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Steady-state concentration is when there is no change in the amount of a substance in the body or in a chemical process over time. In drug therapy, repeated blood tests are done to determine the constant level of drug needed. Continuous reactors are used in chemical processing to maintain a constant amount of finished product. Both steady-state conditions can vary slightly over time. Control systems are used to correct any changes and maintain chemical equilibrium.
Steady-state concentration refers to the amount of a substance in the body or in a chemical process when no change occurs over time. In humans, this can occur when a drug is given to a patient over a long period and reaches a constant level in the bloodstream. During chemical reactions, steady state concentration occurs when the amount of raw materials equals the amount of finished product in a continuous reaction.
Drug therapy often requires a patient to receive a continuous level of drug for medical care. When drugs enter the body, they are metabolized or consumed by the body and finally removed by the kidneys into the patient’s urine. If a constant level of drug is needed, repeated blood tests are done over time to determine how much the patient needs to be given to maintain a constant level. These tests determine the steady-state concentration of the drug.
The pills usually don’t create a constant concentration in the body because they are introduced as separate doses, not administered continuously. This is why a doctor may prescribe multiple doses of the drug over several days. Researchers have tested the drugs and determined how they are removed from the body. Repeated doses may give a blood level similar to a steady state concentration.
Chemical processing can use continuous reactors that take raw materials and produce finished products. These systems are different from batch reactors, where all materials are introduced and reacted until the raw materials are consumed. Continuous reactions are based on steady-state concentration, since a specific amount of feedstock must be introduced to maintain a constant amount of finished product.
If the raw material rate is increased, more finished product can be created than can be handled downstream. Another effect is that the chemical reaction can be different and create the wrong end product or a different chemical mixture. In both cases, the steady state concentration is disturbed and the control systems are programmed to correct the flow rates and return the process to chemical equilibrium, or steady state.
All steady state conditions, both within the body and in chemical reactors, will vary slightly over time. In the body, changes in body temperature or metabolism, such as might occur with exercise, can cause the body to metabolize a drug differently. If a minimum drug concentration is required, the manufacturer can test the effects of different body conditions on the steady-state concentration. If a consistent level of the drug is critical to the patient’s treatment, the drugs may need to be given in a hospital so that repeat blood tests can be done.
The chemical reactions will use instrumented control systems to monitor the process for steady-state behavior. When the process changes slightly, control systems can make changes to flow rates, temperatures or pressures. Steady-state concentration may vary slightly, which is called in-range variation, but will still produce a finished product that meets specifications.
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