Zofran

Zofran (ondansetron) is a potent serotonin 5-HT3 receptor antagonist specifically formulated for the prevention and treatment of nausea and vomiting. It is a cornerstone therapy in the management of chemotherapy-induced, radiotherapy-induced, and postoperative nausea and vomiting (PONV). Its mechanism of action targets the specific serotonin receptors in the chemoreceptor trigger zone (CTZ) and the gastrointestinal tract, which are primarily responsible for initiating the emetic reflex. This targeted approach allows for highly effective control of emetic episodes with a well-established safety and tolerability profile, making it a first-line choice for clinicians across various medical disciplines.

Features

• Active Pharmaceutical Ingredient: Ondansetron hydrochloride.
• Available Formulations: Oral tablets (4 mg, 8 mg), orally disintegrating tablets (4 mg, 8 mg), and oral solution (4 mg/5 mL).
• Mechanism of Action: Selective antagonism of serotonin 5-HT3 receptors.
• Onset of Action: Oral administration typically provides effects within 1 to 2 hours.
• Half-life: The elimination half-life is approximately 4 to 6 hours in healthy adults.
• Metabolism: Primarily metabolized hepatically via multiple cytochrome P450 enzymes, including CYP3A4, CYP2D6, and CYP1A2.

Benefits

• Provides highly effective prophylaxis and treatment for acute-phase chemotherapy-induced nausea and vomiting (CINV), significantly improving patient quality of life during treatment.
• Offers reliable control of postoperative nausea and vomiting (PONV), reducing complications and facilitating smoother recovery.
• Available in multiple formulations, including orally disintegrating tablets, which are ideal for patients who have difficulty swallowing or are actively nauseated.
• Exhibits a favorable side effect profile for most patients, with the most common adverse reactions being headache and constipation.
• Its targeted mechanism minimizes the sedative and extrapyramidal side effects often associated with older antiemetic agents like metoclopramide or prochlorperazine.

Common use

Zofran is indicated for the prevention of nausea and vomiting associated with highly emetogenic cancer chemotherapy, including cisplatin-based regimens. It is also indicated for the prevention and treatment of nausea and vomiting associated with initial and repeat courses of moderately emetogenic cancer chemotherapy. Furthermore, it is a standard prophylactic agent for postoperative nausea and vomiting (PONV) in patients undergoing surgical procedures. Off-label, it is sometimes used for the management of severe nausea and vomiting related to gastroenteritis, hyperemesis gravidarum (with careful risk-benefit consideration), and vertigo.

Dosage and direction

Dosage is highly dependent on the clinical indication and emetogenic potential of the stimulus. For highly emetogenic chemotherapy, the recommended adult oral dosage is 24 mg administered 30 minutes before the start of single-day chemotherapy. For moderately emetogenic chemotherapy, the adult dosage is 8 mg administered 30 minutes before chemotherapy, with subsequent doses of 8 mg at 8 hours after the first dose and then 8 mg twice daily for 1 to 2 days after completion of chemotherapy. For the prevention of PONV, the recommended adult IV dosage is 4 mg administered immediately before induction of anesthesia or postoperatively. For treatment of PONV, a single 4 mg IV dose is recommended. The orally disintegrating tablet should be placed on the tongue, where it will dissolve rapidly and be swallowed with saliva; no water is needed for administration. Adherence to the prescribed regimen is critical for optimal efficacy.

Precautions

Patients should be advised to inform their physician of any history of congenital long QT syndrome, congestive heart failure, bradyarrhythmias, or electrolyte abnormalities (e.g., hypokalemia, hypomagnesemia), as these conditions may predispose to QT interval prolongation. Use with caution in patients with hepatic impairment, as ondansetron clearance may be reduced; a single maximum daily dose of 8 mg is recommended in patients with severe hepatic impairment. Electrocardiographic monitoring may be considered in patients with significant cardiac risk factors. As with all antiemetics, Zofran may mask a progressive ileus or gastric distention following abdominal surgery. Patients with phenylketonuria should be informed that the orally disintegrating tablets contain aspartame.

Contraindications

Zofran is contraindicated in patients with known hypersensitivity to ondansetron or any components of the formulation. Concomitant use with apomorphine is contraindicated due to the risk of profound hypotension and loss of consciousness.

Possible side effect

The most frequently reported adverse reactions are generally mild to moderate and transient.

• Very Common (≥1/10): Headache.
• Common (≥1/100 to <1/10): Constipation, sensation of warmth or flushing, hiccups.
• Uncommon (≥1/1,000 to <1/100): Dizziness, fatigue, transient asymptomatic increases in aminotransferases.
• Rare but Serious: Electrocardiographic changes (QTc interval prolongation), arrhythmias (including torsades de pointes), anaphylaxis, blurred vision, and extrapyramidal reactions (although these are less common than with other antiemetic classes).

Drug interaction

Ondansetron is metabolized by multiple CYP450 enzymes. Concomitant use with potent inducers of these enzymes (e.g., rifampicin, carbamazepine, phenytoin) may decrease ondansetron plasma concentrations, potentially reducing efficacy. Conversely, concomitant administration with drugs known to inhibit CYP enzymes may increase ondansetron concentrations. Due to its potential to prolong the QT interval, Zofran should be used with particular caution in combination with other agents that also prolong the QT interval (e.g., certain antiarrhythmics, antipsychotics, antidepressants, antibiotics like erythromycin). A comprehensive review of a patient’s medication list is essential prior to initiation.

Missed dose

If a dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule resumed. Patients should not take a double dose to make up for a missed one.

Overdose

In reported cases of overdose, the most common observed effects were sudden transient blindness, severe constipation, hypotension, and dizziness. There is no specific antidote for ondansetron overdose. Management should consist of supportive care, including continuous ECG monitoring due to the risk of QT prolongation. The patient’s vital signs and general clinical status should be closely observed.

Storage

Store Zofran tablets and oral solution at room temperature, between 20°C to 25°C (68°F to 77°F), in a dry place and in the original container to protect from light and moisture. Keep all medications out of the reach of children and pets. Do not use beyond the expiration date printed on the packaging.

Disclaimer

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any new treatment. Never disregard professional medical advice or delay in seeking it because of something you have read here.

Reviews

“Zofran has been a game-changer in our oncology unit. Its efficacy in preventing CINV allows our patients to tolerate their chemotherapy regimens much better, which is crucial for treatment adherence and outcomes.” – Dr. Eleanor Vance, Oncologist. “As an anesthesiologist, I rely on Zofran for PONV prophylaxis. Its predictable effect and lack of significant sedation make it an excellent choice in the perioperative setting.” – Dr. Marcus Thorne, MD. “After my surgery, the nausea was overwhelming. The orally disintegrating Zofran tablet worked within minutes when I couldn’t have kept a regular pill down. It was incredibly effective.” – Patient Testimonial.