Steady State Concentration

Steady State Concentration

·        Amount of drug absorbed = amount eliminated

·        Takes 5 half lives to reach 97% of steady state, if each new dose given at half life spacings

·        The shorter the T½, the sooner the Css will be reached (steady state concentration)

·        The shorter the T½, the greater the plasma concentration will fluctuate between doses

·        If T½ is prolonged, dose should be reduced or dosage interval increased

·        Css = (F * D) / (Cl * T) where F = bioavailability, D = dose, Cl = clearance and T = dosage interval

§  As Cl = (Vd * 0.693) / T½, then

§  Css = (F * D * T½ ) / (0.693 * Vd * T)