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Antimicrobial Agents and Chemotherapy, October 2002, p. 3323-3326, Vol. 46, No. 10
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.10.3323-3326.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
In Vitro Synergistic Interaction between Amphotericin B and Pentamidine against Scedosporium prolificans
Javier Afeltra,1 Eric Dannaoui,1 Jacques F. G. M. Meis,2 Juan L. Rodriguez-Tudela,3 Paul E. Verweij,1* and and Eurofung Network
Department of Medical Microbiology, University Medical Center Nijmegen,1
Department of Medical Microbiology and Infectious Diseases, Canisius Wilhelmina Hospital, Nijmegen, The Netherlands,2
Unidad de Micología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain3
Received 5 February 2002/
Returned for modification 29 May 2002/
Accepted 11 July 2002

ABSTRACT
To develop new approaches for the treatment of invasive infections
caused by
Scedosporium prolificans, the in vitro interaction
between amphotericin B and pentamidine against 30 clinical isolates
was evaluated using a checkerboard microdilution method based
on the National Committee for Clinical Laboratory Standards
M38-P guidelines. The interaction between the drugs was analyzed
using fractional inhibitory concentration index (FICI) analysis
and response surface modeling. Amphotericin B alone was inactive
against all the isolates. The geometric mean MIC for pentamidine
was 57 µg/ml (range, 8 to 256 µg/ml; MIC at which
50% of the isolates tested were inhibited [MIC
50], 64 µg/ml;
MIC
90, 128 µg/ml). The combination was synergistic against
28 of 30 isolates (93.3%) by FICI analysis and 30 of 30 (100%)
by response surface modeling analysis. Antagonism was not observed.

TEXT
The in vitro susceptibility of
Scedosporium prolificans to antifungal
agents has been tested in several studies (
5,
7,
22), and although
the methodological conditions differed in the various studies,
in general, their results correlated with the observed poor
clinical outcomes. The new azoles, such as ravuconazole, voriconazole,
and posaconazole, showed poor in vitro activity (
5,
7), with
the exception of the experimental azole UR-9825, which showed
some activity against
S. prolificans (
5). Pentamidine (PN) displayed
good in vitro and in vivo activity against
Pneumocystis carinii,
a microorganism that now is believed to belong to the fungal
kingdom (
12,
24,
28). Also, in combination with amphotericin
B (AMB), the drug displayed in vivo and in vitro synergistic
activity against other eukaryotic microorganisms such as
Leishmania donovani (
21,
28). To develop new therapeutic strategies to
treat invasive scedosporiosis, we investigated the in vitro
activity of AMB and PN, alone or in combination, using two different
criteria, the fractional inhibitory concentration index (FICI)
(
10) and response surface modeling (
13).
Thirty clinical isolates (3) of S. prolificans were tested. The isolates were subcultured on potato dextrose agar (PDA) for 5 to 7 days at 30°C. Candida parapsilosis (ATCC 22019) and Candida krusei (ATCC 6258) were used as quality control strains. All isolates were tested in duplicate on two different days. Conidia were obtained from fresh cultures each time. All solutions were prepared ex novo with powders from the same lot.
MICs were determined by a broth microdilution method according to the National Committee for Clinical Laboratory Standards guidelines (M38-P) (25).
Conidia were collected with a cotton stick and suspended in sterile water. After the heavy particles were allowed to settle, the turbidity of the supernatants was measured spectrophotometrically (Spectronic 20D; Milton Roy, Rochester, N.Y.) at 530 nm and the transmission was adjusted to 68 to 70% and diluted 1:50 in RPMI medium to obtain two times the desired inoculum concentration. The inoculum size was verified by determination of the number of viable CFU after plating serial dilutions of the inoculum onto Sabouraud dextrose agar. These cultures showed that the final inoculum concentrations ranged between 1.5 x 104 and 5 x 104 CFU/ml, which is within the recommended upper and lower limits. The drugs used in this study were AMB (Bristol-Myers Squibb, Woerden, The Netherlands) and PN (Sigma-Aldrich Chemie GmbH, Steinheim, Germany). The final concentrations of the drugs ranged from 0.03 to 16 µg/ml for AMB and from 1 to 128 µg/ml for PN. AMB was dissolved in dimethyl sulfoxide (Merck, Darmstadt, Germany), and PN was dissolved in water.
Drug dilutions were made in RPMI 1640 medium (with L-glutamine and without bicarbonate) (GIBCO BRL, Life Technologies, Woerden, The Netherlands) buffered to pH 7.0 with 0.165 M morpholinepropanesulfonic acid (MOPS) (Sigma-Aldrich Chemie). Susceptibility testing was performed in 96-well flat-bottom microtitration plates, which were kept at -70°C until the day of testing. After inoculation and agitation, the plates were incubated at 35°C for 72 h and the MICs were read visually and spectrophotometrically. Growth was graded on a scale of 0 to 4 as follows: 4 indicated no reduction in growth, 3 indicated a 25% reduction of growth, 2 indicated a 50% reduction of growth, 1 indicated a 75% reduction of growth, and 0 indicated an optically clear well. The MIC endpoint was defined as the lowest concentration showing an optically clear well or absence of growth (MIC 0,
95% inhibition) for the drugs alone as well as for the combination. The optical density (OD) was measured with a spectrophotometer (MS2 reader, Titertek-plus; ICN Biomedical Ltd., Basingstoke, United Kingdom) at 405 nm. The OD of the blank, to which a conidium-free inoculum had been added, was subtracted from the OD values. The percentage of growth for each well was calculated by comparing the OD of the well with that of the drug-free control.
The in vitro fungicidal activity (minimal fungicidal concentration [MFC]) of each agent was determined by streaking 100 µl from each well that showed complete inhibition (
95% inhibition or an optically clear well) onto Sabouraud dextrose agar plates. The plates were incubated at 35°C for 72 h, the MFC was the lowest drug concentration at which there was either no growth or only a single colony, which corresponds with 99.9% killing. The drug was considered fungicidal if the ratio of MFC to MIC did not exceed a value of 4. If the ratio was greater than 4, the activity was considered to be fungistatic (15).
A two-dimensional, two-agent broth microdilution checkerboard technique was used to study the interaction between both drugs. Drug interaction was analyzed by two different methods, the FICI and the response surface model of Greco et al. (13, 14).
FICI values were calculated as follows: MIC of AMB-PN/MIC of AMB + MIC of AMB-PN/MIC of PN. The interpretation of the FICI was determined as follows:
0.5, synergistic effect; >0.5 but
1, additive effect; >1 but
4, indifferent effect; and >4, antagonistic effect (10). In practice, synergism or antagonism calculated in this way is equivalent to a reduction or increase of at least two dilution steps in the MICs of both drugs when they are combined compared to the MICs for the drugs alone.
Because there is no definition of PN MIC endpoint for fungi, alone or in combination with AMB, we used the response surface modeling described by Greco et al. (13, 14). The model is described by the formula below and was used previously to characterize the interaction of antiviral, antifungal, and antineoplastic agents (11, 14, 20, 28a):
where
D1 and
D2 are the concentrations of drug 1 and drug 2 (AMB and PN),
IC
50,1 and IC
50,2 are the concentrations of drug 1 and drug
2 resulting in 50% inhibition,
E is the measured response, Econ
is the control response,
m1 and
m2 are the slope parameters
for drugs 1 and 2 in constant ratios, and

is the synergism-antagonism
interaction parameter (IC

). If

is zero, the combination is
additive; if

is positive, the interaction is synergistic. A
negative

value indicates antagonism. The estimate of

has an
associated 95% confidence interval; if the confidence interval
does not overlap zero, this provides the statistical significance
for the estimate of interaction. A computer program (ModLab;
Medimatics, Maastricht, The Netherlands) was used to fit the
data to this model (
28a). The program also determined the 95%
confidence interval for each parameter.
The MICs of AMB and PN, based on 95% reduction of growth for C. krusei (ATCC 6258), were 0.5 and 16 µg/ml, respectively, and for C. parapsilosis (ATCC 22019) were 0.25 and 4 µg/ml, respectively. The MICs for the quality control strains were within the reference ranges for AMB, but there is no reference MIC described for PN.
AMB was inactive in vitro against most isolates: MIC at which 50% of the isolates were inhibited (MIC50) and MIC90 were 32 µg/ml, and the geometric mean MIC was 22.62 µg/ml (range, 4 to 32 µg/ml). The geometric mean MIC for PN was 57 µg/ml (range, 8 to 256 µg/ml; MIC50, 64 µg/ml; MIC90, 128 µg/ml). The geometric means of the MFCs of AMB and PN were 30.55 µg/ml (range, 16 to 32 µg/ml) and 165 µg/ml (range, 16 to 256 µg/ml), respectively. The MFC/MIC ratios were more than 4 for all the strains, indicating fungistatic activity.
Synergism was found for 28 of 30 isolates (93.3%), according to the FICI. The remaining two isolates showed an additive effect (Table 1). According to the Greco model, AMB and PN showed synergistic interaction against all S. prolificans isolates. The 95% confidence interval of the
values did not overlap zero, indicating significant synergism (Table 1).
Disseminated infection by
S. prolificans most commonly occurs
in neutropenic patients with hematologic malignancies. It is
a rapidly fatal infection characterized by fever and multiorgan
failure. Many patients have been treated with AMB and occasionally
with other antifungals but commonly with unsuccessful outcomes
(
3,
5,
18).
PN is an aromatic diamidine that displays multiple effects and is active in vitro against a number of different bacteria, protozoa, and fungi, such as Blastomyces dermatitidis, Saccharomyces cerevisiae, Candida species, and Cryptococcus neoformans (2, 8, 19, 23, 27, 29). Patients who receive 4 mg/kg of body weight daily by slow intravenous infusion can achieve a blood concentration of 0.5 to 3.2 µg/ml. However, much higher levels are found in tissue, with concentrations of up to 56 µg/g in lung, 35 to 300 µg/g in liver, 40 to 368 µg/g in spleen, and 8.5 to 123 µg/g in kidney tissue (4, 9). When drug levels were related to MICs, 20 of 30 of the S. prolificans isolates were considered susceptible to this drug in vitro. Considering the MIC/MFC ratios, fungistatic activity was observed for PN.
A promising approach to treatment of invasive scedosporiosis might be that of combining antifungal drugs with different mechanisms of action. PN in combination with AMB showed synergistic interaction in most of the strains, using either the FICI or the Greco model. Several different mechanisms of antimicrobial activity have been proposed for PN, such as inhibition of DNA, RNA, phospholipid, and protein synthesis (8, 28). However, because the mechanism of action is not fully understood, it is difficult to characterize the synergistic interaction with AMB.
AMB in combination with tetracyclines, azithromycin, or rifampin was synergistic in vitro against Aspergillus spp. (6, 16, 17, 26). As with PN, the above-mentioned antibacterial drugs inhibit the protein synthesis, and this could be an explanation of their positive interaction. A disadvantage of the combination of AMB and PN was that it caused acute reversible renal failure in vivo, and therefore, caution should be used when these agents are given concomitantly (1). However, since the most frequent portal of entry of the fungus appears to be the respiratory tract, administration of aerosolized PN, combined with systemic administration of AMB, could reduce toxicity.
In conclusion, this is the first description of activity of PN alone or in combination with AMB against S. prolificans in vitro.
Further studies with this and other combinations in appropriate animal models are required to develop therapeutic strategies for treatment of invasive scedosporiosis.
(This work was presented in part at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, Ill., 16 to 19 December 2001.)

ACKNOWLEDGMENTS
This work was supported by a grant from the EC-TMR-EUROFUNG
network (ERBFMXR-CT970145) and by the Mycology Research Center
of Nijmegen.

FOOTNOTES
* Corresponding author. Mailing address: Department of Medical Microbiology, University Medical Center Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands. Phone: 31-24-3614356. Fax: 31-24-3540216. E-mail:
p.verweij{at}mmb.azn.nl.

The Eurofung Network consists of the following participants: Emmanuel Roilides, coordinator, and Nicos Maglaveras, Aristotle University, Thessaloniki, Greece; Tore Abrahamsen and Peter Gaustad, Rikshospitalet National Hospital, Oslo, Norway; David W. Denning, University of Manchester, Manchester, United Kingdom; Paul E. Verweij and Jacques F. G. M. Meis, University of Nijmegen, Nijmegen, The Netherlands; Juan L. Rodriguez-Tudela, Instituto de Salud Carlos III, Madrid, Spain; and George Petrikkos, Athens University, Athens, Greece. 

REFERENCES
1 - Antoniskis, D., and R. A. Larsen. 1990. Acute, rapidly progressive renal failure with simultaneous use of amphotericin B and pentamidine. Antimicrob. Agents Chemother. 34:470-472.[Abstract/Free Full Text]
2 - Barchiesi, F., M. Del Poeta, V. Morbiducci, F. Ancarani, and G. Scalise. 1994. Effect of pentamidine on the growth of Cryptococcus neoformans. J. Antimicrob. Chemother. 33:1229-1232.[Free Full Text]
3 - Berenguer, J., J. L. Rodriguez-Tudela, C. Richard, M. Alvarez, M. A. Sanz, L. Gaztelurrutia, J. Ayats, J. V. Martinez-Suarez, et al. 1997. Deep infections caused by Scedosporium prolificans. A report on 16 cases in Spain and a review of the literature. Medicine (Baltimore) 76:256-265.[CrossRef][Medline]
4 - Bernard, E. M., H. J. Donnelly, M. P. Maher, and D. Armstrong. 1985. Use of a new bioassay to study pentamidine pharmacokinetics. J. Infect. Dis. 152:750-754.[Medline]
5 - Carrillo, A. J., and J. Guarro. 2001. In vitro activities of four novel triazoles against Scedosporium spp. Antimicrob. Agents Chemother. 45:2151-2153.[Abstract/Free Full Text]
6 - Clancy, C. J., Y. C. Yu, A. Lewin, and M. H. Nguyen. 1998. Inhibition of RNA synthesis as a therapeutic strategy against Aspergillus and Fusarium: demonstration of in vitro synergy between rifabutin and amphotericin B. Antimicrob. Agents Chemother. 42:509-513.[Abstract/Free Full Text]
7 - Cuenca-Estrella, M., B. Ruiz-Diez, J. V. Martinez-Suarez, A. Monzon, and J. L. Rodriguez-Tudela. 1999. Comparative in-vitro activity of voriconazole (UK-109,496) and six other antifungal agents against clinical isolates of Scedosporium prolificans and Scedosporium apiospermum. J. Antimicrob. Chemother. 43:149-151.[Abstract/Free Full Text]
8 - Donkor, I. O., and A. M. Clark. 1999. In vitro antimicrobial activity of aromatic diamidines and diimidazolines related to pentamidine. Eur. J. Med. Chem. 34:639-643.[Medline]
9 - Donnelly, H., E. M. Bernard, H. Rothkotter, J. W. Gold, and D. Armstrong. 1988. Distribution of pentamidine in patients with AIDS. J. Infect. Dis. 157:985-989.[Medline]
10 - Eliopoulos, G. M., and R. C. Moellering. 1996. Antimicrobial combinations, p. 330-396. In V. Lorain (ed.), Antibiotics in laboratory medicine, 4th ed. The Williams & Wilkins Co., Baltimore, Md.
11 - Faessel, H. M., H. K. Slocum, R. C. Jackson, T. J. Boritzki, Y. M. Rustum, M. G. Nair, and W. R. Greco. 1998. Super in vitro synergy between inhibitors of dihydrofolate reductase and inhibitors of other folate-requiring enzymes: the critical role of polyglutamylation. Cancer Res. 58:3036-3050.[Abstract/Free Full Text]
12 - Fishman, J. A. 1998. Prevention of infection due to Pneumocystis carinii. Antimicrob. Agents Chemother. 42:995-1004.[Free Full Text]
13 - Greco, W. R., G. Bravo, and J. C. Parsons. 1995. The search for synergy: a critical review from a response surface perspective. Pharmacol. Rev. 47:331-385.[Medline]
14 - Greco, W. R., H. S. Park, and Y. M. Rustum. 1990. Application of a new approach for the quantitation of drug synergism to the combination of cis-diamminedichloroplatinum and 1-beta-D-arabinofuranosylcytosine. Cancer Res. 50:5318-5327.[Abstract/Free Full Text]
15 - Hazen, K. C. 1998. Fungicidal versus fungistatic activity of terbinafine and itraconazole: an in vitro comparison. J. Am. Acad. Dermatol. 38:S37-S41.[CrossRef][Medline]
16 - Hughes, C. E., C. Harris, J. A. Moody, L. R. Peterson, and D. N. Gerding. 1984. In vitro activities of amphotericin B in combination with four antifungal agents and rifampin against Aspergillus spp. Antimicrob. Agents Chemother. 25:560-562.[Abstract/Free Full Text]
17 - Hughes, C. E., C. Harris, L. R. Peterson, and D. N. Gerding. 1984. Enhancement of the in vitro activity of amphotericin B against Aspergillus spp. by tetracycline analogs. Antimicrob. Agents Chemother. 26:837-840.[Abstract/Free Full Text]
18 - Idigoras, P., E. Perez-Trallero, L. Pineiro, J. Larruskain, M. C. Lopez-Lopategui, N. Rodriguez, and J. M. Gonzalez. 2001. Disseminated infection and colonization by Scedosporium prolificans: a review of 18 cases, 1990-1999. Clin. Infect. Dis. 32:E158-E165.[CrossRef][Medline]
19 - Ludewig, G., J. M. Williams, Y. Li, and C. Staben. 1994. Effects of pentamidine isethionate on Saccharomyces cerevisiae. Antimicrob. Agents Chemother. 38:1123-1128.[Abstract/Free Full Text]
20 - Maga, G., U. Hübscher, M. Pregnolato, D. Ubiali, G. Gosselin, and S. Spadari. 2001. Potentiation of inhibition of wild-type and mutant human immunodeficiency virus type 1 reverse transcriptases by combinations of nonnucleoside inhibitors and D- and L-(ß)-dideoxynucleoside triphosphate analogs. Antimicrob. Agents Chemother. 45:1192-1200.[Abstract/Free Full Text]
21 - Mbongo, N., P. M. Loiseau, D. G. Craciunescu, and M. Robert-Gero. 1998. Synergistic effect of Ir-(COT)-pentamidine alizarin red and pentamidine, amphotericin B, and paromomycin on Leishmania donovani. Acta Trop. 70:239-245.[CrossRef][Medline]
22 - Meletiadis, J., J. W. Mouton, J. L. Rodriguez-Tudela, J. F. Meis, and P. E. Verweij. 2000. In vitro interaction of terbinafine with itraconazole against clinical isolates of Scedosporium prolificans. Antimicrob. Agents Chemother. 44:470-472.[Abstract/Free Full Text]
23 - Miletti, K. E., and M. J. Leibowitz. 2000. Pentamidine inhibition of group I intron splicing in Candida albicans correlates with growth inhibition. Antimicrob. Agents Chemother. 44:958-966.[Abstract/Free Full Text]
24 - Morris-Jones, S. D., and P. J. Easterbrook. 1997. Current issues in the treatment and prophylaxis of Pneumocystis carinii pneumonia in HIV infection. J. Antimicrob. Chemother. 40:315-318.[Free Full Text]
25 - National Committee for Clinical Laboratory Standards. 1998. Reference method for broth dilution antifungal susceptibility testing of conidium-forming filamentous fungi. Proposed standard M38-P. National Committee for Clinical Laboratory Standards, Wayne, Pa.
26 - Nguyen, M. H., C. J. Clancy, Y. C. Yu, and A. S. Lewin. 1997. Potentiation of antifungal activity of amphotericin B by azithromycin against Aspergillus species. Eur. J. Clin. Microbiol. Infect. Dis. 16:846-848.[CrossRef][Medline]
27 - Nolan, A., P. J. Lamey, T. W. MacFarlane, T. C. Aitchison, J. Shaw, and J. Y. Sirel. 1994. The effect of nebulised pentamidine on the concentration of intra-oral Candida albicans in HIV-infected patients. J. Med. Microbiol. 41:95-97.[Abstract/Free Full Text]
28 - Sands, M., M. A. Kron, and R. B. Brown. 1985. Pentamidine: a review. Rev. Infect. Dis. 7:625-634.[Medline]
28 - Te Dorsthorst, D. T. A., P. E. Verweij, J. F. G. M. Meis, N. C. Punt, and J. W. Mouton. 2002. Comparison of fractional inhibitory concentration index with response surface modeling for characterization of in vitro interaction of antifungals against intraconazole-susceptible and -resistant Aspergillus fumigatus isolates. Antimicrob. Agents Chemother. 46:702-707.
29 - Tracy, J. A., and L. T. Webster. 1996. Drugs used in the chemotherapy of protozoal infections: malaria, p. 965-985. In J. Hardman, A. Gilman, and L. Limbird (ed.), Goodman and Gilman's the pharmacological basis of therapeutics, 9th ed. McGraw-Hill Companies, New York, N.Y.
Antimicrobial Agents and Chemotherapy, October 2002, p. 3323-3326, Vol. 46, No. 10
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.10.3323-3326.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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