Poorly Permeable Research Articles

Formulation and evaluation of ivermectin emulgel formulations

Ivermectin, a broad-spectrum antiparasitic agent, has demonstrated significant therapeutic efficacy against various skin conditions. However, it's poor skin permeability and limited stability often hinder its clinical application. Emulgel, a hybrid dosage form combining the advantages of both emulsions and gels, has emerged as a promising topical delivery system to enhance the skin permeation and stability of poorly permeable drugs. In this study, we aimed to formulate and characterize an Ivermectin emulgel to address the challenges associated with its topical delivery. The emulgel was prepared using a two-step method, involving the preparation of an oil-in-water (o/w) emulsion, which was then gelled with suitable gelling agents. Different concentrations of Ivermectin, oil phase, surfactants, and gelling agents were screened to optimize the formulation for maximum drug loading and stability. The optimized Ivermectin emulgel was characterized for its physicochemical properties, including pH, viscosity, spreadability, drug content, and rheological behavior. The study's findings support the potential application of the emulgel in treating various skin conditions caused by parasites and infectious agents. Further, in vivo studies and clinical trials are required to validate its safety and effectiveness in a clinical setting.

Solid Lipid Nanoparticles: A Potential Option for Enhancing Oral Bioavailability of Highly Soluble and Poorly Permeable (BCS Class III) Drugs.

Oral administration of drug is the most preferred one among the other routes for the majority of clinical applications. As compared to the parenteral method of administration, it has potential benefits such as increased patient compliance, fewer problems, and reduced treatment costs. Regardless of these factors, inadequate bioavailability owing to poor solubility or permeability limits the therapeutic effectiveness of orally given drugs. Though most current research focuses on BCS II (drugs with low solubility and high permeability), BCS III (drugs with high solubility and low permeability) also has poor oral bioavailability due to their limited permeability across lipid membranes and is usually administered through the parenteral route. The need for an oral alternative to parenteral administration has prompted a renewed focus on the development of innovative dosage forms that support the absorption of medicines that are poorly permeable through the intestinal epithelium. Because of their unique sizedependent feature in enhancing transmembrane permeability, ability to incorporate both lipophilic and hydrophilic drugs and biocompatible nature of components, the use of nanoparticles for improving drug bioavailability has been a focus of current study in the field of drug delivery in recent years. The lipidbased nanoparticle method presents a potential new avenue for manufacturing BCS Class III medicines with enhanced bioavailability, as poor permeability is the main issue for these agents. This research aims to assess the potential of lipid nanoparticles for improving the oral bioavailability of medicines with permeability-restricted oral absorption, such as pharmaceuticals in Biopharmaceutical Classification System (BCS) class III.

Orally Administrable Therapeutic Nanoparticles for the Treatment of Colorectal Cancer.

Colorectal cancer (CRC) is one of the most common and lethal human malignancies worldwide; however, the therapeutic outcomes in the clinic still are unsatisfactory due to the lack of effective and safe therapeutic regimens. Orally administrable and CRC-targetable drug delivery is an attractive approach for CRC therapy as it improves the efficacy by local drug delivery and reduces systemic toxicity. Currently, chemotherapy remains the mainstay modality for CRC therapy; however, most of chemo drugs have low water solubility and are unstable in the gastrointestinal tract (GIT), poor intestinal permeability, and are susceptible to P-glycoprotein (P-gp) efflux, resulting in limited therapeutic outcomes. Orally administrable nanoformulations hold the great potential for improving the bioavailability of poorly permeable and poorly soluble therapeutics, but there are still limitations associated with these regimes. This review focuses on the barriers for oral drug delivery and various oral therapeutic nanoparticles for the management of CRC.

Poly(ethylene glycol) based nanotubes for tuneable drug delivery to glioblastoma multiforme.

Glioblastoma multiforme (GBM) is the most aggressive type of malignant brain tumour, which is associated with a poor two-year survival rate and a high rate of fatal recurrence near the original tumour. Focal/local drug delivery devices hold promise for improving therapeutic outcomes for GBM by increasing drug concentrations locally at the tumour site, or by facilitating the use of potent anti-cancer drugs that are poorly permeable across the blood brain barrier (BBB). For inoperable tumours, stereotactic delivery to the tumour necessitates the development of nanoscale/microscale injectable drug delivery devices. Herein we assess the ability of a novel class of polymer nanotube (based on poly(ethylene glycol) (PEG)) to load doxorubicin (a mainstay breast cancer therapeutic with poor BBB permeability) and release it slowly. The drug loading properties of the PEG nanotubes could be tuned by varying the degree of carboxylic acid functionalisation and hence the capacity of the nanotubes to electrostatically bind and load doxorubicin. 70% of the drug was released over the first seven days followed by sustained drug release for the remaining two weeks tested. Unloaded PEG nanotubes showed no toxicity to any of the cell types analysed, whereas doxorubicin loaded nanotubes decreased GBM cell viability (C6, U-87 and U-251) in a dose dependent manner in 2D in vitro culture. Finally, doxorubicin loaded PEG nanotubes significantly reduced the viability of in vitro 3D GBM models whilst unloaded nanotubes showed no cytotoxicity. Taken together, these findings show that polymer nanotubes could be used to deliver alternative anti-cancer drugs for local therapeutic strategies against brain cancers.

Bioinspired Liposomes for Oral Delivery of Colistin to Combat Intracellular Infections by Salmonella enterica.

Bacterial invasion into eukaryotic cells and the establishment of intracellular infection has proven to be an effective means of resisting antibiotic action, as anti-infective agents commonly exhibit a poor permeability across the host cell membrane. Encapsulation of anti-infectives into nanoscaled delivery systems, such as liposomes, is shown to result in an enhancement of intracellular delivery. The aim of the current work is, therefore, to formulate colistin, a poorly permeable anti-infective, into liposomes suitable for oral delivery, and to functionalize these carriers with a bacteria-derived invasive moiety to enhance their intracellular delivery. Different combinations of phospholipids and cholesterol are explored to optimize liposomal drug encapsulation and stability in biorelevant media. These liposomes are then surface-functionalized with extracellular adherence protein (Eap), derived from Staphylococcus aureus. Treatment of HEp-2 and Caco-2 cells infected with Salmonella enterica using colistin-containing, Eap-functionalized liposomes resulted in a significant reduction of intracellular bacteria, in comparison to treatment with nonfunctionalized liposomes as well as colistin alone. This indicates that such bio-invasive carriers are able to facilitate intracellular delivery of colistin, as necessary for intracellular anti-infective activity. The developed Eap-functionalized liposomes, therefore, present a promising strategy for improving the therapy of intracellular infections.

Lipid-Based Nanocarriers for Lymphatic Transportation

The effectiveness of any drug is dependent on to various factors like drug solubility, bioavailability, selection of appropriate delivery system, and proper route of administration. The oral route for the delivery of drugs is undoubtedly the most convenient, safest and has been widely used from past few decades for the effective delivery of drugs. However, despite of the numerous advantages that oral route offers, it often suffers certain limitations like low bioavailability due to poor water solubility as well as poor permeability of drugs, degradation of the drug in the physiological pH of the stomach, hepatic first-pass metabolism, etc. The researchers have been continuously working extensively to surmount and address appropriately the inherent drawbacks of the oral drug delivery. The constant and continuous efforts have led to the development of lipid-based nano drug delivery system to overcome the aforesaid associated challenges of the oral delivery through lymphatic transportation. The use of lymphatic route has demonstrated its critical and crucial role in overcoming the problem associated and related to low bioavailability of poorly water-soluble and poorly permeable drugs by bypassing intestinal absorption and possible first-pass metabolism. The current review summarizes the bonafide perks of using the lipid-based nanocarriers for the delivery of drugs using the lymphatic route. The lipid-based nanocarriers seem to be a promising delivery system which can be optimized and further explored as an alternative to the conventional dosage forms for the enhancement of oral bioavailability of drugs, with better patient compliance, minimum side effect, and improved the overall quality of life.

GM1-Binding Conjugates To Improve Intestinal Permeability.

Drugs and proteins with poor intestinal permeability have a limited oral bioavailability. To remediate this problem, a receptor-mediated endocytosis and transcytosis approach was explored. Indeed, the nontoxic β subunit of cholera toxin (CTB) can cross the intestinal barrier by binding to receptor GM1. In this study, we explored the use of GM1-binding peptides and CTB as potential covalent carriers of poorly permeable molecules. GM1-binding peptides (G23, P3) and CTB were conjugated to poorly permeable fluorescent probes such as fluorescein isothiocyanate (FITC) and albumin-FITC using triethylene glycol spacers and click chemistry. The affinity of the peptide conjugates with receptor GM1 was confirmed by isothermal titration calorimetry or microscale thermophoresis, and the results suggested the involvement of nonspecific interactions. Conjugating the model drugs to G23 and P3 improved the internalization into Caco-2 and T84 cells, although the process was not dependent on the amount of GM1 receptor. However, conjugation of bovine serum albumin FITC to CTB increased the internalization in the same cells in a GM1-dependent pathway. Peptide conjugates demonstrated a limited permeability through a Caco-2 monolayer, whereas G23 and CTB conjugates slightly enhanced permeability through a T84 cell monolayer compared to model drugs alone. Since CTB can improve the permeability of large macromolecules such as albumin, it is an interesting carrier for the improvement of oral bioavailability of various other macromolecules such as heparins, proteins, and siRNAs.

Pharmacokinetic characterization of anhuienoside C and its deglycosylated metabolites in rats

1. Anhuienoside C (AC), a triterpenoid saponin derived from the traditional Chinese medicine (TCM) “Di Wu”, has significant anti-inflammatory and anti-rheumatoid arthritis activities. Here we aimed to characterize the pharmacokinetics of AC and its deglycosylated metabolites in rats.2. AC was administered to rats by intravenous injection or oral gavage. AC and its four deglycosylated metabolites (M1, M2, M3 and M4) in biological samples were quantified using a UPLC-QTOF/MS system. The pharmacokinetic data were analyzed by compartmental modeling. The metabolism of M1, M2, M3 and M4 was determined using rat liver microsomes (RLM) and rat intestine microsomes (RIM). The intestinal permeabilities of AC and its metabolites were evaluated using Parallel artificial membrane permeability assay (PAMPA) and MDR1-transfected Madin–Darby canine kidney cell (MDCK–MDR1) cell model.3. AC pharmacokinetics was well described by the one-compartment model. The oral bioavailability of AC was exceedingly low (F = 0.03%). Consistently, AC was poorly distributed (< 0.08 μM) in major organs including the heart, liver, spleen, lung and kidney after oral uptake. Three of four deglycosylated metabolites (M2, M3, and M4) underwent further metabolism in RLM, generating five, two and five oxidized products, respectively. Both PAMPA and MDCK-MDR1 experiments showed that AC and its metabolites were poorly permeable. Furthermore, the net flux ratios derived from MDCK-MDR1 versus wild-type MDCK cells were, respectively 1.3, 1.5, 0.7, 1.2 and 0.6 for AC, M1, M2, M3 and M4, suggesting that these compounds were non-substrates of P-glycoprotein.4. In conclusion, extensive pre-systemic metabolism and poor permeability were the main causes of low systemic exposures of oral AC and its four metabolites.

A poly-l-glutamic acid functionalized nanocomplex for improved oral drug absorption.

Poor permeability of the intestinal epithelium limits the oral absorption of many drugs. Here, a poly-l-glutamic acid (PGA)-based functional ternary nanocomplex (TC) is reported for enhancing the intestinal absorption of poorly permeable drug doxorubicin hydrochloride (Dox·HCl). The particle size and zeta potential of TC were 189.3 ± 13.7 nm and -29.1 ± 7.4 mV, respectively. The TC was shown to be more stable under simulated gastrointestinal changing pH or electrolyte content conditions than the binary nanocomplex Dox·HCl/PGA. Cellular uptake and the apparent permeability coefficient value (Papp) of the TC were determined to be 5.2- and 4.6-fold higher than that of Dox·HCl solutions, respectively. Mechanistic studies showed that active endocytosis caused by specific interactions between γ-glutamyl terminal groups of PGA and membrane-bound γ-glutamyl transferase contributed much to the TC-dependent Dox·HCl absorption. Studies on the rat model also demonstrated the highest efficiency for Dox·HCl absorption by the TC throughout the intestinal tract, with 2.6- and 4.2-fold higher Cmax and AUC0-24h values compared to Dox·HCl solutions. In conclusion, the TC is a promising carrier for improving Dox·HCl intestinal absorption, and the rational design of carriers with functional polymer PGA could implement the efficient active absorption of poorly permeable drugs.

Novel approach to enhance oral bioavailability of drugs with poor permeability

T epithelial enterocyte barrier of the gastrointestinal (GI) tract limits the absorption of many oral drugs to the systemic circulation. Modulation of intercellular tight junctions has long been considered a potential tool to enhance drug delivery across these biological barriers. However, early modulators (e.g., Ca2+ chelators, surfactants, modified fatty acids and esters, and polymers) had unspecific modes of action and insufficient separation between efficacy and toxicity, precluding their clinical use. Recent knowledge regarding the molecular composition and mechanisms regulating tight junctions and adherens junctions has led to a new generation of intercellular junction modulators based on junction protein/peptide mimetics and relevant signaling pathways. E-cadherin peptides (ECPs) represent a class of these new modulators and have shown promise in enhancing small molecule drug delivery across the blood-brain barrier via reversible modulation. Here, the potential of ECPs to enhance oral bioavailability of small molecule drugs that have limited gut absorption was investigated. In vitro permeability and in vivo pharmacokinetic studies have been performed to demonstrate the feasibility of the ECP-based oral drug delivery approach. Results showed that ECPs substantially increased the permeability of the model drugs, as well as their systemic exposure after oral administration. In conclusion, ECPs-based formulations should be further developed as a vehicle to enhance oral bioavailability of poorly permeable drugs.

Progressive Applications of Dissolution, Its Impact, and Implications in the Pharmaceutical World

Progressive Applications of Dissolution, Its Impact, and Implications in the Pharmaceutical World

Enhanced Oral Delivery of Paclitaxel Using Acetylcysteine Functionalized Chitosan-Vitamin E Succinate Nanomicelles Based on a Mucus Bioadhesion and Penetration Mechanism

In addition to being a physiological protective barrier, the gastrointestinal mucosal membrane is also a primary obstacle that hinders the oral absorption of many therapeutic compounds, especially drugs with a poor permeability. In order to resolve this impasse, we have designed multifunctional nanomicelles based on the acetylcysteine functionalized chitosan-vitamin E succinate copolymer (CS-VES-NAC, CVN), which exhibit marked bioadhesion, possess the ability to penetrate mucus, and enhance the oral absorption of a hydrophobic drug with a poor penetrative profile, paclitaxel. The intestinal absorption (Ka = 0.38 ± 0.04 min(-1), Papp = 0.059 cm · min(-1)) of CVN nanomicelles was greatly improved (4.5-fold) in comparison with paclitaxel solution, and CLSM (confocal laser scanning microscope) pictures also showed not only enhanced adhesion to the intestinal surface but improved accumulation within intestinal villi. The in vivo pharmacokinetics indicated that the AUC0-t (586.37 ng/mL · h) of CVN nanomicelles was markedly enhanced compared with PTX solution. In summary, the novel multifunctional CVN nanomicelles appear to be a promising nanocarrier for insoluble and poorly permeable drugs due to their high bioadhesion and permeation-enhancing capability.

Solubility and Dissolution of Drug Product: A Review

The oral route of drug administration is the most common and preferred method of delivery due to convenience and ease of ingestion. From a patient’s perspective, swallowing a dosage form is a comfortable and a familiar means of taking medication. As a result, patient compliance and hence drug treatment is typically more effective with orally administered medications as compared with other routes of administration, for example, parenteral. Although the oral route of administration is preferred, for many drugs it can be a problematic and inefficient mode of delivery for a number of reasons. Limited drug absorption resulting in poor bioavailability is paramount amongst the potential problems that can be encountered when delivering an active agent via the oral route. Drug absorption from the gastrointestinal (GI) tract can be limited by a variety of factors with the most significant contributors being poor aqueous solubility and/or poor membrane permeability of the drug molecule. When delivering an active agent orally, it must first dissolve in gastric and/or intestinal fluids before it can then permeate the membranes of the GI tract to reach systemic circulation. Therefore, a drug with poor aqueous solubility will typically exhibit dissolution rate limited absorption, and a drug with poor membrane permeability will typically exhibit permeation rate limited absorption. Hence, two areas of pharmaceutical research that focus on improving the oral bioavailability of active agents include: (i) enhancing solubility and dissolution rate of poorly water-soluble drugs and (ii) enhancing permeability of poorly permeable drugs. In this article, solubility and dissolution will be discussed.DOI: http://dx.doi.org/10.3329/ijpls.v2i1.15133 International Journal of Pharmaceutical and Life Sciences Vol.2(1) 2013: 33-41

Self-Assembled Porphyrin Nanodiscs with Structure-Dependent Activation for Phototherapy and Photodiagnostic Applications

The abilities to deliver and subsequently activate a therapeutic at the intended site of action are two important challenges in the synthesis of novel nanoparticles. Poor tumor permeability as a result of a dense microenvironment can impede the delivery of nanoparticles to the site of action. The design of a sub-40 nm activatable porphyrin nanodisc, based on protein-induced lipid constriction, is described. The biophotonic nanoparticle, self-assembled from aggregated porphyrin-lipid, is stabilized by an amphipathic alpha helical protein and becomes photoactive when its structure is perturbed. Enzymatic cleavage of the constricting protein leads to conversion of the particle from a disc- to a vesicle-shaped structure and provides further evidence that the apolipoprotein serves a functional role on the nanodisc. Fluorescence measurements of these nanodiscs in a detergent show that fluorescence is over 99% quenched in the intact state with a 12-fold increase in singlet oxygen generation upon disruption. Cellular fluorescence unquenching and dose-dependent phototoxicity demonstrate that these nanodiscs can be internalized and unquenched intracellularly. Finally, nanodiscs were found to display a 5-fold increase in diffusion coefficient when compared with the protein-free control ((3.5±0.1)×10(-7) vs (0.7±0.03)×10(-7) cm2 s(-1)). The ability to incorporate large amounts of photosensitizer drugs into its compact structure allows for phototherapeutic action, fluorescence diagnostic applications, and the potential to effectively deliver photosensitizers deep into poorly permeable tumors.

Predicting the oral absorption of a poorly soluble, poorly permeable weak base using biorelevant dissolution and transfer model tests coupled with a physiologically based pharmacokinetic model

For predicting food effects and simulating plasma profiles of poorly soluble drugs, physiologically based pharmacokinetic models have become a widely accepted tool in academia and the pharmaceutical industry. Up till now, however, simulations appearing in the open literature have mainly focused on BCS class II compounds, and many of these simulations tend to have more of a “retrospective” than a prognostic, predictive character.In this work, investigations on the absorption of a weakly basic BCS class IV drug, “Compound A”, were performed. The objective was to predict the plasma profiles of an immediate release (IR) formulation of Compound A in the fasted and fed state. For this purpose, in vitro biorelevant dissolution tests and transfer model experiments were conducted. Dissolution and precipitation kinetics were then combined with in vivo post-absorptive disposition parameters using STELLA® software. As Compound A not only exhibits poor solubility but also poor permeability, a previously developed STELLA® model was revised to accommodate the less than optimal permeability characteristics as well as precipitation of the drug in the fasted state small intestine. Permeability restrictions were introduced into the model using an absorption rate constant calculated from the Caco-2 permeability value of Compound A, the effective intestinal surface area and appropriate intestinal fluid volumes.The results show that biorelevant dissolution tests are a helpful tool to predict food effects of Compound A qualitatively. However, the plasma profiles of Compound A could only be predicted quantitatively when the results of biorelevant dissolution test were coupled with the newly developed PBPK model.

Identification of permeability-related hurdles in oral delivery of curcumin using the Caco-2 cell model

Curcumin a poly-phenolic compound possesses diverse pharmacologic activities; however, its development as a drug has been severely impeded by extremely poor oral bioavailability. Poor aqueous solubility and extensive metabolism have been implicated for this but the role of membrane permeability has not been investigated. In the present study, permeability of curcumin was assessed using the Caco-2 cell line. Curcumin was poorly permeable with a Papp (A→B) value of 2.93±0.94×10−6cm/s. Papp value in (B→A) study was found out to be 2.55±0.02×10−6cm/s, thus ruling out the role of efflux pathways in poor oral bioavailability of curcumin. Studies using verapamil, a P-gp inhibitor, further confirmed this finding. Detailed mass balance studies showed loss of curcumin during transport. Further experiments using lysed cells revealed that 11.78% of curcumin was metabolized during transport. Studies using itraconazole, a CYP3A4 inhibitor, established its role in curcumin metabolism. Curcumin was also found to accumulate in cells as revealed by CLSM studies. Sorption and desorption kinetic studies further confirmed accumulation of curcumin inside the cells. Amount accumulated was quantitated by HPLC and found to be >20%. Thus, intestinal first-pass metabolism and intracellular accumulation played a role in poor permeability of curcumin. Based on its poor aqueous solubility and intestinal permeability, curcumin can be classified as a BCS Class IV molecule. This information can facilitate designing of drug delivery systems for enhancement of oral bioavailability of curcumin.

Enhancement of the intestinal absorption of peptides and nonpeptides

It is not uncommon for peptides and structurally-similar non-peptides to have poor intestinal permeability and low oral bioavailability. One possible way to solve a permeability problem is to formulate the compound with membrane permeation-enhancing excipients. Important criteria for success of this approach are: (1) achieving reproducible intestinal permeation, (2) doing so without causing toxicity, and (3) understanding the mechanisms of permeation enhancement. Some effective and potentially safe permeation enhancers are fatty acids, glycerides, surfactants, acyl carnitines, and bile salts. The literature on permeation enhancement with these agents is briefly reviewed. We evaluated permeation enhancement approaches to increase the oral bioavailability of a non-metabolized, cyclic peptide fibrinogen antagonist, DMP 728. Sodium caprate (15 mM) increased the in vitro intestinal permeation rate 3-fold. Oral absorption in dogs was also increased approximately 3-fold using a formulation containing 150 mg sodium caprate. Inter-animal variability in absorption was considerable, though. A diacidic, non-peptide angiotensin II antagonist, DuP 532, presented another case of a poorly membrane permeable lead compound. Sodium caprate did not affect DuP 532 oral bioavailability in rats. However, oral bioavailability of DuP 532 in rats and dogs was increased approximately 3-fold using glyceride vehicles. These excipients have the advantage of already being used in marketed products. As with DMP 728, there was substantial inter-animal variability of DuP 532 oral bioavailability, and optimization of the formulation would be required to improve reproducibility. These examples demonstrate the possibilities of significantly improving oral bioavailability of poorly permeable drugs using seemingly acceptable excipients.

Flood Irrigation of a Cracked Soil

Flood Irrigation of a Cracked Soil

Hepatic microcirculation in the perfused cirrhotic rat liver.

Liver microcirculation in the perfused rat liver was assessed by the multiple indicator dilution technique. Comparative studies were carried out in noncirrhotic rats and in rats with cirrhosis secondary to chronic exposure to phenobarbital and carbon tetrachloride. The alterations of the sinusoidal bed were characterized by changes in the displacement of hepatic venous outflow curves of various diffusible substances (labeled albumin, sucrose, and water) relative to that of labeled erythrocytes (vascular reference). Outflow recoveries of lidocaine (a substance that penetrates the liver cell membrane freely and completely) and of labeled microspheres (15 microns diam) were also appraised. In all cirrhotic rats, unimodal erythrocytes and albumin curves were obtained. The sinusoidal space was significantly decreased when compared with normal rats (P less than 0.001) and the total space accessible to albumin became progressively restricted. In seven cirrhotic rats, the profiles of labeled sucrose and water curves were compatible with a flow-limited diffusion and the total distribution volumes were not significantly different from values found in noncirrhotic rats (P = NS), which indicates that sucrose and water were still able to diffuse into an extravascular space not accessible to albumin. In the other cirrhotic rats, labeled sucrose and water curves showed progressive bimodal changes not compatible with a flow-limited diffusion. Such alterations were not due to large intrahepatic shunts, since only 0.25% of the 15-microns microspheres were recovered in the outflow of cirrhotic rats. However, an early lidocaine outflow peak related in time to the peak erythrocyte curve was observed in cirrhotic, but not in noncirrhotic, rats. Lidocaine recovery varied greatly in cirrhotic rats and appeared to increase as the liver disease progressed. These data can be explained by capillarization of sinusoids and/or by the development of channels with poor permeability. Electron microscopic observations of these rat livers favored the latter. Thus, in cirrhotic rat liver, two kinds of alteration are likely: (a) the vascular space is decreased with collagenization of the extravascular space, limiting the diffusion of large molecules such as albumin; and (b) small channels with poorly permeable walls develop, limiting the diffusion of small molecules such as lidocaine, sucrose, and water. Large intrahepatic shunts are not a common feature.