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.