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.
Confidence votes 692. Buprenorphine (Suboxone) has an elimination half-life of about 37 hours. This means that every 37 hours, half of the buprenorphine left in your body is removed. After the first 37 hours, only 1 mg will be left, after 74 hours, 0.5mg are left, etc. In short, most of the drug will be gone in 4 or 5 days, but it will be weeks before all of it is gone.