How long after taking Zithromax can you take safely take Zofran?
At a glance
- There is a known drug interaction between azithromycin and ondansetron, both prolong the “QT interval”
- Most azithromycin courses of therapy are 3 or 5 days, but they last significantly longer in your system, about 10 days.
- This combination may actually be safe for you depending on any existing cardiac issues, your age, and gender.
Hi Kas and thanks for reaching out to us.
Azithromycin is a very commonly used antibiotic to treat a variety of infections such as sinus infections, ear infections, upper respiratory infections, and several other common bacterial infections. Ondansetron (or by the brand Zofran) is a very effective nausea medication.
One of the big advantages of using azithromycin is the ease of dosing. Azithromycin is taken just once a day for 3-5 days. This is due to its long half-life. Half-life is the amount of time that it takes for your body to metabolize half of the medication and remove it from your body. Half-life for adults is variable, but for azithromycin, it averages at 68 hours. What this means is that after you finish your azithromycin course it keeps working by preventing bacteria from growing and it still has detectable levels in your system for over 10 days.
Next up is are these two medications safe to take together… that depends. There is a drug interaction between them. Both medications individually increase the “QT interval” and it increases even more when combined. Your heartbeat can be broken down into several parts. I’m sure that you’ve seen someone hooked up to an electrocardiogram; even in a movie or TV show. Some medications can cause small changes to your heart rhythm. We are concerned here about some of your medications causing QT prolongation, or your heart taking a bit longer to recharge between beats. Many medications cause this and it’s usually not a significant issue unless the person is on multiple medications that cause this, or has high risk factors. If too much QT prolongation occurs, an arrhythmia can occur or even cardiac arrest.
The next question is does this matter for you? That is something that I don’t know. There are a few risk factors that you should be on the lookout for. Are you on other medications that cause QT prolongation (you might need to ask your physician, pharmacist, or write us back)? Females are at greater risk. So are the elderly, and people with preexisting cardiac issues. It’s also dose related. If you are planning on taking a single 4mg ondansetron once or twice a day, you are at lower risk. If you routinely take 8mg three times daily, your risk is increased.
Now that I’ve explained the risks, if you are at a lower risk (small dose of ondansetron, not elderly, not on many other medications that can cause QT prolongation) then the risk is small and you can probably safely take that ondansetron. If you are at a higher risk then I would suggest waiting at least 4-5 days before you take that ondansetron. Lastly, if you’ve had a recent electrocardiogram and your QT interval or QTc is below 450ms, then you should be safe to take it.
I hope this helps! Feel free to write us again in the future.
- Zithromax Prescribing Information , Pfizer
- Zofran Prescribing Information, FDA
- Drug Interaction Report, Lexicomp (Subscription Required)
- Drug-Induced Long QT Interval, Pharmacist’s Letter (subscription required)