How many hours should you wait between taking ondansetron and then switching to promethazine?

Hi,

I believe you must get your Dr. to guide as with every interaction there are potential risks involved everyone wants to avoid and your Dr. is responsible for your treatment and above all your safety.

Interactions between your drugs
Moderate
promethazine ondansetron
Applies to: promethazine, ondansetron

Using promethazine together with ondansetron can increase the risk of an irregular heart rhythm that may be serious and potentially life-threatening, although it is a relatively rare side effect. You may be more susceptible if you have a heart condition called congenital long QT syndrome, other cardiac diseases, conduction abnormalities, or electrolyte disturbances (for example, magnesium or potassium loss due to severe or prolonged diarrhea or vomiting). Talk to your doctor if you have any questions or concerns. You should seek immediate medical attention if you develop sudden dizziness, lightheadedness, fainting, shortness of breath, or heart palpitations during treatment with these medications, whether together or alone. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

Source: https://www.drugs.com/interactions-check.php?drug_list=1752-0,1949-0

All the best, masso