fasted states. After equilibration, precipitated wells were subjected to HPLC analysis. A spreadsheet calculated solubility automatically from HPLC output. Intra-day, inter-day, and inter-plate reproducibility were within 15% RSTD for the tested drugs with the primary source of variability being injection precision of our injector system. The reported solubility from screening assays was well correlated with literature data (r(2) = 0.80) with a slope of 0.86 and (r(2) = 0.99) with a slope of 0.89. This screening assay converts conventional solubility measurements to a 96-well format for increased throughput (>12 samples/h), reduces fluid needs, and minimizes drug consumption.

Lipid excipients and delivery systems for pharmaceutical development: a regulatory perspective

The use of lipid-based dosage forms for enhancement of drug absorption or delivery has drawn considerable interest from pharmaceutical scientists. The unique characteristics of these dosage forms, however, present significant challenges to pharmaceutical industry and regulatory agencies in many ways. For example, safety assessment is necessary when the use of a new lipid excipient is considered. An important question for lipid formulation is whether the drug remains in solubilised form along the gastrointestinal (GI) tract after it is administered. Certain lipid excipients and surfactants have been reported to change intestinal permeability or interfere with enzyme/transporter activity, thereby affecting drug bioavailability. The potential influence of biopharmaceutical and/or pathophysiological factors on the drug or lipid excipient(s) needs to be explored. For a complex lipid-based dosage form, the conventional in vitro dissolution methods may not be appropriate for predicting in vivo performance in view of the convoluted GI processing of the lipid vehicle and formulation Of paramount importance is to identify any gaps in the scientific understanding of lipid-based dosage forms so that regulatory issues can be addressed. More mechanistic studies should be encouraged to facilitate a better understanding of the pharmaceutical characteristics of lipid formulations and complex interactions between lipid excipient, drug and physiological environment. This review discusses some regulatory considerations in the use of lipid excipients and delivery systems for pharmaceutical development. Implications in the regulatory determination of pharmaceutical equivalence, bioequivalence and therapeutic equivalence are also illustrated.

Structure-Interaction Relationships between the Bile Acid GCA and Pharmaceuticals using Multivariate Data Analysis and Capillary Electrophoresis

Capillary electrophoresis (CE) has been used in an interaction study of 66 pharmaceutical compounds with the bile acid glycocholate (GCA). The developed method proved to have a high precision in its ability to determine the mobility of drugs in buffer and buffer bile acids solutions. The relationship between solute structure and interaction with GCA was studied using two-dimensional descriptors with the in-house software SELMA and a three-dimensional model (quantum mechanical descriptors) in combination with the experimental CE-interaction data. The multivariate analysis method used was projection to latent structures by means of partial least squares (PLS). Two selections of training and test set were used for evaluation of a two-class model on interaction data. In the first selection all observations were used for training set, for example, creating a model, and re-predicting the observations on the model. A successful prediction on 85% of the drugs was observed using this model. The second selection used the 21 first tested compounds in the training set, where 78% of the compounds were correctly predicted using the two-dimensional model (SELMA) on the remaining 45 compounds and, respectively, 82% using the three-dimensional (quantum mechanical) model. Analysis of the impact of the descriptors showed that descriptors relating to hydrophobicity have a large positive effect on the interaction. Descriptors relating to polar properties have a pronounced negative effect on the interaction of drugs with bile acids.

Low dose lipid formulations: effects on gastric emptying and biliary secretion

PURPOSE

Food stimulates changes to gastrointestinal secretion and motility patterns, however, the effect of smaller quantities of lipid, such as that contained in a lipid-based drug formulation, has not been detailed. This study aimed to examine the effects of small quantities of lipid on gastric emptying and biliary secretion.

METHODS

The influence of oral administration of three lipid-based formulations and a negative control formulation on gastric emptying and biliary secretion was evaluated in 16 healthy male subjects using gamma scintigraphy, ultrasonography and duodenal aspiration.

RESULTS

Low quantities (2 g) of long chain lipid stimulated gall bladder contraction and elevated intestinal bile salt, phospholipid and cholesterol levels. Changes in gastric emptying were also evident, although these did not reach statistical significance. Administration of a similar quantity of medium chain lipid, however, had little effect on gastric emptying and gallbladder contraction and did not stimulate appreciable increases in intestinal concentrations of biliary-derived lipids.

CONCLUSIONS

The quantities of long chain lipid that might be administered in a pharmaceutical formulation stimulate gallbladder contraction and elevate intestinal levels of bile salt and phospholipid. This effect is a likely contributor to the ability of lipid based formulations to enhance the absorption of poorly water-soluble drugs.

Morphological observations on a lipid-based drug delivery system during in vitro digestion

The in vitro digestion of a self nano-emulsifying drug delivery system (SNEDDS) was visualized by cryogenic transmission electron microscopy (Cryo-TEM). The dynamic lipolysis model, simulating the environment of the gastrointestinal tract in fasted conditions, was used for this purpose. The results revealed that micelles are present during the entire lipolysis process. Oil droplets from the self nano-emulsifying drug delivery system are transformed to spherical or elongated unilamellar vesicles as lipolysis progresses. Low numbers of bilamellar and open vesicles were detected. After 50% hydrolysis a decrease in the number of unilamellar vesicles and oil droplets was observed. Furthermore, the electrical properties of the oil droplets were investigated by measuring their zeta-potential values as a function of time. An increase (in absolute values) to the zeta-potential of the hydrolyzing SNEDDS droplets observed versus time implying (binding or incorporation) of the micelles to the surface. The current data emphasize that Cryo-TEM combined with the in vitro dynamic lipolysis model can offer useful information on the formation of the various colloid phases during in vitro digestion of lipid-based formulations. Furthermore, it can provide a better understanding of the in vivo behavior of these systems, as well the solubilization of lipophilic drug compounds, offering new insights for designing and optimizing oral lipid-based formulations and possibly predicting their in vivo behavior. Such methodology can be a useful tool for the strategic development of lipid-based formulations.

Structural Development of Self Nano Emulsifying Drug Delivery Systems (SNEDDS) During In Vitro Lipid Digestion Monitored by Small-angle X-ray Scattering

PURPOSE

To investigate the structural development of the colloid phases generated during lipolysis of a lipid-based formulation in an in vitro lipolysis model, which simulates digestion in the small intestine.

MATERIALS AND METHODS

Small-Angle X-Ray scattering (SAXS) coupled with the in vitro lipolysis model which accurately reproduces the solubilizing environment in the gastrointestinal tract and simulates gastrointestinal lipid digestion through the use of bile and pancreatic extracts. The combined method was used to follow the intermediate digestion products of a self nano emulsified drug delivery system (SNEDDS) under fasted conditions. SNEDDS is developed to facilitate the uptake of poorly soluble drugs.

RESULTS

The data revealed that a lamellar phase forms immediately after initiation of lipolysis, whereas a hexagonal phase is formed after 60 min. The change of the relative amounts of these phases clearly demonstrates that lipolysis is a dynamic process. The formation of these phases is driven by the lipase which continuously hydrolyzes triglycerides from the oil-cores of the nanoemulsion droplets into mono- and diglycerides and fatty acids. We propose that this change of the over-all composition of the intestinal fluid with increased fraction of hydrolyzed nanoemulsion induces a change in the composition and effective critical packing parameter of the amphiphilic molecules, which determines the phase behavior of the system. Control experiments (only the digestion medium) or the surfactant (Cremophor RH 40) revealed the formation of a lamellar phase demonstrating that the hexagonal phase is due to the hydrolysis of the SNEDDS formulation.

CONCLUSIONS

The current results demonstrate that SAXS measurements combined with the in vitro dynamic lipolysis model may be used to elucidate the processes encountered during the digestion of lipid-based formulations of poorly soluble drugs for oral drug delivery. Thus the combined methods may act as an efficient screening tool.

Lipids and lipid-based formulations: optimizing the oral delivery of lipophilic drugs

Highly potent, but poorly water-soluble, drug candidates are common outcomes of contemporary drug discovery programmes and present a number of challenges to drug development - most notably, the issue of reduced systemic exposure after oral administration. However, it is increasingly apparent that formulations containing natural and/or synthetic lipids present a viable means for enhancing the oral bioavailability of some poorly water-soluble, highly lipophilic drugs. This Review details the mechanisms by which lipids and lipidic excipients affect the oral absorption of lipophilic drugs and provides a perspective on the possible future applications of lipid-based delivery systems. Particular emphasis has been placed on the capacity of lipids to enhance drug solubilization in the intestinal milieu, recruit intestinal lymphatic drug transport (and thereby reduce first-pass drug metabolism) and alter enterocyte-based drug transport and disposition.

A century of dissolution research: from Noyes and Whitney to the biopharmaceutics classification system

Dissolution research started to develop about 100 years ago as a field of physical chemistry and since then important progress has been made. However, explicit interest in drug related dissolution has grown only since the realisation that dissolution is an important factor of drug bioavailability in the 1950s. This review attempts to account the most important developments in the field, from a historical point of view. It is structured in a chronological order, from the theoretical foundations of dissolution, developed in the first half of the 20th century, and the development of a relationship between dissolution and bioavailability in the 1950s, going to the more recent developments in the framework of the Biopharmaceutics Classification System (BCS). Research on relevant fields of pharmaceutical technology, like sustained release formulations, where drug dissolution plays an important role, is reviewed. The review concludes with the modern trends on drug dissolution research and their regulatory implications.

Canine Intestinal Contents vs. Simulated Media for the Assessment of Solubility of Two Weak Bases in the Human Small Intestinal Contents

PURPOSE

This study was conducted to assess the relative usefulness of canine intestinal contents and simulated media in the prediction of solubility of two weak bases (dipyridamole and ketoconazole) in fasted and fed human intestinal aspirates that were collected under conditions simulating those in bioavailability/bioequivalence studies.

METHODS

After administration of 250 mL of water or 500 mL of Ensure plus [both containing 10 mg/mL polyethylene glycol (PEG) 4000 as nonabsorbable marker], intestinal aspirates were collected from the fourth part of the duodenum of 12 healthy adults and from the mid-jejunum of four Labradors. Pooled samples were analyzed for PEG, pH, buffer capacity, osmolality, surface tension, pepsin, total carbohydrates, total protein content, bile salts, phospholipids, and neutral lipids. The shake-flask method was used to measure the solubility of dipyridamole and ketoconazole in pooled human and canine intestinal contents and in fasted-state-simulating intestinal fluid (FaSSIF) and fed-state-simulating intestinal fluid (FeSSIF) containing various bile salts and pH-buffering agents.

RESULTS

For both compounds, solubility in canine contents may be predictive of human intralumenal solubility in the fasting state but not in the fed state. The poor agreement of results in canine and human aspirates can be attributed to the higher bile salt content in canine bile. Solubility in FaSSIF containing a mixture of bile salts from crude bile predicted satisfactorily the intralumenal solubility of both drugs in the fasted state in humans. Solubility in FeSSIF, regardless of the identity of bile salts or of the buffering species, deviated from intralumenal values in the fed human aspirates by up to 40%. This was attributed to the lack of lipolytic products in FeSSIF, the higher bile salt content of FeSSIF, and the lower pH of FeSSIF.

CONCLUSIONS

FaSSIF containing a mixture of bile salts from crude bile, and FeSSIF containing lipolytic products and, perhaps, having lower bile salt content but slightly higher pH, should be more useful than canine intestinal aspirates for predicting intralumenal solubilities in humans.

A clinical single-pass perfusion investigation of the dynamic in vivo secretory response to a dietary meal in human proximal small intestine

PURPOSE

To investigate the gastrointestinal secretory and enzymatic responses to a liquid meal during in vivo perfusion of the proximal human jejunum.

METHODS

Human intestinal fluid was collected from the proximal jejunum by single-pass in vivo perfusion (Loc-I-Gut). The fluid was quantitatively collected at 10-min intervals during 90 min while perfusing a nutritional drink at 2 mL/min. Quantification of lipids in the fluid leaving the segment was performed by using novel chromatographic methods.

RESULTS

The overall bile acid concentration varied between 0.5 and 8.6 mM with a peak level 40 min after the start of the liquid meal perfusion. The total concentration of phospholipids was between 0.1 and 3.9 mM and there was a rapid degradation of phosphatidylcholine to lysophosphatidylcholine. The tri-, di-, monoglycerides and free fatty acid levels increased sharply in the beginning and reached steady-state levels between 7 and 9.5 mM.

CONCLUSIONS

There is a rapid secretion of bile in response to food. Most of the dietary lipids are found in the form of their degradation products in vivo in human jejunum. This novel in vivo characterization, based on direct and high-recovery sampling of intestinal fluids, forms a basis for further development of improved in vitro drug dissolution test media.

Biorelevant dissolution media: Aggregation of amphiphiles and solubility of estradiol

Biorelevant dissolution media containing bile salt and lecithin at concentrations appropriate for fed and fasted state are useful when testing oral solid formulations of poorly water-soluble drugs. Dilution of amphiphile solutions affects the aggregation state of the amphiphiles because bile salt is partitioned between the aqueous phase and the aggregates. The aim of the investigation was to study the effect of dilution on the size distribution of aggregates and its effect on the solubilization capacity. Clear buffered solutions of four intestinal amphiphiles (sodium glycocholate, lecithin, monoolein, and oleic acid) and a combination of these were prepared at high bile salt concentration. Micelles in the glycocholate solutions decreased in size when diluted. The addition of insoluble amphiphiles led to bigger micelles with no clear correlation between size of the micelles and amphiphile concentration. Dilution of the two- and four component media caused enlargement of the mixed micelles and formation of vesicles. The solubility of estradiol in the buffer solution was increased with addition of the amphiphiles. A good correlation (R(2) = 0.987) was found between estradiol solubility and mass concentration of the amphiphiles. The results demonstrate that, in the case of estradiol, the concentration of amphiphiles rather than the aggregation state determines the solubilization capacity of the medium.