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Overview :
The half-life of a drug is the time needed for the
concentration of the drug to decrease by half.
T(half) =
= (0.693 / (elimination rate constant)) =
= (0.693 * (volume of distribution) / (clearance))
Half-life is not linearly related to clearance.
Half-life is determined by both clearance and volume of
distribution:
(1) The
half-life increases with reduced clearance.
(2) The
half-life decreases with increased clearance (for example, with enzyme
induction).
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