Conditions for naltrexone treatment?

A person has to have a healthy liver (no cirrhosis or hepatitis) and has to be clean from opioids for at least a week to ten days. An opioid test must be conducted, and if it is negative, a Naloxon (short acting agonist) is administered while patient is monitored for signs of withdrawal for less than thirty minutes. These cautionary tests have to be performed, in order to be absolutely sure that there are no opioids in the system because administering Naltrexone in this condition would cause instantaneous acute withdrawal syndrome.