Approximately what percentage of topical drug concentration is lost due to evaporation upon instillation?

The correct choice reflects the understanding of how topical medications behave once they are applied to a surface, such as the eye. Upon instillation of a topical drug, a significant portion of the drug can be lost due to evaporation, which can decrease the effective concentration of the medication available for absorption.

Research indicates that approximately 25% of the drug concentration may evaporate shortly after application. This loss is particularly critical in ophthalmology, where maintaining an adequate concentration of medication is essential for therapeutic efficacy. Therefore, considering the pharmacokinetics of topical medications, choosing the answer that reflects a loss of about 25% due to evaporation aligns with established data on drug stability and absorption dynamics.