Advancements in Colon-Targeted Drug Delivery: A Comprehensive Review on Recent Techniques with Emphasis on Hot-Melt Extrusion and 3D Printing Technologies

This review investigates the progression and effectiveness of colon-targeted drug delivery systems, offering a comprehensive understanding of the colon’s anatomy and physiological environment. Recognizing the distinctive features of the colon is crucial for successfully formulating oral dosage forms that precisely target specific areas in the gastrointestinal tract (GIT) while minimizing side effects through mitigating off-target sites. This understanding forms the basis for designing effective targeted drug delivery systems. The article extensively examines diverse approaches to formulating drugs for colonic targeting, highlighting key polymers and excipients in their production. Special emphasis is given to innovative approaches such as hot-melt extrusion (HME) and three-dimensional printing (3D-P), renowned for their accuracy in drug release kinetics and intricate dosage form geometry. However, challenges arise regarding material standardization and the complex network of regulatory clearances required to confirm safety and effectiveness. The review provides insights into each application’s advantages and potential challenges. Furthermore, it sheds light on the local diseases that necessitate colon targeting and the available marketed products, providing an overview of the current state of colon-targeted drug delivery systems. Additionally, the review emphasizes the importance of testing drugs in a controlled in vitro environment during the development phase. It also discusses the future directions for successful development in this field. By integrating knowledge across anatomy, formulation techniques, and assessment methodologies, this review is a valuable resource for researchers navigating the dynamic field of colonic drug delivery.

Introduction

The oral route of drug administration is the most common and convenient method for patients, but it presents several challenges [1]. Drugs may be degraded by the acidic environment of the stomach or metabolized by enzymes in the small intestine before they can reach the colon [2]. Moreover, certain drugs require localized delivery to the colon to achieve optimal therapeutic efficacy and minimize adverse effects. As a result, colon-targeted drug delivery emerges as a critical area of pharmaceutical research, offering modified release strategies that ensure the drug reaches the colon before it is released from the oral dosage form. This approach is particularly beneficial for treating conditions such as inflammatory bowel disease (IBD), colorectal cancer, and other localized gastrointestinal disorders.

A deep understanding of the colon’s anatomy, physiology, and microbiology is essential for designing effective colon-targeted drug delivery systems, as it provides insights into the unique environment of the colon including its high surface area, microbial population, pH, and slow transit time [3]. The colon is a 1.5-m-long tube with a complex structure that is divided into the proximal colon (cecum, ascending colon, and transverse colon) and the distal colon (descending colon, sigmoid colon, rectum, and anus). This extensive surface area provides opportunities for drug interactions and absorption. Figure 1 illustrates the anatomy of the small and large intestines [4, 5].

The colon hosts a diverse microflora that ferments undigested dietary components, producing short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate, which contribute to overall health [6]. The presence of these microbes can be exploited for microbial-triggered drug delivery systems, where drugs are released upon interaction with specific bacterial enzymes.

The colon generally has an alkaline pH, typically ranging between 5.5 and 7.5, which is relatively higher than that of the upper gastrointestinal (GI) tract. This pH can vary based on factors like diet, microbial activity, and the production of SCFAs which can decrease or increase the colon’s pH by modulating the activity of bicarbonate transporters in the colonic epithelium [7]. The colon’s elevated pH environment can be utilized for targeting strategies by designing pH-sensitive drug delivery systems [8, 9].

The colon is characterized by a long transit time that can reach up to 20 -30 h for monolithic tablets. This slow movement allows drugs to remain in the colon for an extended period, enhancing the opportunity for drug absorption and interaction with the colonic mucosa. This characteristic is particularly beneficial for extended-release formulations, ensuring prolonged drug action at the targeted site [10]. Another crucial factor in achieving successful colon-targeted drug delivery is the use of polymers that capitalize on the unique colon characteristics. The chemistry of these polymers, including their solubility profiles, molecular weight, and functional groups, plays a vital role in ensuring that the drug is released at the right site. For example, polymers such as cellulose acetate phthalates (CAP), hydroxypropyl methyl-cellulose phthalate (HPMCP), and copolymers of methacrylic acid and methyl methacrylate are anionic polymers designed to withstand the low pH of the stomach and proximal small intestine but dissolve at specific pH levels found in the terminal ileum and colon [11]. Natural polymers like pectin and chitosan offer biodegradability and mucoadhesion properties that enhance localized delivery [12]. Colon-targeted drug delivery strategies encompass both well-established methods and cutting-edge technologies, each contributing uniquely to the field. Traditional approaches, such as time-dependent and pH-dependent systems, as well as strategies based on colonic pressure and microbial activity, have been extensively researched and have provided a strong foundation for targeted drug delivery to the colon [9]. On the other hand, recent advancements such as multi and nano-particulate systems, hot-melt extrusion (HME), and three-dimensional (3D) printing represent the next generation of drug delivery technologies. These innovations offer precision in controlling drug release profiles and allow for the customization of dosage forms to meet individual patient needs.

This review article provides a comprehensive overview of the traditional and most recent trends in the field of colonic drug delivery. The investigation covers the potential benefits and barriers associated with each strategy. Furthermore, the article delves into the role of polymers in colonic targeting. Special attention is given to local diseases requiring colon-targeted therapies, along with an overview of currently marketed products. The review also underscores the importance of in vitro testing during the development phase and explores future research directions, including the investigation of personalized medicine, novel materials, and advanced predictive technologies such as in silico modeling and machine learning to further enhance the field of colonic drug delivery.

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Table V Drug Candidates for Colon Diseases

Alshammari, N.D., Elkanayati, R., Vemula, S.K. et al. Advancements in Colon-Targeted Drug Delivery: A Comprehensive Review on Recent Techniques with Emphasis on Hot-Melt Extrusion and 3D Printing Technologies. AAPS PharmSciTech 25, 236 (2024). https://doi.org/10.1208/s12249-024-02965-w

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