Fixed-Dose Combination Formulations in Solid Oral Drug Therapy: Advantages, Limitations, and Design Features.

Whilst monotherapy is traditionally the preferred treatment starting point for chronic conditions such as hypertension and diabetes, other diseases require the use of multiple drugs (polytherapy) from the onset of treatment (e.g., human immunodeficiency virus acquired immunodeficiency syndrome, tuberculosis, and malaria). Successful treatment of these chronic conditions is sometimes hampered by patient non-adherence to polytherapy. The options available for polytherapy are either the sequential addition of individual drug products to deliver an effective multi-drug regimen or the use of a single fixed-dose combination (FDC) therapy product. This article intends to critically review the use of FDC drug therapy and provide an insight into FDC products which are already commercially available. Shortcomings of FDC formulations are discussed from multiple perspectives and research gaps are identified. Moreover, an overview of fundamental formulation considerations is provided to aid formulation scientists in the design and development of new FDC products.

Formulation of Chitosan Microparticles for Enhanced Intranasal Macromolecular Compound Delivery: Factors That Influence Particle Size during Ionic Gelation.

Therapeutic macromolecules (e.g., protein and peptide drugs) present bioavailability challenges via extravascular administration. The nasal route presents an alternative non-invasive route for these drugs, although low bioavailability remains challenging. Co-administration of permeation enhancers is a promising formulation approach to improve the delivery of poorly bioavailable drugs. The aim of this study was to prepare and characterize chitosan microparticulate formulations containing a macromolecular model compound (fluorescein isothiocyanate dextran 4400, FD-4) and a bioenhancer (piperine). Ionic gelation was used to produce chitosan microparticle delivery systems with two distinct microparticle sizes, differing one order of magnitude in size (±20 µm and ±200 µm). These two microparticle delivery systems were formulated into thermosensitive gels and their drug delivery performance was evaluated across ovine nasal epithelial tissues. Dissolution studies revealed a biphasic release pattern. Rheometry results demonstrated a sol-to-gel transition of the thermosensitive gel formulation at a temperature of 34 °C. The microparticles incorporating piperine showed a 1.2-fold increase in FD-4 delivery across the excised ovine nasal epithelial tissues as compared to microparticles without piperine. This study therefore contributed to advancements in ionic gelation methods for the formulation of particulate systems to enhance macromolecular nasal drug delivery.

Comparison of RPMI 2650 cell layers and excised sheep nasal epithelial tissues in terms of nasal drug delivery and immunocytochemistry properties.

Nasal drug administration has been identified as a potential alternative to oral drug administration, especially for systemic delivery of large molecular weight compounds. Major advantages of nasal drug delivery include high vascularity and permeability of the epithelial membranes as well as circumvention of first-pass metabolism. RPMI 2650 cell layers (in vitro cell model) and excised sheep nasal mucosal tissues (ex vivo sheep model) were evaluated with regard to epithelial thickness, selected tight junction protein expression (i.e. claudin-1, F-actin chains, zonula occludin-1), extent of p-glycoprotein (P-gp) related efflux of a model compound (Rhodamine-123, R123) and paracellular permeation of a large molecular weight model compound (FITC-dextran 4400, FD4). The cell model grown under liquid cover conditions (LCC) was thinner (24 ± 4 µm) than the epithelial layer of the sheep model (53 ± 4 µm), whereas the thickness of cell model grown under air liquid interface (ALI) conditions (53 ± 8 µm) compared well with that of the sheep model. Although the location and distribution of tight junction proteins and F-actin differed to some extent between the cell model grown under ALI conditions and the sheep model, the extent of paracellular permeation of FD4 was similar (Papp = 0.48 × 10-6 cm.s-1 and 0.46 × 10-6 cm.s-1, respectively). Furthermore, the bi-directional permeation of R123 yielded the same efflux ratio (ER = 2.33) in both models. The permeation results from this exploratory study indicated similarity in terms of compound permeation between the RPMI 2650 nasal epithelial cell line and the excised sheep nasal epithelial tissue model.

Molecular mechanisms and associated cell signalling pathways underlying the anticancer properties of phytochemical compounds from Aloe species (Review).

Naturally occurring components from various species of Aloe have been used as traditional folk medicine since the ancient times. Over the last few decades, the therapeutic effects of extracts and phytochemical compounds obtained from Aloe vera have been proven in preclinical and clinical studies. Recently, compounds from other Aloe species apart from Aloe vera have been investigated for the treatment of different diseases, with a particular focus on cancer. In the present review, the effects of phytochemical compounds obtained from different Aloe species are discussed, with a specific focus on the effects on cell signalling in cancer and normal cells, and their selectivity and efficacy. This information will be useful for the application of Aloe-derived compounds as therapeutic agents, either alone or in combination with other standard drugs for cancer treatment.

Formulation of Medicated Chewing Gum Containing Sceletium tortuosum and Process Optimization Utilizing the SeDeM Diagram Expert System.

Sceletium tortuosum is one of the most promising medicinal plant species for treating anxiety and depression. Traditionally, aerial parts are chewed (masticatory herbal medicine) providing fast relief and rendering the masticatory route for delivery, ideal. This study intended formulating novel medicated chewing gum containing S. tortuosum to alleviate depression and anxiety. S. tortuosum extract was formulated into directly compressed medicated chewing gum (MCG) containing different Health-in-Gum® (HIG) bases through process optimization with the SeDeM Diagram Expert System. Physical properties of MCGs were characterized, and specialized drug release studies performed. According to the manufacturer, only HIG-03 was specifically developed for direct compression; however, the SeDeM System was successfully applied to all HIG-bases investigated. HIG-01 and HIG-04 are also considered useful in direct compression as no considerable differences in these MCG formulations' physical properties were recognized. Inclusion of a lubricant, however, is deemed essential, and MCG comprising HIG-01, most suited for direct compression. Dissolution experiments found only two alkaloids used as markers, mesembrine and mesembrenone, were released in quantifiable concentrations regardless formulation constituents. Novel directly compressed MCG-containing S. tortuosum extract was successfully formulated by which the biologically active phytochemicals of S. tortuosum can be scientifically delivered through the traditionally applied mastication method.

Physicochemical Stability of Enriched Phenolic Fractions of Cyclopia genistoides and ex vivo Bi-directional Permeability of Major Xanthones and Benzophenones.

Fractions of an ultrafiltered Cyclopia genistoides extract, respectively enriched in xanthones and benzophenones, were previously shown to inhibit mammalian α-glucosidase in vitro. The present study investigated ex vivo intestinal transport of these fractions, using excised porcine jejunal tissue, to determine whether the gut could be a predominant in vivo site of action. The major bioactive compounds, the xanthones (mangiferin, isomangiferin) and benzophenones (3-ß-D-glucopyranosyliriflophenone, 3-ß-D-glucopyranosyl-4-O-ß-D-glucopyranosyliriflophenone) exhibited poor permeation in the absorptive direction with a relatively high efflux ratio (efflux ratio > 1). The efflux ratio of 3-ß-D-glucopyranosyl-4-O-ß-D-glucopyranosyliriflophenone (3.05) was similar to rhodamine 123 (2.99), a known substrate of intestinal P-glycoprotein 1 efflux transporters. Low epithelial membrane transport rates, coupled with efflux mechanisms, would effectively concentrate these bioactive compounds at the target site (gut lumen). Storage stability testing and moisture sorption assays of the xanthone-enriched fraction, benzophenone-enriched fraction, and ultrafiltered Cyclopia genistoides extract were performed to determine their susceptibility to physical and chemical degradation during storage. Hygroscopicity of the powders, indicated by moisture uptake, decreased in the order: benzophenone-enriched fraction (22.7%) > ultrafiltered Cyclopia genistoides extract (14.0%) > xanthone-enriched fraction (10.7%). 3-ß-D-Glucopyranosylmaclurin, a minor benzophenone, was the least stable of the compounds, degrading faster in the benzophenone-enriched fraction than in ultrafiltered Cyclopia genistoides extract, suggesting that the ultrafiltered extract matrix may provide a degree of protection against chemical degradation. Compound degradation during 12 wk of storage at 40 °C in moisture-impermeable containers was best explained by first order reaction kinetics.

Models used to screen for the treatment of multidrug resistant cancer facilitated by transporter-based efflux.

PURPOSE: Efflux transporters of the adenosine triphosphate-binding cassette (ABC)-superfamily play an important role in the development of multidrug resistance (multidrug resistant; MDR) in cancer. The overexpression of these transporters can directly contribute to the failure of chemotherapeutic drugs. Several in vitro and in vivo models exist to screen for the efficacy of chemotherapeutic drugs against MDR cancer, specifically facilitated by efflux transporters. RESULTS: This article reviews a range of efflux transporter-based MDR models used to test the efficacy of compounds to overcome MDR in cancer. These models are classified as either in vitro or in vivo and are further categorised as the most basic, conventional models or more complex and advanced systems. Each model's origin, advantages and limitations, as well as specific efflux transporter-based MDR applications are discussed. Accordingly, future modifications to existing models or new research approaches are suggested to develop prototypes that closely resemble the true nature of multidrug resistant cancer in the human body. CONCLUSIONS: It is evident from this review that a combination of both in vitro and in vivo preclinical models can provide a better understanding of cancer itself, than using a single model only. However, there is still a clear lack of progression of these models from basic research to high-throughput clinical practice.

A sub-chronic Xysmalobium undulatum hepatotoxicity investigation in HepG2/C3A spheroid cultures compared to an in vivo model.

ETHNOPHARMACOLOGY RELEVANCE: Traditional herbal medicines are utilized by 27 million South Africans. Xysmalobium undulatum (Uzara) is one of the most widely used traditional medicinal plants in Southern Africa. A false belief in the safety of herbal medicine may result in liver injury. Herb-induced liver injury (HILI) range from asymptomatic elevation of liver enzymes, to cirrhosis and in certain instances even acute liver failure. Various in vitro and in vivo models are available for the pre-clinical assessment of drug and herbal hepatotoxicity. However, more reliable and readily available in vitro models are needed, which are capable of bridging the gap between existing models and real human exposure. Three-dimensional (3D) spheroid cultures offer higher physiological relevance, overcoming many of the shortcomings of traditional two-dimensional cell cultures. AIMS OF THIS STUDY: This study investigated the hepatotoxic and anti-prolific effects of the crude X. undulatum aqueous extract during a sub-chronic study (21 days), in both a 3D HepG2/C3A spheroid model and the Sprague Dawley rat model. METHODS: HepG2/C3A spheroids were treated with a known hepatotoxin, valproic acid, and crude X. undulatum aqueous extract for 21 days with continuous evaluation of cell viability and proliferation. This was done by evaluating cell spheroid growth, intracellular adenosine triphosphate (ATP) levels and extracellular adenylate kinase (AK). Sprague Dawley rats were treated with the same compounds over 21 days, with evaluation of in vivo toxicity effects on serum chemistry. RESULTS: The results from the in vitro study clearly indicated hepatotoxic effects and possible liver damage following treatment with valproic acid, with associated growth inhibition, loss of cell viability and increased cytotoxicity as indicated by reduced intracellular ATP levels and increased AK levels. These results were supported by the increased in vivo levels of AST, ALT and LDH following treatment of the Sprague Dawley rats with valproic acid, indicative of hepatic cellular damage that may result in hepatotoxicity. The in vitro 3D spheroid model was also able to predict the potential concentration dependant hepatotoxicity of the crude X. undulatum aqueous extract. Similarly, the results obtained from the in vivo Sprague Dawley model indicated moderate hepatotoxic potential. CONCLUSION: The data from both the 3D spheroid model and the Sprague Dawley model were able to indicate the potential concentration dependant hepatotoxicity of the crude X. undulatum aqueous extract. The results obtained from this study also confirmed the ability of the 3D spheroid model to effectively and reliably predict the long-term outcomes of possible hepatotoxicity.

Drug Bioavailability Enhancing Agents of Natural Origin (Bioenhancers) that Modulate Drug Membrane Permeation and Pre-Systemic Metabolism.

Many new chemical entities are discovered with high therapeutic potential, however, many of these compounds exhibit unfavorable pharmacokinetic properties due to poor solubility and/or poor membrane permeation characteristics. The latter is mainly due to the lipid-like barrier imposed by epithelial mucosal layers, which have to be crossed by drug molecules in order to exert a therapeutic effect. Another barrier is the pre-systemic metabolic degradation of drug molecules, mainly by cytochrome P450 enzymes located in the intestinal enterocytes and liver hepatocytes. Although the nasal, buccal and pulmonary routes of administration avoid the first-pass effect, they are still dependent on absorption of drug molecules across the mucosal surfaces to achieve systemic drug delivery. Bioenhancers (drug absorption enhancers of natural origin) have been identified that can increase the quantity of unchanged drug that appears in the systemic blood circulation by means of modulating membrane permeation and/or pre-systemic metabolism. The aim of this paper is to provide an overview of natural bioenhancers and their main mechanisms of action for the nasal, buccal, pulmonary and oral routes of drug administration. Poorly bioavailable drugs such as large, hydrophilic therapeutics are often administered by injections. Bioenhancers may potentially be used to benefit patients by making systemic delivery of these poorly bioavailable drugs possible via alternative routes of administration (i.e., oral, nasal, buccal or pulmonary routes of administration) and may also reduce dosages of small molecular drugs and thereby reduce treatment costs.

Beneficial Pharmacokinetic Drug Interactions: A Tool to Improve the Bioavailability of Poorly Permeable Drugs.

Simultaneous oral intake of herbs, supplements, foods and drugs with other drug(s) may result in pharmacokinetic or pharmacodynamic interactions with the latter. Although these interactions are often associated with unwanted effects such as adverse events or inefficacy, they can also produce effects that are potentially beneficial to the patient. Beneficial pharmacokinetic interactions include the improvement of the bioavailability of a drug (i.e., by enhancing absorption and/or inhibiting metabolism) or prolongation of a drug's plasma level within its therapeutic window (i.e., by decreasing excretion), whereas beneficial pharmacodynamic interactions include additive or synergistic effects. Mechanisms by which pharmacokinetic interactions can cause beneficial effects include enhancement of membrane permeation (e.g., structural changes in the epithelial cell membranes or opening of tight junctions), modulation of carrier proteins (e.g., inhibition of efflux transporters and stimulation of uptake transporters) and inhibition of metabolic enzymes. In the current review, selected pharmacokinetic interactions between drugs and various compounds from different sources including food, herb, dietary supplements and selected drugs are discussed. These interactions may be exploited in the future to the benefit of the patient, for example, by delivering drugs that are poorly bioavailable in therapeutic levels via alternative routes of administration than parenteral injection.

Toxicity and anti-prolific properties of Xysmalobium undulatum water extract during short-term exposure to two-dimensional and three-dimensional spheroid cell cultures.

Xysmalobium undulatum (Uzara) is one of the most widely used indigenous traditional herbal remedies in Southern Africa. Commercially available Uzara plant material was used to prepare a crude aqueous extract, of which the toxicity potential was investigated in the hepatic HepG2/C3A cell line in both traditional two-dimensional (2D) and rotating three-dimensional (3D) spheroid cell cultures. These cultures were treated over a period of 4 days at concentrations of 200, 350, 500, and 750 mg/kg plant extract to protein content. Basic physiological parameters of the cell cultures were measured during exposure, including cell proliferation, glucose uptake, intracellular adenosine triphosphate levels, and adenylate kinase release. The results indicated that all physiological parameters monitored were affected in a dose dependent manner, with the highest concentration of Uzara crude water extract (750 mg/kg) resulting in toxicity. Anti-proliferating effects of Uzara crude water extract were observed in both the 2D and 3D cell cultures, with the most pronounced effects at concentrations of 350, 500, and 750 mg/kg. Discrepancies between results obtained from the 2D and 3D cell culture models may be attributed to the type of repair system that is initiated upon exposure, depending on where cells are within the cell cycle. DNA repair systems differ in cells within the G1 phase and non-diving cells, (i.e. cells found predominantly in in vitro 3D and the in vivo situation).

Excipient-drug pharmacokinetic interactions: Effect of disintegrants on efflux across excised pig intestinal tissues.

Pharmaceutical excipients were designed originally to be pharmacologically inert. However, certain excipients were found to have altering effects on drug pharmacodynamics and/or pharmacokinetics. Pharmacokinetic interactions may be caused by modulation of efflux transporter proteins, intercellular tight junctions and/or metabolic enzyme amongst others. In this study, five disintegrants from different chemical classes were evaluated for P-glycoprotein (P-gp) related inhibition and tight junction modulation effects. Bi-directional transport studies of the model compound, Rhodamine 123 (R123) were conducted in the absence (control group) and presence (experimental groups) of four concentrations of each selected disintegrant across excised pig jejunum tissue. The results showed that some of the selected disintegrants (e.g. Ac-di-sol® and Kollidon® CL-M) increased R123 absorptive transport due to inhibition of P-gp related efflux, while another disintegrant (e.g. sodium alginate) changed R123 transport due to inhibition of P-gp in conjunction with a transient opening of the tight junctions in a concentration dependent way. It may be concluded that the co-application of some disintegrants to the intestinal epithelium may lead to pharmacokinetic interactions with drugs that are susceptible to P-gp related efflux. However, the clinical significance of these in vitro permeation findings should be confirmed by means of in vivo studies.

Recent advances in three-dimensional cell culturing to assess liver function and dysfunction: from a drug biotransformation and toxicity perspective.

The liver is a vital organ fulfilling a central role in over 500 major metabolic functions, including serving as the most essential site for drug biotransformation. Dysfunction of the drug biotransformation processes may result in the exposure of the liver (and other organs) to hepatotoxins, potentially interacting with cellular constituents and causing toxicity and various lesions. Hepatotoxicity can be investigated on a tissue, cellular and molecular level by employing various in vivo and in vitro techniques, including novel three-dimensional (3 D) cell culturing methods. This paper reflects on the liver and its myriad of functions and the influence of drug biotransformation on liver dysfunction. Current in vivo and in vitro models used to study liver function and dysfunction is outlined, emphasizing their advantages and disadvantages. The advantages of novel in vitro 3 D cell culture models are discussed and the possibility of novel models to bridge the gap between in vitro and in vivo models is explained. Progression made in the field of cell culturing methods such as 3 D cell culturing techniques over the last decade promises to reduce the use of in vivo animal models in biotransformation and toxicological studies of the liver.

Recent developments in our understanding of the implications of traditional African medicine on drug metabolism.

INTRODUCTION: The use of traditional herbal medicines has become increasingly popular globally, but in some countries, it is the main or sometimes even the only healthcare service available in the most rural areas. This is especially true for Africa where herbal medicines form a key component of traditional medicinal practices and there is access to a diversity of medicinal plants. Although many benefits have been derived from the use of traditional herbal medicines, many concerns are associated with their use of which herb-drug interactions have been identified to have a rising impact on patient treatment outcome. One type of pharmacokinetic interaction involves the modulation of drug metabolizing enzymes, which may result in enhanced or reduced bioavailability of co-administered drugs. Areas covered: This review highlights the current information available on drug metabolism-associated information with regards to traditional African medicines related to some of the most prevalent diseases burdening the African continent. Expert opinion: It is clear from previous studies that enzyme modulation by traditional African medicines plays a significant role in the pharmacokinetics of some co-administered drugs, but more research is needed to provide detailed information on these interactions, specifically for treatment of prevalent diseases such as tuberculosis and hypertension.

Topical Delivery of Withania somnifera Crude Extracts in Niosomes and Solid Lipid Nanoparticles.

BACKGROUND: Withania somnifera is a medicinal plant native to India and is known to have anticancer properties. It has been investigated for its anti-melanoma properties, and since melanoma presents on the skin, it is prudent to probe the use of W. somnifera in topical formulations. To enhance topical drug delivery and to allow for controlled release, the use of niosomes and solid lipid nanoparticles (SLNs) as delivery vesicles were explored. OBJECTIVE: The objective of this study is to determine the stability and topical delivery of W. somnifera crude extracts encapsulated in niosomes and SLNs. MATERIALS AND METHODS: Water, ethanol, and 50% ethanol crude extracts of W. somnifera were prepared using 24 h soxhlet extraction which were each encapsulated in niosomes and SLNs. Franz cell diffusion studies were conducted with the encapsulated extracts to determine the release and skin penetration of the phytomolecules, withaferin A, and withanolide A. RESULTS: The niosome and SLN formulations had average sizes ranging from 165.9 ± 9.4 to 304.6 ± 52.4 nm with the 50% ethanol extract formulations having the largest size. A small particle size seemed to have correlated with a low encapsulation efficiency (EE) of withaferin A, but a high EE of withanolide A. There was a significant difference (P < 0.05) between the amount of withaferin A and withanolide A that were released from each of the formulations, but only the SLN formulations managed to deliver withaferin A to the stratum corneum-epidermis and epidermis-dermis layers of the skin. CONCLUSION: SLNs and niosomes were able to encapsulate crude extracts of W. somnifera and release the marker compounds, withaferin A, and withanolide A, for delivery to certain layers in the skin. SUMMARY: Withania somnifera crude extracts were prepared using ethanol, water, and 50% ethanol as solvents. These three extracts were then incorporated into niosomes and solid lipid nanoparticles (SLNs) for use in skin diffusion studies, thus resulting in six formulations (ethanol niosome, water niosome, 50% ethanol niosome, ethanol SLN, water SLN, and 50% ethanol SLN). The diffusion of two marker compounds (withaferin A and withanolide A) from the formulations into the skin was then determined. Abbreviations used: API: Active pharmaceutical ingredient, ANOVA: Analysis of variance, ED: Epidermis-dermis, HPLC: High-performance liquid chromatography, HLB: Hydrophilic-lipophilic balance, NMR: Nuclear magnetic resonance spectroscopy, PDI: Polydispersity index, SLN: Solid lipid nanoparticle, SD: Standard deviation, SCE: Stratum corneum-epidermis, TEM: Transmission electron microscopy.

In vitro wound healing and cytotoxic activity of the gel and whole-leaf materials from selected aloe species.

ETHNOPHARMACOLOGICAL RELEVANCE: Aloe vera is one of the most important medicinal plants in the world with applications in the cosmetic industry and also in the tonic or health drink product market. Different parts of Aloe ferox and Aloe marlothii are used as traditional medicines for different applications. Although wound healing has been shown for certain aloe gel materials (e.g. A. vera ) previously, there are conflicting reports on this medicinal application of aloe leaf gel materials. AIM OF THE STUDY: The present study aimed at determining the wound healing properties of the gel and whole-leaf materials of Aloe vera, Aloe ferox and Aloe marlothii, as well as their cytotoxic effects on normal human keratinocyte cells (HaCaT). MATERIALS AND METHODS: Nuclear magnetic resonance spectroscopy was used to chemically fingerprint the aloe gel and whole-leaf materials by identifying characteristic marker molecules of aloe gel and whole-leaf materials. An MTT assay was performed to determine the cytotoxicity of the various aloe whole-leaf and gel materials on HaCaT cells. Wound healing and in vitro cell migration were investigated with HaCaT cells by means of the CytoSelect™ assay kit. RESULTS: The in vitro wound healing assay suggested that all the aloe gel and whole-leaf materials examined, exhibited faster wound healing activity than the untreated control group. After 48h, all the aloe gel and whole-leaf materials almost completely caused full wound closure, displaying 98.07% (A. marlothii whole-leaf), 98.00% (A. vera gel), 97.20% (A. marlothii gel), 96.00% (A. vera whole-leaf), 94.00% (A. ferox gel) and 81.30% (A. ferox whole-leaf) wound closure, respectively. It was noteworthy that the gel materials of all the three aloe species exhibited significantly faster (p<0.05) wound healing actions when compared to their respective whole-leaf materials at 32h. CONCLUSION: The gel and whole-leaf materials of A. vera, A. ferox and A. marlothii have shown the ability to heal wounds at a faster rate and to a larger extent than untreated keratinocytes. The MTT assay results suggested that the gel and whole-leaf materials of all the selected Aloe species showed negligible toxicity towards the HaCaT cells.

Isolation and in vitro permeation of phenylpropylamino alkaloids from Khat (Catha edulis) across oral and intestinal mucosal tissues.

ETHNOPHARMACOLOGICAL RELEVANCE: Khat, the leaves of Catha edulis, is used as a "natural amphetamine-like" stimulant in eastern and southern Africa, as well as in the Arabian Peninsula. Leaves are masticated to elicit a state of euphoria. Although the psychostimulatory effects of the leaves are attributed to the presence of phenylpropylamino alkaloids (i.e. cathinone, cathine and norephedrine), the extent of permeation of these alkaloids across the oral and intestinal mucosa has not been established. MATERIALS AND METHODS: Cathinone was isolated in the form of the oxalate salt from young buds, following acid-base extraction. High performance countercurrent chromatography (HPCCC) was used to isolate cathine and norephedrine, following borohydride reduction of a mixture of the three alkaloids. The in vitro permeability of these three alkaloids in their pure form, as well as in a crude extract, was evaluated across Caco-2 cell monolayers and across excised porcine intestinal, sublingual and buccal tissues. RESULTS: The purities of the isolated cathine and norephedrine were in excess of 90%, thereby proving that HPCCC can be applied for efficient separation of these alkaloids from extracts of Khat. The apparent permeability (Papp) coefficients for the Khat alkaloids in their pure form were all above 1.0×10-6cm/s, indicating that the transport of the three alkaloids across the selected biological membranes is comparable to that of the highly permeable reference compound, caffeine. Although readily transported across the various membranes, the alkaloids were transported to a lesser extent when present in a leaf extract, suggesting that other phytochemicals present in the extract influence their permeation. CONCLUSIONS: These results provide evidence that chewing of Khat contributes to the buccal and sublingual absorption of the psychoactive alkaloids in the bloodstream directly across the oral mucosal membranes. In addition, it confirms that these metabolites will be readily absorbed from the gastrointestinal tract when swallowed.

Combining Chemical Permeation Enhancers for Synergistic Effects.

Currently, macromolecular drugs such as proteins are mainly administered by means of injections due to their low intestinal epithelial permeability and poor stability in the gastrointestinal tract. This study investigated binary combinations of chemical drug absorption enhancers to determine if synergistic drug absorption enhancement effects exist. Aloe vera, Aloe ferox and Aloe marlothii leaf gel materials, as well as with N-trimethyl chitosan chloride (TMC), were combined in different ratios and their effects on the transepithelial electrical resistance (TEER), as well as the transport of FITC-dextran across Caco-2 cell monolayers, were measured. The isobole method was applied to determine the type of interaction that exists between the absorption enhancers combinations. The TEER results showed synergism existed for the combinations between A. vera and A. marlothii, A. marlothii and A. ferox as well as A. vera and TMC. Antagonism interactions also occurred and can probably be explained by chemical reactions between the chemical permeation enhancers, such as complex formation. In terms of FITC-dextran transport, synergism was found for combinations between A. vera and A. marlothii, A. marlothii and A. ferox, A. vera and TMC, A. ferox and TMC and A. marlothii and TMC, whereas antagonism was observed for A. vera and A. ferox. The combinations where synergism was obtained have the potential to be used as effective drug absorption enhancers at lower concentrations compared to the single components.