This occurs when a substance passes from the fluid in the tubular lumen through the apical membrane, across the cytosol , and then into the interstitial fluid.
Yes, it's potent stuff. Cat receive it either as an injection or orally. It takes effect in roughly half an hour, lasting about 8 hours before another administration is necessary. Cats usually react negatively to opiates, but buprenorphine is an exception. That's one reason vets use it if they can receive the necessary special certification.
Suboxone will be mostly out of your system within 36 hours, by this time you will feel no effects of the drug (by this we mean no positive effects, but rather the individual could experience withdrawal for several days), but the half life of buprenorphine(which one of two drugs in suboxone) is up to 42 hours.