02.05.5 Maintenance Doses and Loading Doses

A maintenance dose is a small, fixed dose. When you use maintenance doses, it may take long time to reach the minimum effective concentration, as the plasma concentration only slowly builds up to reach and then exceed the minimum effective concentration (top, Figure 2.12). This is an inappropriate way to administer drugs in serious conditions or emergency situations, where you need the drug to be effective immediately.

With some drugs, especially those with a large volume of distribution, it may be necessary to give a loading dose (a big dose) initially to get above the minimum effective concentration and get the beneficial effect quickly. In such situations, a loading dose is used to reach the minimum effective concentration, and then maintenance doses are given to maintain the minimum effective concentration (bottom, Figure 2.12). With a loading dose, the minimum effective concentration is reached much quicker than using the maintenance dose.

Figure 2.12 Maintenance doses and loading dose (Copyright QUT, Sheila Doggrell)

An example of a drug that is used with a loading dose and maintenance doses is the anti-platelet drug clopidogrel. Intravenous clopidogrel is given as a loading dose in percutaneous coronary intervention to prevent clotting straightaway, and this is followed by oral maintenance doses to prevent coagulation, as the subject recovers from the surgery.

Steady-state concentrations are eventually reached with both maintenance and loading/maintenance dosing (Figure 2.12).