Comparative physiological pharmacokinetics of fentanyl and alfentanil in rats and humans based on parametric single-tissue models

The objectives of this investigation were to characterize the disposition of fentanyl and alfentanil in 14 tissues in the rat, and to create physiological pharmacokinetic models for these opioids that would be scalable to man. We first created a parametric submodel for the disposition of either drug in each tissue and then assembled these submodels into whole-body models. The disposition of fentanyl and alfentanil in the heart and brain and of fentanyl in the lungs could be described by perfusion-limited 1-compartment models. The disposition of both opioids in all other examined tissues was characterized by 2- or 3-compartment models. From these models, the extraction ratios of the opioids in the various tissues could be calculated, confirming the generally lower extraction of alfentanil as compared to fentanyl. Assembly of the single-tissue models resulted in a whole-body model for fentanyl that accurately described its disposition in the rat. A similar assembly of the tissue models for alfentanil revealed non-first-order elimination kinetics that were not apparent in the blood concentration data. Michaelis-Menten parameters for the hepatic metabolism of alfentanil were determined by iterative optimization of the entire model. The parametric models were finally scaled to describe the disposition of fentanyl and alfentanil in humans. Supported in part by the National Institute on Aging, RO1-AG-4594, and the Anesthesia/Pharmacology Research Foundation.     

Stereoselective pharmacokinetics of flurbiprofen in humans and rats

Flurbiprofen, a 2-arylpropionic acid (2-APA) nonsteroidal anti-inflammatory drug (NSAID), exists as racemate and is used as such. Although the activity of 2-APAs is due mainly to their S-enantiomers, information on the pharmacokinetics of flurbiprofen is usually based on the measurement of total concentrations of S- and R-flurbiprofen. In this work, the pharmacokinetics of flurbiprofen enantiomers following single doses were studied in humans and rats. Upon iv administration of 10 mg/kg of racemic flurbiprofen to male Sprague-Dawley rats, the plasma concentrations were consistently higher for S-flurbiprofen than for R-flurbiprofen (AUC = 134 +/- 39 versus 41 +/- 9 mg.L-1 h). In bile duct-cannulated rats, the biliary excretion contained only 3.6-5.2% of the dose as conjugated flurbiprofen (S:R = 1.2-2.1). After administration of R-flurbiprofen to the rat, both enantiomers were found in plasma [AUC(R):AUC(S) = 0.10-0.16], indicating a limited extent of enantiomeric bioinversion. This is consistent with the previously reported limited extent of flurbiprofen uptake into fat. In healthy volunteers also, significant stereoselectivity was observed in the plasma concentration of the drug after 100-mg oral racemic doses [AUC-(S):AUC(R) = 45.4 +/- 12.7:40.1 +/- 14.3 mg.L-1.h]. As compared with the R-enantiomer, S-flurbiprofen has a smaller volume of distribution (7.23 +/- 1.9 versus 8.41 +/- 3.0 L) and total clearance (1.23 +/- 0.34 versus 1.47 +/- 0.50 L/h), but an equal half-life (4.21 +/- 1.2 versus 4.18 +/- 1.3 h). In urine, on the other hand, the R-configuration was predominant, as greater amounts of the R-enantiomer were found both as conjugated flurbiprofen and as an unidentified metabolite. Negligible amounts of intact flurbiprofen enantiomers were detected in urine. The observed stereoselectivity in humans cannot be attributed to enantiomeric bioinversion, as S-flurbiprofen was not detected in plasma and urine after oral administration of R-flurbiprofen.     

Comparative pharmacokinetics of lovastatin, simvastatin and pravastatin in humans.

Twelve healthy male volunteers received single market-image 40-mg oral doses of lovastatin and simvastatin (both lactone prodrugs), or pravastatin (a beta-hydroxyacid) at 1 week intervals in a three-way crossover study to quantify HMG-CoA reductase inhibitors in plasma. Multiple plasma samples were collected up to 24 hours after the dose and assayed for active and total HMG-CoA reductase inhibitors. After equal oral doses, higher plasma concentrations of HMG-CoA reductase inhibitory activity after pravastatin than after either lovastatin of simvastatin (2-3 fold greater area under the concentration-time curve) suggest a greater potential availability of pravastatin-related inhibitory activity to peripheral tissues.     

Comparative study on pharmacokinetics of Cephradine in diabetic and normal rats

Objective To study effects of diabetes mellitus(DM)on pharmacokinetics of cephradine(CED)by comparing the difference in pharmacokinetic behaviours of CED between diabetic and normal rats.Methods DM was induced in male rats by a single iv injection of alloxan 60 mg·kg-1;rats whose blood glucose was over 16 mmol·L-1 were taken as DM group.The rats were divided into DM group and normal control(CTL)group,which were subdivided into low dose(90 mg·kg-1)and high dose(180 mg·kg-1)subgroups.CED was administered by iv or po routes.Blood samples collected at different time post dosing were analyzed by RP-HPLC to yield CED plasma concentration time course.Chromatographic separation was achieved on a Kromasil C18 column(250×4.6 mm ID,5 μm);mobile phase,consisting of 0.025 mol·L-1 KH2PO4-MeOH-CH3CN(87;6∶7 v/v),was delivered at 1.0 mL·min-1;UV detector was set at 261 nm.The peak area ratio of CED to cephalexin(CEX)as internal standard vs concentraion of CED was used to construct calibration curve.50 μL aliquots of TCA-deproteined plasma samples were injected into chromatograph.Results The methodology validation including specificity,precision,accuracy,recovery,limit of quantitation,linearity,stability,etc.,showed that the HPLC assay developed by us completely met requirements of pharmacokinetic study Both DM and CTL groups showed the two-compartment model for iv dosing and extravascular one-compartment model for po dosing as well as first-order kinetics.However,in iv experiment,DM group,when compared with CTL group,presented a significantly shortened t1/2β and MRT as well as increased CL,reflected by t1/2 β 84-91 vs 116-120 min,MRT 61-70 vs 103-119 min;CL 23-25 vs 18-19 mL·min-1·kg-1(P<0.05);in po experiment,a markedly shorter t1/2 K and tmax as well as greater CL and Cmax in DM group than in CTL group were found;meanwhile,DM rats suffered from remarkably increased kidney weight(KW)and KW/BW ratio relative to CTL rats.Conclusions DM pathological status can speed up elimination of CED from body of rats;the compensatory hypertrophy and thereby hyperfunction of kidneys in early-stage diabetics may explain in part at least this accelerated elimanation.     

Comparative pharmacokinetics of lovastatin extended-release tablets and lovastatin immediate-release tablets in humans

The pharmacokinetics of lovastatin and its active metabolite lovastatin acid was evaluated in 9 healthy subjects in a three-period crossover study following a single oral dose of lovastatin extended-release (ER) tablets and lovastatin immediate-release (IR) tablets. Participants were dosed with lovastatin IR 40 mg tablets following a standard breakfast, lovastatin ER 40 mg tablets following a standard breakfast, and lovastatin ER 40 mg tablets underfasting conditions. Serial plasma samples were collected for up to 48 hours postdose and assayed for lovastatin and lovastatin acid using a liquid chromatography/mass spectroscopy/mass spectroscopy method. Lovastatin ER tablets, unlike lovastatin IR tablets, exhibited delayed- and extended-release characteristics. The relative bioavailability, in terms of area under the curve values, of lovastatin (156%) and lovastatin acid (124%) was greater from lovastatin ER tablets as compared with lovastatin IR tablets when given with breakfast. An even greater increase in the bioavailability of lovastatin (261%) and lovastatin acid (231%) was observed when the lovastatin ER tablets were administered under fasting conditions. Thus, greater gastrointestinal tract drug absorption of lovastatin from lovastatin ER tablets was demonstrated. Ingestion of a standard breakfast prior to administration of lovastatin ER tablets decreased absorption of lovastatin by approximately 40%, relative to lovastatin ER tablets under fasting conditions.     

Comparative pharmacokinetics of alprazolam and lorazepam in humans and in African Green Monkeys

The comparative pharmacokinetics of alprazolam and lorazepam were evaluated in African Green Monkeys and in healthy male human volunteers. Six monkeys received a single 250 µg/kg oral dose of alprazolam and of lorazepam on two separate occasions. Mean kinetic values for the two drugs, respectively, were: elimination half-life, 5.7 and 1.7 h; oral clearance, 5.5 and 40.2 ml/min/kg. Healthy male volunteers (n=22) received a single 1 mg oral dose of alprazolam; another group (n=24) received a single 2 mg oral dose of lorazepam. Mean values of elimination half-life in humans (11.5 and 12.4 h, for alprazolam and lorazepam, respectively) were substantially longer than corresponding values in the primate animal model, and human values of clearance (0.85 and 1.40 ml/min/kg) likewise were much lower. However, in humans, kinetic differences between the two drugs were much smaller than in the primate animals. Thus comparative studies of the behavioral effects of these two drugs in African Green Monkeys should utilize relative dosages that reflect the pharmacokinetic properties of the drugs in that species. Use of dosage ratios analogous to those used in humans may lead to results that cannot be extrapolated to humans.Supported in part by Grants MH-34223 and DA-05258 from the United States Public Health Service     

Prediction of aztreonam pharmacokinetics in humans based on data from animals

Interspecies correlations of pharmacokinetic parameters obtained in animals were used to predict human pharmacokinetics in order to design the first clinical study of an investigational drug. The serum pharmacokinetics of aztreonam, a novel monocyclic beta-lactam antibiotic, were described for mice, rats, rabbits, and monkeys, using serum clearance and apparent volume of distribution. A one-compartment pharmacokinetic model yielded predictions for aztreonam clinical pharmacokinetics that were very helpful in choosing doses and serum sampling times for the first kinetic study in healthy male volunteers. Predicted serum aztreonam concentrations agreed well with subsequently measured values in man.     

Prediction of aztreonam pharmacokinetics in humans based on data from animals

Interspecies correlations of pharmacokinetic parameters obtained in animals were used to predict human pharmacokinetics in order to design the first clinical study of an investigational drug. The serum pharmacokinetics of aztreonam, a novel monocyclic beta-lactam antibiotic, were described for mice, rats, rabbits, and monkeys, using serum clearance and apparent volume of distribution. A one-compartment pharmacokinetic model yielded predictions for aztreonam clinical pharmacokinetics that were very helpful in choosing doses and serum sampling times for the first kinetic study in healthy male volunteers. Predicted serum aztreonam concentrations agreed well with subsequently measured values in man.     

Comparative target site pharmacokinetics of immediate- and modified-release formulations of cefaclor in humans

Optimal dosing of beta-lactam antibiotics aims at maximizing the time at which drug levels in the interstitial space fluid (ISF)--the fluid that surrounds the causative microorganisms at the target site--exceed the minimal inhibitory concentration (MIC). One potentially attractive strategy to achieve this goal is to administer antibiotics as oral sustained-release formulations. The present study was designed to test the hypothesis that sustained-release formulations could lead to a more suitable pharmacokinetic profile in the ISF at the relevant target site. For this purpose, time versus cefaclor concentration profiles attained in the ISF were measured following administration of two formulations, an immediate- (500 mg IR) and a modified-release formulation in two different doses (500 mg MR and 750 mgMR) in a three-way crossover study of healthy male volunteers (n = 12). For the measurement of unbound cefaclor concentrations in the ISF of human skeletal muscle, the in vivo microdialysis technique was employed. For all three formulations, unbound cefaclor concentration in the ISF closely followed individual plasma concentration profiles in a dose-dependent pattern, with ISF to unbound plasma ratios ranging from 0.67 to 0.73. The mean residence time was found to be significantly longer for the MR formulations versus the IR formulation. The data of the present study indicate that time above MIC values at the target site can be substantially prolonged if an antibiotic is administered as a sustained-release product.     

Modeling interindividual variation in physiological factors used in PBPK models of humans

Modeling interindividual variation in internal doses in humans using PBPK models requires data on the variation in physiological parameters across the population of interest. These data should also reflect the correlations between the values of the various parameters in a person. In this project, we develop a source of data for human physiological parameters where (1) the parameter values for an individual are correlated with one another, and (2) values of parameters capture interindividual variation in populations of a specific gender, race, and age range. The parameters investigated in this project include: (1) volumes of selected organs and tissues; (2) blood flows for the organs and tissues; and (3) the total cardiac output under resting conditions and average daily inhalation rate. These parameters are expressed as records of correlated values for the approximately 30,000 individuals evaluated in the NHANES III survey. A computer program, Physiological Parameters for PBPK Modeling (P3M), is developed that allows records to be retrieved randomly from the database with specification of constraints on age, sex, and ethnicity. P3M is publicly available. The database and accompanying software provide a convenient tool for parameterizating models of interindividual variation in human pharmacokinetics.     

The effect of chloroquine on the pharmacokinetics and metabolism of praziquantel in rats and in humans

It is likely that a proportion of people treated with the anti-schistosomicidal drug praziquantel (PZQ) is also taking other drugs such as chloroquine (CHQ), a widely used anti-malarial. The effect of CHQ on the pharmacokinetics and metabolism of PZQ in rats and in humans was therefore studied. CHQ decreased the bioavailability of PZQ and reduced its maximum serum concentrations to a significant extent in rats and in humans. The clearance was increased to a statistically significant extent in rats but not in humans because of the wide interindividual variation. The effect of CHQ on PZQ pharmacokinetics was unexpected since drugs that inhibit hepatic drug metabolism usually increase the bioavailability of PZQ. We found that CHQ inhibits non-competitively the metabolism of PZQ to its major metabolite, 4-hydroxy-praziquantel, with a K_i of 1.65 mM in rat hepatic microsomes. Maximum concentrations attained by CHQ in serum, however, are low compared to the K_i value and significant inhibition is therefore unlikely in vivo. The explanation for CHQ's effect on the pharmacokinetics of PZQ may be due to other effects of CHQ rather than to a direct effect on drug-metabolizing enzymes.     

Anatomical and physiological parameters affecting gastrointestinal absorption in humans and rats.

Anatomical and physiological parameters of the gastrointestinal (GI) tract dramatically affect the rate and extent of absorption of ingested compounds. These parameters must be considered by nutritionists, pharmacologists and toxicologists when describing or modeling absorption. Likewise, interspecies extrapolation (e.g. from rat to human) requires species-to-species comparison of these parameters. The present paper (1) describes the alimentary canal and the barrier to absorption; (2) relates the major sites of absorption; (3) compares the dimensions and surface areas of human and rat intestinal tracts; (4) discusses motility of the gut and transit times through regions of the alimentary canal; (5) explains how luminal contents are altered by physical, chemical and metabolic processes; and (6) describes the flow of blood and lymph from the GI tract to the systemic circulation, including the enterohepatic circulation. Despite strong morphological similarities between humans and rats at the microscopic level, gross anatomical differences in the relative absorptive surface areas provide a basis for concluding that the human GI tract is capable of absorbing materials faster and to a greater extent than that of the rat. Differences in the environment of the GI lumen of the two species make it possible to infer which substances are more likely to be present in a dissolved/non-ionized state for each species. Taken together, these differences may be of sufficient magnitude to alter the assessment of risks/benefits for a given compound when those risks/benefits are based on interspecies extrapolations.     

Cyclosporine pharmacokinetics in rats and interspecies comparison in dogs, rabbits, rats, and humans

The pharmacokinetics of cyclosporine, a potent immunosuppressive agent, are described for rats given 5 mg/kg iv, measuring blood concentrations by a specific HPLC method. Cyclosporine followed first-order kinetics and blood concentrations vs. time data were adequately described by a three-compartment open model system. The mean half-life of the lambda 1 phase was 0.11 hr, that of the lambda 2 phase was 1.82 hr, and the half-life of the estimated lambda 3 phase was 23.79 hr. The mean apparent volume of distribution and Vss were 5.69 and 4.54 liters/kg, respectively. The mean blood total body clearance was 3.38 ml/min/kg. The literature was reviewed to obtain comparable data from other mammalian species, and satisfactory kinetic information was found for humans, dogs, and rabbits. Interspecies variants in physiological parameters and cyclosporine pharmacokinetics were considered and treated as a property and consequence of body size (allometry), nullifying anatomical and physiological differences between species. A relationship between pharmacokinetic time (a variable in terms of chronological time) and body weight was found. It is suggested that the metabolic capacity (based on liver weight) to eliminate cyclosporine is similar in humans, rabbits, and rats, whereas the dog showed a potentially double capacity to metabolize the drug. However, metabolic and pharmacodynamic studies are also needed to predict toxicity accurately among species.     

Quercetin pharmacokinetics in humans

The purpose of this study was to examine the pharmacokinetics of quercetin aglycone as well as its conjugated metabolites and to develop a population pharmacokinetic model for quercetin that incorporates enterohepatic recirculation. The stability of quercetin in different matrices at various temperatures and pH, and the quercetin content of six capsules of the herbal preparation Quercetin-500 Plus were determined by HPLC. Subjects received quercetin 500 mg three times daily and blood and urine samples were obtained. The concentration of quercetin aglycone and conjugated metabolites were assayed using a liquid chromatography-tandem mass spectrometry assay. Pharmacokinetic parameters were determined using noncompartmental analysis with WinNonlin. A population compartment model incorporating input from the gallbladder was developed to account for the enterohepatic recirculation observed with quercetin. The oral clearance (CL/F) was high (3.5 x 10(4)l/h) with an average terminal half-life of 3.5 h for quercetin. The plasma concentration versus time curves exhibited re-entry peaks. A one-compartment model that included enterohepatic recirculation best described the plasma data. This represents the first comprehensive evaluation of the pharmacokinetics and enterohepatic recirculation of quercetin in humans. Population pharmacokinetic models adapted for enterohepatic recirculation allowed an assessment of the magnitude and frequency of the enterohepatic recirculation process.     

Comparative pharmacokinetics of trypan blue in female Sprague-Dawley and Long-Evans rats

Administration of trypan blue to pregnant Sprague-Dawley or Long-Evans rats, during an identical stage of embryogenesis, has been associated with malformations in 97 and 17% of the offspring, respectively (Gunberg, Anat. Rec. 1958, 130, 310). In the present study the comparative pharmacokinetics of trypan blue in the two strains were investigated. Female Sprague-Dawley and Long-Evans rats were injected sc with 10 mg trypan blue/rat [0.5 ml 2% (w/v) trypan blue in distilled water]. Blood samples were collected from the post-orbital plexus at times ranging from 5 min to 480 hr after dosing. The peak serum concentration of trypan blue was greater in Sprague-Dawley rats. Pharmacokinetic analyses of concentrations of trypan blue in serum resulted in fitting a two-compartment open model, with first order absorption, for both strains. Elimination of trypan blue from the central compartment was faster in Sprague-Dawley rats. This phenomenon was associated with a net movement out of the central compartment, predicted by the ratio of intercompartment rate constants. It is possible that the reported differences between the two strains in the teratogenic effects of trypan blue could be attributable, in part, to these observed pharmacokinetic dissimilarities.     

Comparative pharmacokinetics of breviscapine liposomes in dogs, rabbits and rats

AIM: To compare pharmacokinetics of intravenous breviscapine liposomes in Beagle dogs, rabbits and rats. METHODS: Six Beagle dogs, 6 rabbits and 12 rats were intravenously administrated with breviscapine liposomes and commercial injection (breviscapine solution) by the crossover design (two periods), respectively. Plasma concentration of scutellarin, the main active component in breviscapine, at different time intervals was determined by reverse phase-HPLC. The pharmacokinetic parameters including area under the curve (AUC), clearance (CL(s)) and volume of distribution (V(c)) were calculated. RESULTS: The plasma concentration-time profiles were fitted to a two-compartment model. Breviscapine liposomes exhibited significant difference from injection in CL((s)) and AUC, examined by a one-way analysis of variance (ANOVA). With regard to both breviscapine liposomes and commercial injection (free breviscapine), the logarithm values of AUC, CL(s) and V(c) were all related to the logarithm of the body weight by the allometric equation: Y=axW(b). CONCLUSION: The allometric equation might be applied to extroplate dosage for human from animal data and also for dosage adjustment of breviscapine liposomes in order to achieve same AUC as commercial injection. Compared with the breviscapine solution, breviscapine liposomes delivered more scutellarin into the plasma.     

Comparative oxycodone pharmacokinetics in humans after intravenous, oral, and rectal administration.

The pharmacokinetics of oxycodone have been determined after single-dose administration by the intravenous (4.6-7.3 mg), oral (tablets, 9.1 mg and syrup, 9.1 mg), and rectal (30 mg) routes, in 48 patients undergoing minor surgery. There were no significant differences in the mean elimination half-lives between the intravenous (5.45 +/- 1.43 h), oral tablets (5.65 +/- 1.13 h), oral syrup (4.80 +/- 1.13 h), and rectal suppository (5.40 +/- 1.19 h) formulations of oxycodone. After intravenous administration, the mean plasma clearance of oxycodone was 25.5 +/- 10.1 L/h and the mean volume of distribution at steady state was 2.5 +/- 0.8 L/kg. The mean normalized area under the curve (AUC/D) obtained after intravenous dosing (48.2 +/- 30.2 micrograms.h/L/mg) was more than twice the AUC/D values obtained after the administration of oxycodone tablets (19.8 +/- 3.5 micrograms.h/L/mg), oxycodone syrup (17.5 +/- 5.3 micrograms.h/L/mg), and rectal suppository (20.3 +/- 5.1 micrograms.h/L/mg), indicating that the amount of oxycodone reaching the systemic circulation after the extravascular routes of administration was < 50% of that obtained after intravenous dosing. The mean absorption lag times after oxycodone tablets (0.52 +/- 0.33 h), oxycodone syrup (0.48 +/- 0.40 h), and rectal suppository (0.76 +/- 0.47 h) were consistent with the onset of pharmacological effects reported by the patients.     

党参超微粉与细粉在大鼠体内的药动学比较研究

目的：对党参超微粉与细粉中的有效成分党参炔苷在大鼠体内的药动学进行比较。方法：采用高效液相质谱（HPLC）法分别测定灌服两种样品的大鼠体内党参炔苷的血药浓度,通过DAS 2.0药动学软件处理数据,比较党参超微粉及其细粉在大鼠体内的药动学参数和相对生物利用度。结果：党参炔苷在大鼠体内的血药浓度-时间数据符合单室模型;C_max分别为1.408,1.932 μg·mL^-1;t_max分别为1,1.5 h;t_1/2分别为0.243,0.674 h;V分别为34.701,50.745 L;CL分别为5.281,3.779 L·h^-1。党参超微粉相对于细粉,其生物利用度提高了39.7%。结论：党参经超微粉碎后可促进其党参炔苷在大鼠体内的吸收,提高生物利用度。     

Comparative pharmacokinetics of coumarin anticoagulants XV: relationship between pharmacokinetics of dicumarol and warfarin in rats.

The distribution, elimination, and anticoagulant effect of dicumarol and warfarin were determined in adult males rats following intravenous injection of single doses of these drugs in crossover experiments. The biological half-life of dicumarol ranged from 5 to 28 hr; that of warfarin ranged from 9 to 30 hr. There was a statistically significant correlation between the following pharmacokinetic characteristics of dicumarol and warfarin in individual animals: biological half-life, apparent volume of distribution, total plasma clearance, and concentration in plasma eliciting one-half the maximum anticoagulant effect (effective concentration). The mean ratio of the respective biological half-lives (warfarin/dicumarol) was 1.42, and that of the apparent volumes of distribution was 1.50. The ratio of the effective plasma concentrations (dicumarol/warfarin) was correlated negatively with the half-life of dicumarol and positively with the ratio of the half-life values (warfarin/dicumarol) in individual animals. Additional studies with serum samples from other rats showed pronounced interindividual differences in the serum protein binding of both dicumarol and warfarin and a strong correlation between the protein binding of these two drugs in serum of individual animals. The results of this study, together with the results of previous studies in this series, indicate that serum protein binding is the major determinant of interindividual differences in the pharmacokinetics of dicumarol and warfarin in rats under these experimental conditions.