Antifungal combination therapy in localized candidosis

A mouse model of localized candidosis in air-filled subcutaneous cysts imitating thrush has been developed. We have now tested various antifungal combinations in this animal model. Flucytosine (5-FC) + amphotericin B (Amph B) showed the highest efficacy, a clear additive or even synergistic effect was seen. The combination of 5-FC + imidazole or triazole derivative was less efficacious, an additive effect was rare. The combination of 5-FC + Amph B was also tested against Candida albicans strains showing various degrees of 5-FC-resistance. A significant reduction in 5-FC-resistant mutants was seen after the treatment with the combination.     

Evaluation of in vitro interaction of daptomycin with gentamicin or beta-lactam antibiotics against Staphylococcus aureus and Enterococci by FIC index and timed-kill curves

The interactions of daptomycin with gentamicin and 5 beta-lactam agents were determined by checkerboard and timed-kill studies. Eighty isolates were tested by checkerboard: 20 each of methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible Staphylococcus aureus (MSSA), vancomycin-susceptible Enterococcus faecalis (VSEF) and vancomycin-resistant enterococci (VRE). Time kill curves were performed on 8 selected isolates: 2 each of MRSA, MSSA, VSEF and VRE. Checkerboard results showed highest frequency of synergistic effects against VSEF (35-75%) with daptomycin combined with ceftriaxone, cefepime or imipenem; a modest effect with most combinations against VRE and MRSA (5-20%); and indifference with daptomycin and most agents against MSSA (0-5%); except with daptomycin with oxacillin where 10-20% synergy was observed. Synergistic interaction was confirmed by time kill studies in seven of ten isolates where checkerboard suggested synergy. A bactericidal effect was exerted in 5/7 synergistic combinations. The in vitro data suggest that daptomycin combined with other antibiotics may be microbiologically beneficial and not antagonistic.     

In vitro effects of sulbactam combinations with different antibiotic groups against clinical Acinetobacter baumannii isolates

Abstract

Treatment of multidrug resistant (MDR) Acinetobacter baumannii infections causes some problems as a result of possessing various antibacterial resistance mechanisms against available antibiotics. Combination of antibiotics, acting by different mechanisms, is used for the treatment of MDR bacterial infections. It is an important factor to determine synergy or antagonism between agents in the combination for the constitution of effective therapy. The study aimed to determine in vitro interactions interpreted according to calculated fractional inhibitory concentration (FIC) index between sulbactam and ceftazidime, ceftriaxone, cefepime, ciprofloxacin, gentamicin, meropenem, tigecycline, and colistin. Ten clinical isolates of A. baumannii were tested for determination of synergistic effects of sulbactam with different antimicrobial combinations. Minimal inhibitory concentration (MIC) values of both sulbactam and combined antibiotics decreased 2- to 128-fold. Synergy and partial synergy were determined in combination of sulbactam with ceftazidime and gentamicin (FIC index: ≤0·5 or >0·5 to <1) and MIC values of both ceftazidime and gentamicin for five isolates fell down below the susceptibility break point. Similarly, MIC value of ciprofloxacin for six ciprofloxacin resistant isolates was determined as below the susceptibility break point in combination. However, all isolates were susceptible to colistin and tigecycline, MIC values of both were decreased in combination with sulbactam. Although synergistic and partial synergistic effects were observed in the combination of sulbactam and ceftriaxone, all isolates remained resistant to ceftriaxone. The effect of cefepime–sulbactam combination was synergy in five, partial synergy in one and indifferent in four isolates. Meropenem and sulbactam showed a partial synergistic effect (FIC index: >0·5 to <1) in three, an additive effect (FIC index: 1) in one and an indifferent effect (FIC index: >1–2) in six isolates. Antagonism was not determined in any combination for clinical A. baumannii isolates in the study. In conclusion, sulbactam is a good candidate for combination treatment regimes for MDR A. baumannii infections.     

Evaluation of In Vitro Interaction of Daptomycin with Gentamicin or Beta-lactam Antibiotics Against taphylococcus aureus and Enterococci by FIC Index and Timed-Kill Curves

Abstract

The interactions of daptomycin with gentamicin and 5 β-lactam agents were determined by checkerboard and timed-kill studies. Eighty isolates were tested by checkerboard: 20 each of methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible Staphylococcus aureus (MSSA), vancomycin-susceptible Enterococcus faecalis (VSEF) and vancomycin-resistant enterococci (VRE). Time kill curves were performed on 8 selected isolates: 2 each of MRSA, MSSA, VSEF and VRE. Checkerboard results showed highest frequency of synergistic effects against VSEF (35-75%) with daptomycin combined with ceftriaxone, cefepime or imipenem; a modest effect with most combinations against VRE and MRSA (5-20%); and indifference with daptomycin and most agents against MSSA (0-5%); except with daptomycin with oxacillin where 10-20% synergy was observed.

Synergistic interaction was confirmed by time kill studies in seven of ten isolates where checkerboard suggested synergy. A bactericidal effect was exerted in 5/7 synergistic combinations.

The in vitro data suggest that daptomycin combined with other antibiotics may be microbiologically beneficial and not antagonistic.     

Evaluation of antifungal combination against Cryptococcus spp.

The second cause of death among systemic mycoses, cryptococcosis treatment represents a challenge since that 5‐flucytosine is not currently available in Brazil. Looking for alternatives, this study evaluated antifungal agents, alone and combined, correlating susceptibility to genotypes. Eighty Cryptococcus clinical isolates were genotyped by URA5 gene restriction fragment length polymorphism. Antifungal susceptibility was assessed following CLSI‐M27A3 for amphotericin (AMB), 5‐flucytosine (5FC), fluconazole (FCZ), voriconazole (VRZ), itraconazole (ITZ) and terbinafine (TRB). Drug interaction chequerboard assay evaluated: AMB + 5FC, AMB + FCZ, AMB + TRB and FCZ + TRB. Molecular typing divided isolates into 14 C. deuterogattii (VGII) and C. neoformans isolates were found to belong to genotype VNI (n = 62) and VNII (n = 4). C. neoformans VNII was significantly less susceptible than VNI (P = 0.0407) to AMB; C. deuterogattii was significantly less susceptible than VNI and VNII to VRZ (P < 0.0001). C. deuterogattii was less susceptible than C. neoformans VNI for FCZ (P = 0.0170), ITZ (P < 0.0001) and TRB (P = 0.0090). The combination FCZ + TRB showed 95.16% of synergistic effect against C. neoformans genotype VNI isolates and all combinations showed 100% of synergism against genotype VNII isolates, suggesting the relevance of cryptococcal genotyping as it is widely known that the various genotypes (now species) have significant impact in antifungal susceptibilities and clinical outcome. In difficult‐to‐treat cryptococcosis, terbinafine and different antifungal combinations might be alternatives to 5FC.     

The FLT3 inhibitor PKC412 in combination with cytostatic drugs in vitro in acute myeloid leukemia

An internal tandem duplication of FLT3 (FLT3/ITD) occurs in approximately 25% of newly diagnosed AML. PKC412 inhibits the growth of leukemic cell lines with FLT3 mutations such as the MV4-11. This study evaluated the in vitro effects of the combination of PKC412 and ara-C or daunorubicin, studying the effect of co-incubation, pre-incubation and sequential incubation of the drugs in patient samples and cell lines. Thirty-three patients with AML were included. Two cell lines were studied; MV4-11 that expresses the FLT3/ITD and HL-60 that does not. In the patient cells PKC412 exerted its effect at concentrations between 0.1 and 2.0 microM. For MV4-11 cells concentrations down to 1 nM were effective. In patient samples, the results of co-incubation of PKC412 with ara-C were synergistic in 5%, additive in 67%, sub additive in 17% and antagonistic in 11% of the cases. In patient cells, incubations with ara-C and PKC412 resulted in synergistic effects in 17% of the FLT3/ITD positive samples compared to 0% synergistic in the FLT3/ITD negative samples (p < 0.01). Antagonistic effects were more common in the FLT3/ITD negative samples. The timing of the drugs had little impact on the effect. In cell lines, antagonistic effects were seen frequently in HL-60 (90%) and less so in MV4-11 (60%) regardless of sequence or timing of the drugs. The combination of daunorubicin and PKC412 resulted in more synergistic and less antagonistic effects compared to combinations with ara-C, in both patient material and cell lines. The combination of Lonafarnib, a farnesyl-transferase inhibitor (FTI) and PKC412 had additive and synergistic effects in both FLT3/ITD positive and negative cell lines. In conclusion, the combination of PKC412 together with chemotherapeutic drugs is more effective in FLT3/ITD positive AML cells. Antagonistic effects can be seen, especially in patient samples without FLT3/ITD. Also, the combination of PKC412 and the farnesylinhibitor lonafarnib should be further explored.     

Susceptibility of yeast isolates from defined German patient groups to 5-fluorocytosine.

Susceptibility and development of resistance to 5-fluorocytosine (5-FC) in Candida strains isolated from defined German groups of probands was investigated. 5-FC susceptibility was determined in a microdilution assay in yeast nitrogen base after 24 h of incubation at 37 degrees C. The range of 5-FC concentration investigated was between 0.015 and 16 micrograms ml-1. Isolates with a minimum inhibitory concentration (MIC) of > 16 micrograms ml-1 were regarded as 5-FC resistant. In total 335 Candida isolates were investigated, and 20 of them (6.0%) were found to be resistant. The Candida isolates were rather different with respect to their origin: out of 57 vaginal isolates from non-risk patients from Southern Germany 3.5% were 5-FC-resistant strains. One hundred and fifty-nine isolates from the urine of long-term intensive care patients from the whole of Germany showed 5-FC resistance (6.3%). Out of 74 isolates of different localization from intensive care patients of the University Clinics of Freiburg, 10.8% showed 5-FC resistance. Among 45 isolates from the oral cavity of HIV-positive patients from the Frankfurt region, no 5-FC-resistant strain was found. The epidemiology of 5-FC resistance is based mainly on the percentage of non-albicans isolates of the proband groups (C. tropicalis, C. krusei and others), and is less based on the frequency of Candida albicans serotype B isolates. In sequential observations with individual intensive care patients, no increase of 5-FC resistance in their Candida isolates could be observed with longer periods of hospitalization.     

Schedule-dependent interaction between raltitrexed and 5-fluorouracil in human colon cancer cell lines in vitro

Raltitrexed (Tomudex) is a novel thymidylate synthase inhibitor with significant activity against advanced colorectal cancer. We studied the cytotoxic interactions of raltitrexed and 5-fluorouracil (5-FU) in four human colon cancer cell lines on various schedules. The cell growth inhibition after 5 days was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cytotoxic interactions at the IC80 level were evaluated by the isobologram method. Simultaneous exposure to raltitrexed and 5-FU for 5 days produced additive to synergistic effects in Colo201 cells, and produced additive effects in Colo321, LoVo, and WiDr cells. Simultaneous exposure to raltitrexed and 5-FU for 24 h produced additive effects in Colo201, LoVo, and WiDr cells, and produced antagonistic effects in Colo320 cells. Sequential exposure to raltitrexed for 24 h followed by 5-FU for 24 h produced additive effects in Colo201, Colo320, and LoVo cells, and produced antagonistic effects in WiDr cells. The reverse sequence produced additive effects in Colo201 cells, and produced antagonistic effects in Colo320, LoVo, and WiDr cells. Simultaneous exposure to raltitrexed and 5-FU for 4 h and sequential exposure to raltitrexed for 4 h followed by 5-FU for 4 h with a 20-h interval produced additive effects, while the reverse sequence produced antagonistic effects in LoVo and WiDr cells. These findings suggest that the simultaneous administration of raltitrexed and 5-FU or the sequential administration of raltitrexed followed by 5-FU may be the optimal sequence, while the reverse sequence may be inappropriate. Preclinical and clinical studies of the simultaneous administration of raltitrexed and 5-FU and the sequential administration of raltitrexed followed by 5-FU are required to better understand the antitumor, toxic, and pharmacokinetic interactions of this combination in order to develop the combination chemotherapy of raltitrexed and 5-FU.     

Evaluation of amphotericin B and micafungin combination against clinical isolates of Aspergillus species

We aimed to evaluate the efficacy of a combination of amphotericin B (AMB) and micafungin (MCFG) against 25 clinical isolates of Aspergillus species in vitro. We examined fungal growth in the presence of these drugs using a checkerboard method with the tetrazolium salt: 2,3-bis (2- methoxy-4-nitro-5-sulphophenyl)-2H-tetrazolium-5-carboxyanilide inner salt (XTT) to determine the efficacy of an AMB/MCFG combination in inhibition of filamentous fungal growth, evaluated based on 50% reduction of metabolic activity. The fractional inhibitory concentration index showed that the drugs synergistically inhibited 36% of the isolates. Activity was judged as indifferent for 64% isolates; antagonistic interaction was not detected. The AMB/MCFG combination was more effective than AMB alone when sub-inhibitory concentrations of AMB were used. This report demonstrates the efficacy of AMB/MCFG combination for inhibiting the growth of Aspergillus species in vitro, warranting the extension of such studies to animal models.     

In vitro and in vivo Effects of Cisplatin and Etoposide in Combination on Small Cell Lung Cancer Cell Lines

The effects of cisplatin (CDDP) and etoposide (ETP) in combination were evaluated in vitro and in vivo using small cell lung cancer cell lines. The combination effects in vitro were investigated using isohologram analysis. Used together, CDDF and ETP showed a synergistic effect against cell growth on only 1 cell line (SBC-3), additive effects on 6 (SBC-2, SBC-5, Lul30, Lul34AH, Lul35T and H69) and an antagonistic effect on 1 (SBC-1). In the in vivo experiment, nude mice were inoculated with SBC-1, SBC-3 and SBC-5 cells. Two or 5 mgAg CDDP and 10 or 30 mgAg ETP were administered intraperitoneally alone and simultaneously in combination to nude mice. The in vivo effects of the combination were determined by comparing the observed growth ratio in mice treated with the combination with the expected value of this ratio calculated based on the assumption that the effects of the drugs were simply additive. According to this definition, synergistic effects were observed against all 3 tumors. Thus, the in vivo and in vitro effects differed. The toxicity of the combination therapy, which was analyzed by estimating the body weight change of mice, was no higher than that of CDDP or ETP alone. These results suggest that the excellent clinical effects of CDDP and ETP combination therapy may he attributable not to drug interaction at the cellular level hut to the feasibility of combined use of them at full doses without overlapping side effects.     

Combination studies of antifolates with 5-fluorouracil in colon cancer cell lines

The combined cytotoxic effects of the thymidylate synthase (TS) inhibitors 5-fluorouracil (5FU) and different antifolates were studied in seven colon cancer cell lines. Growth inhibition of the antifolates, Nolatrexed, Raltitrexed, GW1843U89, or MTA in combination with 5FU, was determined and multiple drug effect analysis showed that the drugs acted mostly additively. The only synergistic interaction was found for 5FU and Nolatrexed in the LS174T cell line. Also Raltitrexed and 5FU were slightly synergistic in WiDr/F cells grown at low folate levels, but for the other cell lines grown at high folate levels this combination was more antagonistic. GW1843U89 and 5FU were mainly additive, while 5FU and MTA showed antagonism in WiDr and additivity in LS174T. The effect of the drugs at their target was evaluated by in situ TS inhibition. We observed lower TS activity in all cells when two drugs were used instead of one. Statistical analysis revealed that none of the values of the combinations was higher or lower than could be expected from the product of the effect of single drugs. We concluded that the effects on TS inhibition were additive for all 5FU/antifolate combinations in all cell lines. DNA strand break formation, as a result of TS inhibition, was measured by means of a fluorometric analysis of DNA unwinding. Raltitrexed-induced DNA damage was significantly increased by 5FU in WiDr cells [single agent: 67% double stranded (ds) DNA, combination: 39% ds DNA, P<0.0001]. In LS174T a trend for antagonistic effects was observed for combinations of MTA, GW1843U89, or Raltitrexed and 5FU. The combinations showed additive effects in WiDr/F cells. The overall conclusion of the three assays in each of the cell lines indicated that 5FU and antifolate combinations were predominantly additive in colon cancer cells.     

In vitro cytotoxic effects of fludarabine (2-F-ara-A) in combination with commonly used antileukemic agents by isobologram analysis.

Fludarabine phosphate (2-F-ara-AMP) is an adenine nucleoside analogue that shows significant activity against chronic lymphocytic leukemia and indolent lymphoma. We assessed the cytotoxic interaction produced by the combination of the active metabolite of fludarabine phosphate, fludarabine (9-beta-D-arabinofuranosyl-2-fluoroadenine, 2-F-ara-A), and some commonly used antileukemic agents against human hairy cell leukemia cell line JOK-1, human chronic lymphocytic leukemia cell line SKW-3, and adult T cell leukemia cell lines ED-40810 (-) and SALT-3. The leukemia cells were exposed simultaneously to 2-F-ara-A and to the other agents for 4 days. Cell growth inhibition was determined using MTT reduction assay. The isobologram method of Steel and Peckham was used to evaluate the cytotoxic interaction. 2-F-ara-A and cytarabine showed synergistic effects in SKW-3 cells, additive and synergistic effects in JOK-1 and SALT-3 cells, and additive effects in ED-40810(-) cells. 2-F-ara-A and doxorubicin showed additive effects in SKW-3, ED-40810(-) and SALT-3 cell lines, and additive and synergistic effects in JOK-1 cells. 2-F-ara-A showed additive effects with etoposide, 4-hydroperoxy-cyclophosphamide, and hydroxyurea in all four cell lines. 2-F-ara-A showed antagonistic effects with methotrexate and vincristine in all four cell lines. Our findings suggest that the simultaneous administration of fludarabine phosphate with cytarabine, doxorubicin, etoposide, cyclophosphamide, or hydroxyurea would be advantageous for cytotoxic effects. Among these agents, cytarabine may be the best agent for the combination with fludarabine phosphate. The simultaneous administration of fludarabine phosphate with methotrexate or vincristine would have little cytotoxic effect, and this combination may be inappropriate. These findings may be useful in clinical trials of combination chemotherapy with fludarabine phosphate and these agents.     

Schedule-dependent synergism and antagonism between paclitaxel and methotrexate in human carcinoma cell lines

Paclitaxel and methotrexate are active against a variety of solid tumors. Because of differences in their mechanisms of action and toxicity profiles, the combination of these two agents has clinical potential. Clinical studies of this combination are in progress. We studied the optimal schedule of paclitaxel and methotrexate in combination at various schedules in vitro using human lung cancer A549, breast cancer MCF7, ovarian cancer PA1, and colon cancer WiDr cells. Cells were simultaneously exposed to paclitaxel and methotrexate for 24 h and sequentially exposed to paclitaxel for 24 h followed by methotrexate for 24 h or vice versa. Cell growth inhibition after 5 days was determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The effects of drug combinations at the concentration of drug that produced 80% cell growth inhibition (the IC80 level) were analyzed by the isobologram method. The simultaneous exposure to paclitaxel and methotrexate produced additive to antagonistic effects in the A549 and PA1 cells, and antagonistic effects in the MCF7 and WiDr cells. The sequential exposure to paclitaxel followed by methotrexate produced additive effects in all four cell lines. The reverse sequence produced synergistic effects in the A549, MCF7, and WiDr cells, and additive effects in the PA1 cells. These findings suggest that a sequential administration of methotrexate followed by paclitaxel may be the appropriate schedule for this combination. On the basis of the observed in vitro synergism, further in vivo and clinical studies are necessary to clarify the toxicity and proposed antitumor effects of this schedule.     

In vitro and in vivo activity of antifungal agents in combination with fleroxacin, a new quinolone

The in vitro and in vivo interaction of fleroxacin with amphotericin B (Amph B), flucytosine (5-FC) and azoles against Candida albicans strains was tested. In vitro the interaction between fleroxacin and various antifungals was not dependent on the incubation time. Fleroxacin neither enhances nor antagonizes the in vitro activity of Amph B at high concentration (50-100 micrograms/ml). Fleroxacin has a synergistic effect with ketoconazole (KETO), but this is not observed with itraconazole (ITRA) or fluconazole (FLU). In no instance antagonism was observed. The activity of 5-FC was antagonized by fleroxacin being generally reduced by 2-4 dilution steps. In murine candidosis the efficacies of all antifungal drugs were not influenced by addition of 100 mg/kg fleroxacin. Therefore, the effects seen in in vitro tests are most probably not relevant for the clinical use of a combination of fleroxacin with antifungal drugs.     

Enhanced antitumor activity of irofulven in combination with 5-fluorouracil and cisplatin in human colon and ovarian carcinoma cells

Irofulven (6-hydroxymethylacylfulvene, MGI-114, NSC 683863) is a semisynthetic derivative of illudin S, a natural product obtained from the Omphalotus mushroom. Irofulven has demonstrated potent activity against a broad range of solid tumors in both cellular and xenograft models and has shown promising activity in clinical trials. To guide the clinical use of irofulven, the present study used the MTT viability assay to examine the cytotoxic effects obtained by combining irofulven with two other anticancer agents: cisplatin and 5-fluorouracil (5-FU). The study was carried out with HT-29 and HCT-116 colorectal and A2780 ovarian carcinoma cells as well as with their irofulven- (HT-29/IF2, HCT-116/IF27) or cisplatin-resistant (A2780/CP70) variants. The combinations showed strong sequence specificity. Simultaneous exposure to cisplatin and irofulven was at least additive for four cell lines including the cisplatin-resistant A2780/CP70 ovarian cells which exhibit a multifactorial resistance phenotype. Cisplatin followed by irofulven was additive for parental HCT-116 and A2780 cells whereas irofulven followed by cisplatin was antagonistic in all cellular models. Simultaneous exposure to 5-FU and irofulven was at least additive for all six cell lines. 5-FU followed by irofulven was additive for the parental HT-29 and A2780 cells and synergistic for the irofulven-resistant HCT-116 cell line. Irofulven followed by 5-FU was synergistic for the two ovarian cell lines and additive for the two parental colon cell lines. These studies demonstrate that simultaneous exposure to irofulven and cisplatin is at least additive for most cell lines whereas simultaneous exposure to irofulven and 5-FU is additive to synergistic for all the cell lines tested, including the irofulven- and cisplatin-resistant variants. The enhanced cytotoxicity of irofulven in combination with cisplatin and 5-FU support the clinical application of these regimens.     

Antifungal susceptibilities of Cryptococcus neoformans cerebrospinal fluid isolates from AIDS patients in Kenya

Poor susceptibility of Cryptococcus neoformans to fluconazole (FLC) is a matter of concern among clinicians in Africa. The emergence of resistance to FLC was recently reported in Kenya, but it is not known whether it is widespread. Thus, there is need for more antifungal drug susceptibility studies in Kenya. The aim of this study was to measure the in vitro antifungal drug susceptibilities of incident C. neoformans isolates from acquired immunodeficiency syndrome patients in Kenya. Antifungal susceptibility testing was performed in 67 C. neoformans isolates by broth microdilution method as outlined in the Clinical and Laboratory Standards Institute document M27-A3 using FLC, amphotericin B (AMB), voriconazole (VOR), ravuconazole (RAV) and flucytosine (5-FC). Isolates were grown on l-canavanine glycine bromothymol blue medium for serotype identification. Six per cent of the isolates were identified as C. neoformans var. gattii serotype B or C and 94% as C. neoformans var. neoformans. All isolates tested were susceptible to AMB, VOR and RAV (100%), and high susceptibilities were seen to FLC (97%), and 5-FC (90%). Only 3% and 10% of the isolates' susceptibility to FLC and 5-FC, respectively, was dose-dependent or intermediate. These results demonstrate high susceptibilities of incident C. neoformans isolates to FLC and AMB, antifungals used for treatment of cryptococcal meningitis in Kenya.     

Schedule-dependent synergism and antagonism between pemetrexed and docetaxel in human lung cancer cell lines in vitro

Background  Pemetrexed and docetaxel show clinical activities against a variety of solid tumors including lung cancers. To identify the optimal schedule for combination, cytotoxic interactions between pemetrexed and docetaxel were studied at various schedules using three human lung cancer cell lines A-549, Lu-99, and SBC-5 in vitro. Methods  Cells were incubated with pemetrexed and docetaxel simultaneously for 24 or 120 h. Cells were also incubated with pemetrexed for 24 h, followed by a 24 h exposure to docetaxel, and vice versa. Growth inhibition was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell cycle analysis. Cytotoxic interactions were evaluated by the isobologram method. Results  Simultaneous exposure to pemetrexed and docetaxel for 24 and 120 h produced antagonistic effects in all three cell lines. Pemetrexed (24 h) followed by docetaxel (24 h) produced additive effects in A-549 cells and synergistic effects in Lu-99 and SBC-5 cells. Docetaxel followed by pemetrexed produced additive effects in A-549 and Lu-99 cells and antagonistic effects in SBC-5 cells. The results of cell cycle analysis were fully consistent with those of isobologram analysis, and provide the molecular basis of the sequence-dependent difference in cytotoxic interactions between the two agents. Conclusions  Sequential administration of pemetrexed followed by docetaxel may provide the greatest anti-tumor effects for this combination in the treatment of lung cancer.     

In-vitro synergistic effect of fluconazole with nonsteroidal anti-inflammatory agents against Candida albicans strains

The in-vitro interaction and synergistic activity of the combination of fluconazole with some nonsteroidal anti-inflammatory drugs (sodium salicylate, piroxicam, tenoxicam and diclofenac sodium) were investigated in Candida albicans strains (n=7) by the microdilution checkerboard assay. The results were evaluated visually and by a spectrophotometric microplate reader at 492 nm wavelength. Fractional inhibitory index was calculated for every strain and combination according to the minimal inhibitory concentration (MICs). The combination of fluconazole with sodium salicylate, tenoxicam and diclofenac sodium showed synergy against 5, 5 and 3 of the C. albicans strains, respectively. The effect of fluconazole with piroxicam was synergistic against one strain but indifferent/additive against the others. These data suggest that combinations of sodium salicylate, tenoxicam and diclofenac sodium with fluconazole may prove to be useful as chemotherapeutic agents for the treatment of C. albicans infections caused by especially fluconazole-resistant strains. However, additional preclinical work and in vivo studies are necessary to determine their definite clinical use.     

In Vitro Efficacy of Levofloxacin Alone or in Combination Tested Against Multi-Resistant Pseudomonas aeruginosa Strains

Abstract

Levofloxacin, the S(-) isomer of ofloxacin, demonstrates In Vitro activity against Pseudomonas aeruginosa. To further characterize this activity, levofloxacin was tested against three populations of recent clinical isolates categorized by their resistance patterns to several other anti-pseudomonal agents. Results demonstrate the minimum inhibitory concentrations (MICs) for levofloxacin were generally two- to fourfold higher than for ciprofloxacin. Higher fluoroquinolone MICs were associated with MIC increases in other drugs. Levofloxacin demonstrated cross resistance against ciprofloxacin-resis-tant strains. Combinations of levofloxacin and several co-drugs revealed that the majority of evaluable interactions demonstrated indifferent action. Levofloxacin exhibited enhanced activity (additive or degrees of synergy) principally with piperacillin, aztreonam, or ceftazidime. The synergy and additive rate (21 to 30%) compared favorably with the enhanced interactions observed with gen-tamicin combined with piperacillin or ceftazidime (27 to 30%). Levofloxacin activity against P. aeruginosa was most comparable to that of ciprofloxacin, which was applicable against > 90% of strains found to be resistant to other classes of antimicrobial agents.     

Schedule-dependent synergism and antagonism between pemetrexed and paclitaxel in human carcinoma cell lines in vitro

Pemetrexed is a novel multitargeted antifolate with significant clinical activity against a variety of tumors. We studied the schedule-dependent cytotoxic effects of pemetrexed in combination with paclitaxel in vitro to improve our understanding of how this combination might be used clinically. Human lung cancer A549 cells, breast cancer MCF7, ovarian cancer PA1, and colon cancer WiDr cells were exposed to both pemetrexed and paclitaxel in vitro. Cell growth inhibition after 5 days was determined and the effects of drug combinations were analyzed by the isobologram method (Steel and Peckham). Simultaneous exposure to pemetrexed and paclitaxel for 24 h produced antagonistic effects in A549 and PA1 cells, additive/antagonistic effects in MCF7 cells, and additive effects in WiDr cells. Pemetrexed for 24 h followed by paclitaxel for 24 h produced synergistic effects in A549 and MCF7 cells and additive effects in PA1 and WiDr cells, while the reverse sequence produced additive effects in all four cell lines. Cell cycle analysis supported these observations. Our findings suggest that the simultaneous administration of pemetrexed and paclitaxel is suboptimal. The optimal schedule of pemetrexed in combination with paclitaxel is the sequential administration of pemetrexed followed by paclitaxel, and this schedule should be assessed in clinical trials for the treatment of solid tumors.