What Drugs Can Be Absorbed Through the Skin?

Discover what drugs can be absorbed through the skin, their risks, and the future of transdermal delivery.

Published On

June 13, 2024

Dove Recovery's Team

What Drugs Can Be Absorbed Through the Skin?

Understanding Skin Absorption

To comprehend the risks of drugs that can be absorbed through the skin, it's essential to first grasp the mechanism of skin absorption and the factors that influence skin permeability.

Mechanism of Skin Absorption

Skin absorption is a process that involves the body breaking down drugs, separating active ingredients from inactive ones, and allowing these active ingredients to enter the bloodstream, leading to the drug's effects [1]. Passive diffusion is the most common route of drug absorption through the skin, where drugs move from an area of higher concentration to an area of lower concentration across the skin layers [2].

The stratum corneum, the outermost layer of the epidermis, plays a critical role in this process. It acts as a selective barrier that controls the passage of molecules based on their physicochemical properties. The lipophilic nature of the stratum corneum allows for the absorption of lipid-soluble drugs more easily compared to hydrophilic drugs.

Factors Influencing Skin Permeability

Several factors influence skin permeability and the absorption of drugs through the skin. The skin is the principal barrier to percutaneous transport, with the stratum corneum being the main barrier within the skin. A mathematical model has been developed to correlate the permeability of the membrane to a specific penetrant with the water solubility of the penetrant and with its lipid-protein partition coefficient [3].

The skin's barrier function is primarily accomplished by the stratum corneum, a unique biomembrane that is thin, least permeable, and forms a laminate of compressed keratin-filled corneocytes anchored in a lipophilic matrix. The architecture of the stratum corneum plays a key role in the skin's barrier function, making it 1000-times less permeable to water compared to other biomembranes. Visualization studies have shown the twisting pathway of corneocyte arrangement in a lipid continuum, which contributes to the barrier function of the skin.

Understanding these mechanisms and factors is crucial in comprehending how certain drugs can pose risks when absorbed through the skin. The ability to get 'beneath the surface' helps in understanding the dangers of certain drugs and the potential harm they can cause.

Drugs Absorbed Through Skin

To understand the answer to the question "what drugs can be absorbed through the skin?", it's crucial to know that various substances can permeate the skin and enter the bloodstream. Some medications are specifically designed to be administered this way due to their unique properties and intended effects.

Pain Relief Medications

Pain relief medications like ibuprofen, lidocaine, and diclofenac can be absorbed through the skin using topical creams, gels, or patches for transdermal delivery. This method targets the affected area directly, providing relief while minimizing systemic side effects. The medication is absorbed directly into the skin at the site of pain, bypassing the digestive system, which can often lead to unwanted side effects when taken orally [5].

Type	Examples
Topical creams	Lidocaine
Gels	Diclofenac
Patches	Ibuprofen

Hormonal Patches

Another category of drugs that can be absorbed through the skin includes hormonal patches. These patches contain hormones like estrogen or progestin, which can be absorbed for systemic effects. They are commonly used for birth control or hormone replacement therapy, offering a controlled and steady release of hormones. This is a valuable alternative to oral medications that may cause stomach upset or have inconsistent absorption rates due to varying digestive conditions [5].

Type	Examples
Hormonal patches	Estrogen, Progestin

Nicotine Replacement Therapy

Nicotine replacement therapy (NRT) products, such as patches, gums, lozenges, and sprays, are another group of drugs that can be absorbed through the skin. These products deliver controlled amounts of nicotine to help individuals quit smoking. They work by reducing withdrawal symptoms and cravings, allowing for gradual weaning from cigarettes and managing nicotine addiction.

Type	Examples
NRT products	Nicotine patches, gums, lozenges, sprays

Understanding how drugs can be absorbed through the skin aids in grasping the potential risks, benefits, and implications of various medications. It's always essential to consult with a healthcare provider before starting any new medication regimen, whether it's administered orally, transdermally, or through other routes.

Enhancing Drug Absorption

While the skin acts as a natural barrier protecting the body from potential harm, it is also a viable route for drug administration. A variety of methods have been developed to enhance drug absorption through the skin, which are critical for the effectiveness of treatments involving skin absorption.

Transdermal Drug Delivery Systems

Transdermal drug delivery systems have been employed to facilitate the controlled release of drugs into the body through the skin. This method bypasses the gastrointestinal system, reducing the risk of systemic side effects and increasing drug bioavailability. However, the stratum corneum, the outermost layer of the skin, poses a significant barrier to drug absorption. Therefore, various strategies have been developed to enhance permeability.

One such strategy involves the use of permeation adjuvants like dimethyl sulfoxide, which can significantly enhance skin permeability. The effects of this adjuvant are consistent with accepted sorption-diffusion models of membrane transport, factoring in changes in penetrant activity induced by osmotic shock.

Physical Methods for Enhanced Penetration

Physical methods, such as iontophoresis, ultrasound, laser, and microneedles, have been employed to improve the therapeutic efficacy of transdermal drugs. These methods enhance drug penetration by temporarily and reversibly modifying the stratum corneum barrier, aiding in drug permeation. This is particularly useful when delivering larger molecules that wouldn't typically be able to pass through the skin on their own [6].

Role of Nanocarriers

Nanocarriers, including nanoparticles, ethosomes, dendrimers, and liposomes, have emerged as a promising approach for enhancing drug absorption through the skin. These carriers encapsulate drugs and deliver them across the stratum corneum, offering versatility in drug delivery for both lipophilic and hydrophilic drugs.

In particular, lipid nanoparticles like solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), liposomes, niosomes, and nanocrystals have been widely used for transdermal drug delivery. These nanoparticles offer benefits such as controlled release, enhanced drug diffusion, and improved bioavailability of drugs for dermal and transdermal applications.

The combination of nanocarriers with physical methods like iontophoresis, ultrasound, laser, and microneedles has the potential to further improve the therapeutic efficacy of transdermal drugs.

In conclusion, enhancing drug absorption through the skin is a complex process that involves multiple factors and strategies. By understanding these factors, scientists can develop more effective transdermal drug delivery systems and improve patient outcomes.

Skin Barrier Function

The skin acts as a formidable barrier to the passage of substances, including drugs. Its outermost layer, the stratum corneum, plays a significant role in protecting the body from unwanted substances and retaining bodily fluids. Understanding the skin barrier function is crucial in the context of what drugs can be absorbed through the skin.

The Role of Stratum Corneum

The stratum corneum, the outermost layer of the skin, is primarily responsible for the skin's barrier function. This unique biomembrane is thin but least permeable, forming a laminate of compressed keratin-filled corneocytes anchored in a lipophilic matrix. The skin's barrier function is attributed to the staggered corneocyte arrangement in a lipid continuum, making it 1000-times less permeable to water compared to other biomembranes [4].

It consists of dead skin cells and a lipid matrix that restricts the movement of molecules. The size, lipophilicity, and charge of drug molecules influence their ability to diffuse through this barrier [7].

Chemical Permeation Enhancers

Overcoming the skin's barrier function for drug delivery can be facilitated through chemical permeation enhancers. These are substances that alter the structure and properties of the skin barrier to make it more permeable. Chemical enhancers interact with the lipids in the stratum corneum, temporarily disrupting the skin barrier and thereby allowing drugs to pass through more easily [7].

Chemical permeation enhancers, such as fatty acids, alcohols, surfactants, and terpenes, can disrupt the lipid bilayer of the stratum corneum, enhancing drug absorption through the skin. They interact with the skin to improve drug permeation.

Tape Stripping Method

The tape stripping method is another technique used to measure skin permeability and the effectiveness of various transdermal drug delivery systems. It involves the application of a piece of tape to the skin surface, which is then removed, stripping off a layer of the stratum corneum. This method can provide valuable information about the skin's barrier function and the ability of drugs to permeate the skin.

The skin's barrier function is a crucial factor in determining what drugs can be absorbed through the skin. By understanding this function and the methods to enhance drug permeability, healthcare providers can make informed decisions about the best methods of drug delivery for their patients.

Advantages of Transdermal Delivery

Transdermal drug delivery systems, which allow the administered drug to be absorbed into the systemic circulation via blood vessels in the skin, offer several significant advantages over more traditional drug administration routes. This includes bypassing the gastrointestinal system, enhancing drug bioavailability, and providing advantages over conventional routes such as oral or injectable drug administration.

Bypassing Gastrointestinal System

One of the primary benefits of transdermal delivery is that it bypasses the gastrointestinal system. This is particularly beneficial for drugs that are susceptible to degradation in the stomach or liver. It also helps avoid potential side effects associated with gastrointestinal drug absorption, such as stomach upset or liver damage. Moreover, transdermal delivery avoids the first-pass metabolism, which can significantly reduce the effectiveness of certain drugs.

Enhancing Drug Bioavailability

Transdermal delivery also enhances drug bioavailability. Bioavailability refers to the proportion of a drug that enters the systemic circulation when introduced into the body and so is able to have an active effect. By delivering drugs directly into the bloodstream, transdermal systems can increase the bioavailability of a drug, enhancing its therapeutic effect and potentially reducing the required dose.

Advantages Over Conventional Routes

Transdermal drug delivery provides several advantages over conventional routes like oral or injectable routes. These include being less invasive and reducing the frequency of drug administration. Also, transdermal systems do not require expert personnel for administration, making them a convenient and user-friendly option. Furthermore, it allows both lipophilic and hydrophilic drugs to be delivered through the stratum corneum with the possibility of having local or systemic effects to treat various diseases.

The transdermal route also reduces toxicity and local irritation due to multiple sites for absorption and offers the option of avoiding systemic side effects. However, the effective barrier of the stratum corneum of the skin can pose difficulty for drug penetration. Fortunately, non-invasive methods and the use of nanocarriers have emerged as valuable alternatives for enhancing transdermal drug delivery.

While these advantages offer a promising outlook for transdermal drug delivery systems, it's important to remember that every drug is unique and not all drugs are suitable for this method of administration. Always consult with a healthcare provider to determine the most appropriate drug delivery system for each individual circumstance.

Future Trends in Transdermal Drug Delivery

In the field of transdermal drug delivery, there are several promising advancements and trends that are shaping the future. This includes the development of nanocarriers, innovations in physical methods, and significant market growth.

Nanocarriers Advancements

Nanocarriers, such as solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), liposomes, niosomes, and nanocrystals, have shown significant potential in the realm of transdermal drug delivery. These carriers offer numerous benefits including controlled release, improved bioavailability, increased skin penetration, and reduced systemic side effects.

Furthermore, the combined application of nanocarriers with physical methods, including sonophoresis, iontophoresis, microporation, and heating, has shown enhanced drug penetration compared to their individual use. These combined strategies improve drug delivery profiles, increase drug bioavailability, and amplify drug penetration for various therapeutic applications.

Physical Methods Innovations

A variety of physical methods such as iontophoresis, ultrasound, laser, and microneedles are being explored to improve the therapeutic efficacy of transdermal drugs. These methods enhance drug penetration through the skin by temporarily and reversibly modifying the stratum corneum barrier, assisting in drug permeation.

The integration of these innovative physical methods with advanced nanocarriers is a promising trend in the field, potentially leading to superior delivery mechanisms and improved therapeutic outcomes.

Market Growth and Potential

The market for transdermal drug delivery systems is showing robust growth, surpassing the pharmaceutical industry's average growth rate. Global sales of these systems reached US$12.7 billion in 2005, US$21.5 billion in 2010, and US$31.5 billion in 2015, demonstrating an average annual growth rate of 17.8%.

This growth trend underscores the potential in transdermal drug delivery, driven by advancements in technology, increasing research, and the rising prevalence of chronic diseases that require consistent drug administration.

The evolution of transdermal drug delivery is an exciting field to watch. With the advancements in nanocarriers and physical methods coupled with the growing market, the future holds promising possibilities for drugs that can be absorbed through the skin. This can potentially lead to improved treatment outcomes and better patient experiences in the future.