Multiple-Dosing Regimens (Repetitive Dosing)
Medical drugs are seldomly administered in a single dose to produce a desired effect. Drugs are frequently administered in successive doses to bring about lasting and effectual results. Thus, to avoid the toxic concentrations of a drug as well as to maintain its therapeutically effective concentration within the plasma, one must properly contrive a multiple-dosing regimen. These regimens are designed with ease if the pharmacokinetic parameters of the drug are known.
When a drug is administered on a multiple-dosing regimen, each successive dosage(s) are administered before the preceding doses are completely eliminated. Accumulation of the drug would resultingly occur within the body yielding a higher plasma drug concentration. The accumulation phenomenon however does not cause the plasma concentration to rise indefinitely (see graph). The concentration plateaus to where the same maximum (Cmax) and minimum (Cmin) concentrations are reproduced repeatedly. In designing a dosing regimen then, one's objectives would be to keep the Cmin above the minimum effective concentration (MEC) and to keep the Cmax below the minimum toxic concentration (MTC) as shown in the graph.