I was curious so I went and looked....

Azithromycin will be in your system for around 15.5 days, after the last dose.

Azithromycin has an elimination half-life of 68 hours. The prolonged terminal half-life is thought to be due to extensive uptake and subsequent release of drug from tissues.

It takes around 5.5 x elimination half life's for a medicine to be out of your system. Therefore it would take 374 hours about 15.5 days (5.5 x 68 hours) for it to be eliminated from the system. So it'll be in your system for that period of time, after the last dose.

Other factors to consider:

1. How much and how often you have taken the drug.
2. Your metabolic rate – a slower metabolism will increase the time a drug remains in your system.
3. Your age and health – older age and poor health will generally increase the time the drug stays in your system.
4. Body mass – generally the bigger you are the longer a drug will remain in your system.

https://www.drugs.com/pro/azithromycin-tablets.html