How long does zytiga last?

Presumably you mean"How long does Zytiga continue to keep working". The response to Zytiga generally lasts for about 1 year, but can vary from 6 months to 6 years.

Do you mean how long Zytiga will be in your system?

It takes 5.5 x elimination half lifes for a medicine to be cleared from ones system.

The elimination half life of Zytiga (abiraterone) is 12 ± 5 hours. If we use a maximum of 17 hours then it would take 93.5 hours i.e. approximately 4 days (5.5 x 17 hours) for Zytiga to be cleared from your system.

If I understood your question incorrectly then I am sorry.