Triterpene antioxidants from ganoderma lucidum

Ganoderma lucidum was studied for its antioxidative activity by bioassay guided isolation in conjunction with in vitro tests. The powdered crude drug was treated with boiling water and the aqueous extract (Ex1) was further separated to obtain terpene and polysaccharide fractions. The two fractions and Ex1 were screened for their antioxidative effect against pyrogallol induced erythrocyte membrane oxidation and Fe (II)-ascorbic acid induced lipid peroxidation. All tested samples showed antioxidative activities in a dose dependent manner and the terpene fraction was found to possess the highest effect compared with the others. Chemical isolation of the terpene fraction resulted in the detection of ganoderic acids A, B, C and D, lucidenic acid B and ganodermanontriol as major ingredients.

Effects of order of magnesium exposure on the postantibiotic effect and bactericidal activity of ciprofloxacin

Quinolone antibiotics are known to form chelates with various metal cations. It has also been recognized that the physicochemical properties of the chelated antibiotic differ significantly from its unchelated form, thereby causing a reduction in antimicrobial activity. In addition, the formation of metal chelates is also believed to be the reason for the significant reduction in oral bioavailability for the quinolones when concomitantly dosed with oral cation containing agents. This has prompted the adoption of an alternate dosing regimen by introducing an adequate interval between the two. As a result of this dosing strategy, pathogens are exposed to the quinolones and metal cations in alternate orders. Using magnesium, ciprofloxacin, and Escherichia coli as the test organism, investigations were conducted to study the changes in bactericidal activity and postantibiotic effect (PAE) in relation to the orders of cation/antibiotic exposure. Results showed a parallel decrease in both bactericidal activity and PAE when the test organism was exposed to the two agents simultaneously; however, no apparent influences on these two antimicrobial effects were observed when Mg2+ was presented before or after ciprofloxacin exposure. In line with the current dosing recommendations, the interval spaced between ciprofloxacin and Mg2+ should preserve both the bactericidal activity and PAE exhibited by the antibiotic. How the present data are to be extrapolated to other quinolones and cations should be the subject of future studies.

Influence of Sanguisorba officinalis, a mineral-rich plant drug, on the pharmacokinetics of ciprofloxacin in the rat

The significance of an interaction between ciprofloxacin and Sanguisorba officinalis L. (SO), a mineral-rich herbal medicine, was evaluated in this study. Male Sprague-Dawley rats (220-250 g) receiving ciprofloxacin dosages of 20 mg/kg po were concomitantly dosed with an aqueous extract of SO (equivalent to 2 g/kg crude drug). Blood and urine samples were collected over 6 and 24 h, respectively, for the quantitation of ciprofloxacin by HPLC. The presence of SO reduced significantly (P < 0.05) the maximum plasma concentration, the area under the concentration-time curve and the urinary recovery of ciprofloxacin, by 94%, 78% and 79%, respectively, compared with rats receiving only ciprofloxacin. The presence of SO also caused an eight-fold and two-fold increase in drug distribution (Vd, lambda(z)/F) and terminal elimination half-life (t1/2, lambda(z)) from 30.8 L/kg and 1.96 h, respectively. Therefore, should the use of both agents be required, sufficient time should be allowed to ensure the efficacy of ciprofloxacin.

Achieving an optimal outcome in the treatment of infections. The role of clinical pharmacokinetics and pharmacodynamics of antimicrobials

Over the past few decades, the importance of applying pharmacokinetic principles to the design of drug regimens has been increasingly recognised by clinicians. From the perspective of antimicrobial chemotherapy, an improvement in clinical outcome and/or a reduction in toxicity are of primary interest. Before application of these pharmacokinetic theories can be effective, the interrelationships between antimicrobial, pathogen and host factors must be clearly defined. Information regarding the pharmacokinetics of the antimicrobial and the quantification of pathogen susceptibility is required. Even though susceptibility end-points such as minimum inhibitory concentration (MIC) and minimum bactericidal concentration are widely employed, they do not provide any information on dynamic changes of bacterial densities. In this regard, time-kill studies can provide more basic knowledge of the complex bacterial responses to the antimicrobial. Better prediction of these responses can be afforded by the use of mathematical models. More recently, various surrogate end-points employing a combination of suitable pharmacokinetic parameters and susceptibility data, for example the ratio of peak concentration to MIC, the area under the concentration-time curve above the MIC (AUC > MIC), the time above the MIC, or the area under the inhibitory curve (AUIC), have been suggested for better prediction of the activity of different classes of antimicrobials. To allow more extensive investigations of the contribution of pharmacokinetics to the pharmacodynamics of antimicrobials, various in vitro kinetic models have been developed. However, certain limitations exist, and it is necessary to avoid over-interpretation of the data generated by these models. Two important microbial dynamic responses, postantibiotic effect and resistance selection, must be further explored before the full impact of pharmacokinetics on antimicrobial chemotherapy can be depicted. The present paper aims at discussing all the relevant factors and provides some pertinent information on the use of pharmacokinetic-pharmacodynamic principles in antimicrobial therapy.

Netilmicin pharmacokinetics in Hong Kong Chinese cancer patients

OBJECTIVES

To study the pharmacokinetics of netilmicin in Chinese haematology-oncology patients and to determine the pharmacokinetic differences, if any, between this patient subpopulation of Chinese and Caucasians.

METHODS

A prospective study was carried out in the adult oncology unit of a major hospital in Hong Kong. During a 6 week period in 1997, all patients commencing on netilmicin therapy were monitored; the patients' demographics, clinical status, netilmicin dose and regimen, and drug administration/blood sampling time were collected. Pharmacokinetic parameters were generated using the USC*PACK package based on specifics of the patients themselves and Caucasians matched for the same patients' parameters using the Bayesian alogrithms.

RESULTS

A total of 22 patients were enrolled into the study. Twenty-nine sets of levels were drawn, but only 25 sets from 18 patients (86%) were interpretable. The predicted peak (7.47+/-1.46 microg ml-1 ) and trough levels (1.39+/-0.96 microg ml-1 ) generated by USC*PACK were found to be significantly higher than the levels observed (6.01+/-1.14 microg ml-1 and 0.93+/-0.71 microg ml-1, respectively). Netilmicin clearance, volume of distribution and rate of elimination were all significantly higher in this Chinese subpopulation than those predicted for matched Caucasians. Conclusion Alterations in the netilmicin pharmacokinetics observed in our study population might be related to the disease state and/or ethics of the study patient population. Direct application of Caucasian based population pharmacokinetic parameters to this subgroup of Chinese patients may not be appropriate and may result in underdose.

Long-term efficacy of plasma-derived hepatitis B vaccine: a 15-year follow-up study among Chinese children

To determine necessity and timing of booster of hepatitis B vaccine, we need to observe the duration of its protection. We report the results of a 15-year follow-up of a cohort of 649 children who participated a randomized, double blind, placebo-controlled trial on a plasma-derived hepatitis B vaccine in 1982. During the 15 years after vaccination, more vaccinated children had anti-HBs of 10 S/N ratios or over, compared with the controls, at all nine observations. At 15 years 50.0% (26/52) of the participants studied in the vaccinated group and 33.3% of the tested controls (18/54) retained anti-HBs levels of S/N ratios> or =10 (P < 0.09). However, since 5 years after vaccination, median S/N ratios of anti-HBs among the vaccinated children with detectable anti-HBs were lower than those of the controls except that detected at 15 years. 16.7% (9/54) of the tested children in the control group were HBsAg positive at 15 years after vaccination, in comparison with 1.9% (1/52) of the tested children in the vaccinated (P < 0.02). 28 chronic HBsAg carriers were identified in the control cohort over the 15 years, whereas only 1 case was noted in the vaccinated group (8.2% vs. 0.3%, P < 0.00001), corresponding to an efficacy of 96%.

Effects of taraxacum mongolicum on the bioavailability and disposition of ciprofloxacin in rats

Taraxacum mongolicum (TM), also known as dandelion, is a herb widely used in the East for its antibacterial activity. The high mineral content of TM presents a potential problem for the absorption of quinolone antibiotics. This study was undertaken to discern the significance of a drug-drug interaction between TM and ciprofloxacin. Two groups of Sprague Dawley rats (220-250 g) were employed; one received a single oral dose of ciprofloxacin (20 mg/kg) with concomitant oral administration of an aqueous TM extract (2 g crude drug/kg) while the control group received oral ciprofloxacin (20 mg/kg) only. Ciprofloxacin in plasma and urine, collected over 6 and 24 h, respectively, was determined by HPLC. Noncompartment analysis was employed for pharmacokinetic parameter estimation. Results indicated that, as compared to control, maximum plasma concentration (Cmax) of ciprofloxacin was significantly lowered by 73% in rats receiving concurrent TM dosing. Oral TM also caused a 3-fold increase in both apparent drug distribution volume (Vd,lambdaz/F: 92. 0 vs 30.8 L/kg) and terminal elimination half-life (t1/2,lambdaz; 5. 71 vs 1.96 h). Partly due to the changes in drug distribution and elimination, relative bioavailability of ciprofloxacin, as assessed by AUC0-->infinity, remained similar for both dosing groups. These findings suggest the possibility of a multifactorial drug-drug interaction between TM and ciprofloxacin. Thus, the implications of concomitant dosing of the two agents should not be overlooked.

Nuclear factor-kappaB plays an essential role in the late phase of ischemic preconditioning in conscious rabbits

Although it is recognized that late preconditioning (PC) results from upregulation of cardioprotective genes, the specific transcription factor(s) that govern this genetic adaptation remains unknown. The aim of this study was to test the hypothesis that the development of late PC is mediated by nuclear factor-kappaB (NF-kappaB) and to elucidate the mechanisms that control the activation of NF-kappaB after an ischemic stimulus in vivo. A total of 152 chronically instrumented, conscious rabbits were used. A sequence of six 4-minute coronary occlusion/4-minute reperfusion cycles, which elicits late PC, induced rapid activation of NF-kappaB, as evidenced by a marked increase in p65 content (+164%; Western immunoblotting) and NF-kappaB DNA binding activity (+306%; electrophoretic mobility shift assay) in nuclear extracts isolated 30 minutes after the last reperfusion. These changes were attenuated 2 hours after ischemic PC and resolved by 4 hours. Competition and supershift assays confirmed the specificity of the NF-kappaB DNA complex signals. The mobility of the NF-kappaB DNA complex was shifted by anti-p65 and anti-p50 antibodies but not by anti-c-Rel antibodies, indicating that the subunits of NF-kappaB involved in gene activation after ischemic PC consist of p65-p50 heterodimers. Pretreatment with the NF-kappaB inhibitor diethyldithiocarbamate (DDTC; 150 mg/kg IP 15 minutes before ischemic PC) completely blocked the nuclear translocation and increased DNA binding activity of NF-kappaB. The same dose of DDTC completely blocked the cardioprotective effects of late PC against both myocardial stunning and myocardial infarction, indicating that NF-kappaB activation is essential for the development of this phenomenon in vivo. The ischemic PC-induced activation of NF-kappaB was also blocked by pretreatment with Nomega-nitro-L-arginine (L-NA), a nitric oxide synthase (NOS) inhibitor, N-2-mercaptopropionyl glycine (MPG), a reactive oxygen species (ROS) scavenger, chelerythrine, a protein kinase C (PKC) inhibitor, and lavendustin A, a tyrosine kinase inhibitor (all given at doses previously shown to block late PC), indicating that ischemic PC activates NF-kappaB via formation of NO and ROS and activation of PKC- and tyrosine kinase-dependent signaling pathways. A subcellular redistribution and increased DNA binding activity of NF-kappaB quantitatively similar to those induced by ischemic PC could be reproduced pharmacologically by giving the NO donor diethylenetriamine/NO (DETA/NO) (at a dose previously shown to elicit late PC), demonstrating that NO in itself can activate NF-kappaB in the heart. Taken together, these results provide direct evidence that activation of NF-kappaB is a critical step in the signal transduction pathway that underlies the development of the late phase of ischemic PC in conscious rabbits. The finding that four different pharmacological manipulations (L-NA, MPG, chelerythrine, and lavendustin A) produced similar inhibition of NF-kappaB suggests that this transcription factor is a common downstream pathway through which multiple signals elicited by ischemic stress (NO, ROS, PKC, tyrosine kinases) act to induce gene expression. To our knowledge, this is the first demonstration that NO can promote NF-kappaB activation in the heart, a finding that identifies a new biological function of NO and may have important implications for various pathophysiological conditions in which NO is involved and for nitrate therapy.

PKC-dependent activation of p44/p42 MAPKs during myocardial ischemia-reperfusion in conscious rabbits

Using conscious rabbits, we examined the effect of ischemic preconditioning (PC) on p44 and p42 mitogen-activated protein kinases (MAPKs). We found that both isoforms contribute significantly to total MAPK activity in the heart (in-gel kinase assay: p44, 59 +/- 1%; p42, 41 +/- 1%). Ischemic PC (6 cycles of 4-min occlusion/4-min reperfusion) elicited a pronounced increase in total cellular MAPK activity (+89%). This increase, which occurred exclusively in the nuclear fraction, was contributed by both isoforms (in-gel kinase assay: p44, +97%; p42, +210%) and was accompanied by migration of the two proteins from the cytosolic to the nuclear compartment. In control rabbits, MAPK kinase (MEK)1 and MEK2, direct activators of p44 and p42 MAPKs, were located almost exclusively in the cytosolic fraction. Ischemic PC induced a marked increase in cytosolic MEK activity (+164%), whereas nuclear MEK activity did not change, indicating that MEK-induced activation of MAPKs occurred in the cytosolic compartment. Activation of MAPKs after ischemic PC was completely blocked by the protein kinase C (PKC) inhibitor chelerythrine. Selective overexpression of PKC-epsilon in adult rabbit cardiomyocytes induced activation of both p44 and p42 MAPKs and reduced lactate dehydrogenase release during simulated ischemia-reperfusion, which was abolished by the MEK inhibitor PD-98059. The results demonstrate that 1) ischemic PC induces a rapid activation of p44 and p42 MAPKs in hearts of conscious rabbits; 2) the mechanism of this phenomenon involves activation of p44 and p42 MAPKs in the cytosol and their subsequent translocation to the nucleus; and 3) it occurs via a PKC-mediated signaling pathway. The in vitro data implicate PKC-epsilon as the specific isoform responsible for PKC-induced MAPK activation and suggest that p44/p42 MAPKs contribute to PKC-epsilon-mediated protection against simulated ischemia. The results are compatible with the hypothesis that p44 and p42 MAPKs may play a role in myocardial adaptations to ischemic stress.

Isoform-selective activation of protein kinase C by nitric oxide in the heart of conscious rabbits: a signaling mechanism for both nitric oxide-induced and ischemia-induced preconditioning

Although isoform-selective translocation of protein kinase C (PKC) epsilon appears to play an important role in the late phase of ischemic preconditioning (PC), the mechanism(s) responsible for such translocation remains unclear. Furthermore, the signaling pathway that leads to the development of late PC after exogenous administration of NO in the absence of ischemia (NO donor-induced late PC) is unknown. In the present study we tested the hypothesis that NO activates PKC and that this is the mechanism for the development of both ischemia-induced and NO donor-induced late PC. A total of 95 chronically instrumented, conscious rabbits were used. In rabbits subjected to ischemic PC (six 4-minute occlusion/4-minute reperfusion cycles), administration of the NO synthase inhibitor Nomega-nitro-L-arginine (group III), at doses previously shown to block the development of late PC, completely blocked the ischemic PC-induced translocation of PKCepsilon but not of PKCeta, indicating that increased formation of NO is an essential mechanism whereby brief ischemia activates the epsilon isoform of PKC. Conversely, a translocation of PKCepsilon and -eta quantitatively similar to that induced by ischemic PC could be reproduced pharmacologically with the administration of 2 structurally unrelated NO donors, diethylenetriamine/NO (DETA/NO) and S-nitroso-N-acetylpenicillamine (SNAP), at doses previously shown to elicit a late PC effect. The particulate fraction of PKCepsilon increased from 35+/-2% of total in the control group (group I) to 60+/-1% after ischemic PC (group II) (P<0.05), to 54+/-2% after SNAP (group IV) (P<0.05) and to 52+/-2% after DETA/NO (group V) (P<0.05). The particulate fraction of PKCeta rose from 66+/-5% in the control group to 86+/-3% after ischemic PC (P<0.05), to 88+/-2% after SNAP (P<0.05) and to 85+/-1% after DETA/NO (P<0.05). Neither ischemic PC nor NO donors had any appreciable effect on the subcellular distribution of PKCalpha, -beta1, -beta2, -gamma, -delta, - micro, or -iota/lambda; on total PKC activity; or on the subcellular distribution of total PKC activity. Thus, the effects of SNAP and DETA/NO on PKC closely resembled those of ischemic PC. The DETA/NO-induced translocation of PKCepsilon (but not that of PKCeta) was completely prevented by the administration of the PKC inhibitor chelerythrine at a dose of 5 mg/kg (group VI) (particulate fraction of PKCepsilon, 38+/-4% of total, P<0.05 versus group V; particulate fraction of PKCeta, 79+/-2% of total). The same dose of chelerythrine completely prevented the DETA/NO-induced late PC effect against both myocardial stunning (groups VII through X) and myocardial infarction (groups XI through XV), indicating that NO donors induce late PC by activating PKC and that among the 10 isozymes of PKC expressed in the rabbit heart, the epsilon isotype is specifically involved in the development of this form of pharmacological PC. In all groups examined (groups I through VI), the changes in the subcellular distribution of PKCepsilon protein were associated with parallel changes in PKCepsilon isoform-selective activity, whereas total PKC activity was not significantly altered. Taken together, the results provide direct evidence that isoform-selective activation of PKCepsilon is a critical step in the signaling pathway whereby NO initiates the development of a late PC effect both after an ischemic stimulus (endogenous NO) and after treatment with NO-releasing agents (exogenous NO). To our knowledge, this is also the first report that NO can activate PKC in the heart. The finding that NO can promote isoform-specific activation of PKC identifies a new biological function of this radical and a new mechanism in the signaling cascade of ischemic PC and may also have important implications for other pathophysiological conditions in which NO is involved and for nitrate therapy.

Receptor binding activities of Schefflera triterpenoids and oligosaccharides

Roots and leaves of Schefflera bodinieri were studied for their activity in the central nervous system (CNS) by bioassay-guided isolation in conjunction with receptor binding assays. As demonstrated in preliminary screening, ethanol extracts of leaves and roots of S. bodinieri showed strong binding affinity to a number of CNS receptors. Chemical investigation of this plant species was then conducted and fourteen plant ingredients were obtained. In this study, nine of these isolated compounds were tested by fifteen receptor binding assays for their CNS activities. Results showed that three compounds, namely bodinone, bodinone glycoside and D-sorbitol, were able to selectively bind to muscarine receptors, a trisaccharide bound to Ca2+ channel and 5HT-2 receptors, stigmasterol 3-O-glucoside bound to 5HT-2 receptors, and bodirin A bound to dopamine-2 receptors with IC50 values at microM level. In the drug-interaction studies, bodinone, bodinone glycoside, bodirin A, bodinitin A and the trisaccharide were found to affect binding affinity of certain specific binding agents to the 5HT1C, 5HT2, opiate, beta-adrenergic and histamine 1 receptors. These observations suggest interactions between the plant ingredients and receptors as well as synergistic effect of various compounds at receptor level.

Possible influences of ginseng on the pharmacokinetics and pharmacodynamics of warfarin in rats

We evaluated the significance of a reported clinical case of drug-drug interaction between ginseng and warfarin using a robust pharmacokinetic/pharmacodynamic approach in a rat model. The influence of ginseng on the pharmacokinetics and pharmacodynamics of oral warfarin after a single dose (2 mg kg(-1)) and at steady state (0.2 mg kg(-1) daily x 6 days) was studied in male Sprague-Dawley rats. Prothrombin time was employed as a pharmacodynamic index. Warfarin plasma concentration and vitamin K content in the ginseng extract were assessed by validated HPLC assays. The pharmacokinetics of warfarin after a single dose were not altered in the presence of ginseng; peak plasma concentration (control 7.8+/-0.5; ginseng 7.3+/-2.5 microg mL(-1)), time to peak (control 2.6+/-1.0; ginseng 3.1+/-1.1 h), elimination half-life (control 14.3+/-5.8; ginseng 10.6+/-3.1 h), and oral clearance (control 17.5+/-3.3; ginseng 20.2+/-5.5 mL h(-1)) were not significantly different (P>0.05). Similarly, alterations in the pharmacokinetics of warfarin were not detected under the multiple dosing paradigm. Under both dosing conditions, ginseng also showed no significant impact on the pharmacodynamics of warfarin as assessed by the area under the prothrombin time vs time curve (multiple dosing; control 3776+/-619, ginseng 3830+/-362 sh) and maximum prothrombin time (control 57.2+/-11.8, ginseng 63.3+/-9.1 s). Furthermore, the content of vitamin K was undetectable in the ginseng decoction. In conclusion, current data obtained in the rat showed no significant impact of ginseng on the pharmacokinetics/pharmacodynamics of warfarin when they are concomitantly administered.

Markedly different rates and resistance profiles exhibited by seven commonly used and newer beta-lactams on the selection of resistant variants of Enterobacter cloacae

Seven beta-lactam antibiotics (cefepime, cefoperazone, ceftazidime, ceftriaxone, cefamandole, imipenem and meropenem) were tested for their potential to select resistance in standard and clinical strains of Enterobacter cloacae (n = 9). The strains were subcultured daily with the test antibiotics at doubling concentrations starting at 0.125 x MIC. Development of resistance throughout the passages was detected by a disc diffusion test. Ceftazidime, ceftriaxone and cefamandole selected resistance at a faster rate than cefoperazone, cefepime and meropenem. Imipenem did not select resistance in the nine strains tested and was the only antibiotic that eradicated all the strains during selection. The resistance patterns of strains selected by meropenem, cefepime and the other cephalosporins were markedly different, although cross-resistance to the early generation cephalosporins was common. The resistance phenotypes of most strains remained stable upon serial passages in antibiotic-free medium. The findings of this study highlight the importance of the choice of antibiotic for therapy not only on the basis of its antibacterial activity, but also on its potential to select resistance to itself and other antibiotics.

Assessment of presystemic factors on the oral bioavailability of rifampicin following multiple dosing

This study was carried out to elucidate the possible mechanism(s) responsible for reduced oral rifampicin bioavailability after multiple dosing. In addition to autoinduction, the relative contribution of the two possible controlling factors, e.g., intestinal metabolism and microbial degradation, was investigated using a rat model. Pharmacokinetic studies were carried out to assess the absolute rifampicin bioavailability by both oral and intravenous drug administration before and after 8 daily doses of 25 mg/kg. To estimate the possible involvement of microbial degradation, rifampicin kinetics were also assessed in rats on day 8 after receiving multiple oral dosing and concurrent administration of nonabsorbable triple antibiotics for gut sterilization 3 days prior to the study day. Pharmacokinetic parameters were generated by noncompartmental analysis. The results revealed a significant decrease in rifampicin levels for rats after multiple exposure, compared to single dosing; the mean clearance determined by intravenous dosing increased by 43% from 3.7 ml/min/kg and the half-life decreased by 24% from 238 min. However, the extent of decrease in rifampicin exposure following multiple dosing was substantially greater for rats dosed orally than intravenously; estimated absolute oral bioavailability decreased by 15% from 0.89 on day 1 to 0.76 on day 8. No apparent alterations in any of the pharmacokinetic parameters were observed after gut sterilization, suggesting minimal contribution of microbial degradation to the reduction in oral rifampicin absorption after multiple dosing. In addition to hepatic enzyme autoinduction, these results strongly suggest the involvement of enhanced intestinal metabolism as a contributing factor to the decrease in oral rifampicin bioavailability following prolonged exposure.

Impact of pharmacokinetics on the postantibiotic effect exhibited by Pseudomonas aeruginosa following tobramycin exposure: application of an in-vitro model

The postantibiotic effect (PAE) exhibited by Pseudomonas aeruginosa after exposure to single doses of tobramycin was investigated under various pharmacokinetic conditions using an established in-vitro kinetic model. At equal doses of the antibiotic stimulating an intravenous bolus condition, the effects of varying elimination half-life on PAE were assessed. The PAE was longer when the rate of antibiotic elimination was lower. However, after correcting for the different degrees of antibiotic exposure using the area under the concentration-time curve above the MIC (AUC > MIC), a coherent PAE versus antibiotic exposure profile was obtained. The effects of increasing tobramycin dose and exposure time on PAE were investigated in another series of experiments; PAE was assessed during antibiotic exposure when the exponentially decreasing concentrations were above the MIC, at the MIC and below the MIC. A longer PAE was achieved at higher doses and changes were dependent on both the degree and time of exposure. For all the doses tested, the PAE was longest when the decreasing antibiotic concentrations were near or at the MIC. Shorter PAEs were detected at sub-MIC concentrations and diminished rapidly as antibiotic concentrations continued to decline. Such a decrease in PAE was counteracted by the longer exposure time, so that the total time for which the organism was under the influence of the antimicrobial effects, i.e. the sum of exposure time and PAE, remained steady at sub-MIC concentrations. Under these simulated pharmacokinetic conditions, present data support a substantial impact of pharmacokinetics on PAE. Along with MIC, AUC > MIC can be a useful pharmacokinetic parameter for PAE assessments. Should PAE be a relevant factor in antibiotic chemotherapy, both time and degree of antibiotic exposure would have to be considered.

Parameterization of inoculum effect via mathematical modeling: aminoglycosides against Staphylococcus aureus and Escherichia coli

Inoculum effect describes the inoculum size dependent changes in minimum inhibitory concentrations (MIC) exhibited by antibiotic-bacterium combinations demonstrating such effect. Traditionally, inoculum effect has been loosely defined based on the extent of increase in the MIC with respect to the increase in inoculum size. In most studies, assessment of MIC data has relied on the arbitrary selection of a point of reference for both baseline MIC and inoculum size. More importantly, this conventional method of assessment does not permit information conveyed in a complete MIC versus inoculum size profile to be fully explored. To undertake these issues, a mathematical model was developed for the description of the entire inoculum effect profile. With the employment of three key parameter estimates, i.e., the baseline MIC, the threshold inoculum size at which the increase in MIC commences, and the rate of increase in MIC with respect to inoculum size, both the shape and location of the profile could be adequately defined. To verify the application of this model, a series of four aminoglycosides were tested against standard strains of E. coli and S. aureus. Results showed a good degree of organism specificity and antibiotic-class dependency of the inoculum effect profiles. Analysis of the parameter estimates obtained provided further support for these observations. In conclusion, the mathematical model developed in the present study adequately described the inoculum effect exhibited by the various aminoglycoside-bacterium combinations tested. The parameter estimates generated by the modeling approach allowed comparison and quantitative analysis of the inoculum effect profiles with minimal difficulties.

CLS advanced degrees and career enhancement. Part 2--A comparison of perceptions

OBJECTIVE

To determine whether recipients of clinical laboratory science (CLS) advanced degrees (MS) perceive greater career enhancement value related to earning an advanced degree than is perceived by their baccalaureate level (BS) colleagues.

DESIGN

Two questionnaires were used-one for certified or licensed CLS professionals who had earned MS CLS degrees; the other for matched BS CLS colleagues.

SETTING

Five academic programs that conduct both National Accrediting Agency for Clinical Laboratory Sciences accredited CLS education and CLS MS degree programs participated.

PARTICIPANTS

The number of survey respondents was 220 (117-MS; 103-BS level controls). The groups were matched for gender, residence region, and years of experience.

MAIN OUTCOME MEASURES

The primary outcome measurements were the perceived benefits of having a CLS MS degree, the reasons for and against obtaining a CLS MS degree, and the overall evaluation of CLS degree programs at both levels.

RESULTS

The highest perceived benefit of having a CLS MS degree was the same in both groups, "enhanced self esteem and confidence". The highest priority motivation of MS degree recipients for obtaining a CLS advanced degree was "personal satisfaction". The highest priority reason of the BS group for not obtaining a CLS advanced degree was "family obligation". In both levels of degree programs the subject most commonly cited as needing modification was laboratory management.

CONCLUSION

The results indicate that CLS professionals who have CLS MS degrees perceive a greater career enhancement value of advanced CLS degrees than their BS level colleagues.

CLS advanced degrees and career enhancement. Part 1--Comparison of career data

OBJECTIVE

Determine whether recipients of clinical laboratory science (CLS) advanced degrees (MS) experience greater career achievements than their baccalaureate level (BS) colleagues.

DESIGN

Two similar questionnaires were used-one for certified or licensed CLS professionals who had earned advanced CLS degrees (MS); the other for matched BS CLS colleagues.

SETTING

Five academic programs that conduct both National Accrediting Agency for Clinical Laboratory Sciences accredited CLS education and CLS MS degree programs participated.

PARTICIPANTS

The number of survey respondents was 220, 117 with advanced CLS degrees and 103 BS level controls. There were 99 matched pairs, i.e., 198 individuals were matched for gender, residence region, and years of experience.

MAIN OUTCOME MEASURES

Careers of BS vs. MS respondents were statistically compared, e.g., fractions with managerial level jobs, relative earnings increases per year, numbers of publications and reports, and other professional contributions.

RESULTS

Compared to their BS degree controls, MS degree respondents had more managerial level jobs (62% MS; 36% BS), a higher frequency of job change (once per 4.3 years MS; once per 5.9 years BS), and a higher increase per year of earnings (9.1% MS; 8.1% BS). A greater percentage of the MS degree graduates (77%) than the BS level controls (33%) had authored external publications; the responses related to authorship of institutional reports and procedures were less different-84% MS and 64% BS. Professional contributions to their institutions or profession were cited slightly more frequently by the MS graduates (65%) than by the BS level controls (55%).

CONCLUSION

Compared to their matched BS level CLS colleagues, CLS MS degree recipients had greater job mobility, greater management authority, higher salary, and more numerous professional contributions.

Relationship between isokinetic concentric and eccentric contraction modes in the knee flexor and extensor muscle groups

We investigated whether in normal subjects isokinetic concentric and eccentric strength variables were related in order to have a better picture in relation to rehabilitation and possible injury prevention. We studied the relationship between isokinetic concentric and eccentric peak torque, total work, and average power of knee extension and knee flexion at 60 degrees/sec and 120 degrees/sec in 42 young Chinese adults (22 males, age = 27 +/- 6.9 years; 20 females, age = 24.9 +/- 5.05 years) using the Cybex 6000 isokinetic dynamometer. Repeated analysis of covariance was used to compare the means between concentric and eccentric variables adjusted by limb dominance, speed of testing, and the muscle groups tested. A highly significant correlation was found between all concentric and eccentric variables, with correlation coefficients (r) ranging from 0.67 to 0.93. All but two of the eccentric variables were significantly greater than the concentric variables. Concentric and eccentric knee flexion to knee extension (H:Q) ratios were poorly correlated, with r ranging from 0.359 to 0.645. Although there is an acceptably high correlation between isokinetic concentric and eccentric strength variables of knee flexion and extension in young healthy individuals, we recommend measuring concentric and eccentric strength to plan a proper rehabilitation program and to assess muscle groups in a given contraction mode.

Efficient high-performance liquid chromatographic assay for the simultaneous determination of metoprolol and two main metabolites in human urine by solid-phase extraction and fluorescence detection

An improved, more efficient method for the determination of metoprolol and its two metabolites in human urine is reported. The simultaneous analysis of the zwitterionic metoprolol acidic metabolite (III, H117/04) with the basic metabolites alpha-hydroxymetoprolol (II, H119/66), metoprolol (I) and guanoxan (IV, internal standard) was achieved employing solid-phase extraction and isocratic reversed-phase HPLC. The analytes were extracted from urine (100 microliters) using C18 solid-phase extraction cartridges (100 mg), and eluted with aqueous acetic acid (0.1%, v/v)-methanol mixture (40:60, v/v, 1.2 ml). The eluents were concentrated (250 microliters) under vacuum, and aliquots (100 microliters) were analysed by HPLC with fluorescence detection at 229 nm (excitation) and 309 nm (emission) using simple isocratic reversed-phase HPLC (Novapak C18 radial compression cartridge, 4 microns, 100 x 5 mm I.D.). Acetonitrile-methanol-TEA/phosphate buffer pH 3.0 (9:1:90, v/v) was employed as the eluent (1.4 ml/min). All components were fully resolved within 18 min, and the calibration curves for the individual analytes were linear (r2 > or = 0.996) within the concentration range of 0.25-40.0 mg/ml. Recoveries for all four analytes were greater than 76% (n = 4). The assay method was validated with intra-day and inter-day variations less than 2.5%.

Antibiotic exposure and its relationship to postantibiotic effect and bactericidal activity: constant versus exponentially decreasing tobramycin concentrations against Pseudomonas aeruginosa

In vitro postantibiotic effects (PAEs) exhibited by a standard strain of Pseudomonas aeruginosa following exposure to tobramycin at constant concentrations were compared to those at exponentially decreasing concentrations. Exposure to a constant concentration showed more extensive bacterial killing and resulted in longer PAEs at comparable areas under the concentration-time curves above the MIC. This phenomenon suggests a significant contribution of pharmacokinetics to antimicrobial pharmacodynamics.

Rifabutin absorption in the gut unaltered by concomitant administration of didanosine in AIDS patients

Didanosine (ddI) is currently used in the management of patients infected by the human immunodeficiency virus. Rifabutin (RBT) is being extensively used for prophylaxis against Mycobacterium avium complex (MAC) infections. Due to its acid-labile characteristics, ddI must be administered with a buffer. Recent reports have indicated that absorption of ketoconazole, ciprofloxacin, and dapsone, etc., in the gut is altered by concomitant ddI dosing. We have assessed whether concomitant dosing of ddI as antiretroviral therapy modifies RBT absorption in the gut, its steady-state pharmacokinetics, and/or safety in 15 patients with AIDS. Of the 15 patients enrolled, 12 completed the study and 3 receiving 600 mg of RBT with concomitant ddI administration withdrew prematurely from the study. Steady-state RBT pharmacokinetics were assessed on day 13 (ddI plus RBT) and day 16 (RBT alone). The ddI doses (adjusted for body weight) were 167 to 375 mg twice daily, while RBT was administered as a single 300- or 600-mg daily dose. No statistically significant (P > 0.05) differences were seen in RBT absorption parameter estimates between days 13 and 16: maximum concentration in plasma (Cmax; 511 +/- 341 ng/ml versus 525 +/- 254 ng/ml) and the time at which Cmax was observed (3.0 versus 2.5 h). The mean RBT estimates for area under the concentration-time curve from 0 to 24 h (AUC(0-tau)) (5,650 versus 5,023 ng x h/ml) and for oral clearance (1.28 versus 1.18 liter/h/kg) on both study days were also similar. Assessment based on urinary recovery of RBT (3.1 versus 3.7 mg) and its predominant deacetyl metabolite, LM565 (1.6 versus 1.4 mg), showed no apparent effect of ddI. The fraction of the RBT dose converted to LM565, as suggested by the ratio of AUC of the metabolite to AUC of the parent drug, was also unaltered (0.15 versus 0.12). A ratio analysis (day 13/day 16) of the RBT pharmacokinetic estimates showed that the 95% confidence intervals for all parameters were inclusive of one. Furthermore, the brief interruption of ddI therapy over this short study period at steady state produced no clinically significant changes in body weight, hematology, and renal and pancreatic functions. Therefore, concomitant administration of ddI appears not to affect RBT absorption in the gut and its disposition or safety in patients with AIDS.

Correlation between bactericidal activity and postantibiotic effect for five antibiotics with different mechanisms of action

Theoretically, if the postantibiotic effect (PAE) reflects the duration of cellular recovery, then the extent of cellular damage inflicted on bacteria by an antibiotic, as suggested by the degree of bactericidal activity, should reflect the length of PAE; this is especially true if binding of the antibiotic to bacterial receptors is irreversible. To test this hypothesis, correlation between PAEs and bactericidal rate constants measured simultaneously at various antibiotic concentrations was examined for five antibiotic-bacterium combinations. Each of the five antibiotics used, i.e. tobramycin, ciprofloxacin, dicloxacillin, trimethoprim and tetracycline, has a different mechanism of action: the first three bind irreversibly to bacterial receptors, while trimethoprim and tetracycline bind reversibly. Both PAE and bactericidal activity increased nonlinearly with concentrations in a saturable manner for all the combinations studied. Linear least-square regression analyses showed strong correlations (P < 0.01) between the two responses for individual combinations. Such a linear relationship also extended, with good correlation (P < 0.05), across the five combinations when individual maximal bactericidal rate constants and PAEs were considered separately. These observations suggest that cellular recovery from nonlethal damage following antibiotic exposure may be a major determinant of PAE.

In vitro models for prediction of antimicrobial activity: a pharmacokinetic and pharmacodynamic perspective

The endpoints associated with conventional susceptibility testing, e.g., the minimum inhibitory concentration or minimum bactericidal concentration (MIC or MBC), are discrete in nature. These endpoint measurements do not provide any information, regarding the pharmacodynamic changes exhibited by the bacteria in reaction to the antibiotic activity during the incubation period. Another limitation of these susceptibility tests is the maintenance of constant antibiotic concentrations; this condition contrasts sharply to the continuously changing concentrations observed in vivo. To tackle these problems, various in vitro pharmacokinetic/pharmacodynamic models have been developed. Taking into consideration various pharmacokinetic determinants, such models allow more comprehensive study of the pharmacodynamic effects demonstrated by antibiotics. In this paper, the implications and usefulness of these in vitro models to the characterization of antimicrobial activity are discussed. Limitations associated with their use are also addressed.