Before applying a transdermal patch, what is the necessary action to prevent medication toxicity?

To prevent medication toxicity before applying a transdermal patch, it is essential to remove any previous patch and cleanse the area. Removing the old patch is critical because it prevents overlapping doses of medication, which can lead to an accumulation of the drug in the system and increase the risk of toxicity. Cleansing the application site helps to ensure that the skin is clean and free of any residues that might affect the adhesion of the new patch or potentially cause skin irritation.

By preparing the skin properly, the new patch can adhere correctly and deliver the medication effectively without the risks associated with residual medication from the previous patch. The other options do not address the fundamental need to avoid overlapping medication or ensure a safe application site.