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ISMP Safe Medicine May/June 2009, Volume 7, Number 3. ©2009 ISMP

Brand name medicines appear in green; generic medicines appear in red.

It may not be safe to cut a medicine patch

Consumers as well as some health professionals may not know that most medicine patches should never be cut before being applied to the skin. Patches are designed to give a constant amount of medicine over a certain period of time, which may range from several hours to a month. The medicine reaches your body by going through the blood vessels under your skin. If the patch is cut, the medicine in each half of the patch might be released too quickly, leading to a serious overdose.

In one case, a doctor instructed a homecare nurse to cut a 50 mcg/hour fentanyl patch and apply it to a cancer patient. Fentanyl patches provide a powerful pain reliever to patients with severe, long-term (chronic) pain when other prescription pain medicines have not been able to control the pain. The doctor believed the 50 mcg/hour fentanyl dose could be cut in half to deliver a 25 mcg/hour dose. Another visiting nurse discovered the cut patch on the patient’s skin shortly after it was applied and removed it. Fortunately, the patient suffered no harmful effects. However, serious harm, including death, has been reported when cut fentanyl patches were applied to the skin.

Several types of medicine patches exist.

Medicine in one large reservoir:
The medicine in this type of patch is sandwiched between the leak-proof backing, the part of the patch that does not touch the skin, and the “inside” layer of the patch that sits against the skin. The inside layer is like a membrane, allowing the medicine to be absorbed at a constant rate through the skin. The membrane controls how fast the medicine is released. Cutting the patch destroys the membrane and can make the entire dose available immediately. This is the type of patch mentioned in the fentanyl example.

Medicine in small reservoirs:
The medicine in this type of patch is contained in many small pouches called micro-reservoirs. Cutting the patch opens some of the pouches while others remain intact. The open pouches can provide the medicine too fast. But the main problem with cutting these types of patches is that the amount of drug in each half may not be equal. Thus, you cannot be sure what dose you are getting.

Medicine in the adhesive: 
The medicine in this type of patch is mixed into the adhesive layer of the patch. This is the side of the patch that is applied to the skin. The amount of medicine absorbed by the skin is directly controlled by the size of the patch. Therefore, cutting the patch may safely decrease the amount of drug absorbed.

Most patches come with medicine in either small or large reservoirs, so they should never be cut. While patches that have the medicine in the adhesive may be cut, some drug companies warn against this practice since the safety of using cut patches has not been tested. It is best to avoid cutting any patch before use. If the dose is changed, a new prescription should be written.

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