Ondansetron is a 5-HT3 receptor antagonist used to prevent and treat nausea and vomiting.

Applications:

• Prevents nausea and vomiting from chemotherapy, radiation, and surgery.

• Sometimes used for severe morning sickness in pregnancy.

Side Effects:

• Common: headache, constipation, dizziness.

• Serious (rare): QT prolongation, allergic reactions, serotonin syndrome (when combined with other serotonergic drugs).

Fosaprepitant is an antiemetic used to prevent nausea and vomiting caused by chemotherapy.

Applications:

• Prevents acute and delayed nausea/vomiting from highly emetogenic chemotherapy.

• Often used in combination with other antiemetics (like dexamethasone and a 5-HT3 antagonist).

Side Effects:

• Common: fatigue, headache, hiccups, and constipation.

• Serious (rare): infusion site reactions, allergic reactions, liver enzyme elevation.

Brands: Emend (IV).

Dimenhydrinate is an antihistamine primarily used to prevent and treat motion sickness and nausea.

Applications:

• Prevents and relieves nausea, vomiting, and dizziness from motion sickness.

• Used for vertigo and inner ear disturbances like Ménière’s disease.

Side Effects:

• Common: drowsiness, dry mouth, dizziness, and blurred vision.

• Serious (rare): confusion (especially in elderly), fast heartbeat, and urinary retention.

Applications:

Chemotherapy-Induced Nausea/Vomiting (CINV): Prevents acute/delayed nausea from highly emetogenic chemo (e.g., cisplatin).
Moderately Emetogenic Chemo: Used with dexamethasone + 5-HT3 blockers (e.g., ondansetron).
Postoperative Nausea/Vomiting (PONV): Alternative for high-risk surgeries (less common).

Side Effects:

Common: Fatigue, hiccups, constipation, headache, loss of appetite.
Serious (Rare):

• Liver toxicity (elevated LFTs).

• Hypersensitivity (rash, anaphylaxis).

• Drug interactions (CYP3A4 inhibitor—affects warfarin, birth control, some chemo drugs).

Note: Avoid with pimozide (QT prolongation risk). IV form (fosaprepitant) available.