Relationship between loading dose and infusion rate to achieve any fraction of the steady-state level in any compartment model.

When a drug is infused at a constant rate K0, the time necessary for the concentration to reach a satisfying threshold of effectiveness may be too long. To achieve this level faster, it is useful to give simultaneously a dose D, of the same drug by intravenous injection. This paper proposes the calculation, as a function of K0 and model parameters, of the loading dose D necessary to reach, in a time T, any fraction of the asymptotic value of the amount of drug in a compartment receiving a constant rate infusion, for any n-compartment model. As an example, the expression of D for mammillary and catenary pharmacokinetic models is derived.