Transdermal patches: characteristics and uses

The transdermal patches have their antecedents in the medicines that, since time immemorial, were applied through the skin. Liniments, plasters and ointments were already used in ancient Greece, as a means to administer medications.

In the nineteenth century the thesis arose that the skin was impenetrable for some medications. This was maintained until the twentieth century, when it was proved that it was possible to administer various drugs through the skin. Over time, the transdermal patches were developed and turned out to be very functional.

Transdermal patches are part of the so-called "controlled release therapeutic systems". They are based on a principle postulated by John Urquhart, creator of the first patch for the skin, according to which the therapeutic efficacy of a substance does not depend on the dose, but on the speed and degree of its absorption.

What are transdermal patches?

Transdermal patches are devices that are used to administer medications. They are fixed to the skin by means of an adhesive and release a drug continuously, so that it is absorbed by the skin. That is, it traverses the successive layers of skin, until it reaches the blood.

For a drug to be administered through the skin, it must meet certain characteristics. The molecules that compose it must be lipophilic (that is, capable of transporting in lipids) and of low molecular weight.

Likewise, they must have a great pharmacological potency. This is because the body will only be able to absorb a small amount of product through the transdermal patches. At most, 10 milligrams per day.

Read also: Anatomy of the skin

Characteristics and operation

The transdermal patches are made up of four parts:

• A waterproof sheet of coating.
• A matrix or reservoir of the active ingredient, where the drug is housed.
• A adhesive.
• A plastic sheet which is removed before applying the patch.

Some patches differ from others, mainly, by the way in which the drug is stored and by the way in which the release of the drug occurs. From that point of view, there are basically three types of transdermal patches:

• Reservoir or reservoir systems. The active substance is dispersed in another substance and is released through a membrane. This may be of polypropylene, ethylene vinyl acetate copolymer or non-porous membrane.
• Matrix systems. The active principle is found in a matrix and is released by diffusion, without the help of a semipermeable membrane.
• Mixed systems. They combine the two previous systems.

Uses of transdermal patches

Currently there are several diseases, symptoms and problems that can be treated by transdermal patches. Among them: different types of pain, addiction to tobacco, Alzheimer's disease, Parkinson's disease and several other applications.

The active ingredients more administered in the form of parche are the following:

• Nitroglycerine. Mainly to prevent angina.
• Fentanyl and Buprenorphine. They are opiates that are used for analgesic purposes.
• Nicotine. To help in overcoming tobacco addiction.
• Ethinylestradiol + Norelgestromin. Of contraceptive effects.
• Estradiol, norethisterone. It is used as a hormonal treatment during menopause.
• Testosterone. To treat the effects of surgical menopause.
• Rotigotine. For the treatment of Parkinson's.
• Rivastigmine. For the treatment of Alzheimer's.

Likewise, There are several transdermal patches that are used for cosmetic purposes. Among them are body fat reducers, skin firming and anti-cellulite.

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Other data of interest

The Food and Drug Administration (FDA), Food and Drug Administration of the United States, has warned about drugs with which it is necessary to be especially careful when they are administered transdermally. These are, basically, contraceptives, opioid analgesics and rivastigmine.

The main advantages of these patches are:

• They facilitate the administration of drugs to people who have difficulty taking them orally.
• Offers more constant and sustained levels of the medication in the blood.
• Avoid metabolizing the medication through the liver, thus limiting several side effects.
• Sometimes, allow to reduce the frequency of administration and improve compliance with the posology.

The main drawback of these patches is that, sometimes, they produce an allergic reaction on the skin. Likewise, when an adverse reaction appears, it takes longer to disappear. They can also be aesthetically uncomfortable and limited to only a small group of drugs.