Final answer:
The therapeutic response to megestrol in an HIV positive client is an increased appetite, which aids in combating weight loss associated with AIDS.
Step-by-step explanation:
The therapeutic response to the prescription of megestrol 400 mg daily for an HIV positive client would be D. Increased appetite. Megestrol is a medication that is used to treat anorexia, cachexia, or an unexplained, significant weight loss in patients with AIDS. It is not prescribed for the direct treatment of HIV itself; therefore, options A, B, and C are not considered therapeutic responses to this medication. Megestrol works by increasing appetite and is often used in the management of wasting syndrome associated with HIV, contributing to improved nutritional status and quality of life for patients.