Inject the Tylan sub q at a dosage of 50m / kg. Repeat the injections 3 times with a 3 day interval between injections. You will need to divide this by a factor of 4 for your Tylan 200.
Here are a couple threads that discuss Tylan usage:
http://www.faunaclassifieds.com/foru...ad.php?t=81922
http://www.faunaclassifieds.com/foru...ad.php?t=81144
Good luck with your snake - that's one big boa.