![]() ![]() The loading dose to achieve a desired concentration is determined by the volume of distribution (VD). ![]() The effect of a loading dose before an intravenous infusion has been discussed in Article 2 ('Volume of distribution' Aust Prescr 1988 11:36-7). the steady state plasma concentration averaged over the dosing interval is the same as the steady state plasma concentration for a continuous infusion at the same dose rate (see Fig.the amount of drug in the body shortly after each dose is equivalent to twice the maintenance dose.the plasma concentration fluctuates two-fold over the dosing interval.At steady state with a dosing interval equal to the half-life: The plasma concentration is then at steady state (rate of administration equals rate of elimination where each is one dose per dosing interval). The drug continues to accumulate with continued dosing until there is double the dose in the body, at which point the equivalent of one dose is eliminated each dosing interval (half-life). Therefore, after the second dose there are 1.5 doses in the body and half of this amount is eliminated before the third dose. If intermittent bolus doses are given every half-life (8 hours in this case for theophylline), half the first dose is eliminated over the first dosing interval. The time to reach steady state is determined by the half-life (3-5 half-lives, see Article 3 'Half-life' Aust Prescr 1988 11:57-9). The maintenanceĭose rate to achieve a desired concentration can be calculated if the clearance is known.ĭesired concentration (C ss) = maintenance dose rate / CL ![]() ![]() Given as a continuous infusion, the drug accumulates to a steady state concentration (C ss) determined only by the dose rate and clearance (CL) (see Article 1 'Clearance' Aust Prescr 1988 11:12-3). 1 illustrates the plasma concentration time course of theophylline given intravenously. Intravenous infusion and intermittent intravenous bolus dosingĬontinuous intravenous infusions and intermittent intravenous boluses are common ways of administering drugs such as gentamicin, lignocaine and theophylline. Information from previous articles in this series can be used to design dose regimens.ġ. ![]()
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