What is the half life of kenalog

It depends on what form of Kenalog you are being treated with. Kenalog can be a topical cream, a spray, taken orally, or given as a deep muscle injection.
Kenelog can have a half life as short as 88 minutes, as listed on the Wikipedia site, but that is for the shorter acting methods of using the drug.
It can also be as long as three weeks, when given as a deep muscle injection.