Physicochemical characterization of solid dispersions of the antiviral agent UC-781 with polyethylene glycol 6000 and Gelucire 44/14

The purpose of this study was to prepare and characterize solid dispersions of the antiviral thiocarboxanilide UC-781 with PEG 6000 and Gelucire 44/14 with the intention of improving its dissolution properties. The solid dispersions were prepared by the fusion method. Evaluation of the properties of the dispersions was performed using dissolution studies, differential scanning calorimetry, Fourier-transform infrared spectroscopy and X-ray powder diffraction. To investigate the possible formation of solid solutions of the drug in the carriers, the lattice spacings [d] of PEG 6000 and Gelucire 44/14 were determined in different concentrations of UC-781. The results obtained showed that the rate of dissolution of UC-781 was considerably improved when formulated in solid dispersions with PEG 6000 and Gelucire 44/14 as compared to pure UC-781. From the phase diagrams of PEG 6000 and Gelucire 44/14 it could be noted that up to approximately 25% w/w of the drug was dissolved in the liquid phase in the case of PEG 6000 and Gelucire 44/14. The data from the X-ray diffraction showed that the drug was still detectable in the solid state below a concentration of 5% w/w in the presence of PEG 6000 and Gelucire 44/14, while no significant changes in the lattice spacings of PEG 6000 or Gelucire 44/14 were observed. Therefore, the possibility of UC-781 to form solid solutions with the carriers under investigation was ruled out. The results from infrared spectroscopy together with those from X-ray diffraction and differential scanning calorimetry showed the absence of well-defined drug–polymer interactions.     

Physical stability of solid dispersions of the antiviral agent UC-781 with PEG 6000, Gelucire 44/14 and PVP K30

This paper describes the physical stability of solid dispersions of UC-781 with PEG 6000, Gelucire 44/14 and PVP K30 prepared by the solvent and melting methods. The concentration of the drug in the solid dispersions ranged from 5 to 80% w/w. The solid dispersions were stored at 4-8 and 25 degrees C (25% RH), then their physicochemical properties were analysed by differential scanning calorimetry (DSC), X-ray powder diffraction and dissolution studies as a function of storage time. The DSC curves of solid dispersions of UC-781 with PVP K30 did not show any melting peaks corresponding to UC-781 after storage, indicating no recrystallization of the drug. The DSC data obtained from PEG 6000 and Gelucire 44/14 showed some variations in melting peak temperatures and enthalpy of fusion of the carriers. It was shown that the enthalpy of fusion of PEG 6000 in the dispersions increased after storage; it was more pronounced for samples stored at 25 degrees C compared to those at 4-8 degrees C indicating the reorganization of the crystalline domains of the polymer. Similarly, the enthalpy of fusion of Gelucire 44/14 in the solid dispersions increased as a function of time. Dissolution of UC-781 from all solid dispersions decreased as a function of storage time. While these observations concurred with the DSC data for all solid dispersions, they were not reflected by X-ray powder diffraction data. It was concluded that it is the change of the physical state of the carriers and not that of the drug, which is responsible for the decreased dissolution properties of the solid dispersions investigated.     

In vitro-in vivo evaluation of supercritical processed solid dispersions: permeability and viability assessment in Caco-2 cells

In this study improvement in the bioavailability of carbamazepine (CBZ) prepared as solid dispersions by conventional solvent evaporation and supercritical fluid (SCF) processing methods was assessed, along with the elucidation of the mechanism of improved absorption. Solid dispersions of CBZ in polyethylene glycol (PEG) with either Gelucire 44/14 or vitamin E-TPGS (TPGS) were evaluated by intrinsic dissolution. Directional transport through Caco-2 cell monolayers was determined in the presence and absence of TPGS. Cell viability in presence of various concentrations of amphiphilic carriers was seen. In vivo oral bioavailability was determined in rats. The apparent intrinsic dissolution rates (IDR) of both conventional- and SCF-CBZ/PEG 8000/TPGS solid dispersions were increased by 13- and 10.6-fold, respectively, relative to neat CBZ. CBZ was not a substrate of P-glycoprotein. Higher CBZ permeability was seen in presence of 0.1% TPGS. Cell viability studies showed significant cytotoxicity only at or above 0.1% amphiphilic carrier. Supercritical treated formulation (without amphiphilic carrier) displayed oral bioavailability on par with those conventional solid dispersions augmented with amphiphilic carriers. An in vitro-in vivo correlation was seen between IDR and the AUC of the various CBZ solid dispersions. Bioavailability of CBZ was more a function of dissolution as opposed to membrane effects. Although bioavailability from SCF processed dispersions was better than conventionally processed counterparts (except for one formulation containing Gelucire 44/14), an interaction of processing method and inclusion of an amphiphilic carrier, rather by one factor alone contributed to optimal absorption, thus giving contradictory results for Gelucire 44/14 and TPGS formulations.     

The effects of common solubilizing agents on the intestinal membrane barrier functions and membrane toxicity in rats

The use of solubilizing agents to improve the solubility of poorly water-soluble drugs often results in an alteration of intestinal membrane barrier function and intestinal membrane damage. In this study, 5(6)-carboxyfluorescein (CF) and fluorescein isothiocyanate-labeled dextran (MW 4400, FD4) were used as model compounds to examine the effects of twelve common solubilizing agents, sodium taurocholate (NaTC), Labrasol, polyethylene glycol 400 (PEG 400), Transcutol P, propylene glycol, Gelucire 44/14, HCO-60, ethanol, Cremophor EL, Tween 80, 2 hydroxypropyl-β-cyclodextrin (2HP-β-CyD) and dimethylsulfoxide (DMSO), on intestinal membrane barrier function and membrane toxicity in rats. Intestinal transport and absorption of CF were examined using an in vitro diffusion chamber and an in situ closed-loop technique. The in vitro diffusion chamber study showed that only 5 and 10% (w/v) NaTC significantly increased the transport of CF across the intestinal membrane. The in situ closed-loop study showed a remarkable increase in the absorption of CF and a bioavailability of more than 30% in the presence of 5 and 10% (v/v) Labrasol, 5 and 10% (w/v) NaTC and 10% (v/v) Transcutol P. Furthermore, we evaluated the effect of NaTC and Labrasol on the intestinal absorption of FD4, a high molecular weight compound. The results indicated that the absorption of FD4 also increased in the presence of 5 and 10% (w/v) NaTC and 10% (v/v) Labrasol, suggesting that these concentrations of NaTC and Labrasol may alter the intestinal membrane barrier functions in rats. We measured the release of protein and lactate dehydrogenase (LDH) from the intestinal membrane to examine the safety of solubilizing agents in the intestine. 5 and 10% (w/v) NaTC and 5 and 10% (v/v) Gelucire 44/14 significantly increased the presence of these toxicity markers compared to the control. The LDH level was also increased in the presence of 10% (v/v) of Cremophor EL. These findings suggest that the solubilizing agents at these concentrations except for NaTC, Gelucire 44/14 and Cremophor EL are considered safe and do not cause intestinal membrane damage. In conclusion, this study provides a basic approach in screening and predicting the effects of solubilizing agents for intestinal absorption studies using drugs poorly soluble in water.     

Prediction of dissolution-absorption relationships from a dissolution/Caco-2 system

While the analysis of in vitro dissolution-in vivo absorption relationships from oral solid dosage forms provides biopharmaceutical insight and regulatory benefit, no well developed method exists to predict dissolution-absorption relationships a priori to human studies. The objective was to develop an integrated dissolution/Caco-2 system to predict dissolution-absorption relationships, and hence the contributions of dissolution and intestinal permeation to overall drug absorption for fast and slow formulations of piroxicam, metoprolol, and ranitidine. Dissolution studies were conducted on fast and slow dissolving immediate-release formulations of piroxicam, metoprolol tartrate, and ranitidine HCl. Dissolution samples were treated with concentrated buffers to render them suitable (i.e., isotonic and neutral pH) for Caco-2 monolayer permeation studies. The dissolution/Caco-2 system yielded a predicted dissolution-absorption relationship for each formulation which matched the observed relationship from clinical studies. The dissolution/Caco-2 system's prediction of dissolution or permeation rate-limited absorption also agreed with the clinical results. For example, the dissolution/Caco-2 system successfully predicted the slow piroxicam formulation to be dissolution rate-limited, and the fast piroxicam formulation to be permeation rate-limited. Moreover, the system predicted this change from dissolution rate-limited absorption for slow piroxicam to permeation rate-limited absorption for fast piroxicam, in spite of piroxicam's high permeability and low solubility. The dissolution/Caco-2 system may prove to be a valuable tool in formulation development. Broader evaluation of such a system is warranted.     

Sulfasalazine transport in in-vitro, ex-vivo and in-vivo absorption models: contribution of efflux carriers and their modulation by co-administration of synthetic nature-identical fruit extracts

Sulfasalazine is characterised by low oral bioavailability. In this study, its intestinal transport characteristics were studied in an in-vitro, ex-vivo and in-situ system. The absorptive transport of sulfasalazine across Caco-2 monolayers appeared to be lower than the secretory transport (P(app-abs) = 0.21 +/- 0.02 x 10(-6) cm s(-1) and P(app-secr) = 2.97 +/- 0.30 x 10(-6) cm s(-1), respectively). This polarity in transport of sulfasalazine was not mediated by P-glycoprotein (P-gp), as inclusion of verapamil (100 microM) did not have any effect on the transport polarity of sulfasalazine. However, inclusion of the multidrug resistance-associated protein (MRP) inhibitors benzbromarone (50 microM) and sulfinpyrazone (1 mM), and the glutathione-depleting agent chlorodinitrobenzene (100 microM), resulted in an increased absorptive transport of sulfasalazine in the Caco-2 system (P(app-abs) = 0.64 +/- 0.02, 0.51 +/- 0.04 and 0.60 +/- 0.03 x 10(-6) cm s(-1), respectively). The interference of carriers implies that, during absorption, interactions with food components may occur at the level of this carrier. Therefore, the effect of food extracts was studied in a parallel set of experiments. For two standardized nature-identical fruit extracts (pineapple and apricot extract) a concentration-dependent absorption-enhancing effect could be observed in the Caco-2 system. The functional expression of similar carriers was also demonstrated in rat ileum in the Ussing chamber system. Interaction studies with fruit extracts in the Ussing chamber system, as well as in the in-situ intestinal perfusion study, revealed a 2- to 4-fold increase in the absorptive transport of sulfasalazine. These results indicate that food components in the intestinal lumen can have a significant impact on the intestinal absorption characteristics of sulfasalazine by modulating the biochemical barrier function of the intestinal mucosa.     

Biopharmaceutics classification and intestinal absorption study of apigenin

The aim of the study was to characterize the biopharmaceutics classification system (BCS) category of apigenin (AP) using intrinsic dissolution rate (IDR) and rat intestinal permeability, and to investigate the intestinal absorption mechanism of AP in rats. In the present investigation, equilibrium solubility and intrinsic dissolution rate (IDR) of AP were estimated in phosphate buffers. Effective intestinal permeability (P(eff)) of AP was determined using single-pass intestinal perfusion (SPIP) technique in four segments (duodenum, jejunum, ileum and colon) of rat intestine at three concentrations (10, 50 and 100μg/ml). The aqueous solubility of AP in tested phosphate buffers was very poor with maximum solubility of 2.16μg/ml at pH 7.5. The IDR of AP was very low with a value of 0.006mg/min/cm(2). The minimum and maximum P(eff)s determined by SPIP were 0.198×10(-4) and 0.713×10(-4)cm/s at jejunum and duodenum site, respectively. In addition, the concentration-dependent permeability behavior was observed in the duodenum and jejunum, which suggested that AP was transported by both passive and active carrier-mediated saturable mechanism in these two intestinal segments. However, the observed concentration-independent permeability behavior in ileum and colon indicated primarily passive transport mechanism of absorption of AP in the last two intestinal segments. AP was classified as class II drug of the BCS due to its low solubility and high intestinal permeability. AP could be well absorbed in the whole intestine with the main absorption site at duodenum. The absorption of AP in four intestinal segments exhibited different transport mechanisms.     

Enhancing effect of N-octyl-O-sulfate chitosan on etoposide absorption

P-glycoprotein (P-gp), expressed in the apical membranes of the epithelial cells of the intestine, can reduce the oral bioavailability of a wide range of drugs. Many surfactants/excipients have been demonstrated to potentially increase drug absorption by inhibiting P-gp. The purpose of the present study was to evaluate the effect of N-octyl-O-sulfate chitosan (NOSC) on the absorption of etoposide (VP16), a substrate of P-gp with low water solubility. The rat intestinal circulating perfusion in situ and Caco-2 cell uptake and monolayer membrane penetration in vitro were performed to investigate the enhancing ability of NOSC in comparison with some other P-gp inhibitors. The results indicated that various concentrations of NOSC all increased the intestinal absorption of VP16 in rat jejunum and ileum obviously and there was no significant difference in ileum between the enhancing effects of NOSC and other P-gp inhibitors. The VP16 uptake of Caco-2 cell was increased by NOSC solution with different concentrations. As the NOSC concentration was close to its critical micelle concentration (CMC), the cell uptake of VP16 reached to a maximum value. Both NOSC and verapamil (Ver) enhanced dramatically the transport of VP16 from apical side to basolateral side in Caco-2 cell monolayers. Moreover, they both decreased notably the transport of VP16 from basolateral side to apical side, but this effect of NOSC was weaker than that of Ver. However, transepithelial electrical resistance (TEER) of Caco-2 cell monolayers had no significant change during the study. These studies demonstrated that NOSC had the potential by inhibiting P-gp to improve the absorption of oral drugs which were P-gp substrates.     

Development and characterisation of a self-microemulsifying drug delivery systems (SMEDDSs) for the vaginal administration of the antiretroviral UC-781

UC-781 is highly selective and potent against HIV-1. However, its hydrophobic nature (log P 5.1) and lack of aqueous solubility have limited its development as a HIV microbicide. Self-microemulsifying drug delivery systems (SMEDDSs) have been developed to enhance the water solubility and bioavailability of hydrophobic drugs, such as UC781. In this study, we show the development of UC781-loaded SMEDDS and their enhanced release of UC781 from hard gelatine capsules, when compared to UC781 powder only. The majority of antiretrovirals being evaluated as potential HIV microbicides are hydrophobic. Therefore, a SMEDDS formulation offers an alternative approach to enhancing the vaginal absorption of these microbicidal candidates.     

Enhancement of solubility and permeability of Candesartan cilexetil by using different pharmaceutical interventions

The poor solubility and wettability of Candesartan cilexetil (CAN) leads to poor dissolution and hence, low bioavailability after oral administration. The aim of the present study was to improve the solubility and dissolution rate and hence the permeability of CAN by preparing solid dispersions/inclusion complexes. Solid dispersions were prepared using PEG 6000 [hydrophilic polymer] and Gelucire 50/13 [amphiphilic surfactant] by melt agglomeration (MA) and solvent evaporation (SE) methods in different drug-to-carrier ratios, while inclusion complexes were made with hydroxypropyl-β-cyclodextrin (HP-β-CD) [complexing agent] by grinding and spray drying method. Saturation solubility method was used to evaluate the effect of various carriers on aqueous solubility of CAN. Based on the saturation solubility data, two drug-carrier combinations, PEG 6000 (MA 1:5) and HP-β-CD (1:1 M grinding) were selected as optimized formulations. FTIR, DSC, and XRD studies indicated no interaction of the drug with the carriers and provided valuable insight on the possible reasons for enhanced solubility. Dissolution studies showed an increase in drug dissolution of about 22 fold over the pure drug for PEG 6000 (MA 1:5) and 12 fold for HP-β-CD (1:1 M grinding). Ex-vivo permeability studies revealed that the formulation having the greatest dissolution also had the best absorption through the chick ileum. Capsules containing solid dispersion/ complex exhibited better dissolution profile than the marketed product. Thus, the solid dispersion/inclusion complexation technique can be successfully used for enhancement of solubility and permeability of CAN.     

Cefuroxime axetil solid dispersion with polyglycolized glycerides for improved stability and bioavailability

Objectives Cefuroxime axetil (CA), a poorly soluble, broad spectrum cephalosporin ester prodrug, is hydrolysed by intestinal esterase prior to absorption, leading to poor and variable bioavailability. The objective was therefore to formulate a stable amorphous solid dispersion of the drug with enhanced solubility and stability against enzymatic degradation. Methods Spray drying was used to obtain a solid dispersion of CA with Gelucire 50/13 and Aerosil 200 (SDCAGA), and a solid dispersion of CA with polyvinyl pyrrolidone (SDCAP); amorphous CA (ACA) was obtained by spray drying CA alone. The formulations were characterized by differential scanning calorimetry, X‐ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy studies, and compared for solubility, dissolution and bioavailability in rats. Key findings SDCAP and SDCAGA showed improved solubility and dissolution profiles owing to amorphization and formation of solid dispersions with hydrophilic carriers. The improved stability of amorphous CA in solid dispersions compared to ACA alone was attributed to hydrogen bonding interactions involving the amide of CA with the carbonyl of polyvinyl pyrrolidone in SDCAP, whereas in SDCAGA the interactions were at multiple sites involving the amide and carbonyl of CA with the carbonyl and hydroxyl of Gelucire 50/13. However, SDCAGA showed superior bioavailability compared to SDCAP, ACA and CA. Conclusions Improvement in physical stability of solid dispersions was attributed to hydrogen bonding, while improvement in bioavailability of SDCAGA compared to SDCAP, in spite of comparable solubility and dissolution profile, may be attributed to Gelucire, which utilizes intestinal esterase for lipolysis, protecting the prodrug from enzymatic degradation to its non‐absorbable base form.     

Prediction of dissolution-absorption relationships from a continuous dissolution/Caco-2 system

The objectives were 1) to design a continuous dissolution Caco-2 system to predict the dissolution-absorption relationships for fast and slow dissolving formulations of piroxicam, metoprolol tartrate, and ranitidine HCl, and compare the predicted relationships with observed relationships from clinical studies; 2) to estimate the effect of croscarmellose sodium on ranitidine dissolution-absorption relationships; and 3) to estimate the effect of solubilizing agents on piroxicam dissolution-absorption relationships. A continuous dissolution/Caco-2 system was constructed from a dissolution apparatus and a diffusion cell, such that drug dissolution and permeation across a Caco-2 monolayer would occur sequentially and simultaneously. The continuous system generally matched observed dissolution-absorption relationships from clinical studies. For example, the system successfully predicted the slow metoprolol and slow ranitidiine formulations to be permeation-rate-limited. The system predicted the slow piroxicam formulation to be dissolution-rate-limited, and the fast piroxicam formulation to be permeation-rate-limited, in spite of piroxicam’s high permeability and low solubility. Additionally, the system indicated croscarmellose sodium enhanced ranitidine permeability and predicted solubilizing agents to not modulate permeability. These results suggest a dissolution/Caco-2 system to be an experimentally based tool that may predict dissolution-absorption relationships from oral solid dosage forms, and hence the relative contributions of dissolution and permeation to oral drug absorption kinetics.     

Proliposomes of exemestane for improved oral delivery: Formulation and in vitro evaluation using PAMPA, Caco-2 and rat intestine

The aim of the present study was to develop proliposomal formulations to enhance the oral bioavailability of exemestane by improving solubility, dissolution and/or intestinal permeability. Proliposomal powder formulations were prepared using different ratios of drug (exemestane), distearoyl–phosphatidylcholine (DSPC), cholesterol and dimyristoyl–phosphatidylglycerol (DMPG) by solvent evaporation method. The effect of phospholipid composition and drug:lipid ratio on in vitro performance of proliposomes was studied. Proliposomes were characterized for their particle size distribution, thermal characteristics by differential scanning calorimetry (DSC) and dissolution behavior. Further, the formulated proliposomes were subjected to in vitro permeation or transport studies using different models such as rat intestine, parallel artificial membrane permeability assay (PAMPA) and Caco-2 cell line. Proliposomes provided enhanced exemestane dissolution due to incorporation into the phospholipid bilayers and change in the physical state from crystalline to amorphous. The in vitro transport studies in rat intestine, PAMPA and Caco-2 models revealed that the proliposomes were successful in enhancing the permeation of exemestane. These proliposomal formulations of exemestane could provide improved oral bioavailability due to enhanced solubility, permeability and hence absorption.     

Ordered mesoporous silica induces pH-independent supersaturation of the basic low solubility compound itraconazole resulting in enhanced transepithelial transport

The majority of innovative drug candidates are poorly water soluble and exhibit basic properties. This makes them highly dependent on the in vivo encountered acid–neutral pH sequence to achieve a sufficient dissolution and thus absorption. In this study, we evaluated the pH-independent generation of intraluminally induced supersaturation of the model compound itraconazole and its beneficial effect on the extent of absorption in the Caco-2 system and the rat in situ perfusion system. Local supersaturation was obtained by means of a solvent shift method and a novel formulation strategy based on ordered mesoporous silica (OMS) as a carrier. In vitro results evidenced that both methods were capable of creating a supersaturated state of itraconazole in fasted state simulated intestinal fluid (FaSSIF) when no preceding acidic dissolution was simulated. The extent of supersaturation exceeded 21.9 and 9.6 during at least 4 h for the solvent shift method and OMS as a carrier, respectively. As compared to saturation conditions (0.09 ± 0.01 μg), supersaturation induced by the solvent shift method as well as by the use of OMS increased transport across a Caco-2 cell monolayer more than 16-fold, resulting in the basolateral appearance of 2.20 ± 0.29 μg and 1.46 ± 0.03 μg itraconazole after 90 min, respectively. In the absence of an acid–neutral pH sequence, the performance of the marketed product Sporanox^® was inferior with total transport amounting to 0.12 ± 0.03 μg after 90 min. Enhanced absorption was confirmed in the in situ perfusion model where OMS was able to boost total transport of itraconazole after 60 min from 0.03 ± 0.01 nmol cm⁻¹ to 0.70 ± 0.09 nmol cm⁻¹ compared to saturated equilibrium conditions in FaSSIF. The solid dosage form Sporanox^® again failed to achieve a similar extent of absorption enhancement (0.29 ± 0.01 nmol cm⁻¹). These findings suggest that intraluminal supersaturation can be created by the use of OMS and that preceding dissolution of basic compounds in the acidic medium of the stomach is not required to allow for efficient intestinal absorption. The use of OMS appears to be a promising strategy for the delivery of especially basic low solubility compounds in patients suffering from hypochlorhydria; the pH independency may also result in a more reproducible systemic exposure.     

In vitro, ex vivo, and in situ intestinal absorption characteristics of the antiviral ester prodrug adefovir dipivoxil

Caco-2 monolayers (in vitro), rat intestinal sheets mounted in modified Ussing Chambers (ex vivo), and in situ intestinal perfusion of rat ileum were used as models to determine and compare the absorption characteristics of the antiviral agent 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA, adefovir) and its bis(pivaloyloxymethyl)-ester prodrug [bis(POM)-PMEA, adefovir dipivoxil]. Although metabolism of adefovir dipivoxil was more pronounced in the ex vivo and in situ models than in the Caco-2 system, the transport of 'total adefovir' [= adefovir dipivoxil and its metabolites mono(POM)-PMEA and adefovir] was comparable in the three models. Compared with transport of the parent compound (adefovir), use of adefovir dipivoxil resulted in a significant increase in transport of total adefovir in the in vitro ( approximately 100-fold) and the in situ ( approximately 10-fold) models; in contrast, the ex vivo method failed to demonstrate a remarkable transport enhancement when using the ester prodrug. Similar to the results obtained in the Caco-2 model, the inclusion of the P-glycoprotein inhibitor verapamil resulted in transport enhancement during in situ perfusion of rat ileum with adefovir dipivoxil; however, no effect of verapamil could be observed in the ex vivo model. The results of this study confirm the utility of both the in vitro and in situ models to assess intestinal transport and metabolism of adefovir dipivoxil. The ex vivo model appeared to be less appropriate because of its inability to discriminate transport following administration of adefovir or adefovir dipivoxil and because of the absence of an effect of verapamil on transport when using adefovir dipivoxil.     

Increased absorption of the antiviral ester prodrug tenofovir disoproxil in rat ileum by inhibiting its intestinal metabolism.

Previous studies have shown that strawberry extract increases the transepithelial transport of tenofovir disoproxil, an esterase-sensitive prodrug of the antiviral compound tenofovir (formerly PMPA), across Caco-2 monolayers. This increase in transport was at least partially due to inhibition of its intestinal metabolism. To further study the feasibility of this absorption enhancing strategy, the influence of various concentrations of strawberry extract (0-2%) on the intestinal absorption of tenofovir disoproxil (100 microM) was assessed using an in situ perfusion model with immediate blood sampling from the mesenteric vein, a model closer to the in vivo situation than the in vitro Caco-2 system. Inclusion of strawberry extract (1%) resulted in a 7-fold increase in the appearance of tenofovir equivalents. The metabolism of tenofovir disoproxil in the intestinal perfusate was significantly lower in the presence of strawberry extract (1%), showing that the metabolism of tenofovir disoproxil is reduced by the flavoring extract.     

High throughput screening of pharmacokinetics and metabolism in drug discovery (I)--establishment of assessment system for absorption to compounds with a wide diversity of physical properties

The application of combinatorial chemistry and high-throughput screening to biological targets has led to efficient identification of lead compounds in wide therapeutic areas. However, the physicochemical properties of some lead compounds are lipophilic with low water soluble. Since these parameters determine in vivo absorption, we established robust screening methods for solubility and Caco-2 membrane permeability which are applicable to our screening strategy based on the structure-pharmacokinetic parameter relationship (SPR). Of test compounds with different core structures, turbidimetric solubility and apparent solubility as determined by HPLC-UV analysis after dilution of aqueous media from DMSO stock solution was overestimated in comparison with the corresponding thermodynamic solubility obtained using a traditional shake-flask method. A new powder-dissolution method providing thermodynamic solubility similar to that in the traditional method was developed using 96-well plates for equilibrium dialysis. The throughput of the method was the almost the same as that using the apparent solubility method. In a conventional Caco-2 assay, membrane permeability (P(app)) of some lipophilic compounds was underestimated due to low solubility in the apical site and adhesion to the device, resulting in a poor relationship between the in vivo absorption fraction and the P(app) values. The addition of 0.1% Gelucire 44/14 into the apical site and 4% bovine serum albumin into the basolateral site improved the relationship. These newly developed methods are therefore useful to optimize lead compounds with less water solubility and high lipophilicity on the basis of SPR.     

Improved solubility and dissolution rate of piroxicam using gelucire 44/14 and labrasol

Piroxicam is a nonsteroidal anti-inflammatory drug that is characterized by low solubility-high permeability. The present study was designed to improve the dissolution rate of piroxicam at the physiological pH's through its increased solubility by preparing semi-solid dispersions of drug using Gelucires and Labrasol. These excipients are essentially characterized by their melting points and HLB (hydrophilic-lipophilic balance) values. The dissolution tests of the preparations were performed in the media with different pH's. Differential scanning calorimetry (DSC), were used to examine the interaction between piroxicam and excipients. Gelucire 44/14 and Labrasol at the concentration of 15% w/v in water provided 20- and 50-fold increase in the solubility of piroxicam, respectively. The semi-solid dispersion containing 1/20 of drug/excipient mixture (20% Gelucire 44/14 and 80% Labrasol in w/w) produced the dissolution not less than 85% of piroxicam within 30 min in each dissolution media (simulated gastric fluid (SGF), pH 1.2; phosphate buffers, pH 4.5 and 6.8; and water). DSC analysis of this semi-solid dispersion indicated that there was no chemical reaction between the drug and excipients, and that a solid-state solution of piroxicam with excipient formed.     

Soluplus® as an effective absorption enhancer of poorly soluble drugs in vitro and in vivo

As many new active pharmaceutical ingredients are poorly water soluble, solubility enhancers are one possibility to overcome the hurdles of drug dissolution and absorption in oral drug delivery. In the present work a novel solubility enhancing excipient (Soluplus®) was tested for its capability to improve intestinal drug absorption. BCS class II compounds danazol, fenofibrate and itraconazole were tested both in vivo in beagle dogs and in vitro in transport experiments across Caco-2 cell monolayers. Each drug was applied as pure crystalline substance, in a physical mixture with Soluplus®, and as solid solution of the drug in the excipient. In the animal studies a many fold increase in plasma AUC was observed for the solid solutions of drug in Soluplus® compared to the respective pure drug. An effect of Soluplus® in a physical mixture with the drug could be detected for fenofibrate. In vitro transport studies confirm the strong effect of Soluplus® on the absorption behavior of the three tested drugs. Furthermore, the increase of drug flux across Caco-2 monolayer is correlating to the increase in plasma AUC and C_max in vivo. For these poorly soluble substances Soluplus® has a strong potential to improve oral bioavailability. The applicability of Caco-2 monolayers as tool for predicting the in vivo transport behavior of the model drugs in combination with a solubility enhancing excipient was shown. Also the improvement of a solid dispersion compared to physical mixtures of the drugs and the excipient was correctly reflected by Caco-2 experiments. In the case of fenofibrate the possible improvement by a physical mixture was demonstrated, underscoring the value of the used tool as alternative to animal studies.