New bioavailability parameters to compare the efficacy of antimicrobial drugs in dosage forms.

Pharmacokinetic parameters such as AUC, Cmax and tmax have been used to represent the rate and extent of absorption of drugs from dosage forms in comparative bioequivalence testing. None of these parameters gives a direct indication of how long the drug concentration is maintained above an acceptable level e.g. minimum inhibitory concentration (MIC) or the minimum effective concentration (MEC). This is clinically important in evaluating the onset and duration of a therapeutic effect obtained from a test dosage form in comparison to the reference dosage form. The purpose of this study is to investigate the possibility of a bioavailability parameter which relates the time that the drug concentration in the systemic circulation is maintained above a certain level (te) and the first time that the blood concentration exceeds this level (to). Two methods were used to calculate the time that drug levels are maintained above a certain minimum level. The proposed parameters proved to be valuable when the efficacy of erythromycin was used as an example. Although some problems, such as undefined MIC/MEC may arise, te and to can be used along with the conventional bioequivalence parameters to obtain a better indication of the clinical efficacy.