The Ins and Outs of Transdermal Drug Delivery Systems

Written by Nick Lesniewski-Laas, Director of Electrical Engineering
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When designing new drug therapies, pharmaceutical and medical device companies must determine which method is best for delivering the medication to the target sites. Patients are generally familiar with drugs delivered via oral, topical, intravenous, and intramuscular routes. Transdermal drug delivery is the application of a medicine or drug through the skin, typically by using an adhesive patch, so that it is absorbed slowly into the body. It is becoming an increasingly popular option as it allows for a controlled release of medication while its ease-of-use enhances patient adherence.

 

The ABC’s of TDDS 

A Transdermal Drug Delivery System (TDDS) administers medication through intact human skin at a controlled rate to the systemic circulation. Oftentimes a patch or adhesive is used where the dosage either passes through a porous membrane containing the drug, or body heat melts layers of medication integrated within the adhesive. While oral medications can sometimes prove problematic to the digestive tract and liver, transdermal drugs bypass the digestive system and enter the bloodstream at a controlled rate regulated by the skin. As a result, patients using a TDDS may experience improved dosage efficacy compared to other delivery systems.

 

Advantages and Disadvantages 

Delivery of medication through an oral route isn’t always an available option as the medication may not be properly absorbed due to gastrointestinal acid, enzymatic activity, or interference with food, drink, or other types of oral drugs. Transdermal administration can prove to be a superior alternative in this instance as it avoids first-pass metabolism and drug deactivation by liver enzymes. It is also ideal for drugs that have a narrow therapeutic window. The method is non-invasive and provides extended therapy with a single application. A TDDS patch can be quickly terminated by removing the patch from the skin. Also, because physical patches are visible, emergency responders and clinicians can quickly identify the drug that an unresponsive, unconscious or comatose patient is using.

Transdermal drugs do have some disadvantages. Since the skin provides a barrier it can limit potent drug molecules, prohibiting delivery into the blood. Patches may cause some skin irritation in certain patients, while others may object to their comfort and cosmetic levels, possibly decreasing compliance.

 

Enhancing TDDS with Electronics

Skin tolerability, skin barrier properties, and variability of application site conditions can all be constraints limiting the viability of drug delivery via a transdermal route. With the help of electronics, effective drug delivery via TDDS is possible. Iontophoresis is a technique of introducing ionic medicinal compounds into the body through the skin by applying a local electric current. Another approach to enhancing TDDS is microporation of the biological barrier, which involves applying an alternating current to microelectrodes and making contact with the skin. Additionally, skin microporation can also be achieved by using very short laser pulses.  

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