In patients with healthy kidney function, azithromycin has an average half-life of 68 hours following a 500 milligram dose, meaning it stays in the system around 136 hours, according to RxList. In patients with decreased kidney function, it is cleared from the system at a slower rate.
Azithromycin, also known by the brand name Zithromax, is an antibiotic used to treat many different bacterial infections, according to WebMD. Antibiotics should always be taken according to the pharmacist's instructions. Because the drug stays in the system for several days, it is often given in a large, single dose known as a Z-Pak.