Anti-Nausea and Anti-Acidity Drugs — That Can Affect Your Heart Rhythm

Often nothing at all — which is exactly why the list of medicines to avoid matters more than waiting for symptoms. When symptoms do appear they may include palpitations, a fluttering or racing sensation in the chest, dizziness, or a brief blackout. In some cases the first sign is the dangerous arrhythmia itself, with no warning beforehand. Sudden palpitations, dizziness, or fainting during cancer treatment always need same-day assessment, not a wait-and-see approach.

Not without asking first. Domperidone is one of the most commonly purchased over-the-counter medicines for nausea in India, and many patients do not mention it because it does not feel like a medicine — it feels like a routine remedy. It prolongs the QT interval, and CredibleMeds lists it as carrying known risk of this arrhythmia. Whether it is safe for you depends on what treatment you are on and what your current ECG shows. Send a message to your team before you take it.

Tell your oncology team the same day the other doctor prescribes it. Azithromycin is one of the most widely used antibiotics in India, and most GPs will not have your full cancer medication list in front of them. This is not a criticism — it is a gap you can close by calling your oncology team before or as soon as you start the antibiotic. In most cases the team can confirm it is safe or suggest an alternative that treats the infection without the interaction.

It may be. Fluconazole both prolongs the QT interval directly and blocks the CYP3A4 enzyme, which means it can raise the blood level of your cancer treatment at the same time as adding its own effect on heart rhythm. The combination is among the more significant interactions listed by CredibleMeds. Tell your oncology team before you start it — even if a dermatologist or gynaecologist prescribed it for a separate problem. An alternative antifungal may carry less interaction risk in your specific situation.

Proton pump inhibitors — pantoprazole, omeprazole, rabeprazole — do not significantly prolong the QT interval and are used widely in oncology care to protect the stomach lining. They are a different class of risk from domperidone or azithromycin. They can affect the absorption of some targeted therapies when taken at the same time of day, so timing sometimes matters, but your team will advise on timing rather than avoidance in most cases. Tell your team what you are taking so they can advise on the best time.

Avoid grapefruit and grapefruit juice throughout cancer treatment unless your team has specifically said it is safe for your regimen. Grapefruit contains compounds that block CYP3A4 in a way that is difficult to time around — unlike a tablet, which you can separate by hours, grapefruit's effect on the enzyme persists for an extended period after eating. For treatments that depend on CYP3A4 for their clearance, grapefruit can meaningfully raise blood levels and deepen any QT effect. It is one of the more consistent food-drug interactions in oncology.

Most oncology teams do a baseline ECG before starting a treatment known to prolong QT, and repeat it at intervals during treatment. The measurement they track is the corrected QT interval, adjusted for heart rate. If the interval extends significantly, the team may pause treatment, adjust the dose, or investigate other contributing factors. Low potassium and low magnesium — both common in patients with treatment-related nausea or diarrhoea — independently stretch the QT interval, so electrolyte checks are often part of the same review.

Call your oncology team the same day — do not wait for your next scheduled appointment. If you lose consciousness, recover but feel unwell, or have palpitations with chest pain or breathlessness, go to an emergency department immediately. Bring your full medicine list, including anything bought over the counter. If you have been taking any of the medicines listed on this page without your team's knowledge, tell them — the information is clinically useful, and there is no reason to feel concerned about raising it.