How Long Does Azithromycin Last In Your System?

In our latest question and answer, the pharmacist discusses how long azithromycin lasts in your system.

Question

Hi again. I am still confused as to whether the 14 days that azithromycin is in my system includes the days of taking the medication Or, if the 14 days are after the last tablet. Thanks again for the additional help.

Asked by Beach Gal On Jul 17, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Jul 18, 2018

The metabolism of azithromycin begins after absorption of each dose. Therefore, azithromycin will take approximately 14 days after the last dose to be completely eliminated. 


In regard to your previous inquiry about azithromycin interacting with atorvastatin, the risk and severity of an interaction between the two continues to decrease after the last dose. Based on the 68 hour half-life of azithromycin, here is an approximate concentration chart of azithromycin in your body relative to time after the last dose:

  • 1 Half-life: 68 hours (~3 days): 50% 
  • 2 Half-lives: 136 hours (~6 days): 25% 
  • 3 Half-lives: 204 hours (~9 days): 12.5%
  • 4 Half-lives: 272 hours (~11 days): 6.25% 
  • 5 Half-lives: 340 hours (~14 days): 3.125% 
  • 6 Half-lives: 408 hours (17 days): 1.5625%

As you can see, after around 5 half-lives the percent of azithromycin remaining approaches zero. The risk of the interaction decreases in approximately the same fashion with the remaining drug concentration.


One of the reasons that azithromycin has such a long half-life relative to other drugs is because of its extensive tissue concentration. This is opposed to other drugs that have a higher concentration in the blood and are therefore cleared faster. 


Summary

  • Azithromycin has a long half-life, around 68 hours.
  • For most drugs, it generally takes around 5-6 half-lives to be considered eliminated from the body.
  • Azithromycin lasts on average around 14 days in your body after the last dose.

About the Pharmacist

Dr. Kevin Davis Pharm.D

Dr. Kevin Davis is a licensed pharmacist with experience in retail and hospital pharmacy. He graduated from the University of Florida with a Doctor of Pharmacy degree in 2015 and a Master of Healthcare Administration degree from Adventist University in 2017. He is also a Board Certified Pharmacotherapy Specialist since 2016.

About Azithromycin

Azithromycin (brand name Zithromax) is a semisynthetic antibiotic belonging to the macrolide family, and is similar in structure to erythromycin. However, significant differences exist as azithromycin can be dosed once daily, produces less gastrointestinal side effects and reaches higher intracellular concentrations than does erythromycin. It is used for a variety of indications including sinusitis, pneumonia, bronchitis, certain sexually transmitted diseases and tonsillitis. Azithromycin may be taken with or without food but taking it with food may improve tolerability.

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