Onset Syrup 4mg/5ml (Ondansetron)

Drug Class: Antiemetic — Serotonin 5-HT3 Receptor Antagonist | Form: Oral Syrup | Prescription Status: Prescription Only (Rx) — DRAP Registered

What is Onset Syrup 4mg/5ml?

Onset Syrup 4mg/5ml contains Ondansetron, a medicine used to prevent and treat nausea (متلی) and vomiting (قے) — particularly in children who cannot swallow tablets. It belongs to a group of medicines called antiemetics — medicines that stop or reduce nausea and vomiting. Each 5ml spoonful of Onset Syrup contains 4mg of Ondansetron. The syrup form makes it easier to give the correct dose to children and to patients who have difficulty swallowing tablets. It works by blocking a natural chemical in the body called serotonin, which triggers the vomiting reflex. Onset Syrup must only be used as prescribed by your doctor and the correct dose must always be measured carefully.

What is Onset Syrup 4mg/5ml Used For?

Onset Syrup 4mg/5ml is approved for the prevention and treatment of the following conditions:

• Chemotherapy-Induced Nausea and Vomiting (CINV) — nausea and vomiting caused by cancer medicines in children and adults (کیموتھراپی کی وجہ سے متلی اور قے)
• Radiation-Induced Nausea and Vomiting — nausea and vomiting caused by radiation therapy treatment
• Post-Operative Nausea and Vomiting (PONV) — nausea and vomiting after a surgical procedure or general anaesthesia (آپریشن کے بعد متلی اور قے)
• Prevention Before High-Risk Treatment — given before chemotherapy or surgery begins to stop nausea before it starts

How Does Onset Syrup 4mg/5ml Work?

Ondansetron works by blocking special receptors in the body called 5-HT3 receptors — also known as serotonin receptors. These receptors are found in two important places — the gut and the brain's vomiting centre. When the body is exposed to chemotherapy, radiation, or surgery, it releases large amounts of serotonin — a chemical that activates these receptors and triggers the feeling of nausea and the urge to vomit. By blocking these receptors, Ondansetron prevents serotonin from sending the vomiting signal to the brain, effectively stopping nausea and vomiting before it becomes severe. The syrup form is absorbed through the digestive system and begins working within 30 to 60 minutes of taking the dose.

Dosage and Administration

⚠️ Always give this medicine exactly as your doctor prescribed. Always use the measuring spoon or oral syringe provided — do not use a regular household teaspoon as it may give the wrong amount. The dose is based on the child's body weight or body surface area and will be decided by the doctor.

Children (Chemotherapy-Induced Nausea and Vomiting):

Adults (when syrup is prescribed instead of tablets):

• Measure each dose carefully using the measuring spoon or oral syringe provided
• Can be taken with or without food
• Shake the bottle gently before each use if instructed on the label
• Take at the time advised by your doctor — timing is important for best effect
• Your doctor will decide the exact dose and schedule based on the patient's weight, age, and treatment plan

Active Ingredient

Who Should NOT Use Onset Syrup 4mg/5ml?

Do not give this medicine if the patient:

• Is allergic to Ondansetron or any other 5-HT3 antagonist medicine (e.g., Granisetron, Palonosetron)
• Is currently taking Apomorphine — a medicine used for Parkinson's disease
• Is under 6 months of age — safety has not been established for very young infants
• Has a known heart condition called Congenital Long QT Syndrome
• Has been told by the doctor to avoid this medicine for any reason

Tell your doctor before use if the patient has:

• Any heart condition or irregular heartbeat (دل کی دھڑکن کی بے ترتیبی)
• Liver disease — the dose may need to be reduced
• Low potassium (پوٹاشیم کی کمی) or low magnesium levels in the blood
• Any intestinal blockage or bowel problems
• If the patient is pregnant or breastfeeding — the doctor will assess the risk before prescribing
• Any known allergy to any ingredient in the syrup — check the full ingredient list with your pharmacist

Side Effects

Like all medicines, Onset Syrup 4mg/5ml can cause side effects. Not everyone will experience them.

Common Side Effects (relatively frequent):

• Headache (سردرد) — the most commonly reported side effect
• Constipation (قبض)
• Feeling of warmth or flushing in the face
• Dizziness or lightheadedness
• Diarrhoea in some patients
• Tiredness or general weakness

Serious Side Effects (less common — seek medical help immediately):

• Severe allergic reaction — sudden rash, swelling of the face, lips, or throat, difficulty breathing
• Irregular or fast heartbeat (دل کی دھڑکن کا بے ترتیب ہونا) — sign of a possible heart rhythm problem
• Severe dizziness or fainting
• Muscle stiffness or uncontrolled body movements
• Serotonin Syndrome — agitation, confusion, rapid heartbeat, high temperature, and unusual muscle twitching (rare but serious — seek emergency help immediately)
• Sudden changes in vision

If you notice any serious side effects in yourself or your child, stop the medicine and go to the nearest hospital or emergency immediately.

Drug and Food Interactions

Tell your doctor about ALL medicines the patient is currently taking. Onset Syrup 4mg/5ml may interact with:

There are no specific food interactions with Ondansetron Syrup. However, always inform your doctor about all medicines, vitamins, or herbal products the patient is taking.

Storage Instructions

• Store below 25°C in a cool, dry place
• Keep away from direct sunlight and moisture
• Keep out of reach of children (بچوں کی پہنچ سے دور رکھیں)
• Do not refrigerate or freeze the syrup unless the label specifically instructs otherwise
• Do not use after the expiry date printed on the bottle or box
• Keep the bottle tightly closed after each use
• Do not use the syrup if you notice any change in colour, smell, or appearance — return it to the pharmacy

Frequently Asked Questions

What is Onset Syrup 4mg/5ml used for?

Onset Syrup 4mg/5ml is used to prevent and treat nausea and vomiting caused by cancer chemotherapy, radiation therapy, and surgical procedures. The syrup form is particularly useful for children and for patients who find it difficult to swallow tablets.

How do I measure the correct dose for my child?

Always use the measuring spoon or oral syringe that comes with the syrup. Never use a regular kitchen teaspoon as it does not give an accurate measurement. Your doctor will tell you exactly how many millilitres (ml) to give based on your child's weight. If you are unsure, ask your pharmacist to show you how to measure correctly.

Can Onset Syrup be given to infants?

Onset Syrup should not be given to infants under 6 months of age as safety has not been established for this age group. For children between 6 months and 1 year, it should only be used under close supervision of a specialist doctor. Always follow your doctor's instructions on age-appropriate dosing.

Can Onset Syrup be taken for general vomiting or stomach infection?

Onset Syrup is specifically prescribed for nausea caused by chemotherapy, radiotherapy, and surgery. It is not recommended as a general medicine for everyday vomiting, stomach infections, or travel sickness. Do not give it for reasons other than what your doctor has prescribed it for.

Why does Onset Syrup cause constipation in some children?

Ondansetron blocks serotonin receptors in the gut as well as in the brain. Serotonin plays a role in keeping the bowel moving regularly. Blocking it can slow bowel movement and cause constipation. Make sure the child drinks plenty of water and eats fibre-rich foods. Tell your doctor if constipation becomes a problem or lasts more than 2 to 3 days.

How should I store the syrup after opening?

After opening, store the bottle tightly closed below 25°C away from sunlight and moisture. Do not refrigerate unless the label says to do so. Check the label for the in-use shelf life after opening — typically the syrup should be used within the period stated on the packaging. Discard any remaining syrup after that period.

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⚕️ Medical Disclaimer: This product description is for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified doctor or pharmacist before starting, stopping, or changing any medication. This product is a prescription medicine — it must only be used under the supervision of a licensed healthcare professional.

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DRAP Registered | Prescription Required (Rx) | For use under medical supervision only