The goal of this clinical research study is to compare the effectiveness of receiving a combination of ondansetron and aprepitant to receiving ondansetron alone in helping to prevent nausea and/or vomiting in patients with Acute myeloid leukemia (AML) or high-risk (HR) Myelodysplastic syndromes (MDS) who are receiving cytarabine. The safety of this drug combination will also be studied.

Cytarabine is a drug that is used to treat AML and high-risk MDS. It is known to cause nausea and/or vomiting. All patients that receive cytarabine also receive drugs to help prevent these side effects.

The Study Drugs:

Ondansetron is designed to block the action of serotonin, a substance in the brain that causes chemotherapy-related nausea and vomiting.

Aprepitant is designed to block a different natural substance in the brain that causes chemotherapy-related nausea and vomiting.

Study Groups:

If you are found eligible to take part in this study, you will be randomly assigned (as in the flip of a coin) to 1 of 2 groups. You will have an equal chance of being in either group.

If you are in Group 1, you will receive ondansetron.

If you are in Group 2, you will receive ondansetron and aprepitant.

Study Drug Administration:

Both groups will receive ondansetron by vein from 30 minutes before receiving chemotherapy until 6 to12 hours after chemotherapy. The length of the chemotherapy infusion will be different for all patients.

If you are in Group 2, in addition to ondansetron, you will take 1 capsule of aprepitant every morning while receiving chemotherapy. You will take your last dose of aprepitant the day after your chemotherapy infusion is completed. If you miss a dose of aprepitant, you can take it as soon as you remember.

Study Diary:

You will fill out a study diary every day for the 7 days after the chemotherapy. You will record how often you experience nausea and/or vomiting and any time you need other medications during this study. It should take about 5 minutes to complete each time.

Length of Study:

You will be on study for up to 7 days. You will be taken off study if intolerable side effects occur.

Blood Draws:

Blood (about 1 teaspoon) will be drawn for routine tests after your last dose (+/- 3 days) of study drug.

This is an investigational study. Ondansetron and aprepitant are both FDA approved and commercially available for the prevention of chemotherapy-related nausea and vomiting. Using the drugs in combination is investigational.

Up to 100 participants will take part in this study. All will be enrolled at MD Anderson.

Inclusion Criteria:

1. Patients greater than or equal to 18 years of age.
2. Patients with a diagnosis of acute myelogenous leukemia, high-risk myelodysplastic syndrome, chronic myelogenous leukemia in blast crisis or acute undifferentiated leukemia who will receive chemotherapy with regimens containing high-dose cytarabine (greater or equal 1g/m^2/d for at least 3 days).
3. Patients must sign an informed consent indicating they are aware of the investigational nature of this study, in keeping with the policies of the hospital.

Exclusion Criteria:

1. Patients with emesis or grade 2 or 3 nausea present less than or equal to 24 hours before chemotherapy.
2. Patients with ongoing emesis due to any organic etiology
3. Patients with known hypersensitivity to the study drug or to 5-HT3 receptor antagonists
4. Patients receiving pimozide, terfenadine, astemizole, or cisapride

Registered eligible participants who received one dose of study medication were evaluable for toxicity but had to receive at least five doses to be evaluable for response. Only 90 participants (46 on Group 1 and 44 on Group 2) had one or more doses of study medication.

Adverse events captured from the time of participant consent until 30 days after the last dose of drug. The full study reporting period was three years four months.

Of the 98 participants registered in the study, 90 participants are included in Adverse Event Reporting as evaluable for toxicity having received one dose of treatment medication.