Transdermal Delivery: Why it's better for some molecules

The word transdermal refers to a delivery system that passes through the skin in order to deliver drugs or compounds into the body. Topicals and transdermal patches are becoming increasingly popular in the healthcare industry because they have distinct advantages over other delivery methods, including sprays, tinctures, pills and injections. Let’s take a look at why transdermal delivery is optimal for some molecules.

Transdermal vs. Oral

There are two main routes of drug administration. Some drugs are absorbed through mucous membranes in the mouth, skin, or nose (topical or transdermal). Others are swallowed and metabolized in the gastrointestinal tract before they’re able to reach their target tissues (oral). Each route has advantages and disadvantages. If you want to release a molecule slowly over time, transdermal delivery is more efficient than oral—and potentially safer than injection or inhalation. But most drugs can be absorbed orally, making ingesting your medication an easy-to-swallow pill (or quick sip) far more convenient.

Many people believe that transdermal is best suited for small molecules like vitamins or steroids, while larger biologics like proteins should be administered via IV. This isn’t necessarily true. It depends on whether your drug binds well to fatty acids, which are essential components of human tissue. Because smaller molecules tend to have higher lipid solubility—that is, they dissolve well in fats or lipids—they are usually delivered transdermally. On the other hand, big protein drugs often require high doses because only a certain amount can fit into blood vessels at any given time; these large particles clog arteries if delivered through direct topical application. Additionally, orally delivered drugs must survive the digestive tract and processing by the liver before they are circulated through the body, whereas transdermal medications can directly act on their application site without such steps.

Transdermal = Rapid Absorption

The skin is a highly effective barrier to many chemicals. For example, aspirin takes about an hour to be absorbed through your skin. That’s a long time compared to a pill that dissolves in just a few seconds. Of course, pills have much less surface area than your entire forearm. Transdermal gels and patches have been developed as alternatives because they take advantage of the human body's natural ability to absorb substances through our skin leveraging our metabolism. Metabolism is a term used to describe the process by which chemical compounds entering the body are broken down into smaller components or modified to form new compounds that can be used by our cells in various ways. One kind of metabolism involves metabolic enzymes that alter specific regions of drug molecules so they can cross from one side of a cell membrane to another by following chemical gradients, which allow compounds from areas with higher concentrations to flow freely toward areas with lower concentrations - i.e., from inside cells to outside across membranes.

Not all Molecules are Ideal for Transdermal Delivery

Most people are familiar with oral medications, topical ointments, and injections. However, there is another method of drug administration known as transdermal (also referred to as topical) which is becoming more popular due to its many benefits. To understand these benefits, it is necessary to understand how transdermal medications work. By definition, trans means through or across while derm refers to skin so transdermal drugs are applied to or through your skin.

There are a number of different ways in which transdermal medications work including iontophoresis, phonophoresis, microspheres and ultra-high potency creams. In most cases, transdermal drugs utilize a chemical process called diffusion in order to move from a site on one side of your skin into your bloodstream on the other side. Molecules simply pass from their point of entry to your bloodstream much like water can permeate a sponge when it gets wet. Although simple in theory, there are several characteristics that determine whether or not a molecule will be suited for use by transdermal medication delivery. While pharmacologists specialize in delivering all types of molecules including hydrophilic, lipophilic and amphiphilic, you don’t need a doctorate to understand their foundational logic. Hydrophilic compounds, dissolve best in water as the roots, Hydro- meaning water and -philic meaning loving, indicate. As such, lipophilic compounds do best in oils and will often be described as hydrophobic.

Lastly, amphiphilic compounds are amendable to dissolving in either system. Because our skin is composed of both hydrophobic and hydrophilic components, amphipathic are the among the easiest to deliver by transdermal systems. However, this doesn’t mean that you can rule out hydrophilic and hydrophobic compounds for such systems.