Transdermal patches are medicated adhesive patches that are placed on the skin to deliver a pre-prescribed dose of medication through the skin into the bloodstream. The drug is then carried in the circulatory system in the body to the target site. It does not involve the digestive systems in drug delivery or absorption and thus significantly reduces the common side effects. This non-invasive drug delivery method allows long-term and steady absorption, providing an alternative delivery method to injection and oral medication. It is not only applicable in pharmaceuticals but also in the cosmeceutical industry, including cosmetics and skincare.

Since ancient times, humans have been putting herbs and natural ingredients on their skin for medical benefits and purposes.  However, it was not until 1979, that the U.S. Food and Drug Administration approved the first commercially available prescription patch – Scopolamine – for the treatment of motion sickness. Today, there are many therapeutically active drugs marketed as transdermal patches for different indications. These patches have demonstrated efficacy in addressing a spectrum of conditions, encompassing smoking cessation, attention-deficit/hyperactivity disorder (ADHD), Alzheimer’s disease, Parkinson’s disease, anti-pyretic, and depression.

Advantages and Disadvantages of Transdermal Drug Delivery

Advantages	Disadvantages
Controlled and steady delivery	Skin irritation
Avoid first-pass metabolism	Limited dosing option
Bypass the digestive system	Variability (age, different site on the same person, different person) in the barrier function of the skin
Reduced side effects	A limited type of medication (e.g. not suitable for hydrophilic drugs due to low penetration through the skin)
Less invasive
Easy application

How does Transdermal Drug Delivery Work?

To administer a drug through the skin, it must have certain characteristics. The molecules that compose it must be lipophilic (that is, capable of being transported in lipids), and have a low molecular weight. For the drugs to reach the bloodstream, the molecules must move from the patch through a few skin layers before reaching the bloodstream. First, the molecules need to pass through the stratum corneum, which is the outer layer of dead, flattened skin cells that help prevent toxins and bacteria from getting inside the body. The molecules then go into the epidermis, penetrate into the dermis and are finally absorbed into peripheral capillary vessels to be distributed into the rest of the body.

The Mechanism Behind Transdermal Drug Delivery Patches

Transdermal patches consist of several layers, each serving a specific purpose.

1. Backing layer:

This is the outermost layer that protects the patch from the environment.

2. Drug layer:

Contains the medication. This can either be a separate layer or part of the adhesive layer.

3. Membrane:

Semi-permeable material that controls the release of the drug from the patch.

4. Adhesive Layer:

The sticking layer that adheres the patch to the skin, and in some patches releases the drug.

5. Liner:

The covering for the adhesive, that needs to be removed before applying the patch to the skin

4 Types of Transdermal Patches

There are generally four main types of transdermal patches:

Drug-in-Adhesive: 

This is the simplest form, where the entire patch is made of a single layer of adhesive which includes the drug dosage (single layer), or it contains more than one layer of drug-in-adhesive (multi-layer). The drug mixture is sandwiched between the backing and the liner.

Reservoir: 

The drugs are in the drug reservoir between the backing and the membrane. The drugs are slowly released through the rate-controlling membrane, and then through the adhesive to the skin.

Matrix: 

The drugs are kept in a semi-solid matrix. The adhesive layer in this type of patch usually surrounds this matrix.

Vapour Patch: 

The adhesive layer of a vapour patch releases vapour, which can last up to six hours and is mostly used as a decongestant or sleep aid.

The advent of transdermal patch technology has ushered in a new era of convenience and effectiveness. The ability to deliver medications and cosmetic ingredients directly through the skin has revolutionised the way we approach treatment and self-care. Transdermal patches offer a host of advantages, from consistent and controlled drug delivery to improved patient compliance and reduced side effects. These patches have already proven their worth in addressing various ailments and enhancing cosmetic routines, making a significant impact on health and wellness.

The future of transdermal patch technology holds promise and potential that extend beyond its current applications. Transdermal patches could offer personalised treatments tailored to individual patient needs, allowing for precise dosing and targeted therapies. In cosmetics, the integration of advanced formulations into patches could lead to transformative skincare and beauty routines, maximising the benefits of active ingredients. The combination of transdermal patches with emerging technologies like nanotechnology and wearable devices could open doors to real-time monitoring and adaptive drug delivery. Find out how researchers monitor the efficacy of transdermal formulation and patches.

In conclusion, transdermal patch technology has already proven its worth in addressing various ailments and cosmetic needs. With continuous research and innovation, the horizon is bright for these patches to play an increasingly vital role in shaping the future of healthcare and beauty, providing convenient, effective, and personalised solutions for individuals worldwide.

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References

• Jeong, W.Y., Kwon, M., Choi, H.E. et al. Recent advances in transdermal drug delivery systems: a review. Biomater Res 25, 24 (2021). https://doi.org/10.1186/s40824-021-00226-6
• Wong WF, Ang KP, Sethi G, Looi CY. Recent Advancement of Medical Patch for Transdermal Drug Delivery. Medicina (Kaunas). 2023 Apr 17;59(4):778. doi: 10.3390/medicina59040778.