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PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

The elimination rate constant (K or Kel)

➢ The rate of elimination for most drugs from a tissue or from the body is a first-

order process, in which the rate of elimination is dependent on the amount or

concentration of drug present.

➢ The k represents overall drug elimination from the body, which includes renal

excretion of unchanged drug (u) and/or the formation of metabolites (m).

Hence,

K= K u + K
m

if there are two metabolites

K = Ku + Km1 + Km2

Where,

K u: Excretion rate constant

K m: Metabolic rate constant

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