Pharmacokinetics and Target Attainment of Ceftobiprole in Asian and Non-Asian Subjects.

Ceftobiprole is a broad-spectrum cephalosporin. The objective of this study was to test the hypothesis that the pharmacokinetics (PK) and exposure of ceftobiprole in Asian subjects are similar to those in non-Asian subjects. Three approaches were followed. The first compared the individual PK estimates between the 2 subgroups derived from a population PK model previously built. Next, it was determined whether "Asian subject" was a significant covariate. Finally, a pharmacodynamic analysis was performed by comparing measures of exposure and target attainment. No significant differences were found between PK parameter estimates for Asian and non-Asian subjects, with median values (range) for clearance of 4.82 L/h (2.12-10.47) and 4.97 L/h (0.493-20.6), respectively (P = .736). "Asian subject" was not a significant covariate in the population PK model. There were no significant differences between the measures of exposure. The geometric mean ratio for the fAUC was 1.022 (90%CI, 0.91-1.15), indicating bioequivalence. Taking a target of 60% coverage of the dose interval, more than 90% of the population in both subgroups was adequately exposed. This analysis demonstrated that there are no PK or pharmacodynamic differences between Asian and non-Asian subjects for a ceftobiprole dose of 500 mg every 8 hours as a 2-hour infusion.

Exposure to ceftobiprole is associated with microbiological eradication and clinical cure in patients with nosocomial pneumonia.

The percentage of the dosing interval that the non-protein-bound plasma concentration is above the MIC (%fT>MIC) for cephalosporins has been shown to correlate with microbiological outcomes in preclinical studies. However, clinical data are scarce. Using data from a randomized double-blind phase 3 clinical trial, we explored the relationship of ceftobiprole exposure with microbiological and clinical outcomes in patients with nosocomial pneumonia. The individual ceftobiprole exposure was determined for different pharmacokinetic (PK)/pharmacodynamic (PD) indices using individual pharmacokinetic data and a previously published population model. The MICs used in the analysis were the highest MICs for any bacterium cultured at baseline or the end of treatment (EOT). Outcomes were microbiological cure at EOT and clinical cure at test of cure (TOC). Multiple logistic regression (MLR) and classification and regression tree (CART) analyses were applied to determine the relationships among exposure, patient characteristics, and outcomes. MLR indicated that the %fT>MIC of ceftobiprole was the best predictor for both microbiological eradication and clinical cure. CART analysis showed a breakpoint value of 51.1% (n = 159; P = 0.0024) for clinical cure, whereas it was 62.2% (n = 251; P < 0.0001) for microbiological eradication. Other factors also contributed, particularly to clinical outcome. These included the difference between VAP and non-VAP patients, systemic inflammatory response syndrome (SIRS), creatinine clearance, the use of anti-Pseudomonas combination therapy, and Acute Physiology and Chronic Health Evaluation II (APACHE-II) score. There is a strong correlation between microbiological eradication and clinical cure with exposure to ceftobiprole. The %fT>MIC required to result in a favorable clinical outcome is >51% of the dosing interval, which is in line with the values found for microbiological eradication, the comparator ceftazidime, and preclinical models.

The 'unified hypothesis' of Geddes et al. is not supported by the data.

Inflicted head injury to the developing brain frequently results in serious disability. The pathogenesis of the neuraxial and ocular findings in infants believed to have suffered inflicted head injury remains the subject of considerable debate. Recent neuropathology studies of fatal cases of inflicted head injury and of a foetal/perinatal non-traumatic model have led to the proposal that there is a 'unified hypothesis', the essential feature of which is hypoxic brain swelling secondary to cervicomedullary injury. It has been suggested that less than violent forces may be involved and even that some cases may not be due to trauma at all. The purpose of this paper is to provide a critical review of the data upon which these suppositions are based on a background of what is already known. It is submitted that there are serious flaws in the methodology; the conclusions reached cannot logically be drawn from the data; and the 'unified hypothesis' is not supported by the evidence. On the basis of the data presented, it is also difficult to sustain the secondary hypothesis purporting to describe a minority cohort with 'infantile encephalopathy with subdural and retinal bleeding' of non-traumatic causation.

In vitro interactions between amphotericin B, itraconazole, and flucytosine against 21 clinical Aspergillus isolates determined by two drug interaction models.

Combination therapy of flucytosine (5FC) with other antifungal agents could be of use for the treatment of invasive aspergillosis. However, interpretation of the results of in vitro interactions is problematic. The fractional inhibitory concentration (FIC) index is the most commonly used method, but it has several major drawbacks in characterizing antifungal drug interaction. Alternatively, a response surface approach using the concentration-effect relationship over the whole concentration range instead of just the MIC can be used. We determined the in vitro interactions between amphotericin B (AMB), itraconazole, and 5FC against 21 Aspergillus isolates with a broth microdilution checkerboard method that employs the dye MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide]. FIC indices based on three different MIC endpoints (MIC-0, MIC-1, and MIC-2) and the interaction coefficient alpha were determined, the latter by estimation from the response surface approach described by Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol. Rev. 47:331-385, 1995). The value obtained for the FIC index was found to be dependent on the MIC endpoint used and could be either synergistic, indifferent, or antagonistic. The response surface approach gave more consistent results. Of the three combinations tested, the AMB-5FC combination was the most potent in vitro against Aspergillus spp. We conclude that the use of the response surface approach for the interpretation of in vitro interaction studies of antifungals may be helpful in order to predict the nature and intensity of the drug interaction. However, the correlation of these results with clinical outcome remains difficult and needs to be further investigated.

Dose individualization in PharmDIS-e+.

Individualized dosage regimen calculations require knowledge on the pharmacokinetic and pharmacodynamic properties of the drug and the characteristics of the patient. A PK-PD-based dosage regimen is not easily and generally applicable, mainly because the combination of available PK parameters and therapeutic target levels may be inappropriate for the purpose of predicting a plausible dosage regimen. Within the project PharmDIS-e+, an alternative approach was chosen, and this "PK and standard dose"-based principle is well suited for computerized dosing advice. PharmDIS-e+ aims at the development of several applications for dosing regimen advice for general practitioners, hospital physicians and pharmacists.

In vitro interaction of flucytosine combined with amphotericin B or fluconazole against thirty-five yeast isolates determined by both the fractional inhibitory concentration index and the response surface approach.

Combination therapy could be of benefit for the treatment of invasive yeast infections. However, in vitro interaction studies are relatively scarce and the interpretation of the fractional inhibitory concentration (FIC) index can be contradictory due to various definitions used; not all information on the interaction study is used in the index, and different MIC end points exist for different classes of drugs. Fitting an interaction model to the whole response surface and estimation of an interaction coefficient alpha (IC(alpha)) would overcome these objections and has the additional advantage that confidence intervals of the interaction are obtained. The efficacy of flucytosine (5FC) in combination with amphotericin B (AB) and fluconazole (FCZ) was studied against 35 yeast isolates in triplicate (Candida albicans [n = 9], Candida glabrata [n = 9], Candida krusei [n = 9], and Cryptococcus neoformans [n = 8]) using a broth microdilution checkerboard method and measuring growth after 48 h by a spectrophotometer. The FIC index and IC(alpha) were determined, the latter by estimation from the response surface approach described by Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol. Rev. 47:331-385, 1995) by using a computer program developed for that purpose. For the 5FC-FCZ combination, the interactions determined by the IC(alpha) generally were in concordance with the interactions determined by the FIC index, but large discrepancies were found between both methods for the 5FC-AB combination. These could mainly be explained by shortcomings in the FIC approach. The in vitro interaction of 5FC-AB demonstrated variable results depending on the tested Candida isolate. In general, the 5FC-FCZ combination was antagonistic against Candida species, but for some Candida isolates synergism was found. For C. neoformans the interaction for both combinations was highly dependent on the tested isolate and the method used. Response surface approach is an alternative method for determining the interaction between antifungal agents. By using this approach, some of the problems encountered with the FIC were overcome.

Comparison of fractional inhibitory concentration index with response surface modeling for characterization of in vitro interaction of antifungals against itraconazole-susceptible and -resistant Aspergillus fumigatus isolates.

Although the fractional inhibitory concentration (FIC) index is most frequently used to define or to describe drug interactions, it has some important disadvantages when used for drugs against filamentous fungi. This includes observer bias in the determination of the MIC and no agreement on the endpoints (MIC-0, MIC-1, or MIC-2 [> or = 95, > or = 75, and > or = 50% growth inhibition, respectively]) when studying drug combinations. Furthermore, statistical analysis and comparisons are troublesome. The use of a spectrophotometric method to determine the effect of drug combinations yields quantitative data and permits the use of model fits to the whole response surface. We applied the response surface model described by Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol. Rev. 47:331-385, 1995) to determine the interaction coefficient alpha (ICalpha) using a program developed for that purpose and compared the results with FIC indices. The susceptibilities of amphotericin B (AM), itraconazole (IT), and terbinafine (TB) were tested either alone or in combination against 10 IT-susceptible (IT-S) and 5 IT-resistant (IT-R) clinical strains of Aspergillus fumigatus using a modified checkerboard microdilution method that employs the dye MTT [3-(4,5-dimethyl-2-thiazyl)2,5-diphenyl-2H-tetrazolium bromide]. Growth in each well was determined by a spectrophotometer. FIC indices were determined and ICalpha values were estimated for each organism strain combination, and the latter included error estimates. Depending on the MIC endpoint used, the FIC index ranged from 1.016 to 2.077 for AM-IT, from 0.544 to 1.767 for AM-TB, and from 0.656 to 0.740 for IT-TB for the IT-S strains. For the IT-R strains the FIC index ranged from 0.308 to 1.767 for AM-IT, from 0.512 to 1.646 for AM-TB, and from 0.403 to 0.497 for IT-TB. The results indicate that the degree of interaction is not only determined by the agents themselves but also by the choice of the endpoint. Estimates of the ICalpha values showed more consistent results. Although the absolute FIC indices were difficult to interpret, there was a good correlation with the results obtained using the ICalpha values. The combination of AM with either IT or TB was antagonistic in vitro, whereas the combination of IT and TB was synergistic in vitro for both IT-S and IT-R strains. The use of response surface modeling to determine the interaction of drugs against filamentous fungi is promising, and more consistent results are obtained by this method than by using FIC indices.

Pharmacokinetic-pharmacodynamic modeling of activity of ceftazidime during continuous and intermittent infusion.

We developed and applied pharmacokinetic-pharmacodynamic (PK-PD) models to characterize in vitro bacterial rate of killing as a function of ceftazidime concentrations over time. For PK-PD modeling, data obtained during continuous and intermittent infusion of ceftazidime in Pseudomonas aeruginosa killing experiments with an in vitro pharmacokinetic model were used. The basic PK-PD model was a maximum-effect model which described the number of viable bacteria (N) as a function of the growth rate (lambda) and killing rate (epsilon) according to the equation dN/dt = [lambda - epsilon x [Cgamma(EC50gamma + Cgamma)]] N, where gamma is the Hill factor, C is the concentration of antibiotic, and EC50 is the concentration of antibiotic at which 50% of the maximum effect is obtained. Next, four different models with increasing complexity were analyzed by using the EDSIM program (MediWare, Groningen, The Netherlands). These models incorporated either an adaptation rate factor and a maximum number of bacteria (Nmax) factor or combinations of the two parameters. In addition, a two-population model was evaluated. Model discrimination was by Akaike's information criterion. The experimental data were best described by the model which included an Nmax term and a rate term for adaptation for a period up to 36 h. The absolute values for maximal growth rate and killing rate in this model were different from those in the original experiment, but net growth rates were comparable. It is concluded that the derived models can describe bacterial growth and killing in the presence of antibiotic concentrations mimicking human pharmacokinetics. Application of these models will eventually provide us with parameters which can be used for further dosage optimization.

Calcium antagonists show two modes of protection in ischemic heart failure.

Retrogradely perfused, isovolumically beating, paced rat hearts were subjected to 30 min of global ischemia in the absence and presence of nifedipine, verapamil, bepridil and quaternary bepridil at a concentration ranging from 3 to 10,000 nmol/l. Under constant pressure conditions, the arrest of coronary flow and the reduction of ventricular contraction during global ischemia were readily reversible and quickly returned at reperfusion. During ischemia, however, a diastolic contracture developed, which was slowly reversible upon reperfusion. The calcium antagonists studied appeared to delay and diminish in a concentration-dependent way the diastolic contracture during ischemia. Furthermore, they accelerated the reduction of this contracture at reperfusion. Nifedipine, bepridil and quaternary bepridil showed a 100 to 1000 times higher potency in accelerating the recovery of the diastolic contracture during the reperfusion phase than in reducing the development of diastolic tension during the ischemic period itself, whereas verapamil hardly discriminated these two phases. When the hearts were reperfused with nifedipine under constant flow conditions, reduction of the diastolic contracture during ischemia could still be observed, but the accelerated reduction of end-diastolic pressure during reperfusion was no longer present. The results are discussed in relation to the energy saving, negative inotropic activity of the drugs before the ischemic period and the strong coronary vasodilation, which seems to be involved in the protective activity of the drugs, especially during reperfusion.

Stereoisomers of calcium antagonists distinguish a myocardial and vascular mode of protection against cardiac ischemic injury.

Concentration-dependent effects of the enantiomers of the calcium antagonists, gallopamil, diltiazem, and bepridil have been studied in the Langendorff-perfused rat heart, subjected to 30 min of global ischemia. It is shown that the time course, as well as the height of the energy deprivation-induced left ventricular diastolic contracture that develops during ischemia, can be selectively inhibited by negative inotropic concentrations of the calcium antagonist enantiomers. The time needed for recovery from the diastolic contracture during the reperfusion phase can be shortened significantly by lower, vasodilating concentrations of the drugs. In normoxically perfused hearts, stereoselectivity factors (sf) of the enantiomers of the compounds amounted to 63, 10, and 2 for the negative inotropic and 12.6, 79, and 4 for the vasodilating activities of gallopamil, cis-diltiazem, and bepridil, respectively. The sf values of negative inotropism proved to be remarkably similar to sf values of 50 and 7.9 for gallopamil and cis-diltiazem in the protection of the ischemic contracture during ischemia, whereas the sf values of coronary flow increase closely paralleled the values of 7.9, 63, and 2.5 for gallopamil, cis-diltiazem, and bepridil, respectively, in protection during the reperfusion phase. The results strongly suggest that at reperfusion the vasoselective enantiomers of calcium antagonists provide protection related to improved tissue perfusion, and thereby possibly restoring the distorted ionic and energetic homeostasis, whereas the other enantiomers are more involved in a direct energy-saving activity, resulting in protection during the ischemic period.

Protection by verapamil and nifedipine against ischaemia-induced loss of [3H]-(+)-PN 200-110 binding sites in the rat heart.

We have studied the effects of 60 min global ischaemia and 30 min of subsequent reperfusion on the binding of [3H]-(+)-PN 200-110 and [3H]-(-)-devapamil (desmethoxyverapamil or D888) in rat heart membranes. The hearts were perfused in the Langendorff-mode and pretreated with 1 mumol/l verapamil, 30 nmol/l and 1 mumol/l nifedipine. After 60 min of global ischaemia in the absence of drugs, we found a reduction of [3H]-(+)-PN 200-110 binding sites, without changes in the equilibrium dissociation binding constant (Kd). After the subsequent reperfusion maximum specific binding (Bmax) was further reduced, whereas the Kd remained constant. [3H]-devapamil binding sites were influenced to a lower extend and showed only a decrease in Bmax at reperfusion. Pretreatment with 1 mumol/l verapamil completely prevented the changes which were observed for [3H]-(+)-PN 200-110. Pretreatment with a low, vasodilating concentration (30 nmol/l) of nifedipine displayed selective protection against the extra reduction in Bmax which was observed during reperfusion. It is concluded that calcium antagonists show protection against the ischaemia-induced loss of dihydropyridine binding sites in relation to their negative inotropic, energy-saving activity. Furthermore, nifedipine at low, vasodilating but not negative inotropic concentrations protects against further reperfusion-induced injury, which protection may be related to an improved flow during reperfusion.

Effects of verapamil on ischaemia-induced impairment of ATP-dependent calcium extrusion in rat heart sarcolemma.

1. The effects of ischaemia and reperfusion were studied on adenosine 5'-triphosphate (ATP)-dependent 45Ca2+-transport in rat heart sarcolemma vesicles. 2. The effect of verapamil, 1 mumol l-1, was studied by pretreatment of the hearts during Langendorff-perfusion and in vitro by adding the drug after isolation of the vesicles. 3. Without drug pretreatment the Ca2+-uptake appeared to be strongly reduced after 30 and after 60 min of global ischaemia, whereas after 30 min of reperfusion it was restored to slightly above the control level. 4. Verapamil pretreatment during the Langendorff perfusion significantly increased Ca2+-uptake in sarcolemma vesicles both before the onset of ischaemia and after 30 min of reperfusion, whereas no beneficial effect was found on the impaired uptake activity during the ischaemic period. 5. When tested in vitro after the isolation of the sarcolemma vesicles, verapamil only inhibited the Ca2+-uptake activity with an IC50 of 112 mumol l-1, which was increased to 250 mumol l-1 after ischaemia and reperfusion. 6. The present study indicates that pretreatment with verapamil, 1 mumol l-1, of the intact rat heart activates an ATP-dependent Ca2+ extrusion process that may contribute to decrease cellular calcium levels in control and, more importantly, in a reperfusion situation. In contrast, in vitro only a less potent inhibition of the extrusion process was found, indicating that physiological regulatory mechanisms may be altered in the vesicles.

Stereoisomers of BAY K 8644 show opposite activities in the normal and ischaemic rat heart. A comparison with nifedipine.

The effects of the stereoisomers and the racemate of the calcium agonist BAY K 8644 and the calcium antagonist nifedipine were studied on the Langendorff-perfused rat heart, subjected to 30 min of global ischaemia. The results show that (-)- and (+/-)-BAY K 8644 induced a strong positive inotropic effect at 100 and 1000 nmol/l and a vasoconstricting effect which was most prominent at 1 and 10 nmol/l, respectively. At higher concentrations the flow reduction was inverted to a flow increase, closely related to the positive inotropic activity. The inotropic status induced by the agonist before the onset of ischaemia was reflected in an accelerated development of the diastolic contracture during ischaemia. During the reperfusion, a complex triphasic effect on the recovery was found, in which probably positive inotropism, vasoconstriction, metabolic and mechanical factors are involved. The (+)-enantiomer of BAY K 8644 behaved as a weak calcium antagonist showing merely vasodilatation, which accelerated the recovery from the ischaemic contracture at reperfusion. The calcium antagonistic, vasodilating effects of the (+)-enantiomer were expressed in the racemate only during the reperfusion phase, where it took an intermediate position between the effects of the (-)- and (+)-enantiomer. In contrast, nifedipine, at negative inotropic - energy saving - concentrations, diminished the height and delayed the development of the energy deprivation-induced left ventricular diastolic contracture during ischaemia. The time needed for recovery from the contracture during reperfusion was significantly shortened already at a 100 times lower, vasodilating concentration of nifedipine.

Positive inotropic effects of calcium channel antagonists are not necessarily caused by partial calcium channel agonism.

Recently it has been reported that some dihydropyridine calcium channel antagonists (nifedipine, nimodipine, nitrendipine) are able to produce positive inotropic effects in isolated perfused guinea pig hearts. We studied the effects of nifedipine in isolated perfused paced rat hearts under constant pressure and constant flow perfusion conditions. We found that nifedipine is able to produce a positive inotropic effect under constant pressure conditions but not under constant flow conditions. We conclude that nifedipine does not have partial calcium channel agonistic properties and that the positive inotropic effect seen under constant pressure conditions is a result of the vasodilating properties of the drug. Positive inotropic effects caused by vasodilatation can be explained by the "garden-hose-effect".