Apparent volume of distribution, V. We can use Equation 5.7.1 to calculate the plasma concentration at any time when we know kel and Cp0. However, usually we don't know Cp0 ahead of time, but we do know the dose. A dose in mass units, maybe in mg. To calculate Cp0 we need to know the volume that the drug is distributed into. That is, the apparent volume of the mixing container, the body. This apparent volume of distribution is not a physiological volume. It won't be lower than blood or plasma volume but for some drugs it can be much larger than body volume.
How long after starting antibiotics for a kidney infection should back, side, and abdominal pain go away? It could take up to 3 days depending on the medication. Most people feel slight relief after 24 hours. You should have a follow up with your MD to check that the infection isn't resistant to antibiotics, and is indeed gone. If you are still having minor pain, that is a great time to talk to him.
Antibiotics are effective for most UTIs. You should start to feel better within 1 to 2 days after starting antibiotics. If your symptoms get worse or you don't feel better by the third day, call your doctor. It is important to take all of the antibiotics your doctor has prescribed. Most people begin to feel better soon after they begin the medicine. But if you stop taking the medicine as soon as you feel better, the infection may return. When taken as preventive therapy, antibiotics also reduce the number of recurrent UTIs. But studies show that this kind of treatment is short-acting. When you stop taking an antibiotic, you are likely to get another UTI.