In tropical climates, what issue can affect transdermal drug delivery?

• A. Constant sweating washes out drug on skin surface
• B. Sweating reduces absorption
• C. Humidity has no effect on absorption
• D. Heat reduces blood flow to skin and stops all absorption

Answer: (A)

Transdermal delivery relies on keeping a steady amount of drug at the skin surface so it can diffuse into the skin. In tropical climates, persistent sweating can wash the drug away from the patch–skin interface. This reduces the surface concentration, weakens the diffusion driving force, and leads to lower and more variable absorption. That removal mechanism directly undermines the reservoir needed for steady transdermal delivery, making it the most likely and direct issue.

Humidity and heat don't have the same direct, consistent effect described here. Humidity can alter skin hydration and permeability in ways that aren’t as straightforward, and heat usually increases blood flow and can enhance absorption rather than stopping it altogether.