Benefits of Microspheres in Drug Delivery
There are numerous benefits of using microspheres in drug delivery due to their precise uniform dimensions, larger surface area per unit volume, as well as the ability to be surface-functioalized or loaded with active compounds and other additives. Typically microspheres in drug delivery are manufactured out of biodegradable materials such as PLGA, polylactic acid, or polycaprolactone, but in some cases they may be made out of inert materials that can stay in the body once the therapeutic function has been completed (e.g. radioactive glass microspheres for targeted cancer treatment).
When a drug is encapsulated or embedded in another material, such as a microsphere, the drug is protected from the environmental conditions and released at controlled rates for relatively long periods of time.
- Drug release rates can be tailored to the needs of a specific application; for example, providing a constant rate of delivery or pulsatile release.
- Controlled release systems provide protection of drugs, especially proteins, that are otherwise rapidly destroyed by the body. Better protection of drugs against environment conditions.
- Controlled release systems can increase patient comfort and compliance by replacing frequent (e.g., daily) doses with infrequent (once per month or less) injection. Reduces the dosing frequency and therefore improvement in patient compliance.
- Microsphere-based drug delivery systems provide prolonged and constant therapeutic effect.
- Microspheres in drug delivery produce more reproducible drug absorption.
- Drug discharge in stomach is hindered and that’s why local unwanted effects are reduced.
- Better therapeutic effect for short half-life of drugs can be achieved. Microspheres enhance the biological half-life and also improve the bioavailability.
- Dose dumping effect can be reduced by microspheres.
- Microspheres reduce the chances of G.I. irritation.
- Microspheres provide freedom from drug and recipients incompatibilities especially with buffer.
- Taste and odour of unpleasant drugs can be effectively masked.
- Microspheres reduce the first pass metabolism.
- Microspheres can be easily injected in body because of their small and spherical size.
Surface-Functionalized Microspheres in Drug Delivery
Due to small size and spherical shape, microspheres can be deliverd via oral, parentral, nasal, ophthalmic, transdermal, colonal delivery methods. The plain and fluorescent particles which have surfaces functionalized with carboxyl groups allow for covalent attachment of proteins, peptides, antibodies, antigens, and small molecules. This enables the following functionality:
- Target a specific site, e.g. tumor;34
- Facilitate cell entry;5
- Help cross blood-brain barrier;6
- Increase solubility and bioavailability;7
- Extend plasma circulation time; typically this is done by using PEGylated PLGA nanoparticles.8
Degradex® PLGA particles is an example of a commercially-available biodegradable particle that may also be used as a carrier in which drug molecules can be attached to the particle surface and delivered.
Radioactive Microspheres in Drug Delivery
An example of microspheres used as a medical device for Selective Internal Radiation Therapy (SIRT) for liver tumors are SIR-Spheres® Y-90 resin microspheres.
- SIR-Spheres Y-90 resin microspheres are a permanent implant and for single use only.
- The biocompatible resin microspheres labelled with yttrium-90 have a median diameter of 32.5 microns (range between 20 and 60 microns).
- SIR-Spheres® Y-90 resin microspheres is a prescription device for the treatment of inoperable liver tumors. It is a minimally invasive treatment that delivers high doses of high-energy beta radiation directly to the tumors.
- This therapy is performed using minimally invasive surgical techniques by an interventional radiologist.
- By using the tumors’ blood supply, the microspheres selectively target liver tumors with a dose of radiation that is up to 40 times higher than conventional radiotherapy, while sparing healthy tissue.9
The largest application for microspheres in medicine is drug delivery. Sales of advanced drug delivery systems in the U.S. alone exceeded $13 billion in 1997, and are expected to increase. The medical uses of particulate drug delivery systems cover all areas of medicine such as cardiology, endocrinology, gynecology, immunology, pain management and oncology. 10
Drug delivery systems—designed to provide a therapeutic agent in the needed amount, at the right time, to the proper location in the body, in a manner that optimizes efficacy, increases compliance and minimizes side effects—were responsible for $47 billion in sales in 2002.1
Most of the advanced drug delivery systems utilize microspheres or microcapsules for the encapsulation of drugs and proteins . The drug-loaded microspheres can be applied locally or delivered to the target area after intravenous injection by either passive means (e.g., trapping by size) or active means (e.g., magnetic targeting). From the target area, the encapsulated drug is slowly released over the desired time period, the length of which is determined mainly by the drug’s biological half-life and its release kinetics from the microsphere matrix. 10
This type of encapsulated drug delivery system has the advantage of protecting the encapsulated drug from the in vivo environment until time of release.10
In the video below, Andrew Kennedy, MD, physician-in-chief, Radiation Oncology, Sarah Cannon, director, Radiation Oncology Research, Sarah Cannon Research Institute, discusses the utilization of radioactive microspheres for controlling liver tumors.
Despite dramatic growth and acceleration in the last decade, the utilization of microspheres in drug delivery is still in its infancy and a lot more research needs to take place in order to improve the efficiency of microsphere manufacturing processes and the availability of biodegradable materials to use for these applications.
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- Solanki, Neeta. (2018). Microspheres an innovative approach in drug delivery system. MOJ Bioequivalence & Bioavailability. 5. 10.15406/mojbb.2018.05.00083.
- Brigger, I.; Dubernet, C.; Couvreur, P. Nanoparticles in Cancer Therapy and Diagnosis. Adv. Drug Deliv. Rev. 2002, 54, 631-651.
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- Hillaireau, H.; Couvreur, P. Nanocarriers’ entry into the cell: relevance to drug delivery. Cell. Mol. Life Sci. 2009, 66, 2873-2896.
- Nanoneuroscience and Nanoneuropharmacology. In Progress in Brain Research. Sharma, H. S., Eds.; Elsevier: Amsterdam, 2009; pp198.
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- Moffatt, S. Nanoparticle PEGylation for Cancer Therapy. MOJ Proteom. Bioinform. 2015, 2.
- Urs Häfeli, Review: Radioactive Microspheres for Medical Applications, Cleveland Clinic Foundation, Radiation Oncology Department T28 9500 Euclid Ave., Cleveland, OH 44195