Insight into Drug Delivery Methods

By Marzia KhanReviewed by Emily Henderson, B.Sc.

The branch of medicine that encapsulates drug delivery has been revolutionary for advancing human health and aiding in infection control and prevention to provide a longer life span. This involves a process or method that delivers a drug to humans or animals for a therapeutic effect, which can include many different approaches that will be further discussed.

Image Credit: Kenishirotie

Drug delivery systems that introduce a therapeutic substance into the body include transporting and releasing active ingredients across biological membranes and into the target site.

The choice of drug delivery system utilized for delivering a particular therapeutic substance can be dependent on the disease, the desired effect, and the product itself. The two large subcategories these delivery systems fall under include having a systemic or targeted approach, where the drug is either distributed to the whole body with an effect on the diseased tissue or organ or is administered directly to the target area.

Oral Drug Delivery

This route of drug delivery is used for both conventional as well as novel drug delivery approaches and is considered to be the easiest mode of administration, with patients being very accepting and willing to take medication through this route. This is also a preferred method for patients afraid of needles or those in low-income countries where access to medicine and healthcare is more challenging, especially with higher infection rates. Oral medication can be considered a safer mode of providing therapeutic substances to the body without the dangers of needles and a lack of aseptic conditions.

However, some limitations of this drug administration method include the systemic effect that can cause a variable absorption rate and serum concentrations, but this can be overcome with sustained and controlled release systems. Other limitations include the acids and digestive enzymes that can break down drugs before absorption into the bloodstream.

Parenteral Drug Delivery

Parenteral drug delivery involves injecting active ingredients or substances through subcutaneous, intramuscular, intravenous, or intra-arterial routes. This is the most common invasive method used globally for the delivery of drugs into patients, with many important drugs being only available in a parenteral form. This mode of administration comprises the use of syringes with needles that are either plastic or glass.

The benefits of using this drug administration approach consist of being fast-acting, high reliability of reaching the target site, and avoidance of the gastrointestinal tract, which is a limitation that occurs in the oral drug delivery route. Furthermore, this method is not reliant on the patient, which is beneficial for patients with advanced illnesses or disorders that render them temporarily unconscious such as fainting or being comatose.

However, for awake patients, this mode of drug delivery can be less preferable due to the pain from the needle, so compliance for this administration route is not as high as with oral drug medications. Additionally, this route can also be limited for sustained drug levels, which is something that can be addressed further with novel drug delivery methods.

Transdermal Drug Delivery

This drug administration approach includes the delivery of substances through the skin and can consist of transdermal gels, drug carriers such as liposomes and nanoparticles, which carry the active ingredient to the targeted site, and transdermal patches.

The administration of drugs in this approach can be enhanced through iontophoresis, which includes a voltage gradient on the skin, allowing the therapeutic substances to be transported through the stratum corneum layer, enabling these molecules to bypass the skin barrier.

Microneedles can also be used for this approach, involving a single or array of tiny needles within a possible patch form, allowing the skin to be penetration so the drug can be administered. This is less invasive and painful than normal hypodermic needle drug delivery approaches and can also be easier for healthcare systems as this method requires less staff training.

With the advancement in nanotechnology, which utilizes nanoparticles, the size of 1-100 nm, the field of transdermal drug delivery may have emerging developments that provide both targeted drug delivery through the use of these nanocarriers, with also the benefit of being less invasive and painful.

Other Drug Delivery Methods

Other drug delivery methods can consist of nasal sprays that can be used both topically and systemically; this can be used for allergies and has also been researched for systemic, whole-body delivery routes. Colorectal drug delivery, including the delivery of drugs to the rectum, has been dated to 1500 BC and is considered to provide a safe and slow absorption rate for the drug. However, this method is no longer a preference in modern society.

Pulmonary drug delivery has also been in use since the mid-20^th century, such as for treating respiratory disorders, including asthma; however, this mode of administration may also hold potential for systemic delivery treatments.

Future Outlook

While conventional drug administration routes have been steadfast and reliable for the treatment of diseases and disorders thus far, such as the use of oral drug delivery, eye drops, nasal sprays, and parenteral methods, other delivery methods may become a preferred mode of drug administration, such as transdermal drug delivery. This approach can transport drug molecules across the skin barrier for both systemic and targeted effects and, if combined with nanotechnology advances via nanocarriers, may revolutionize medicine and clinical drug delivery methods, enabling targeted and sustained drug delivery for optimum therapeutic effects.

Further Reading

• All Drug Discovery and Manufacturing Content
• Drug Discovery, Manufacturing, and Development
• What are Peptide Decoys?
• Using Artificial Intelligence to Discover New Antibiotics
• Applications of 3D printing in Drug Delivery