After reading this article you will learn about the dosage regimen of a drug.
Many drugs like antibiotics, cardio tonics, anticonvulsants, hormones etc. are generally given in a multiple-dosage for prolonged therapeutic effect. The plasma concentrations of these drugs must be maintained within narrow limits to achieve maximal clinical effectiveness. A dosage regimen must be established for each drug to provide the correct plasma concentration without excessive fluctuation and drug accumulation.
For antibiotics, a desirable minimum effective plasma concentration can be determined. Other drugs with narrow therapeutic indices require definition of the therapeutic minimum and maximum non-toxic plasma concentration. While calculating a multiple-dosage regimen, the desired plasma concentration is related to the therapeutic response.
The following parameters must be considered while developing a dosage regimen:
(i) The size to the dose of the drugs.
(ii) The frequency of drug administration i.e. the time interval between doses.
Total body clearance of a drug and its steady state plasma concentration (Cpss) are related in the following manner:
Cpss = Dose x Fractions of the dose absorbed/Total clearance x dosing internal
In situations where total body clearance is changing the clinician may maintain the same steady state plasma concentration by altering the dose or the dosing interval proportional to the change in total body clearance.