Accidentally Missed Doses Of Z-Pak (Azithromycin)

In our latest question and answer, the pharmacist discusses what happens and what to do if you miss doses of azithromycin.

Accidentally Missed Doses Of Z-Pak (Azithromycin)
Jan 13, 2019

Sal asked

I recently got prescribed azithromycin for a sinus infection, took the two pills on Thursday, but then went on a weekend trip and forgot to pack my medicine. I’ll be home Sunday, so that means I’ll have missed 2 days of antibiotics. Is this a big deal?

At a glance

  • Missing doses of antibiotics may increase the risk of antibiotic resistance and your infection may not clear. However, azithromycin has a long half-life and may still be effective. Be sure to finish your antibiotic course, even if you have missed doses and speak with your doctor if your symptoms are not improving.


Z-Pak Box

Discontinuing or missing doses of antibiotics, like azithromycin, prior to completion of the full course can lead to antibiotic resistance and make future infections more difficult to treat.

There is a developing school of thought that stopping a course of antibiotics early may not increase the risk of resistance, as discussed in a recent article published in the BMJ.

Nevertheless, most medical guidelines and organizations, including the CDC (Centers for Disease Control) and the WHO (World Health Organization) continue to recommend finishing your full course of antibiotics, even if you feel better.

Another concern with missing doses or stopping your Z-Pak early is that your infection may not be completely resolved.

So, while your situation is not ideal (missing two days of antibiotics), it may not be a significant concern due to the long half-life of azithromycin.

The half-life of azithromycin is 68 hours, which is the time it takes to reach 50% of its max concentration. This means that it will take approximately 14 days to completely be eliminated from the system. In other words, the antibiotic hangs around in your body for a long time, even after one dose and should still be working to eliminate your infection.

Taking the pills once you get home and finishing the course in the subsequent days would likely clear the infection. If the infection doesn’t seem to be improving, it is important to consult the prescriber to determine the next steps.

Z-Pak Info

A Z-pak consists of six tablets of azithromycin 250 mg. Usually, two tablets are prescribed on the first day of therapy, followed by one tablet for the following four days.

Azithromycin is a macrolide antibiotic that can treat a variety of infections including bronchitis, sinus infections, ear infections, skin infections, sexually transmitted infections, and more. Azithromycin can cover several types of bacteria but is not effective in treating the flu, the common cold, or other viral infections.

Like most antibiotics, azithromycin may cause diarrhea, nausea, vomiting, and abdominal pain. Macrolides are more likely to cause these types of side effects, but azithromycin is one of the more tolerable drugs in the class.

Another concern with azithromycin is that it can cause QT prolongation in patients with a past medical history related to the heart. Drug interactions can also be a concern so always check each new medication prior to starting a new therapy.


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