Think back to your knowledge of osmosis and what happens when a concentration gradient is formed. Another way of enhancing excretion is to give a medication that alters the pH of the urine. A drug such as aspirin or sodium bicarbonate would be used. The drug will alter the rate of ongoing physiologic processes but cannot change or create new functions of cells. Agonists activate a receptor while antagonists inhibit the receptor.
Refractoriness is a state of unresponsiveness to a stimuli.
The same refractoriness that can occur in response to prolonged stimulation of a receptor by drug therapy can be found in some disease states. In some cases of non-insulin dependent diabetes related to obesity, chronic stimulation reduces the number of available insulin receptors to transport glucose into the cell. The blood level of any drug depends on many of the factors discussed under absorption, distribution, biotransformation and excretion. A low blood level of a drug may produce some pharmacologic effect, but not the desired effect. This level is normally termed the sub-therapeutic level.