Drug delivery systems control the rate at which a drug is released and the location in the body where it is released. Some systems can control both. Drugs have long been used to improve health and extend lives. The practice of drug delivery has changed dramatically in the past few decades and even greater changes are expected in the near future. Biomedical engineers have taken part substantially to the understanding of the physiological barriers to efficient drug delivery, such as transport in the circulatory system and drug movement through cells and tissues; they have also contributed to the development of several new modes of drug delivery that have entered clinical practice.
Yet, with all of this progress, many drugs, even those discovered using the most advanced molecular biology strategies, have unacceptable side effects due to the drug interacting with healthy tissues that are not the target of the drug. Side effects limit ability to design optimal medications for many diseases such as cancer, neurodegenerative diseases, and infectious diseases.
Drug delivery systems control the rate at which a drug is released and the location in the body where it is released. Some systems can control both.
Administering drugs locally rather than systematically is a common way to decrease side effects and drug toxicity while maximizing a treatment’s impact. A topical antibacterial ointment for a localized infection or a cortisone injection of a painful joint can avoid some of the systemic side effects of these medications. There are other ways to achieve targeted drug delivery, but some medications can only be given systemically.
Routes for Delivery
Medications can be taken in a variety of ways by swallowing, by inhalation, by absorption through the skin, or by intravenous injection. Improving current delivery methods or designing new ones can enhance the use of existing medications.
The more targeted a drug is, the lower its chance of triggering drug resistance, a cautionary concern surrounding the use of broad-spectrum antibiotics. Nanotechnology is opening up new avenues for drug delivery vehicles.
Perhaps the most obvious route to improving disease treatment would be to focus on the medications themselves. In addition to drugs and novel vaccines, researchers are also exploring the use of genes, proteins, and stem cells as treatments.
In drug delivery research, this means starting with a delivery method. The target may be whole organs (heart, lung, brain), tissue types (muscle, nerve), disease-specific structures (tumor cells), or structures inside of cells. Further research aims to develop viral nanoparticles that can deliver chemotherapy drugs directly to tumors. Such an advance would reduce the severe side effects usually associated with cancer treatment.
There are commonly two ways through which nanostructures deliver drugs:
In the passive, drugs are incorporated in the inner cavity of the structure mainly via the hydrophobic effect. When the nanostructure materials are targeted to particular sites, the intended amount of the drug is released because of the low content of the drugs which is encapsulated in a hydrophobic environment. Conversely, in the self-delivery, the drugs intended for release are directly conjugated to the carrier nanostructure material for easy delivery. In this approach, the timing of release is crucial as the drug will not reach the target site and it dissociates from the carrier very quickly, and conversely, its bioactivity and efficacy will be decreased if it is released from its nanocarrier system at the right time.