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Elimination Rate Constant Equation:
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The elimination rate constant (k) is a pharmacokinetic parameter that describes the fraction of drug eliminated per unit time. It is inversely related to the drug's half-life and is used to calculate dosing regimens and predict drug concentrations over time.
The calculator uses the elimination rate constant equation:
Where:
Explanation: The equation shows that drugs with shorter half-lives have higher elimination rate constants, meaning they are cleared from the body more quickly.
Details: The elimination rate constant is fundamental in pharmacokinetics for determining dosing intervals, predicting steady-state concentrations, and calculating drug accumulation during multiple dosing.
Tips: Enter the drug's half-life in hours. The calculator will compute the elimination rate constant in reciprocal hours (hr⁻¹). Half-life must be a positive number.
Q1: What are typical values for elimination rate constants?
A: Values vary widely by drug - from about 0.0001 hr⁻¹ (very long half-life drugs) to 1 hr⁻¹ or more (drugs eliminated very quickly).
Q2: How does elimination rate constant relate to clearance?
A: Clearance = k × Vd, where Vd is the volume of distribution. The elimination rate constant incorporates both clearance and distribution.
Q3: Can this be used for all drugs?
A: This calculation assumes first-order kinetics, which applies to most drugs at therapeutic doses. Some drugs follow zero-order kinetics at higher doses.
Q4: What if my drug's half-life is in minutes?
A: Convert to hours first, or the result will be in min⁻¹ instead of hr⁻¹. 60 minutes = 1 hour.
Q5: How is this used in clinical practice?
A: Clinically, k helps determine appropriate dosing intervals and predict how long a drug will remain in the body after discontinuation.