Bioavailability Challenges in Drug Development

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In the pharmaceutical sciences, bioavailability is one of the most critical factors that dictate whether a new therapeutic agent will be a success or a failure. Bioavailability is a vital parameter quantifying the extent and rate at which a drug reaches its site of action or is absorbed into circulation upon administration. It has proved that optimizing drug bioavailability is difficult. Poorly water-soluble drugs are a considerable proportion of new chemical entities in the pipelines of drug development.

Great bioavailability challenges exist in the design and development phase of drugs. These are mainly determined by the chemical properties of the drug, determining the solubility and permeability of the drug. This is because any dissolved drug is capable of passing through cell membranes. The pharmaceutical industry has made use of numerous creative ways to pass these hurdles, thereby enhancing the solubility and accordingly the bioavailability. 

Solubility Enhancement Techniques

The most important strategies are the solubility enhancement techniques. These include solid dispersions, particle size reduction, and the use of surfactants and solubilizers such as cyclodextrins. The term solid dispersion refers to the process of incorporating one or more active ingredients dispersed in an inert carrier or matrix in a solid state, which can improve the dissolution rate and subsequently the bioavailability of the incorporated compound. Preparations of such dispersions are often carried out through techniques such as spray drying, freeze-drying, or melting methods.

Another important approach includes size reduction of the particle, particularly for enhancing the dissolution rate in poorly water-soluble drugs. Techniques that have been applied include nanonization and micronization to reduce the particle size of the drug, thereby increasing the surface area and hence the dissolution rate.

New Drug Delivery Systems

Advances in drug delivery systems also continue to play their part in overcoming the challenges of bioavailability. For instance, lipid-based formulations, incorporating self-emulsifying drug delivery systems (SEDDS), have been particularly effective in enhancing the oral bioavailability of lipophilic drugs. The rationale is how such systems form fine oil-in-water emulsions upon contact with the GI fluids, making it an avenue for solubilizing the drug.

Moreover, polymeric micelles and liposomes as drug carriers have allowed the encapsulation of hydrophobic drugs in order to enhance their solubility and stability in the biological setting. The carrier protects the drug from enzymatic breakdown but assures better absorption and distribution into the body.

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Role of Prodrugs and Salt Forms

Another method is the employment of prodrugs and salts. Prodrugs are chemically modified derivatives of drug molecules, which undergo enzymatic and/or chemical transformation in vivo for release of the active parent drug. This technique is applied to drugs that are inherently insoluble or unstable at physiological conditions. The formation of salts in the drug can also greatly increase solubility, especially for drugs with ionizable functional groups.

Physiological and Biological Factors

It has to be emphasized that principal challenges from a bioavailability aspect are not only physicochemical but also biological and physiological. Different pH values of the gastrointestinal tract, the presence of food, and the variability of intestinal microflora impact the dissolution and absorption of drugs. Moreover, the role of intestinal efflux and influx transporters within an epithelial layer can play a serious role in the bioavailability of administered drugs. 

The Add-on Method of Solubility in Permeability Enhancement

Although penetration enhancement is as important as improvement in solubility, more bioavailability problems are still tackled under this approach. The human intestinal tract has taken the position of a selective barrier primarily by the epithelium that does not let the absorption of many drugs. This kind of barrier function is maintained both through a physical structure as well as through a number of biological factors that include efflux transport proteins.

These proteins, such as P-glycoprotein (P-gp), actively transport drugs out of cells, thereby reducing their absorption and bioavailability. One approach to this problem is through permeability enhancers, where these agents alter the properties of the intestinal barrier temporarily in such a way that more drugs are able to cross the barrier. Thus substances such as fatty acids and chitosans can open up the tight junctions between epithelial cells, or detergents to inhibit efflux pumps, contributing to higher absorption levels of drugs.

Applying advanced formulation techniques has also dominated the application in enhancing bioavailability. Techniques associated with the use of amorphous solid dispersions involve converting a poorly soluble drug from its crystalline form to an amorphous form that is of high energy. Such alteration increases the solubility and the rate of dissolution of the drug. Maintaining stability in amorphous forms is challenging because they are prone to recrystallization. Polymers and other stabilizers are often used to prevent this, maintaining the drug’s amorphous state and thus its solubility.

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Targeted Drug Delivery Systems

Targeted drug delivery systems are yet another advanced approach at making it possible to solve the problems of bioavailability. In this system, the drug is delivered in a controlled way to specific parts of the body, this is particularly useful with drugs that are poorly soluble or have significant side effects when distributed systemically.

Such techniques under research include magnetic drug targeting, whereby drugs are attached to the magnetic particles and guided by an external magnetic field directly to the target site, and ligand-directed targeting, whereby drugs are conjugated with ligands that recognize specific receptors of target cells.

Future Outlook and Innovation

Excipients and drug carriers should be developed in the future with a view to the improvement of both solubility and permeability. Nanotechnology has emerged as highly promising. The design of particles that enhance the dissolution of poorly soluble drugs and assist their penetration across biological barriers, thereby facilitating absorption, is one such promising area. For example, nanoparticles have surfaces that could be engineered with targeting ligands to guide them to specific points in the body, thereby reducing off-target side effects and improving the efficacy of treatment.

Conclusion

Bioavailability challenges in the development of drugs may be overcome through a multi-paradigmatic approach that combines cutting-edge pharmaceutical technologies, innovative formulation techniques, and an understanding of biological interactions. As far as this field is advancing with research, the developmental better and safer drugs would ostensibly advance to improve people’s lives worldwide, hence changing medicine. In this holistic approach to addressing bioavailability, the therapeutic agents will better be delivered toward the greater goal of personalized medicine because drugs can be tailored to particular patients based on their biological characteristics. It makes available and promises better therapeutic outcomes while minimizing adverse effects, an important advancement in the field of health care.

References

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