Transdermal

Transdermal refers to the method of delivering medication through the skin. This method is used to provide a controlled release of medication into the bloodstream over a period of time. Transdermal delivery systems are often used for medications that require steady blood levels and are an alternative to oral or injectable routes.

Mechanism

Transdermal drug delivery involves the application of a drug formulation onto the skin, where it is absorbed into the bloodstream. The skin acts as a barrier, and the drug must penetrate the outer layer, the stratum corneum, to reach the systemic circulation. This is achieved through the use of transdermal patches, which are designed to adhere to the skin and release the drug at a controlled rate.

Advantages

Transdermal delivery offers several advantages over other routes of administration:

• **Avoidance of the gastrointestinal tract**: This method bypasses the digestive system, reducing the risk of gastrointestinal side effects and drug degradation by stomach acids.
• **Improved patient compliance**: Transdermal patches are easy to apply and can be worn for extended periods, reducing the frequency of dosing.
• **Controlled release**: The delivery system can be designed to release the drug at a constant rate, maintaining steady blood levels.

Disadvantages

Despite its benefits, transdermal delivery also has limitations:

• **Skin irritation**: Some patients may experience irritation or allergic reactions at the site of application.
• **Limited drug types**: Only drugs that are potent and have suitable molecular properties can be effectively delivered transdermally.
• **Variable absorption**: Factors such as skin condition, age, and site of application can affect drug absorption.

Applications

Transdermal patches are used for a variety of medications, including:

• Nicotine replacement therapy for smoking cessation.
• Hormone replacement therapy, such as estrogen patches.
• Pain management with opioid patches like fentanyl.
• Cardiovascular disease treatment with nitroglycerin patches.

History

The concept of transdermal drug delivery has been around for centuries, with early examples including the use of herbal poultices. Modern transdermal patches were developed in the 1970s, with the first FDA-approved patch being a scopolamine patch for motion sickness in 1979.

Research and development

Ongoing research in transdermal delivery focuses on improving patch technology, enhancing drug penetration, and expanding the range of drugs that can be delivered transdermally. Innovations include microneedle patches and iontophoresis, which use electrical currents to enhance drug delivery.

Related pages

• Drug delivery
• Pharmacokinetics
• Topical medication

References

A person applying a transdermal patch.