**Core Concept**
Post-operative vomiting is a common complication after surgery, often caused by the release of various neurotransmitters and hormones in response to surgical stress. Effective management involves the use of antiemetic medications that target these pathways.

**Why the Correct Answer is Right**
Aprepitant is a selective NK1 receptor antagonist, which blocks the action of substance P, a key neurotransmitter involved in the vomiting reflex. By inhibiting substance P, aprepitant reduces the central emetic response, making it an effective treatment for post-operative nausea and vomiting. Aprepitant is often used in combination with other antiemetics, such as ondansetron, to provide enhanced antiemetic effects.

**Why Each Wrong Option is Incorrect**
* **Option A:** Diazepam is a benzodiazepine with anxiolytic and sedative properties but is not typically used as a primary treatment for post-operative vomiting.
* **Option B:** Phenobarbitone is an anticonvulsant and sedative but is not effective in controlling post-operative nausea and vomiting.
* **Option D:** Droperidol is a butyrophenone antipsychotic that has antiemetic properties but is associated with a higher risk of QT prolongation and cardiac arrhythmias, limiting its use.
* **Option E:** Ondansetron is a serotonin 5-HT3 receptor antagonist, which is effective in controlling post-operative nausea and vomiting, but it is not the best answer in this context as aprepitant is specifically used for this indication.

**Clinical Pearl / High-Yield Fact**
Aprepitant is often used in combination with other antiemetics to prevent chemotherapy-induced nausea and vomiting (CINV), as well as post-operative nausea and vomiting (PONV).

**Correct Answer:** C. Aprepitant