Concentration and pH dependent steady-state volume of distribution of methotrexate estimated by a simple physiologically based method

Interspecies pharmacokinetic scaling of DA-8159, a new erectogenic, in mice, rats, rabbits and dogs, and prediction of human pharmacokinetics

Time-averaged total body clearance (Cl) and apparent volume of distribution at steady state (V(SS)) of DA-8159 after intravenous administration to mice (30 mg/kg), rats (30 mg/kg), rabbits (30 mg/kg) and dogs (3 mg/kg) were analysed as a function of species body weight (W) using the allometric equation for interspecies scaling, and were used to predict those in humans. Significant linear relationships were obtained between log Cl (l/h) and log W (kg) (r = 0.992; p = 0.0079) and log V(SS) (l) and log W (kg) (r = 0.999; p < 0.0001). The corresponding allometric equations were Cl = 4.36 W(0.492) and V(SS) = 6.41 W(0.911). These allometric equations were extrapolated to predict the Cl and V(SS) for DA-8159 in humans based on the 70 kg body weights. In addition, concentrations in the plasma-time profile predicted using the four animal data fitted to a complex Dedrick plot of animal data. Our results indicated that the DA-8159 data obtained from four laboratory animals could be utilized to generate preliminary estimates of the pharmacokinetic parameters in humans. These parameters can serve as guidelines for better planning of clinical studies.

Interspecies pharmacokinetic scaling of oltipraz in mice, rats, rabbits and dogs, and prediction of human pharmacokinetics

Dose-independent pharmacokinetics of oltipraz after intravenous and/or oral administration at various doses to mice, rats, rabbits and dogs were evaluated. After both intravenous and/or oral administration of oltipraz to mice (5, 10 and 20 mg/kg for intravenous and 15, 30 and 50 mg/kg for oral administration), rats (5, 10 and 20 mg/kg for intravenous and 25, 50 and 100 mg/kg for oral administration), rabbits (5, 10 and 30 mg/kg for intravenous administration) and dogs (5 and 10 mg/kg for intravenous and 50 and 100 mg/kg for oral administration), the total area under the plasma concentration-time curve from time zero to time infinity (AUC) values of oltipraz were dose-proportional in all animals studied. Animal scale-up of some pharmacokinetics parameters of oltipraz was also performed based on the parameters after intravenous administration at a dose of 10 mg/kg to mice, rats, rabbits and dogs. Linear relationships were obtained between log time-averaged total body clearance (Cl) x maximum life-span potential (MLP) (1 year/h) and log species body weight (W) (kg) (r=0.999; p=0.0015), log Cl (l/h) and log W (kg) (r=0.979; p=0.0209), and log apparent volume of distribution at steady state (V(ss)) (l) and log W (kg) (r=0.999; p=0.0009). The corresponding allometric equations were ClxMLP=49.8 W(0.861), Cl=5.20 W(0.523) and V(ss)=4.46 W(0.764). Interspecies scale-up of plasma concentration-time data for the four species using pharmacokinetic time of dienetichron resulted in similar profiles. In addition, concentrations of oltipraz in a plasma concentration-time profile for humans predicted using the four animal data fitted to the dienetichron time transformation of animal data.

Effects of cilastatin on the pharmacokinetics of a new carbapenem, DA-1131, in rats, rabbits, and dogs

DA-1131, a new carbapenem antibiotic, undergoes renal metabolism by renal dehydropeptidase I (DHP-I), located on the brush border of the proximal tubular cell. Species differences with regard to the effects of cilastatin, a renal DHP-I inhibitor, were investigated after a 1-min intravenous infusion of DA-1131, with or without cilastatin, to rats, rabbits, and dogs. After intravenous infusion, the nonrenal clearance (CL(NR)) of DA-1131 was significantly slower in rats (3.00 versus 8.01 ml/min/kg) and rabbits (2.41 versus 6.77 ml/min/kg) when the drug was coadministered with cilastatin; this could be due to the slower metabolism of DA-1131 by rat and rabbit kidney DHP-I. This indicated that renal metabolism of DA-1131 by renal DHP-I was inhibited by cilastatin. However, coadministration with cilastatin to dogs did not affect the CL(NR) of DA-1131.

Effects of the rate and composition of fluid replacement on the pharmacokinetics and pharmacodynamics of intravenous furosemide

Effects of differences in the rate and composition of intravenous fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of furosemide were evaluated using the dog as a model animal. Each of six dogs received 8-hr constant intravenous infusion of 20 mg (15 mg used in one dog) of furosemide with 0% replacement (treatment I), 50% replacement (treatment II), and 100% replacement (treatment III) with lactated Ringer's solution, as well as with 100% replacement with 5% dextrose in water (treatment IV). Most pharmacokinetic parameters, such as plasma clearance, steady-state volume of distribution, mean residence time, and terminal half-life, were essentially the same in all four treatments. Renal clearances and urinary excretion rates of the drug in treatments II-IV were essentially the same, but about 20% higher than those in treatment I. In spite of the similarities in kinetic properties, diuretic and/or natriuretic effects from furosemide were markedly different among the four treatments. For example, mean 10-hr urine outputs were 646, 1046, 3156, and 1976 ml and mean 10-hr sodium excretions were 87.0, 142, 383, and 97.2 mmole for treatments I-IV, respectively. Except for treatment III, diuresis and/or natriuresis were found to be time-dependent, generally decreasing with time until reaching a low plateau during later hours of infusion. The present findings also showed that no fluid replacement and 100% replacement with 5% dextrose solution both produced the same degree of severe acute tolerance in natriuresis, indicating the insignificance of water compensation in tolerance development; in treatment II, where neutral sodium balance was achieved, the development of acute tolerance in diuresis and natriuresis can mainly be attributed to negative water balance under this special condition; at steady state the hourly diuresis and natriuresis could differ up to about ten times between treatments. Some implications for the kinetic/dynamic relationship or modeling, in the clinical use, and in the bioequivalence evaluation of dosage forms are discussed.

Renal and non-renal clearances of iothalamate

An evaluation of the literature indicated that certain aspects of the disposition kinetics of iothalamate, important to the accurate determination of glomerular filtration rate in dogs and humans, remain to be resolved. The simultaneous clearances of iothalamate and inulin in 5 dogs were determined at three steady-state iothalamate plasma levels (2, 10, and 40 micrograms ml-1) following various rates of intravenous infusion. The iothalamate clearances, both renal and non-renal, were concentration-independent. The overall mean non-renal clearance was 18 per cent (ranging from 9 to 25 per cent) of its plasma clearance. The mean iothalamate/inulin renal clearance ratio was about 0.84 with individual values ranging from 0.72 to 0.95. The significant (4-26 per cent) plasma protein binding of iothalamate in these dogs was the main reason for the lower-than-unity clearance ratios obtained. The literature indicates the existence of up to 25 per cent of non-renal elimination in humans with normal renal function; this is comparable to the present results obtained with dogs but contrary to the assumption, sometimes reported in the literature that non-renal elimination is essentially absent in humans. Binding of iothalamate to plasma proteins from humans was not found in the present study. The above results suggest that for accurate glomerular filtration rate determination in humans and dogs, especially for those with renal impairment, renal clearance rather than plasma clearance should be used, and in the case of dogs it should also be corrected for plasma protein binding. Iothalamate in plasma and urine was analysed by a simple, micro high-performance liquid chromatographic method with UV detection.