Transdermal Delivery of Medications Shows Promise, But Barriers Remain

By Ronald L. Scott
Rscott@central.uh.edu

On November 17, 1998, the United States Patent and Trademark Office (USPTO) issued a patent for the transdermal delivery of medications that uses a combination of “penetration enhancers.”  See Patent 5,837,289, Grasela et al., available at the USPTO web site. The patent claims the invention provides for a “convenient, efficacious and simple transdermal administration of medications from a topically applied cream.”  The composition incorporates “penetration enhancers” which provide for a “rapid but controllable transport of the medication from the cream into the skin.”

Some drugs already are administered transdermally using a patch.  For example, scopolamine is used to prevent motion sickness, nicotine derivatives are used as an aid to stop smoking, and hormones such as estrogen are used in hormonal replacement therapy.  Transdermal administration can be “location specific,” i.e., the medication can be delivered exactly where needed.  For example, a muscle relaxer or a pain reliever could be delivered directly to a sore leg muscle without having to first pass through the gastrointestinal system.  Further, the dosage of medication needed for a transdermal administration may be significantly less than that required for an injection.

The inventors claim that patches do have disadvantages compared to application via a creme or ointment.  First, the delivery of the medication is limited by the rate of passage of the medication through the patch membrane.  Some medications require rapid delivery to be effective and thus may not be good candidates for delivery via a patch.  Also, the adhesive holding the patch to the skin could fail, leaving a quantity of medication in the patch’s reservoir.

Nonsteroidal anti-inflammatory drugs (NSAIDs) including the over-the-counter drugs Advil®, Aleve®, and aspirin, and the prescription drug Celebrex® are often used to treat inflammation such as a muscle sprain.  However, many NSAIDs can cause stomach irritation including nausea and vomiting, ulcers, and kidney damage.  See http://www.nsaid.net/.  Trans-Pharma Corporation and pharmacists at University Compounding Pharmacy (UCP)  jointly developed the patented transdermal delivery system.  The inventors said they have dispensed thousands of prescription drugs transdermally with excellent results during the developmental period.

Transdermal delivery of medications appears to offer significant advantages over injection or ingestion, but barriers remain.  Transdermally delivered NSAIDs are far more common in Europe than in the U.S.  They have been used in Europe for 15 years and account for two-thirds of the most frequently prescribed NSAIDs in Germany.  And six topical NSAIDs have been licensed in the UK.  See http://www.ucprx.com/doctors_info.html.

Yet in the U.S., most transdermally delivered NSAIDs are available only as compounded pharmaceuticals. As such, they are exempt from many of the requirements of the Food, Drug and Cosmetic Act (21 U.S.C. §381 et seq.) including requirements that labeling be reviewed and approved by the Food and Drug Administration (FDA) and important quality control standards for manufacturing pharmaceuticals.  Also, the FDA has sought to limit pharmacies from filling more than 20% of their compounded prescriptions for out-of-state delivery.  See Should FDA Limit Interstate Shipment of Compounded Pharmaceuticals? 

Although some pharmaceutical companies are developing transdermal versions of drugs, their level of interest does not seem commensurate with the potential benefits to patients.  Perhaps money is the problem. Few U.S. patients are aware of the benefits (or even the existence) of transdermally delivered drugs.  There may be little economic incentive for companies to fund the necessary FDA approval process merely to market a different version of a drug that would probably be delivered in much lower doses at a reduced cost.

08/29/01