Medication can be administered through the skin for a wide variety of clinical reasons including pain, Parkinson’s disease, Alzheimer’s disease, restless legs syndrome, angina, urge incontinence, travel sickness, smoking cessation, hormone replacement and contraception.
There are many benefits from administering drugs transdermally, including:
- Appropriate alternative to the oral or parenteral route of administration
- Improved patient compliance
- Avoiding first pass metabolism
- Reduced risk of gastro-intestinal irritation
- Steady absorption of medication over a prolonged period of time
- Reduced frequency of dosing
- Reduced adverse effects through avoidance of high serum drug peaks
However these benefits can be compromised by improper use or alteration of a patch.
Types of transdermal patch
Transdermal delivery systems or patches are typically either matrix or reservoir format.
A matrix patch contains the drug distributed either within the patch adhesive or within a matrix between the patch backing and a separate adhesive layer. Examples of matrix patches include Evorel Conti, Estraderm MX, Evra, Neupro, Matrifen and Durogesic D-Trans.
In contrast, in a reservoir patch the drug is contained in a reservoir between the patch backing and the rate controlling membrane. Some patches contain multiple small reservoirs rather than a single large reservoir; these are referred to as micro-reservoir systems. Examples of reservoir patches include Fentalis, Tilofyl, Victanyl, Scopoderm, Transiderm Nitro and Niquitin.
Cutting or manipulating patches
Transdermal patches are available in a limited selection of dosages that may not always be appropriate for a specific patient. Cutting a patch to reduce the surface area and consequently the dose delivered may be considered an option to provide a reduced dose.
There are very few examples of patches where cutting or amending the active surface area would be considered within the product’s marketing authorisation. One example of a patch that can be cut is the topical lidocaine 5% plaster, Versatis.
Cutting can compromise the products efficacy and/or have an adverse impact on patient safety.
Some patches should never be cut because they are only effective at the marketed dose, for example the contraceptive patch Evra.
Product safety can be adversely affected by cutting or manipulation. Cutting a reservoir patch can result in the immediate release of the entire dose of the drug leading to a potential overdose. In contrast, a matrix patch will release a predetermined amount of drug for each unit of surface area in contact with the skin; this means the matrix patch would be considered the safest option for cutting. However, this would still be outside of the product licence use of the medication.
An additional consideration with cutting a transdermal patch is the removal of the adhesive along the cut edge. Reduced adherence of the patch to the skin can result in reduced medication absorption and potentially reduced clinical effect. To ensure the patch adheres to the skin the patient should be counselled on appropriate use of medical tape or other means of securing the patch.
Patients will also require counselling on cutting the patch to ensure that no sharp edges remain that may irritate or damage the skin.
Patient counselling
In addition to the specific advice relating to cutting of patches patients should be counselled on patch application:
- Patches should be applied to clean, dry, non-hairy, powder and oil free skin
- Wash hands before and after applying the patch.
- Only apply the patch to the area of the body indicated within the Patient Information Leaflet
- Change the patch at the prescribed intervals, removing the old patch before applying the new one
- Apply each new patch to a different body site
- Ensure the patch is firmly stuck to the skin by holding it in place with the palm of the hand for approximately 30 seconds, ensuring the contact is complete especially round the edges
- Used patches should be removed, folded in half with the adhesive side inwards, and disposed of safely.
- Do not expose the patch to external sources of heat e.g. hot water bottle or heat pad.