When is injection ondansetron given before chemotherapy?

AIIMS Rishikesh NO - 2019

Pharmacology

Easy

Appeared in: AIIMS Rishikesh NO - 2019

Explanation

The standard protocol for intravenous (IV) ondansetron is to administer it 30 to 60 minutes before the start of a chemotherapy infusion.
This timing is based on the drug's pharmacokinetics; the onset of action for IV ondansetron is approximately 15-30 minutes.
Administering it 30 minutes prior ensures the medication has reached therapeutic blood levels and is actively blocking serotonin (5-HT3) receptors when the chemotherapy begins.
This proactive approach is critical for preventing acute chemotherapy-induced nausea and vomiting (CINV), which is much harder to control once it starts.

Option A: While administration 60 minutes before is within the acceptable 30-60 minute window, 30 minutes is the more precise and commonly practiced standard for IV administration to ensure peak drug effect coincides with the start of chemo.
Option B: This is far too early. The elimination half-life of ondansetron is 3.5-5 hours, so administering it 6 hours in advance would mean its concentration and effectiveness would be significantly reduced when the chemotherapy is administered.
Option D: This is too late. The onset of action for IV ondansetron is 15-30 minutes. Giving it only 5 minutes before chemotherapy would not allow sufficient time for the drug to become effective, leaving the patient vulnerable to acute nausea.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacology: Administration timing of antiemetic drugs for chemotherapy-induced nausea and vomiting (CINV) as background academic context rather than a clinical decision trigger.
Preventing CINV is a primary nursing goal to improve patient comfort, nutrition, and adherence to the cancer treatment plan. Uncontrolled vomiting can lead to dehydration, electrolyte imbalance, and treatment refusal.
Nurses must assess the emetogenic potential of the specific chemotherapy regimen to anticipate the need for antiemetics. Highly emetogenic drugs (e.g., cisplatin) require a multi-drug antiemetic approach.
Monitor for common side effects of ondansetron, including headache, constipation, and dizziness. A rare but serious side effect is QT interval prolongation, which can lead to cardiac dysrhythmias.

How to Approach the Question

First, identify the core of the question: it's asking for the specific timing of a medication (ondansetron) for a specific purpose (preventing chemo-induced nausea).
Recall the drug class and mechanism. Ondansetron is a 5-HT3 antagonist, and it works prophylactically (preventively).
Think about the principles of prophylaxis: the preventive drug must be active before the noxious stimulus begins. This means it needs to be given with enough lead time to reach therapeutic levels.
Consider the route of administration. The question specifies 'injection' (IV), which has a rapid onset compared to oral medications.
Evaluate the options based on the drug's onset of action (15-30 minutes for IV). Giving it 30 minutes before allows it to start working just in time. 5 minutes is too short. 6 hours is too long, as the drug would wear off. 1 hour is on the outer edge of the acceptable window but 30 minutes is the more standard, optimal time.
Select the option that best aligns with the drug's pharmacokinetic profile for maximum efficacy.

Concept Tested & Keywords

Concept Tested: Pharmacology: Administration timing of antiemetic drugs for chemotherapy-induced nausea and vomiting (CINV).
Stem keywords: injection, ondansetron, chemotherapy
Lead-in keywords: When

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E6 Pharmacology Nursing Lilley 11e Part 3 pp. 188-190, 191-193

E6 Medicine Harrison 22e Part 1 p. 616-618