**Core Concept**
Delayed vomiting, also known as delayed emesis, is a type of chemotherapy-induced nausea and vomiting (CINV) that occurs more than 24 hours after chemotherapy administration. It is a significant concern in cancer treatment, as it can lead to dehydration, electrolyte imbalances, and decreased quality of life. The pharmacological management of delayed vomiting involves the use of specific antiemetic agents that target the underlying pathophysiological mechanisms.

**Why the Correct Answer is Right**
Aprepitant is a substance P/neurokinin 1 (NK1) receptor antagonist that has been shown to be effective in preventing delayed vomiting after chemotherapy. It works by blocking the action of substance P, a neurotransmitter involved in the vomiting reflex. By inhibiting the NK1 receptor, aprepitant reduces the release of other neurotransmitters that contribute to vomiting, such as acetylcholine and serotonin. Aprepitant is typically used in combination with other antiemetics, such as 5-HT3 receptor antagonists and corticosteroids, to provide comprehensive protection against CINV.

**Why Each Wrong Option is Incorrect**
**Option A:** Metoclopramide is a dopamine antagonist that is primarily used to treat acute vomiting, not delayed vomiting. While it can be effective in managing nausea and vomiting, its mechanism of action is different from aprepitant and it is not the preferred choice for delayed vomiting.

**Option B:** Hyoscine is an anticholinergic agent that can be used to treat motion sickness and postoperative nausea and vomiting. However, it is not effective in preventing delayed vomiting after chemotherapy and can actually worsen constipation and other anticholinergic side effects.

**Option C:** Domperidone is a dopamine antagonist that is similar to metoclopramide but with fewer central nervous system side effects. While it can be used to treat nausea and vomiting, it is not the preferred choice for delayed vomiting after chemotherapy and its mechanism of action is different from aprepitant.

**Clinical Pearl / High-Yield Fact**
Aprepitant is often used in combination with other antiemetics to prevent CINV. The addition of aprepitant to standard antiemetic regimens has been shown to significantly reduce the incidence of delayed vomiting after chemotherapy.

**✓ Correct Answer: D. Aprepitant**