A critical issue with benzimidazoles such as fenbendazole and mebendazole is their poor water solubility, which can limit how well the body absorbs them. Many scientific resources are exploring ways to overcome this challenge. Here’s one example.
The poor aqueous solubility of the core benzimidazole scaffold is a primary factor contributing to its low and variable gastrointestinal absorption. Salt-based formulations may help overcome these pharmacokinetic limitations through several key mechanisms.
New patent applications and patented benzimidazole formulations are addressing a major biopharmaceutical challenge for this drug class: poor aqueous solubility and inconsistent oral absorption.
Here’s a quick review detailing how these newer salt-based formulations may improve solubility and in vivo performance:
1. Direct Chemical Modification and Solubilization
Cost-Effective Salification: The patented salt forms are produced through a direct, inexpensive chemical modification of the parent benzimidazole scaffold.
Overcoming Solubility Limits: Parent benzimidazoles possess an inherently hydrophobic structure that resists dissolving in water, leading to inconsistent absorption in the digestive tract. Converting these compounds into saline salt forms directly increases their aqueous solubility.
2. Improved In Vivo Bioavailability and Therapeutic Efficacy
Facilitated Oral Delivery: The marked increase in water solubility enables these compounds to be administered far more easily as oral doses in animal and future clinical studies.
Validated In Vivo Performance: In preclinical animal studies using mice experimentally infected with secondary cystic echinococcosis, the novel albendazole salt formulations showed superior aqueous solubility, enhanced systemic bioavailability, and higher therapeutic efficacy in vivo than the parent drugs.
3. Experimental Handling and Broader Delivery Context
Enhanced Laboratory Handling: Beyond systemic absorption in vivo, the salified derivatives exhibit improved handling characteristics during in vitro cell viability assays and HPLC analytical procedures.
Alternative to Complex Delivery Platforms: These patented saline salts offer a simple chemical alternative to other complex drug-delivery systems designed to address benzimidazole solubility, such as cyclodextrin inclusion complexes, soluble prodrugs, polymorphic solvates, and microemulsions.
The following patent application appears to have expired. However, after reviewing Google Patents, we can find others still in the works. Some combine benzimidazoles with lipids, salts, and other approaches that attempt to create novel solutions for making fenbendazole more soluble.
WO2017021992A1 — “Salts of compounds having a benzimidazolic structure, uses and process for the preparation thereof”
The patent covers salts of anthelmintic (antiparasitic) compounds that have a benzimidazole structure. The named compounds include albendazole (ABZ), fenbendazole (FBZ), triclabendazole (TRBZ) and its sulphoxides, flubendazole (FLZ), mebendazole (MBZ), oxibendazole (OBZ), thiabendazole (TBZ), and cambendazole (CBZ). These are drugs widely used to treat parasitic worm infections in both human and veterinary medicine.
A few key details:
The applicants/assignees are Italian research institutions: the Istituto Superiore di Sanità (ISS), Università degli Studi di Roma “La Sapienza,” and another university. It was filed on August 4, 2016, as PCT application PCT/IT2016/000191, with the international publication on February 9, 2017.
The chemistry is classified under benzimidazole heterocyclic compounds (C07D235 series). The general problem these salts address is that benzimidazole anthelmintics are notoriously poorly water-soluble, which limits their bioavailability; converting them into salt forms is a common strategy to improve solubility, dissolution, and therefore therapeutic performance.
One notable follow-on: some of the inventors (Simone Carradori, Adriano Casulli, Roberto Cirilli) have since worked on repurposing these benzimidazole anthelmintics and their enantiomers as candidate anticancer agents, which is an active area of “drug repurposing” research.