Скачать или смотреть Understanding the Common Dosing Schedules

Here is a brief introduction and explanation to some commonly used dosing schedules.

At its simplest, patients can sometimes (uncommonly) be treated with a single administration of a large dose of a drug, e.g. the use of a cephalosporin in the treatment of gonoccocal urethritis.

More commonly, however, a multidose regimen is used, especially for an illness that lasts for some time. In such cases, there is often an initiation dose regimen. This is because, after initiation of dosing, it takes some time before steady state concentrations are achieved. Recognizing this is important, because it tells you maximum therapeutic, or toxicity effects may not be seen immediately but until towards the end of the initiation period. This initiation segment, is determined by the time to reach steady state concentrations, approximately 5 half-lives.

For drugs with short half-lives, the time to reach steady state is very brief and there is very little accumulation. In such cases, the initiation segment is very short, and maintenance dosing begins almost immediately.

For drugs with long half-lives, the time to reach steady state may be relatively long. In such cases, a loading dose can be administered. The loading dose is estimated based on the anticipated volume of distribution. But this is highly inaccurate.

The loading dose does not allow the patient to attain steady state concentrations faster. Rather, it merely brings the concentration closer to the intended steady state concentrations. It will still require 5 half-lives to reach steady state.

In many situations, a period of optimization is necessary because steady state concentrations are either too high or too low. Dosage adjustments are necessary to bring the patient to the correct therapeutic range of drug concentrations. Understandably this period can be quite long, as each time a dose adjustment is applied, it will require 5 half-lives to reach the new steady state.

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