NOTE: The target plasma concentration for drug therapy is usually the average steady state concentration, not the maximum concentration at steady state.
loading dose =
= ((target maintenance dose) / (fraction of drug lost from the body per dosage interval))
maintenance dose =
= ((loading dose) * (fraction of drug lost from the body per dosage interval))
where:
fraction of drug lost from the body during the dosing interval =
= (1 - (EXP((-1) * (elimination rate constant) * (dosing interval)))
Alternatively:
loading dose =
= ((volume of distribution) * (target plasma concentration) / (fraction orally absorbed))
This equation tends to underestimate the required loading dose.
oral maintenance dose =
= ((average steady state concentration) * (clearance) * (dosing interval) / (fraction of drug absorbed))
Since k = (0.693 / (half-life)) = ((clearance) / (volume of distribution)), this can be rewritten:
oral maintenance dose =
= C(ave-ss) * (volume of distribution) * 0.693 * (dosing interval) / ((fraction of drug absorbed) * (half life))
