What is an important guideline to follow when administering a transdermal patch?

A. Remove the old patch before applying a new one and rotate application sites: Removing the old patch prevents drug overdose from residual medication. Rotating application sites reduces skin irritation and ensures consistent absorption, which is a key safety and efficacy guideline for transdermal therapy. B. Apply the patch to the site of the old patch: Applying a new patch to the same site repeatedly can cause local irritation, skin breakdown, and inconsistent absorption. Rotation of sites is recommended instead. C. Apply the patch to the waist area: The waist is not a standard or recommended site for most transdermal patches. Sites such as the upper arm, chest, or back are preferred for proper adhesion and absorption. D. Apply the patch to an area of skin with or without hair: Hair can interfere with patch adhesion and drug absorption. Patches should be applied to clean, dry, and mostly hairless skin, or hair should be trimmed (not shaved) if necessary.