Answering as a microbiologist, not a pharmacist or MD.
Different bacteria are able to survive different concentrations of antibiotics before they are killed. We call the lowest concentration that is enough to kill them the Minimum Inhibitory Concentration (MIC). In order to treat a patient, we want to make sure they have at least the MIC of the antibiotic, otherwise the bacteria will survive. Additionally, an antibiotic concentration below the MIC won't kill bacteria, but will still provide a stress and create a selective pressure for resistance. Then, upping the concentration to the original MIC won't matter - the bacteria will already be resistant to it, and the new MIC will be higher.
Now the other thing to consider is that once an antibiotic enters the body, it is gradually broken down. This means that if a patient is given a dose of exactly the MIC, the concentration will quickly drop to the point where it won't be helpful, and thus won't be cured. The idea to counter this is to give a higher dose than is needed, and to take a new dose around when the concentration would drop to the MIC. That way, there is always a lethal concentration of antibiotics in the patient's body until all of the disease-causing bacteria are dead (or at least, enough dead that the immune system can take care of any stragglers).
The last consideration is that most antibiotics can have a toxic effect on humans at a high enough concentration. So we want to plan a dose that is high enough to always be above the MIC, but low enough that it doesn't actually harm the patient.
UnchainedSora t1_jdrxo24 wrote
Reply to Is there a difference in effect when dosing antibiotics? by Strong_Camel_4468
Answering as a microbiologist, not a pharmacist or MD.
Different bacteria are able to survive different concentrations of antibiotics before they are killed. We call the lowest concentration that is enough to kill them the Minimum Inhibitory Concentration (MIC). In order to treat a patient, we want to make sure they have at least the MIC of the antibiotic, otherwise the bacteria will survive. Additionally, an antibiotic concentration below the MIC won't kill bacteria, but will still provide a stress and create a selective pressure for resistance. Then, upping the concentration to the original MIC won't matter - the bacteria will already be resistant to it, and the new MIC will be higher.
Now the other thing to consider is that once an antibiotic enters the body, it is gradually broken down. This means that if a patient is given a dose of exactly the MIC, the concentration will quickly drop to the point where it won't be helpful, and thus won't be cured. The idea to counter this is to give a higher dose than is needed, and to take a new dose around when the concentration would drop to the MIC. That way, there is always a lethal concentration of antibiotics in the patient's body until all of the disease-causing bacteria are dead (or at least, enough dead that the immune system can take care of any stragglers).
The last consideration is that most antibiotics can have a toxic effect on humans at a high enough concentration. So we want to plan a dose that is high enough to always be above the MIC, but low enough that it doesn't actually harm the patient.