Transdermal Patches

Transdermal patch is a medicated adhesive pad that is placed on the skin to deliver a time-release dose of medication through the skin into the bloodstream. It is also called skin patch. Skin patches are used as an alternative way of getting medicines into the body.

Transdermal drug delivery

Transdermal drug delivery avoids many problems associated with the oral or intravenous routes: drastic pH changes, the presence of enzymes, variable transit times, pulse entry (rapidly fluctuating drug plasma concentrations), side effects, and inadequate patient compliance, while also eschewing needle delivery and its associated inconvenience and even patient phobia. There is a problem: the main function of skin is preventing things entering our body.

Transdermal patches

Transdermal patch (Skin patch) uses a special membrane to control the rate at which the liquid drug contained in the reservoir within the patch can pass through the skin and into the bloodstream. Some drugs must be combined with substances, such as alcohol, that increase their ability to penetrate the skin in order to be used in a skin patch. Drugs administered through skin patches include scopolamine (for motion sickness), nicotine (for quitting smoking), estrogen (for menopause and to prevent osteoporosis after menopause), nitroglycerin (for angina), and lidocaine to relieve the pain of shingles (herpes zoster). Molecules of insulin and many other substances, however, are too large to pass through the skin.

Patches applied to the skin eliminate the need for vascular access by syringe or the use of pumps. Transdermal patches were developed in the 1970s and the first was approved by the FDA in 1979 for the treatment of motion sickness. It was a three-day patch that delivered scopolamine. In 1981, patches for nitroglycerin were approved, and today there exist a number of patches for drugs such as clonidine, fentanyl, lidocaine, nicotine, nitroglycerin, oestradiol, oxybutinin, scopolamine, and testosterone. There are also combination patches for contraception, as well as hormone replacement. Depending on the drug, the patches generally last from one to seven days.

The major advantages provided by transdermal drug delivery include the following: improved bioavailability, more uniform plasma levels, longer duration of action resulting in a reduction in dosing frequency, reduced side effects and improved therapy due to maintenance of plasma levels up to the end of the dosing interval compared to a decline in plasma levels with conventional oral dosage forms. Transdermal patches have been useful in developing new applications for existing therapeutics and for reducing first-pass drug-degradation effects. Patches can also reduce side effects; for example, oestradiol patches are used by more than a million patients annually and, in contrast to oral formulations, do not cause liver damage.

Non-medicated patch markets include thermal and cold patches, nutrient patches, skin care patches (a category that consists of two major sub-categories - therapeutic and cosmetic), aroma patches, weight loss patches, and patches that measure sunlight exposure.

The main components to a transdermal patch are:
Liner - Protects the patch during storage. The liner is removed prior to use.
Medication - medication solution in direct contact with release liner.
Adhesive - Serves to adhere the components of the patch together along with adhering the patch to the skin.
Membrane - Controls the release of the drug from the reservoir and multi-layer patches.
Backing - Protects the patch from the outer environment.

How to use skin patches. Useful advice.

Carefully remove the patch from its pouch, taking care not to tear the patch. Use your fingers rather than scissors to avoid damaging the patch. Pull off the plastic backing to expose the adhesive. Do not touch the sticky surface of the patch.

Apply the patch firmly with the sticky side down to a clean, dry, non-hairy area of skin, on the area of the body as specified in the instructions on how to use your patch. Do not apply it to broken or irritated skin or spots. Don't put moisturiser, creams or powder on the skin before applying the patch, as this may stop it from sticking properly.

When applying a new patch, remove the old one first and apply the new one to a slightly different area of skin. This avoids irritating the skin.

To remove the patch, peel off one corner and pull the patch smoothly away from the skin. Any glue or sticky residue left on the skin can be removed with baby oil. If a patch falls off, replace it with a new one and keep to your patch change days as normal. If you have just had a bath or shower wait for the skin to cool down before applying a new patch.

Try to avoid wearing the patch under tight clothing or elasticated waistbands.

If you sunbathe while wearing the patch, cover the patch so it is not exposed to direct sunlight.

Exercising or applying heat to the patch may increase the amount of medicine absorbed into the body. This can increase the risk of side effects.

Never divide or cut a patch.