Pharmaceutical researchers are constantly striving to advance the profession and science of drug therapy. However, impeding their potentially life-saving mission are several obstacles that relate to of drug molecules, which include: insufficient bioavailability, poor water solubility, fluctuating plasma levels, and high food dependency.
One approach to developing customized drug carriers that overcome these major obstacles through colloidal carriers (a.k.a. nanosized carriers) – particularly with respect to improving bioavailability of active ingredients. In this article, we begin our look at the some of the drug colloidal systems that are available to pharmaceutical researchers.
Nanosuspensions are generally regarded as the simplest colloidal drug carrier. They are saturated solutions with a drug payload of almost 100%, and have a particle distribution of below one micrometer.
Despite their simplicity, particle growth is a risk factor with nanosuspensions, and can occur when the molecules dissolve in the environment and emerge later on the surface of the larger particles (this is referred to as “Ostwald ripening). As such, extreme care and attention has to be paid when reducing particles for drugs with tiny safety margins. Currently, the only two registered nanosuspensions for immediate delivery are Rapamune™ and Emend™.
Another colloidal drug carrier is liposomes, which are comprised of one or multiple lipid bilayers of amphiphilic lipids (such as cholesterol phospholipids, glycolipids, etc.). Size ranges from about 20 nm to a few micrometers, with membranes of about 5 nm.
Liposomes are classified based on size, number of bilayers, and whether there exists inner vesicles within a vesicle. There are five classifications:
- Large Multilamellar Liposomes (MLV)
- Large Unilamellar Vesicles (LUV)
- Small Unilamellar Vesicles (SUV)
- Oligolamellar Large Vesicles (OLV
- Multivesicular Vesicles (MVV)
Some drug researchers use niosomes in order to prevent liposomes from being rapidly degraded and rendered unstable by several factors, including: pH level in the stomach, intestinal enzymes, bile salts, and during storage when unsaturated fatty acids are hydrolyzed, or when the ester bindings of phospholipids oxidized. There is still ongoing investigation to conclude whether niosomes are superior to liposomes in vivo.
Stay Tuned for Part 2
In part 2 of our overview of colloidal drug carrier systems, we will explore mixed micelles, colloidal liquid crystalline structures and microemulsions.
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