Transdermals

Transdermals are a method of drug delivery that utilizes the skin as a route for systemic administration. This technique involves applying a patch or other dosage form containing a medication directly to the skin. The drug then passes through the epidermis and dermis to enter the bloodstream, bypassing the digestive system and first-pass metabolism in the liver. This can lead to more consistent drug levels and potentially reduce side effects associated with oral medications.

The skin's barrier properties, particularly the stratum corneum, pose a significant challenge for transdermal drug delivery. To overcome this, transdermal systems often incorporate penetration enhancers, which temporarily alter the skin's structure to facilitate drug passage. The design of a transdermal patch typically includes a backing layer, a drug reservoir or matrix, a rate-controlling membrane (in some designs), and an adhesive layer.

Commonly delivered medications via transdermal patches include nicotine for smoking cessation, hormones for hormone replacement therapy, pain relievers like fentanyl, and medications for motion sickness. Advantages of transdermal delivery include ease of use, patient compliance due to infrequent dosing, and avoiding gastrointestinal irritation. However, limitations can include slower onset of action compared to injection, potential for skin irritation at the application site, and the inability to deliver larger or highly water-soluble molecules effectively. The rate of drug release and absorption is influenced by factors such as the drug's properties, the patch design, and the skin's condition and location of application.