As long as nothing changes in the dosing regimen, (i.e. Dose, route, dosing interval, infusion time, the weather, clearance, volume of distribution, etc.) the drug will remain at steady state concentrations. If the drug is given by continuous infusion, it will remain at a single steady state concentration. If it is given.
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Your kidneys, liver, and other organs of elimination don't know how often you take the drug. Time to steady state does not depend at all on dosing interval. The only thing that dosing interval affects is what the steady state concentration is.
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WHY DOES IT TAKE FOUR HALF-LIVES TO REACH A STEADY STATE? Everyone knows how long it takes to reach a steady state if a drug is given at a regular interval: four to five half-lives. Can you explain why? In a single dose, serum concentrations decline to the following levels: 50% of the peak level by one half-life.
Everyone knows how long it takes to reach a steady state if a drug is given at a regular interval: four to five half-lives. Can you explain why? In a single dose, serum concentrations decline to the following levels:.
Then, what defines the steady state serum level?. Assume that a dose is given repeatedly and regularly, and that serum levels during one dosing interval are averaged for the sake of discussion. The average serum level in the second dosing interval is (most likely) higher than that of the first dosing interval, and this trend will continue.
If you have a drug with a long half life, you can achieve a target steady state level more quickly by using a loading dose. For example, perhaps you want to achieve a steady state of concentration (Css) of 10 ng/mL, which requires a 30 mg dose once daily.
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In this hypothetical scenario, the eggs are at steady state because the rate of elimination is equal to the rate of input. Another way to think of this is imagine a carton of eggs in your kitchen. So when you wake up the next morning, the carton is full of eggs. Someone in your house notices the empty spots in the carton of eggs and purchases 2 more eggs and places them in the carton. If this process repeats itself over many days, it would appear that the eggs never change … there are always 12 eggs in the carton even though you use them for various meals and recipes.
Css = concentration of drug in plasma at steady state.This works well Get estimate of CLEARANCE from literature for this drug; Find desired STEADY STATE CONCENTRATION from literature. Formulae used below to calculate Peak and Trough concentrations at steady state and with repeated doses, assume Ka>>Ke.
The plasma concentration of drugs given by infusion at constant rate or by repeated dosing at a constant rate will rise until the concentration high enough that elimination is equal to input. This is termed "accumulation".
mg/L = (mg/Kg) / (L/Kg).
To calculate Peak concentration at steady state (C ss(max) ).
To calculate Trough concentration at steady state (C ss(min) ).
Dosing rate = Clearance * Css (mg/hr = L//hr * mg/L).
Retrieve or remake graph of Miraclemycin from data in the lecture on volume of distribution (Vd). The data to make the graph are repeated here.
Note that the preceding formula can be rearranged to provide an estimate of the amount of drug in the body, a loading dose (DL), or a volume of distribution (Vd). You should be comfortable in using it in all of its forms.
On repeated "bolus" administration of drug, the concentration in the plasma oscillates between the peak and the trough. The importance of the degree of oscillation is drug dependent and depends on the dose, dose interval, and elimination half-life.
Cp(t) = A * e(-Ke * t) (mg/L = mg/L * e (frcn/hr * hr) ) Using a calculator.
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You should be able to use them in solving problems. Consult other portions of these notes for details and qualifications of these terms and formulas. The following formulas and definitions should be understood so well that they are essentially memorized.
Medical Calculators. Disclaimer: All calculations must be confirmed before use. The authors make no claims of the accuracy of the information contained herein; and these suggested doses are not a substitute for clinical judgement.
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The authors make no claims of the accuracy of the information contained herein; and these suggested doses are not a substitute for clinical judgement. Disclaimer: All calculations must be confirmed before use.
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Created: June 8, 2000 Revised: June 5, 2015.
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