Pharmacology & Dosage
Intermediate

First-Order Elimination

Drug concentration decreases exponentially — a constant fraction is eliminated per unit time.

Formula

C(t)=C0×e−ketC(t) = C_0 \times e^{-k_e t}

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Variables

C(t)Concentration at time t
C_0Initial concentration
k_eElimination rate constant
tTime

Example

C₀ = 100 mg/L, kₑ = 0.1/hr → after 7 hr: C = 50 mg/L

Did You Know?

Most drugs follow first-order kinetics, but alcohol is a famous exception — it's eliminated at a constant rate (zero-order) regardless of concentration.

pharmacologyfirst ordereliminationexponential

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