What is The Transdermal Delivery System?

Transdermal delivery involves the absorption of medicinals, nutraceuticals, and even cosmoceuticals and aromatherapy via a patch or liquid (gel, cream, etc) applied directly to the skin. The substance then travels through the outermost layers of skin to the highly vascular dermis layer and subcutaneous tissue, where it enters the bloodstream and exerts its medicinal action. Some systems even claim to bypass these deeper layers, penetrating the muscle layer below.

This absorption through the skin can happen intracellularly (between the cells), through transcellular absorption (across the cells), or via transappendageal penetration, which occurs at hair follicles and sweat and sebum glands.

Common Transdermal Delivery Products

Whether you realize it or not, you are probably familiar with a few well-known examples of transdermal delivery systems. The nicotine patch is the highest-selling transdermal patch in North America. It releases nicotine in small, controlled doses through the dermis (skin) to help with smoking cessation. Hormonal patches have also increased in popularity. Estrogen patches for the treatment of menopausal symptoms, contraceptive patches for birth control, and testosterone patches for both men and women are a few examples. Opiod patches for severe pain relief are also available.

Researchers continue expanding transdermal technology beyond traditional patches. New systems now include microneedles, nanoparticles, liposomes, and smart delivery platforms.

What's The Difference Between Transdermal & Oral Delivery

The Liver's Role in Absorption Rate

The first-pass effect occurs after you take a substance orally. The digestive system sends that substance to the liver before circulation begins. The liver filters and metabolizes many compounds during this process. Substances with strong first-pass effects lose more active compounds during liver metabolism. This process can reduce the amount that reaches target tissues. Transdermal delivery bypasses first-pass matabolism through the liver. This route may improve bioavailability for certain substances. Some compounds require lower doses when delivered transdermally.

Compromised Digestion

As we age, our digestive system, particularly enzymatic reactions that breakdown molecules to allow for easy and effective digestion and absorption of nutrients or medicines, slows down. As such, the older generation, and perhaps the most medicated and in need of nutritional support through supplementation, aren’t always able to take advantage of orally administered substances. Again, transdermal administration bypasses the digestive system completely. This is also of benefit to those with conditions such as IBS, Crohns, and Colitis. In these cases, intestinal permeability can affect nutrient, medication, and supplement absorption. Digestive conditions may reduce absorption through the gastrointestinal tract. Poor absorption can lower the effectiveness of some compounds.

Other Benefits of Transdermal Delivery

  • Transdermal delivery, as in the nicotine patch, also allows for a controlled release of medication into the system.
  • Transdermal delivery is less invasive than parenteral/IV therapy.
  • Transdermal delivery may only require once daily (sometimes once weekly or monthly) dosing/administration = Ease of use.
  • This also creates better patient compliance.

Disadvantages of Transdermal Delivery

The problem with transdermal delivery systems is that only certain types of substances, more specifically, smaller molecules with the ability to diffuse into skin lipids, can pass through the skin for direct absorption into the bloodstream.

Hindrances To Transdermal Delivery Products

The Skin Barrier

The skin is actually an extremely effective barrier system (If it weren’t, we’d be in a lot of trouble!). As such, only small molecules that will effectively diffuse into skin lipids can effectively pass. The challenge is to allow for better penetration through the thick stratum corneum layer of the epidermis (the outermost layer of the skin) without modifying the medicinal substance itself. Drug manufacturers attempt to do this by pairing these medicines with a substance that will change the skin, instead altering the physicochemical properties of the stratum corneum, the structure of the lipids and lipoproteins in the cellular channels, and increasing hydration. When this is not possible, or further help is necessary, they design a carrier mechanism to literally transport the drug across these first layers. Studies using an applied electrical field (iontophoresis) or high frequency ultrasound are also showing promising results and may enable larger molecules to pass.

Limited Product Permeability

These delivery systems are also, at this time, reserved for more potent medications. Potent compounds often require smaller doses for therapeutic effects. Some compounds penetrate the skin barrier more effectively than others. Rotate patch placement regularly to reduce skin irritation. Skin irritation can limit the use of some transdermal products.

Researchers continue developing new transdermal delivery technologies. These innovations may expand future options for medications and natural compounds.