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 for Cats. ... If your cat has suffered from a severe trauma, injury, or a painful surgery, buprenorphine can help him to cope with the pain while his body recovers. This medicine is roughly 30 times more powerful at relieving pain than morphine.