耐药鲍曼不动杆菌对头孢呋辛和头孢他啶的PAE实验观察

目的 观察研究头孢呋辛和头孢他啶对院内感染常见致病菌-多重耐药鲍曼不动杆菌的抗生素后效应(postantibiotic effect,PAE).方法 在不同药物浓度作用下,采用平板倾注法CFU计数,按PAE=T-C计算之,T定义为试验管CFU/ml高于重建后0时的10倍(1 logCFU/ml)所需时间(min),C为对照管CFU/ml上升10倍所需要的时间(min).结果 4倍MIC无明显PAE,10倍MIC也无明显PAE.结论 头孢呋辛和头孢他啶对耐药鲍曼不动杆菌无明显PAE.     

头孢曲松-舒巴坦复方制剂对产ESBLs大肠埃希菌持续效应的研究

目的测定头孢曲松-舒巴坦复方制剂（2：1）对产ESBLs大肠埃希菌的MIC和持续效应。后者包括抗生素后效应（PAE）、内酰胺酶抑制剂后效应（PLIE）和亚抑菌浓度后效应（PASME）。方法以肉汤试管稀释法测定MIC。将大肠埃希菌与一定冲击浓度的头孢曲松-舒巴坦作用2h后，在不同药物浓度条件下继续培养，用倾皿培养法进行菌落计数（CFU／mL），以log（CFU／mL）对培养时间（h）绘制生长曲线，计算PAE、PLIE和PASME。结果①头孢曲松和头孢曲松-舒巴坦对大肠埃希菌的MIC分别为8／4mg／L和大于256mg／L。②头孢曲松和头孢曲松-舒巴坦对大肠埃希菌的PAE为负值或很短。③舒巴坦对大肠埃希菌的PLIE在低冲击浓度（2MIC、4MIC）时为负值或很短，当浓度增加至10MIC时，其PLIE〉6．5h。结论时间依赖的头孢曲松-舒巴坦对产ESBLs大肠埃希菌的PLIE存在明显的浓度依赖效应，为了提高头孢曲松-舒巴坦的临床疗效，其给药方法的设计除了要延长T〉MIC外，适当提高给药的峰浓度或许亦有利于疗效的发挥。     

抗生素后效应与临床应用

抗生素后效应(post antibiotic effect，PAE)指细菌与抗生素短暂接触，当药物浓度下降低于最低抑菌浓度(MIC)或消除后，细菌的生长仍受到持续抑制的效应。20世纪70代中期Mcdonald和cIaig等提出了抗生素后效应这一理论，近年来国内外学者对此十分关注，研究正不断深入和广泛。其临床的意义在于，以前设计抗生素给药方案仅依靠血药浓度、消除速率、组成分布等一些药代动力学数据作为参考，     

头孢哌酮和哌拉西林与β内酰胺酶抑制剂对大肠埃希菌和肺炎克雷伯菌的后效应研究

目的测定头孢哌酮和哌拉西林与克拉维酸、舒巴坦、三唑巴坦3种β内酰胺酶抑制剂的不同复方的最低抑菌浓度（MIC）、抗生素后效应（PAE）、β内酰胺酶抑制剂后效应（PLIE）和亚抑菌浓度后效应（PASME）。方法以肉汤稀释法测定MIC；以菌落计数法测定菌落形成单位（CFU），根据CFU做生长曲线，计算PAE、PLIE、PASME。结果不同比例复方对产β内酰胺酶菌株的MIC较单方呈2—256倍的降低。无论单方还是复方均无长PAE。3种β酰胺酶抑制剂的PLIE对于大肠埃希菌有正有负（－2．25h～〉5h），而对于肺炎克雷伯菌均为正值（0．34h～5．37h）。对于肺炎克雷伯菌，0．2MIC的头孢哌酮／舒巴坦（1／1）的PASME为0．32h，0．1MIC、0．2MIC的哌拉西林／克拉维酸（8／1）的PASME分别为2．96h、4．41h。结论同时具有长PLIE及PASME的复方，PLIE、PASME较其半衰期在给药方案的设计中更为重要；PAE、PLIE、PASME作为重要的药效动力学参数，可应用于评价新抗菌药物的药效学和优化给药方案。     

抗生素后效应与临床意义

抗生素后效应（postantibiotic effect，PAE）是指细菌接触抗生素一定时问后，药物浓度下降至最低抑茵浓度（MIC）或清除时，其生长仍受到持续抑制的效应。近年来，随着国内、外对PAE研究的逐渐深入，人们对临床抗生素类药物的合理应用提出了新的理论和认识。     

抗生素后效应对治疗方式的影响

抗生素后效应 (post- antibiotic effect,PAE)于 2 0世纪 5 0年代被人们发现 ,并于 70年代被更多的关注其临床意义。它是指细菌与抗生素短暂接触 ,当药物浓度低于最低抑制 (细菌 )浓度 (minimal inhibitory concentration,MIC)或消除后 ,细菌的生长仍受到持续抑制的效应。目前 ,对 PAE的研究完善了对抗菌过程的认识 ,并使之成为新的抗生素药效学参数。1　抗生素后效应产生的机理目前尚无明确定论 ,一种基于抗生素作用机理的推测认为 ,药物持续存在于靶细胞的作用部位以及抗生素引起的细菌非致死性损伤产生 PAE[1 ]。另一种机理即抗生素…     

头孢美唑体外抗生素后效应期间大肠埃希菌膜通透性和膜电位变化研究

[目的]研究头孢美唑体外抗生素后效应（postantibiotic effect，PAE）期间E.coli ATCC25922的膜通透性和膜电位动态变化，以期深入探讨头孢美唑PAE形成机制。[方法]采用流式细胞仪（flow eytometry，FCM）技术与荧光探针碘化丙啶和DiBAC4（3）结合，检测低浓度（4MIC）和高浓度（128MIC）的头孢美唑体外PAE期间E.coli ATCC25922的膜通透性和膜电位动态变化特征。[结果]头孢美唑PAE期间E.coli膜电位及膜通透性与空白对照组比较显著增高，且高浓度（128MIC）组较低浓度（4MIC）组增高更明显。[结论]不同浓度的头孢美唑PAE期间E.coli呈现不同的膜通透性和膜电位变化，从而显示了不同浓度的头孢美唑PAE期间对E.coli具有不同的作用靶位。流式细胞仪是研究PAE机制的理想手段。     

临床抗菌药物合理使用问答（4）

问：什么是抗菌药物后效应（PAE）？答：PAE（post—antibioticseffect）是指细菌与抗生素短暂接触,当药物清除后,细菌生长仍然受到持续抑制的效应。由于PAE存在,使血药浓度即使低于MIC水平仍可持续存在抑菌作用。因而更新了传统的认为抗菌药物血药浓度必须高于MIC水平的给药模式。有较长PAE的抗菌药物有氨基糖苷类、氟喹诺酮类、碳青霉烯类等。     

康替唑胺体外抗菌作用研究

目的评价噁唑烷酮类新药康替唑胺对临床分离菌的体外抗菌作用。方法收集全国19所医院1321株的临床分离菌,以琼脂对倍稀释法测定康替唑胺对分离菌的最低抑菌浓度(MIC)并与有关抗菌药物进行比较,测定康替唑胺的杀菌活性、抗菌药物后效应(PAE)以及不同培养条件对康替唑胺抗菌作用的影响。结果康替唑胺对革兰阳性菌中葡萄球菌属、链球菌属和肠球菌属等临床常见分离菌均显示良好的抗菌活性,包括甲氧西林耐药金黄色葡萄球菌(金葡萄)(MRSA)、青霉素耐药肺炎链球菌(PRSP)和万古霉素耐药肠球菌(VRE)等多重耐药菌株。康替唑胺对甲氧西林敏感金葡菌(MSSA)和MRSA的MIC90均为0.5 mg/L,对肺炎链球菌中青霉素敏感株(PSSP)和不敏感菌株(PNSP)的MIC90亦均为0.5 mg/L,对其他链球菌属包括化脓链球菌等β溶血链球菌和草绿色链球菌的MIC90均为1 mg/L,对肠球菌属细菌包括耐万古霉素屎肠球菌的MIC90亦均为1 mg/L。康替唑胺对包括金葡菌在内的葡萄球菌属细菌的抗菌活性较利奈唑胺略高或相仿、亦略高于替考拉宁和万古霉素;对链球菌属细菌的抗菌活性与利奈唑胺相仿,略低于万古霉素和替考拉宁;对肠球菌属细菌的活性亦与利奈唑胺相仿,对万古霉素敏感株的抗菌活性与万古霉素相仿,略低于替考拉宁,但对万古霉素耐药屎肠球菌的活性则明显优于万古霉素和替考拉宁,与利奈唑胺相仿。康替唑胺对受试的葡萄球菌和链球菌属有良好的杀菌活性,尤其对肺炎链球菌具有良好的杀菌活性,但对肠球菌属细菌与利奈唑胺一样仅具抑菌活性。康替唑胺对金葡菌和肺炎链球菌的PAE均值分别为(1.56±0.42)h和(1.77±0.99)h。培养基中pH的改变对康替唑胺体外抗菌作用无明显影响,但细菌接种菌量的改变和血清蛋白含量的增高对康替唑胺的抗菌活性有一定影响。结论康替唑胺作为一种新型的噁唑烷酮类新药,药效学研究显示其对受试的革兰阳性菌,包括MRSA和甲氧西林耐药凝固酶阴性葡萄球菌(MRCNS)、PRSP、VRE等均有强大的体外抗菌活性;并对MRSA、PRSP等具有杀菌活性以及较长的PAE。提示康替唑胺对革兰阳性菌,尤其是其中的多重耐药菌株所致感染的治疗将具有重要作用;有望用于临床对其敏感的革兰阳性菌感染。     

白藜芦醇对葡萄球菌抗菌活性研究

目的 研究自藜芦醇对葡萄球菌的体外抗菌活性,为临床应用和新药研究提供依据.方法 采用微量肉汤稀释法,对20株MSSA,27株MRSA,和32株CONS进行体外最低抑菌浓度(MIC)测定.并比较三类葡萄球菌之间的抑菌效果.结果 白藜芦醇对MSSA,MBSA及CONS的MIC90分别为0.512,0.512和0.256 mg·ml-1.经过统计分析,不能认为白藜芦醇对MSSA,MRSA的抑菌作用有差别.结论 白藜芦醇对葡萄球菌有较强的抑菌效果.     

In vitro pharmacodynamic characteristics of flucytosine determined by time-kill methods

Two Candida albicans isolates, three non-albicans Candida isolates (Candida glabrata, Candida krusei, and Candida tropicalis), and one Cryptococcus neoformans isolate were evaluated by time-kill methods to characterize the relationship of flucytosine concentrations to antifungal activity and the duration of the post-antifungal effect (PAE). Against Candida and Cryptococcusisolates, flucytosine at concentrations > 1 x MIC exhibited fungistatic ( 5 h), suggests lower daily dosing may possible without loss of antifungal efficacy.     

Comparison of two methods for determining in vitro postantibiotic effects of three antibiotics on Escherichia coli.

The postantibiotic effect (PAE) for 10 isolates of Escherichia coli was measured by two methods after 1 h of exposure to ampicillin, ciprofloxacin, or tobramycin. The reference method involved serial colony counting to determine growth after antibiotic exposure in relation to control growth. A spectrophotometric procedure was developed with the Abbott MS-2 research system. This method measured the time to detection of growth after exposure and compared this with the time for growth detection in control chambers having the same initial colony count. A reference curve of time to growth versus log initial CFU per milliliter was used to standardize control growth. PAE was determined after exposure to antibiotic at two and six times the MIC and with inocula ranging from 10(3) to 10(9) CFU/ml. There was a statistically significant correlation between PAE measured by the spectrophotometric and the reference methods, and the residuals about the regression line were normally distributed. The mean PAE determined by both methods was statistically different for tobramycin-exposed, but not for ampicillin- or ciprofloxacin-exposed, organisms. There was a concentration-dependent PAE for ciprofloxacin and tobramycin. The PAEs for ciprofloxacin (151 min) and tobramycin (108 min) at concentrations six times the MIC were prolonged compared with those measured at two times the MIC (69 and 66 min, respectively). PAE was inversely related to the exposed inoculum for ciprofloxacin and tobramycin. The PAE for E. coli exposed to ampicillin was minimal and was not affected by either concentration or inoculum. The MS-2 method for determining PAE yields similar results, but is less laborious than the reference method.     

Pharmacodynamic effects of subinhibitory concentrations of beta-lactam antibiotics in vitro.

The pharmacodynamic effects of subinhibitory concentrations of different beta-lactam antibiotics were investigated. A postantibiotic effect (PAE) was induced for different bacterial species by exposure to 10x MIC of several beta-lactam antibiotics for 2 h in vitro. The antibiotic-bacterial combinations used in this study were imipenem-Pseudomonas aeruginosa, benzylpenicillin-Streptococcus pneumoniae and -Streptococcus pyogenes, cefcanel-S. pyogenes, ampicillin-Escherichia coli, and piperacillin-E. coli. After the induction of the PAE, the exposed cultures as well as the unexposed controls were washed and diluted. Thereafter, the cultures in the postantibiotic phase (PA phase) and the cultures not previously treated with antibiotics were exposed to 0.1, 0.2, and 0.3x MIC of the relevant drug and the growth curves were compared. When bacteria in the PA phase were exposed to sub-MICs, a substantial prolongation of the time before regrowth was demonstrated, especially in antibiotic-bacterial combinations for which a PAE was found. In contrast, sub-MICs on cultures not previously exposed to suprainhibitory antibiotic concentrations yielded only a slight reduction in growth rate compared with the controls. Thus, it seems important to distinguish the direct effects of sub-MICs on bacteria not previously exposed to suprainhibitory concentrations from the effects of sub-MICs on bacteria in the PA phase.     

Antifungal activity of the allylamine derivative terbinafine in vitro

Terbinafine, an allylamine derivative, represents the most effective of this new chemical class of antimycotic compounds. Under in vitro conditions, terbinafine proved to be highly active against dermatophytes (MIC range, 0.001 to 0.01 microgram/ml), aspergilli (MIC range, 0.05 to 1.56 micrograms/ml), and Sporothrix schenckii (MIC range, 0.1 to 0.4 microgram/ml) and also exerted good activity against yeasts (MIC range, 0.1 to greater than 100 micrograms/ml). The growth of Malassezia furfur was inhibited also (MIC range, 0.2 to 0.8 microgram/ml). Terbinafine displays a primary fungicidal action against dermatophytes, other filamentous fungi, and S. schenckii. The type of action against yeasts is species dependent and can be primarily fungicidal (Candida parapsilosis) or fungistatic (Candida albicans). The in vitro activity of terbinafine is pH dependent and rises with increasing pH value.     

In vitro activity of micafungin (FK-463) against Candida spp.: microdilution,time-kill,and postantifungal-effect studies

We evaluated the in vitro activity of the new echinocandin antifungal micafungin against Candida spp. using microdilution and time-kill methods. Additionally, we examined the postantifungal effect (PAFE) of micafungin. Finally, we evaluated the effect of the addition of serum and plasma on the MIC of micafungin. Four Candida albicans isolates and two isolates of each Candida glabrata, Candida krusei, and Candida tropicalis were selected for testing. The MICs of micafungin were determined in RPMI 1640 medium buffered with morpholinepropanesulfonic acid alone and with the addition of 10, 20, and 50% human serum and plasma. MICs were determined by using two endpoints: a prominent reduction in growth (the MIC at which 80% of isolates are inhibited [MIC(80)]) and complete visual inhibition of growth (MIC(100)). The minimum fungicidal concentration (MFC) of micafungin for each isolate was also determined. Time-kill curves were determined for each isolate in RPMI 1640 medium with micafungin at concentrations ranging from 0.125 to 16 times the MIC(80) to assess the correlation between MIC(80) and fungicidal activity. PAFE studies were conducted with each isolate by using concentrations ranging between 0.25 and 4 times the MIC(80). The MIC(80)s for the test isolates ranged from 0.0039 to 0.25 micro g/ml. Overall, the addition of serum or plasma increased the MIC 6 to 7 doubling dilutions for C. albicans and 3 to 4 doubling dilutions for C. krusei and C. tropicalis. Micafungin time-kill studies demonstrated fungicidal activity at concentrations ranging from 4 to 16 times the MIC(80). Micafungin is very potent agent against a variety of Candida spp., producing fungicidal activity against 7 of 10 isolates tested. A PAFE was observed against all isolates. The PAFE was influenced by the drug concentration, with the highest concentration resulting in the longest observed PAFE in each case. The highest concentration tested, four times the MIC, resulted in a PAFE of more than 9.8 h for 5 of 10 isolates tested (range, 0.9 to > or =20.1 h).     

Use of the microbial growth curve in postantibiotic effect studies of Legionella pneumophila

Using the standard Craig and Gudmundsson method (W. A. Craig and S. Gudmundsson, p. 296-329, in V. Lorian, ed., Antibiotics in Laboratory Medicine, 1996) as a guideline for determination of postantibiotic effects (PAE), we studied a large series of growth curves for two strains of Legionella pneumophila. We found that the intensity of the PAE was best determined by using a statistically fitted line over hours 3 to 9 following antibiotic removal. We further determined the PAE duration by using a series of observations of the assay interval from hours 3 to 24. We determined that inoculum reduction was not necessarily the only predictor of the PAE but that the PAE was subject to the type and dose of the drug used in the study. In addition, there was a variation between strains. Only levofloxacin at five and ten times the minimum inhibitory concentration (MIC) resulted in a PAE duration of 4 to 10 h for both strains of L. pneumophila tested. Ciprofloxacin at five and ten times the MIC and azithromycin at ten times the MIC caused a PAE for one strain only. No PAE could be demonstrated for either strain with erythromycin or doxycycline. Using the presently described method of measuring PAE for L. pneumophila, we were able to detect differences in PAE which were dependent upon the L. pneumophila strain, the antibiotic tested, and the antibiotic concentration. We suggest the use of mathematically fitted curves for comparison of bacterial growth in order to measure PAE for L. pneumophila.     

In vitro kill curves of a new semisynthetic echinocandin, LY-303366, against fluconazole-sensitive and -resistant Candida species.

In vitro killing by a new semisynthetic echinocandin, LY-303366, was characterized using clinical isolates of fluconazole-sensitive (Y58) and -resistant (Y180) Candida albicans as well as Candida glabrata (Y7) and Candida krusei (Y171). The 24-h kill curves for Y58 and Y180 demonstrated dose-independent killing of between 1 and 2 log10 with LY-303366 at concentrations of 0.1, 1, 10, 50, 100, and 1,000 times the MIC. Regrowth did not occur at 24 h with either C. albicans isolate at the aforementioned LY-303366 concentrations. At their MICs, LY-303366 and amphotericin B produced similar killing kinetics in cultures of Y58, Y180, Y7, and Y171, while all cultures exposed to fluconazole at its MIC demonstrated stasis or growth over 24 h.     

Postantibiotic effects and postantibiotic sub-MIC effects of roxithromycin, clarithromycin, and azithromycin on respiratory tract pathogens.

Pharmacodynamic parameters have become increasingly important for the determination of the optimal dosing schedules of antibiotics. In this study, the postantibiotic effects (PAEs), the postantibiotic sub-MIC effects (PA SMEs), and the sub-MIC effects (SMEs) of roxithromycin, clarithromycin, and azithromycin on reference strains of Streptococcus pyogenes group A, Streptococcus pneumoniae, and Haemophilus influenzae were investigated. The PAE was induced by 2x MICs (S. pneumoniae) or 10x MICs of the different drugs for 2 h, and the antibiotics were eliminated by washing and dilution. The PA SMEs were studied by addition of 0.1, 0.2, and 0.3x MICs during the postantibiotic phase of the bacteria, and the SMEs were studied by exposition of the bacteria to the drugs at the sub-MICs only. Growth curves were followed by viable counts for 24 h. The SMEs were generally very short. A PAE of 2.9 to 8 h was noted for all antibiotics against all strains. Clarithromycin induced a statistically significantly shorter PAE on S. pneumoniae than did roxithromycin and azithromycin and did so also against H. influenzae in comparison with azithromycin. The PA SMEs were long and varied at 0.3x MIC between 6.4 19.6 h. This pronounced suppression of regrowth of bacteria which are first treated with a suprainhibitory concentration of antibiotics and then reexposed to sub-MIC levels indicates that long dosing intervals for macrolides and azalides can be allowed.     

Postantifungal effects of echinocandin, azole, and polyene antifungal agents against Candida albicans and Cryptococcus neoformans

The postantifungal effect (PAFE) of fluconazole, MK-0991, LY303366, and amphotericin B was determined against isolates of Candida albicans and Cryptococcus neoformans. Concentrations ranging from 0. 125 to 4 times the MIC were tested following exposure to the antifungal for 0.25 to 1 h. Combinations of azole and echinocandin antifungals (MK-0991 and LY303366) were tested against C. neoformans. Fluconazole displayed no measurable PAFE against Candida albicans or Cryptococcus neoformans, either alone or in combination with either echinocandin antifungal. MK-0991, LY303366, and amphotericin B displayed a prolonged PAFE of greater than 12 h against Candida spp. when tested at concentrations above the MIC for the organism and 0 to 2 h when tested at concentrations below the MIC for the organism.     

Pharmacodynamic evaluation of a new glycopeptide, LY333328, and in vitro activity against Staphylococcus aureus and Enterococcus faecium.

The objectives of the present study were to compare the in vitro activity of LY333328 (LY) to that of vancomycin (V) alone and in combination with gentamicin (G) and rifampin (R) against methicillin-resistant Staphylococcus aureus (MRSA) and V-resistant Enterococcus faecium (VREF), by using the killing curve methods. In addition, the effect of the inoculum size and protein on LY's activity was evaluated by using MICs and killing curves. MICs, MBCs, and killing curves were determined with supplemented Mueller-Hinton broth (B), B with albumin (4 g/dl) (A), and B with 50% pooled human serum (S). For MRSA, time to 99.9% killing after exposure to LY at four times the MIC (4x MIC) was achieved at 0.5 +/- 0 h (mean +/- standard deviation) and was significantly faster than that by V (8.54 +/- 0.10 h; P = 0.001). Against VREF, LY decreased the inoculum by 2.2 log10 CFU/ml at 24 h (P = 0.002). With a large inoculum of MRSA, the activity of LY and V at 4x MIC was decreased compared to that with the standard inoculum (P = 0.0003) and regrowth occurred at 24 h. The reduction in the number of CFU per milliliter at 24 h to 2 log10 CFU/ml was restored by increasing the LY concentration to at least 16x MIC. At 24 h, the combinations of LY and G, LY and R, LY and V, and V and G were better than either LY or V alone against a large inoculum of MRSA (P = 0.0002). LY and G achieved 99.9% killing at 1.01 +/- 0.03 h and was more rapid (P < 0.007) than all the other regimens studied except for V and G, which achieved 99.9% killing at 3.59 +/- 0.01 h. Killing curves determined with different media against a standard inoculum of MRSA did not demonstrate a significant difference between LY and V at 24 h. Time to 99.9% killing was more rapid with LY than with V in B, A, and S (P = 0.0002). Times to 99.9% killing by LY in B, A, and S were not significantly different from each other. Against VREF, LY killed better than V in B, A, or S at 24 h (P = 0.0002). LY in B was more active than LY in A or S (P = 0.0002). LY is a new potent glycopeptide with a unique activity profile. It has a greater activity than that of V against MRSA and has activity against VREF. LY demonstrated synergism in combination with gentamicin against MRSA. LY was affected by large inoculum sizes and proteins in time-kill studies. However, the effect was compensated for by increasing the drug concentration to 16x MIC.