For a client who has difficulty swallowing tablets, what is the best nursing action when administering a sublingual tablet?

When administering a sublingual tablet, placing the tablet under the client's tongue is the most appropriate action. Sublingual tablets are specifically designed to dissolve quickly and be absorbed through the mucous membranes in the mouth, providing rapid systemic effects. By placing the tablet under the tongue, the medication can bypass the digestive system and liver metabolism, allowing for faster onset of action.

Crushing the tablet, as suggested in one of the options, can alter its intended absorption and efficacy. Many sublingual tablets have a coating that protects the active ingredients and influences their dissolution; therefore, crushing them can lead to a reduced effect and potentially unwanted side effects.

Administering the tablet with water or instructing the client to chew the tablet before swallowing can hinder the medication's proper absorption. These methods can result in the medication being processed too slowly or being rendered ineffective, as the sublingual route relies on direct contact with the sublingual mucosa for absorption.

Therefore, placing the tablet under the client’s tongue optimally fulfills the requirements for sublingual administration, ensuring quick and effective therapeutic action.