By Shreya Kanade, GCI member-at-large
An efficient way to administer pharmaceutical drugs to a patient is through a tablet. The drugs are measured and coated in a plastic that is broken down when the drugs are injected into the person, and the drug is absorbed into the bloodstream and transported to the tissue it acts upon. The traditional processes of packaging drugs in these plastics, however, often require the usage of high temperatures and solvents that can be harmful. For example, many volatile organic compounds like benzene and chloroform are used. There is the potential for some of the solvent to remain as a residual impurity after the manufacturing process and can be toxic to the patient or the environment. These materials also need specific management to prevent them from escaping into the atmosphere. Even more, the process of coating the drugs sometimes reduces the efficiency of the dose; for instance, high temperatures and volatile solvents can cause up to a 50% drop in efficacy (1).
At the University of Nottingham, Professor Steve Howdle and his team have used green chemistry techniques to design a plastic coating that does not decrease drug efficacy. The plastic degrades in the body at a controlled rate, releasing the drug into the patient over a specific period.
Professor Howdle uses supercritical fluids (Figure 1), specifically supercritical carbon dioxide (sc-CO2), instead of the conventional benzene and chloroform solvents typically used (1). A supercritical fluid has properties of both liquids and gases at a certain pressure and at around room temperature. Using sc-CO2, conventional solvents are not required and biodegradable plastics can be used to make polymers that coat the drugs before being administered to the individual. Furthermore, it has been demonstrated that using sc-CO2 allows for the plasticization of these polymers near room temperature, which means that the drug activity is unaffected. At room temperature, the plastics are solid but when exposed to high pressure (i.e. the critical pressure of sc-CO2), they liquify and allow for the drugs to be mixed in. Once in the blood, the polymers degrade slowly over days, allowing for a steady release of the drug into the patient. This maximizes the effect of the medicine and reduces the duration of the patient’s treatment regime. Polymers can degrade at different rates and the rate of degradation can be matched with the administered drug that best suits the patient’s needs.
These techniques can allow patients to receive medications that were previously unavailable due to the drugs being too delicate or too reactive to withstand the traditional methods of coating. Because proteins are so sensitive, they are not able to withstand elevated temperatures or strong solvents; with Dr. Howdle’s techniques, however, patients will soon have access to these treatments. Furthermore, because these processes do not include volatile organic solvents, there are no residues that could potentially be harmful to the patients or the environment.
- University of Nottingham. Using Green Chemistry To Deliver Cutting-edge Drugs. https://www.sciencedaily.com/releases/2007/09/070913132945.htm (accessed Nov 29, 2020).
- Supercritical fluids. https://equilibriumthermodynamics.weebly.com/supercritical-fluids.html (accessed Nov 29, 2020).