Pharmacokinetics and bioavailability of oral cephalosporins, KR-984055 and its prodrugs, KR-999001 and KR-999002, in the rat.

KR-984055 is a new oral cephalosporin antibiotic with activity against both gram-positive and gram-negative bacteria. Lipophilic ester-type prodrugs of KR-984055, i.e., KR-999001 and KR-999002, have been synthesized in an attempt to increase the oral bioavailability of this broad-spectrum antibiotic agent. In this study we determined the oral bioavailability of KR-984055 and its prodrugs in the rat, and evaluated the pharmacokinetic model that best describes the plasma concentration behavior following single intravenous (i.v.) and oral single dose. In addition, concentrations in plasma as well as biliary and urinary recovery of KR-984055 were determined. Also, protein binding of KR-984055 in plasma was examined in vitro. The degree of protein binding of KR-984055 was in the range of 92.09-94.77%. KR-984055 exhibited poor oral bioavailability (7.02 +/- 1.58%). The observed oral bioavailabilities of KR-984055 from KR-999001 and KR-999002 were 38.77 +/- 2.81% and 39.81 +/- 5.25%, respectively. These data were calculated from the levels of free KR-984055 in plasma. Oral KR-999001 and KR-999002 were not recovered from plasma, suggesting that it was readily cleaved to free KR-984055. KR-999001 and KR-999002 appear to be an efficient oral prodrug of KR-984055 that deserved further clinical evaluation in human.

Pharmacokinetic and pharmacodynamic modeling of the antiplatelet and cardiovascular effects of cilostazol in healthy humans.

OBJECTIVE: Cilostazol is an antiplatelet agent with vasodilating properties. It has been used to treat patients with peripheral ischemia, such as intermittent claudication. We used a pharmacokinetic-pharmacodynamic model to analyze the relation between the plasma concentration of cilostazol, the inhibitory effect of the drug on platelet aggregation, and the cardiovascular effects of the drug on healthy humans. METHODS: A single oral dose of 100 mg cilostazol was administered to 20 healthy volunteers. Serial blood sampling and pharmacodynamic measurements were performed up to 48 hours thereafter. The effects of cilostazol on platelet aggregation, blood pressure, and heart rate were measured during the same period. The plasma concentration of cilostazol was measured with a validated HPLC method that entailed ultraviolet detection. The time courses of plasma cilostazol concentration, platelet aggregation, and cardiovascular effects were analyzed by means of pharmacokinetic-pharmacodynamic modeling with the program ADAPT II. RESULTS: The plasma concentration-time course followed a 2-compartment model. Mean peak concentration was 775 ng/ml approximately 3.65 hours after administration of cilostazol. The maximal effect on platelet aggregation was a 31.14% reduction 6.05 hours after administration. No significant difference in systolic blood pressure was found. The maximal increase in heart rate was 13.49%, whereas the maximal decrease in diastolic blood pressure was 29.51%. Both peak effects were detected approximately 6 hours after administration of the drug. Platelet aggregation and cardiovascular effects (change in diastolic blood pressure and heart rate) were analyzed with the effect-link sigmoid maximal effect model. CONCLUSION: This pharmacokinetic-pharmacodynamic model successfully described the relation between plasma concentration of cilostazol and the antiplatelet and cardiovascular effects of the drug.