Carrier-mediated transport of monocarboxylic acids in primary cultured epithelial cells from rabbit oral mucosa

Advances in Modeling Approaches for Oral Drug Delivery: Artificial Intelligence, Physiologically-Based Pharmacokinetics, and First-Principles Models

Oral drug absorption is the primary route for drug administration. However, this process hinges on multiple factors, including the drug's physicochemical properties, formulation characteristics, and gastrointestinal physiology. Given its intricacy and the exorbitant costs associated with experimentation, the trial-and-error method proves prohibitively expensive. Theoretical models have emerged as a cost-effective alternative by assimilating data from diverse experiments and theoretical considerations. These models fall into three categories: (i) data-driven models, encompassing classical pharmacokinetics, quantitative-structure models (QSAR), and machine/deep learning; (ii) mechanism-based models, which include quasi-equilibrium, steady-state, and physiologically-based pharmacokinetics models; and (iii) first principles models, including molecular dynamics and continuum models. This review provides an overview of recent modeling endeavors across these categories while evaluating their respective advantages and limitations. Additionally, a primer on partial differential equations and their numerical solutions is included in the appendix, recognizing their utility in modeling physiological systems despite their mathematical complexity limiting widespread application in this field.

Mucoadhesive Electrospun Fibre-Based Technologies for Oral Medicine

Oral disease greatly affects quality of life, as the mouth is required for a wide range of activities including speech, food and liquid consumption. Treatment of oral disease is greatly limited by the dose forms that are currently available, which suffer from short contact times, poor site specificity, and sensitivity to mechanical stimulation. Mucoadhesive devices prepared using electrospinning offer the potential to address these challenges by allowing unidirectional site-specific drug delivery through intimate contact with the mucosa and with high surface areas to facilitate drug release. This review will discuss the range of electrospun mucoadhesive devices that have recently been reported to address oral inflammatory diseases, pain relief, and infections, as well as new treatments that are likely to be enabled by this technology in the future.

Manufacture and characterization of mucoadhesive buccal films

The buccal route of administration has a number of advantages including bypassing the gastrointestinal tract and the hepatic first pass effect. Mucoadhesive films are retentive dosage forms and release drug directly into a biological substrate. Furthermore, films have improved patient compliance due to their small size and reduced thickness, compared for example to lozenges and tablets. The development of mucoadhesive buccal films has increased dramatically over the past decade because it is a promising delivery alternative to various therapeutic classes including peptides, vaccines, and nanoparticles. The "film casting process" involves casting of aqueous solutions and/or organic solvents to yield films suitable for this administration route. Over the last decade, hot-melt extrusion has been explored as an alternative manufacturing process and has yielded promising results. Characterization of critical properties such as the mucoadhesive strength, drug content uniformity, and permeation rate represent the major research areas in the design of buccal films. This review will consider the literature that describes the manufacture and characterization of mucoadhesive buccal films.

Current status and the future of buccal drug delivery systems

BACKGROUND

The delivery of drugs through the buccal mucosa has received a great deal of attention over the last two decades, and yet there are not many buccal delivery products available on the market.

OBJECTIVE

This review outlines the advantages and disadvantages of buccal drug delivery, provides a historical perspective and discusses representative developmental and marketed drugs.

METHODS

The structure of the oral mucosa is briefly described to preface a description of the pathways for drug absorption and a critical discussion of permeation experiments. A brief historical perspective followed by a description of some of the currently marketed products provides a picture of where we are today. An indication is given of likely progress in this area and of the attributes of a successful business entity of the future.

CONCLUSION

The authors provide an assessment of the future potential of buccal and sublingual drugs.

Buccal bioadhesive drug delivery--a promising option for orally less efficient drugs

Rapid developments in the field of molecular biology and gene technology resulted in generation of many macromolecular drugs including peptides, proteins, polysaccharides and nucleic acids in great number possessing superior pharmacological efficacy with site specificity and devoid of untoward and toxic effects. However, the main impediment for the oral delivery of these drugs as potential therapeutic agents is their extensive presystemic metabolism, instability in acidic environment resulting into inadequate and erratic oral absorption. Parenteral route of administration is the only established route that overcomes all these drawbacks associated with these orally less/inefficient drugs. But, these formulations are costly, have least patient compliance, require repeated administration, in addition to the other hazardous effects associated with this route. Over the last few decades' pharmaceutical scientists throughout the world are trying to explore transdermal and transmucosal routes as an alternative to injections. Among the various transmucosal sites available, mucosa of the buccal cavity was found to be the most convenient and easily accessible site for the delivery of therapeutic agents for both local and systemic delivery as retentive dosage forms, because it has expanse of smooth muscle which is relatively immobile, abundant vascularization, rapid recovery time after exposure to stress and the near absence of langerhans cells. Direct access to the systemic circulation through the internal jugular vein bypasses drugs from the hepatic first pass metabolism leading to high bioavailability. Further, these dosage forms are self-administrable, cheap and have superior patient compliance. Developing a dosage form with the optimum pharmacokinetics is a promising area for continued research as it is enormously important and intellectually challenging. With the right dosage form design, local environment of the mucosa can be controlled and manipulated in order to optimize the rate of drug dissolution and permeation. A rational approach to dosage form design requires a complete understanding of the physicochemical and biopharmaceutical properties of the drug and excipients. Advances in experimental and computational methodologies will be helpful in shortening the processing time from formulation design to clinical use. This paper aims to review the developments in the buccal adhesive drug delivery systems to provide basic principles to the young scientists, which will be useful to circumvent the difficulties associated with the formulation design.

Buccal penetration enhancers--how do they really work?

Certain agents that increase drug delivery through the skin, including surfactants, bile salts, and fatty acids, have been shown to exert a similar effect on the buccal mucosa. These agents enhance skin permeability by interacting with and disrupting the ordered intercellular lipid lamellae within the keratinized stratum corneum, and it has been assumed that a similar mechanism of action occurs in the nonkeratinized buccal mucosa. However, the chemical and structural nature of the lipids present within the intercellular regions of the buccal mucosa is quite different to that found within the stratum corneum, and so extrapolation of results between these two tissues may be misleading. To assume that the mechanism of action of buccal penetration enhancers is based on the disruption of intercellular lipids may be erroneous, and may result in the inappropriate prediction that certain skin penetration enhancers will similarly enhance drug delivery through the buccal mucosa. The data available in the literature suggest that agents that enhance buccal penetration exert their effect by a mechanism other than by disruption of intercellular lipids. Rather, buccal penetration enhancement appears to result from agents being able to (a) increase the partitioning of drugs into the buccal epithelium, (b) extract (and not disrupt) intercellular lipids, (c) interact with epithelial protein domains, and/or (d) increase the retention of drugs at the buccal mucosal surface. The purpose of this review is to identify the major differences in the structural and chemical nature of the permeability barriers between the buccal mucosa and skin, to clarify the mechanisms of action of buccal penetration enhancers, and to identify the limitations of certain models that are used to assess the effect of buccal penetration enhancers.

Pharmacokinetic analysis of the FDA guidance for industry--'Topical dermatologic corticosteroids: in vivo bioequivalence'

The FDA (Food and Drug Administration) Guidance for Industry 'Topical Dermatologic Corticosteroids: In vivo Bioequivalence' describes two methods for evaluation of cutaneously applied corticosteroid formulations by measurement of the skin blanching response with a chromameter. The experimental options are: staggered application with synchronized removal or synchronized application with staggered removal. From the resulting response vs. time profiles, the areas under the effect curves (AUECs) are calculated and plotted as a function of the exposure time period to obtain dose/response-like relationships. If these experimental procedures are analyzed pharmacokinetically applying the Bateman equation and Fick's First Law of diffusion, several critical factors may be determined that need to be considered in order to avoid misinterpretation of the data. If solution-type preparations are investigated, the applied formulation volume should be the same on all application sites. In the case of suspension-type preparations, the applied drug dose is not critical. Moreover, it is essential to guarantee zero order kinetics during the application time periods, which may only be achieved with suspension-type preparations or a sufficiently high volume of solution-type preparations. If all these critical factors are taken care of, bioavailability factors (solutions) and enhancement factors (suspensions) may be calculated as the quotient of the AUECs of test and reference formulations.

Mucosal drug delivery

This review focuses on epithelial drug transport mechanisms in mucosal drug delivery: the final step of a four-part process. Reference is made to the mucosae lining the oral cavity and the gastrointestinal tract, the two mucosae most often succumbing to the side effects of cytotoxic chemotherapeutic drugs. This review will be devoted to carrier-mediated transport, particularly as it relates to the intestinal dipeptide transporter PepT1. This transporter protein appears to be enriched in tumor epithelial cells, to be rather robust to the cytotoxic effects of chemotherapeutic drugs, and to lend itself to the molecular engineering of drugs that target this transporter in tumor epithelial cells. In contrast to the gastrointestinal tract, much less is known about the type and capacity of drug transport processes in the buccal epithelial cells and about how these processes may be altered in disease state (including cancer) and be manipulated pharmaceutically to optimize drug absorption.

Membrane transporters

Carrier-mediated drug transport is relatively unexplored in comparison with passive transcellular and paracellular drug transport. Yet, there is a host of transporter proteins that can be targeted for improving epithelial drug absorption. Generally, these are transport mechanisms for amino acids, dipeptides, monosaccharides, monocarboxylic acids, organic cations, phosphates, nucleosides, and water-soluble vitamins. Among them, the dipeptide transporter mechanism has received the most attention. Dipeptide transporters are H(+)-coupled, energy-dependent transporters that are known to play an essential role in the oral absorption of beta-lactam antibiotics, angiotensin-converting enzyme (ACE) inhibitors, renin inhibitors, and an anti-tumor drug, bestatin. Moreover, several investigators have demonstrated the utility of the dipeptide transporter as a platform for improving the oral bioavailability of drugs such as zidovudine and acyclovir through dipeptide prodrug derivatization. Thus far, at least four proton-coupled peptide transporters have been cloned. The first one cloned was PepT1 from the rabbit small intestine. The focus of this presentation will be structure-function, intracellular trafficking, and regulation of PepT1. Disease, dietary, and possible excipient influences on PepT1 function will also be discussed.

Carrier-mediated absorption of salicylic acid from hamster cheek pouch mucosa

Previously, we found that monocarboxylic acids undergo carrier-mediated transport in primary cultures of oral mucosal epithelial cells.1 In this study, we investigated whether carrier-mediated absorption of a monocarboxylic acid from the oral mucosa occurs in vivo. Salicylic acid was administered to hamster cheek pouch. At predetermined intervals, the concentration of salicylic acid in the fluid remaining in the cheek pouch lumen and the blood salicylic acid concentration were determined. The absorption of salicylic acid was saturable at high salicylic acid concentrations. Sodium azide, a metabolic inhibitor, and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP), a protonophore, significantly inhibited the absorption of salicylic acid but not the absorption of salicylamide from the oral mucosa. Various monocarboxylic acids inhibited the absorption of salicylic acid, whereas dicarboxylic acids had no such effect. Transfer of [14C]salicylic acid from the cheek pouch mucosa to the systemic circulation was observed, and the blood [14C]salicylic acid concentration in the case of coadministration with propionic acid was significantly lower than that in the case of no propionic acid coadministration. These results show that monocarboxylic acids undergo carrier-mediated absorption from the hamster cheek pouch mucosa.