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.
The effect usually lasts for 5 to 30 minutes and cats will usually visit it again after about 20 to 30 minutes. The silvervine powder for cats allows you to add a bit of fun to any toy or favorite spot OR refresh cat toys. Just a tiny pinch should do the trick!