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.
Buprenorphine may cause life-threatening withdrawal symptoms in a newborn. You should not use this medicine if you are allergic to buprenorphine, or: if you have used another narcotic drug within the past 4 hours. Some medicines can interact with buprenorphine and cause a serious condition called serotonin syndrome.