Antibiotics and phagocytic cells

A N N L D O 5(8) 53--60, 1988

[

ISSN 0738-1751

EDITORIAL BOARD Editor DANIEL AMSTERDAM, PhD,

VOLUME 5, NUMBER 8, AUGUST 1988

Associate Editors STEVEN L. BARRIERE, PharmD,

State University of New York at Buffalo and Erie County Medical Center Buffalo, New York

UCLA Medical Center Los Angeles, California

RONALD N. JONES, MD, Clinical Microbiology Institute Tualatin, Oregon

HAROLD C. NEU, MD, College of Physicians and Surgeons, Columbia University, New York, New York

CLYDE THORNSBERRY, PhD, Center for Infectious Diseases Centers for Disease Control Atlanta, Georgia

LOWELL S. YOUNG, MD, Kuzell Institute for Arthritis and Infectious Diseases Medical Research Institute of San Francisco Pacific Presbyterian Medical Center San Francisco, California

ANTIBIOTICS A N D PHAGOCYTIC CELLS CONTENTS

EDrroR'snOTE

53

D. AMSTERDAM

Antibiotics and Phagocytic Cells

53

W. LEE H A N D Veterans Administration Medical Center (Atlanta), Decatur, Georgia, and Department of Medicine, Emory University School of Medicine, Atlanta, Georgia

W. L. H A N D

Comment: Antifungal Agents of the 1980s

58

C. BRASS

EDITOR'S NOTE In August 1987 (The AMN, Volume 4, page 75) I wrote of the "Alternate Activities of Antibiotics" referring in one specific application to the role that antimicrobics had in modifying cellular activity against infectious agents. In this issue of The AMN Dr. W. Lee Hand summarizes much of his research experience on the interactions of antibiotics and phagocytic cells. He documents the uptake of 17 different antimicrobial agents in three types of h u m a n phagocytic cells: alveolar macrophage, monocytes

ELSEVIER

Antibiotics have biological properties other than direct antimicrobial activity (growth inhibition or killing of microorganisms). For instance, antimicrobial agents may interact with and influence the function of host cells. We have been especially interested in the interactions of antibiotics and phagocytes, and the influence of these drugs on phagoand polymorphonuclear leukocytes. Dr. Hand notes that the inherent chemical properties of antimicrobics such as lipid solubility and other factors (e.g., cigarette smoking) influence the uptake of antibiotics in cells. In another section Dr. C. Brass who wrote earlier on antifungal therapy (The AMN, Volume 1, No. 5, May 1985), comments on Dr. John Graybill's article, which appeared last month. Dr. Brass expresses major concern about the size of the amphotericin B liposome and its suitability for therapy.

cytic cell antimicrobial activity. A major reason for this interest is that survival, and even growth, of certain pathogenic organisms after ingestion by phagocytes (particularly macrophages) may lead to progressive, chronic or recurrent disease. 1,2 Bacteria that clearly exhibit this capability for intraphagocytic survival include Mycobacterium tuberculosis and Legionella pneumophila. To a lesser extent many bacteria, including Listeria, Brucella, and some strains of Staphylococcus aureus and Salmonella, manifest intraphagocytic persistence. The effectiveness of an antibiotic in therapy of infections, especially those due to facultative intracellular organisms, will depend upon both the extracellular drug-bacterial interaction and the ability of the antibiotic to penetrate phagocytes and influence the functions of both the host cells and organisms. Therefore, it is important to study the interactions between antibiotics, phagocytes and bacteria in some detail. In an effort to understand these interactions we have studied: the uptake of antibiotics by various phagocytic cells, the mechanisms of this entry process for specific antibiotics, the influence of certain factors (cigarette smoking, phagocytosis) on antibi0738-1751/88/$0.00 + 2.20

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otic uptake, the influence of antibiotics on survival of intraphagocytic bacteria and the consequences of exposure to antimicrobial agents on antimicrobial functions of phagocytes. ANTIBIOTIC UPTAKE BY PHAGOCYTIC CELLS

To establish those characteristics that determine antibiotic entry into phagocytes, we have studied the uptake of antimicrobial agents by several types of phagocytic cells. These have included: rabbit alveolar macrophages (AM), human AM from cigarette smokers and healthy nonsmokers, and human polymorphonuclear leukocytes (PMN) and monocytes. 3-8 After incubation of phagocytic cells with clinically appropriate concentrations of radiolabeled antibiotics, cellular uptake of antibiotics was determined by a velocity-gradient centrifugation technique. Antibiotic uptake (cellular concentration of drug) was determined, and this was expressed as the ratio of the cellular concentration of antibiotic to the extracellular concentration (C/E). Antibiotics varied greatly in their abilities to enter normal phagocytic cells. However, the relative entries of drug groups into the several types of phagocytes was similar, even though the absolute values differed between phagocytes. 3-8 Beta-lactam antibiotics (penicillin G, cephalosporins) were taken up poorly by all of the tested phagocytic cells (Table 1). Thus, the cellular concentrations of these antibiotics were lower than the extracellular levels (C/E < 1). Imipenem, a novel 13-1actam antibiotic, bound to h u m a n PMN and monocytes rapidly, but cell-associated

T H E A N T I M I C R O B I C N E W S L E T r E R , V O L U M E 5, N U M B E R 8, A U G U S T 1988

TABLE 1. Uptake of Antibiotics by Normal Phagocytes Expressed as a Ratio of

Cellular to Extracellular Concentration (C/E)~ Human Phagocytes Antibiotic Penicillin Cefamandole Cefazolin Cefotaxime Imipenem Gentamicin Isoniazid Metronidazole Tetracycline Rifampin Chloramphenicol Ethambutol Trimethoprim Erythromycin Erythro. Propionate Clindamycin Roxithromycin

Rabbit AM b

AM

PMN

Monocytes

0.07 0.4 0.08 --0.6 0.9 -0.9 2 2 7 -21 32 49 --

0.9 0.8 ---1 1 -4 5 2 4 -18 16 24 --

0.4 <0.01 <0.01 0.3 0.8 0.3 1 1 -2 3 5 9 13 10 11 34

0.8 1 -0.8 0.8 1 -0.5 --3 -4 -5 7 14

a Data summarized from references 3-5, 7, 8. Abbreviations: hAM: alveolar macrophages, PMN: polymorphonuclear leukocytes.

drug declined steadily during the 60-minute incubation period, reaching a C/E < 1. Metronidazole, isoniazid, and gentamicin achieved cellular levels that were equal to or somewhat less than extracellular concentrations. More lipid-soluble antibiotics, such as rifampin and chloramphenicol, entered cells to a greater extent than the drugs we have already mentioned. These antimicrobial agents were concentrated several-fold by phagocytic cells (C/E = 2-5). Tetracycline, which is also rather lipid-soluble, attained cellular levels equal to or greater than the extracellular concentration. In comparison with other tested antibiotics, ethambutol, trimethoprim, clindamycin, erythromycin, erythromycin propionate, and roxithromycin (RU 965) were avidly concentrated by all of the phagocytic cells (C/E = 4-49). Clinda-

mycin uptake was extremely rapid and was maximal in 15-30 minutes. 3-9 Roxithromycin entry into phagocytes was also rapid, and concentration of this drug by h u m a n PMN and monocytes (the only cells evaluated to date) was greater than any of the other antibiotics we have tested. 7,8 It is of note that h u m a n alveolar macrophages from cigarette smokers (most with pulmonary disease) accumulated certain antibiotics more efficiently than did macrophages from nonsmokers. 5,6 Thus, rifampin, erythromycin, and clindamycin attained significantly higher levels in smokers' alveolar macrophages (Table 2). CHARACTERIZATION OF ANTIBIOTIC ENTRY AND MEMBRANE TRANSPORT MECHANISMS We evaluated the characteristics

The Antimicrobic Newsletter (ISSN 0738-1751) is issued monthly in one indexed volume per year by Elsevier Science Publishing Co., Inc., 52 Vanderbilt Avenue, New York, NY 10017. Printed in USA (at Fame Avenue, Hanover, PA 17331). Subscription price per year: $75.00. Outside of the USA, Canada and Mexico, add $33.00. Second-class postage pending at N e w York, NY, and at additional mailing offices. Postmaster: Send address changes to The Antimicrobic Newsletter, Elsevier Science Publishing Co., Inc., 52 Vanderbilt Avenue, New York, NY 10017. NOTICE: No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. No suggested test or procedure should be carried out unless, in the reader's judgment, its risk is justified. Because of rapid advances in the medical sciences, we recommend that the independent verification of diagnoses and drug dosages should be made. Discussions, views and recommendations as to medical procedures, choice of drugs and drug dosages are the responsibility of the authors.

© 1988 BY ELSEVIER S C I E N C E P U B L I S H I N G C O . , I N C .

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THE ANTIMICROBIC NEWSLEH,:R, VOLUME 5, NUMBER 8, AUGUST 1988

TABLE 2. Antibiotic Uptake (C/E) by Human Alveolar Macrophages from Smokers and Nonsmokers"

Antibiotic

Nonsmokers Smokers

Penicillin G Gentamicin Isoniazid Lincomycin Chloramphenicol Ethambutol Rifampin Erythromycin Propionate Clindamycin • Data summarized a n d 6.

0.8 1 1 3 2 4 5 16 24

0.5 1 1 4 4 5 10 28 56

from references 5

and requirements of the uptake process for clindamycin, erythromycin, and roxithromycin, those antibiotics that are most efficiently concentrated by phagocytes. The following observations summarize these findings. Exposure of phagocytes to trypsin or neuraminidase had no inhibitory effect on the concentrations of cell-associated clindamyc~n and erythromycin. Thus, it is very unlikely that simple binding of antibiotic to the plasma cell membrane accounts for the apparent entry of these antibiotics into phagocytes. 3 Cellular entry of clindamycin and the macrolide antibiotics was also dependent upon cell viability and a physiologic environmental temperature. 3,s,7-9 These findings demonstrate that uptake of these drugs is energy-dependent and active in nature. Next, inhibitors of cellular metabolism were examined for their effect on antibiotic accumulation. We found that in each type of phagocytic cell, inhibitors of the predominant energy source depressed antibiotic uptake. Thus, sodium cyanide and 2,4-dinitrophenol, inhibitors of mitochondrial oxidative respiration, depressed clindamycin and erythromycin uptake in rabbit and h u m a n alveolar macrophages. 3,s,9 In contrast, potassium fluoride, which inhibits glycolysis, decreased clindamycin entry into h u m a n PMN. 4,1° In a rather different 0738-1751/88/$0.00 + 2.20

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manner, both fluoride and cyanide mostly decreased roxithromycin entry into PMN. 7 Kinetic analysis of clindamycin (rabbit AM, h u m a n PMN) and roxithromycin (human PMN) uptake revealed that entry of both drugs displayed saturation kinetics, characteristic of carrier-mediated membrane transport systems. 4,7,9 Because phagocytes have specific carrier-mediated transport systems for hexoses, amino acids and nucleosides, we considered the possibility that clindamycin and macrolide antibiotic (roxithromycin, erythromycin) might enter phagocytes by one or more of these systems. Competitive inhibition studies confirmed that clindamycin is transported into macrophages and PMN by the cell membrane nucleoside system. 9,1° In spite of considerable effort, we still do not have a clear idea of how the macrolide antibiotics, that are actively accumulated by phagocytes, actually enter these cells. 7 There is some evidence concerning the intracellular localization of these antibiotics. Other investigators have shown that substantial amounts of clindamycin, erythromycin, and roxithromycin enter lysosomes of h u m a n PMN or macrophages, n-13 Our own studies indicated that PMN cytoplasts, which contain no lysosomes, take up two-thirds as much clindamycin and roxithromycin as intact cells (unpublished observations). As noted above, rifampin, erythromycin and Clindamycin attained

significant higher levels in smokers' alveolar macrophages than in AM of nonsmokers, s,6 It is probable that cigarette smoking per se causes these changes, because the known structural and functional alterations observed in alveolar macrophages from healthy smokers could account for the augmented accumulation of certain antibiotics. Specifically, the increased lipid content of smokers' AM might enhance the uptake of lipid-soluble drugs such as rifampin. Furthermore, stimulated metabolic pathways and altered membrane function in smokers' AM may account for the increased uptake of clindamycin and erythromycin, antibiotics that enter phagocytes by active cell membrane transport systems. Since m a n y pathogenic organisms may persist with phagocytes, we felt that it was important to evaluate the entry of antibiotics into these cells under conditions that mimic in vivo infection. 7,~°,14,1s Ingestion of microbial particles (S. aureus, zymosan) stimulated the entry of clindamycin into PMN (Table 3). 1°,14,1s Because clindamycin uptake in phagocytes is mediated by the nucleoside transport system, we also studied adenosine uptake after phagocytosis. Adenosine uptake increased after ingestion of zymosan or S. aureus, and the presence of clindamycin inhibited this phagocytosis-enhanced uptake of adenosine.I° Thus, clindamycin uptake (mediated by the nucleoside transport system) as well as nucleoside transport per se

TABLE 3. Effects of Microbial Particle Ingestion on Antibiotic Uptake (C/E) by Human Polymorphonuclear Leukocytes (PMN) a

Antibiotic

PMN (Control)

PMN + Zymosan

PMN + S. aureus

Clindamycin Erythromycin Erythro. Propionate Roxithromycin Rifampin Gentamicin Penicillin

11 12 15 34 4 0.7 0.5

30 -11 28 6 -0.6

19 11 -22 5 0.5 0.3

" Data s u m m a r i z e d f r o m references 7, 10, 14, 15. © 1988 BY ELSEVIER SCIENCE PUBLISHING CO., INC.

THEANTIMICROBICNEWSLETTER,VOLUME5, NUMBER8, AUGUST1988

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were augmented by phagocytosis in PMN. Ingestion of microbial partides also stimulated the entry of rifampin (slightly), but not of other antibiotics into PMN. 14,15 Indeed, the entry of macrolide antibiotics into PMN was decreased after phagocytosis, although the cellular levels of these drugs was still quite high.7,10,14

ANTIBIOTICS AND INTRAPHAGOCYTIC BACTERICIDAL ACTIVITY The obvious next step was to examine the consequences of antibiotic uptake by phagocytes on subsequent intracellular bactericidal activity. To date these studies have been performed in human PMN 14,~5 and to a limited extent in rabbit alveolar macrophages (Hand WL, King-Thompson NL, unpublished observations). For experiments in PMN we used five antibiotics- clindamycin, erythromycin, rifampin, gentamicin, and penicillin G - - t h a t differ markedly in their ability to enter phagocytes.14 PMN were incubated in the presence or absence of antibiotics after ingestion of S. aureus. The most striking aspect of the study was the discrepancy between antibiotic entry into phagocytes and the effect of this drug uptake on intraphagocytic bactericidal activity. It was particularly noteworthy that clindamycin, which is markedly concentrated by phagocytes, had relatively little influence on intracellular killing of organisms ingested by human PMN and rabbit AM (Table 4). 14,1s Similar resuits were obtained with erythromycin, another antibiotic that achieves high concentrations in these cells. EFFECTS OF ANTIBIOTICS O N OXIDATIVE A N D N O N O X I D A T I V E ANTIMICROBIAL SYSTEMS IN P M N There are a number of possible exp l a n a t i o n s for the poor correlation

between antibiotic uptake by PMN

TABLE 4. Effects at One and Three Hours of Antibiotics on S. aureus Ingested by Human Polymorphonuclear Leukocytes (PMN) a Experimental g r o u p S. aureus only PMN only PMN + antibiotic Clindamycin Erythromycin Rifampin Penicillin Gentamicin

1 hour

N at start (O-time)

1.2 x 106 1.4 x 106 1.4 x 106

3 hours pb

N

1.5 x 106 8.1 x 10s 5.2 5.9 3.3 7.3 1.8

x x x x x

10s 10s 10s 10s 10s

N

p

4.4 x 107 5.7 x 10s 0.09 0.17 0.02 0.70 0.0008

3.4 5.2 2.3 6.0 7.0

x x x x x

105 10s 10s 10s 104

0.07 0.81 0.03 0.85 0.0002

a Data s u m m a r i z e d from reference 14. b p-values reflect differences b e t w e e n control (PMN only) and experimental (PMN + antibiotic) groups.

and the subsequent effect on intraphagocytic bactericidal activity. In the case of clindamycin, the intracellular drug concentration in both AM and PMN exceeded the MBC for the test organism. Therefore, the possibility that clindamycin's poor intraphagocytic killing might be due to inhibition of the phagocyte's antibacterial function was considered. Because nucleosides (especially adenosine) play a role in regulating the generation of superoxide by activated human PMN, we thought it possible that clindamycin (which enters PMN by the nucleoside transport system) might influence oxidative metabolism in a similar manner. H u m a n PMN incubated in the presence or absence of nucleosides or antibiotics were exposed to microbial particles or soluble agents that stimulate oxidative respiratory burst activity and degranulation. 16 We found that adenosine, certain other nucleosides, and clindamycin inhibited superoxide and hydrogen peroxide generation, but not degranulation, in PMN stimulated by microbial particles, FMLP, or ConA. The accumulated evidence indicated that inhibition of the oxidative respiratory burst by nucleosides, but not clindamycin, was mediated via the binding of cell membrane nucleoside receptors. 16-18 The inhibitory effect of clindamycin was directly related to the quantity of drug that entered the cell, although the pre-

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cise mechanism of action has not yet been defined. Unlike clindamycin, other antibiotics, including erythromycin, chloramphenicol, lincomycin, gentamicin, and penicillin G, had little effect on stimulated superoxide production in PMN.26 Quite recently we documented that roxithromycin also inhibits oxidative metabolism in PMN. Both clindamycin and roxithromycin also block stimulated superoxide production in human peripheral blood monocytes (Hand WL, Hand DL, unpublished observations). DISCUSSION AND CLINICAL SIGNIFICANCE OF ANTIBIOTICPHAGOCYTE INTERACTIONS An ideal antimicrobial agent would not only have activity against extracellular organisms, but would enter phagocytic cells and eradicate the surviving intracellular organisms. Unfortunately, we know that intraphagocytic organisms are protected against many antimicrobial agents. 14,18,19-24 With these points in mind, we have attempted to define the characteristics of drugs and phagocytic cells that determine their interactions. Obviously the entry of antibiotics into phagocytes is an essential prerequisite for activity against intracellular organisms. Thus, we have studied the uptake of antibiotics by several populations of phagocytic cells, including rabbit AM, human 0738-1751/88/$0.00 + 2.20

THE ANTIMICROBIC NEWSLETrER, VOLUME5, NUMBER8, AUGUST 1988

AM from smokers and nonsmokers, and human peripheral blood PMN and monocytes.3-8 Although the absolute uptake values varied considerably, the relative entries of drug groups into the various phagocytes were similar. Beta-lactam antibiotics and gentamicin entered phagocytes poorly. Lipid-soluble agents (rifampin, chloramphenicol) were concentrated several-fold, on the basis of solubility partition, in all phagocytes. Ethambutol and trimethoprim were concentrated 4-8-fold by uncertain, and probably complex, entry mechanisms. The most remarkable aspect of these studies was the striking entry of clindamycin and macrolide antibiotics (erythromycin, roxithromycin) into all phagocytic cells. These agents reached cellular levels 5-50 times the extracellular concentrations. Cellular entry required active, energy-dependent transport. 3-s,7-9 The mechanism for the avid concentration of clindamycin was identified as the cell membrane nucleoside transport system. 9,1° To date we have been unable to identify the means by which macrolides are taken up by phagocytes. Since many pathogenic organisms may persist within phagocytes, we thought it was important to examine the cellular entry of antibiotics under conditions that resemble in vivo infection. Phagocytosis of microbial particles (zymosan, S. aureus) stimulated the uptake of clindamycin (and rifampin slightly, but not the entry of other antibiotics, into human PMN. 1°,14,1s In fact the uptake of roxithromycin and erythromycin by PMN was decreased after phagocytosis, although cellular concentrations of these drugs were still quite high.7,10,14 Obviously, we were anxious to examine the consequences of antibiotic uptake by phagocytes on intracellular bactericidal activity. ~4,~5 The most impressive finding in this study was the discrepancy between antibiotic entry into phagocytic 0738-1751/88/$0.00 + 2.20

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cells and the resulting influence of this drug on intraphagocytic bactericidal activity. For this discussion it is especially noteworthy that clindamycin, which is avidly concentrated by all phagocytic cells, had relatively little effect on the intracellular survival of sensitive S. aureus ingested by human PMN and rabbit AM. Entry into phagocytes is an essential, but certainly not the only, factor that determines an antibiotics's activity against intTacellular organisms. Intraphagocytic antibiotic effect is undoubtedly influenced by multiple factors. These factors might include: 1) the drug's specific intracellular location and local concentration, 2) the agent's native antibacterial properties (mechanism of action, type of activity), 3) effect of the intracellular environment on biological activity of the antibiotic and susceptibility of the organism, and 4) the drug's effect on cellular function (e.g., cell movement, microbicidal systems, phagocytosis). Some of these potential factors are difficult to evaluate, and our own studies thus far have not addressed each of these points directly. However, we were interested in determining why clindamycin, an antibiotic that is well concentrated by all phagocytes, had little effect on the intracellular survival of S. aureus. In this case, one potentially important factor might be the intrinsic inability of this bacteriostatic antibiotic to kill the organism. However, the intracellular clindamycin concentration in both AM and PMN exceeded the MBC for the test strain of S. aureus. Therefore, we considered the possibility that the antibiotic's failure to significantly enhance overall intraphagocytic killing might be due to an adverse influence on phagocyte antibacterial systems. Indeed, we found that clindamycin in therapeutic concentrations inhibited superoxide and hydrogen peroxide generation, but not degranulation, by stimulated human PMN. 16 This

inhibition of the PMN oxidative respiratory burst by clindamycin was not mediated via binding to the cell membrane nucleoside receptors, and the exact mechanism of action has not been determined. Recently we demonstrated that roxithromycin also inhibits oxidative metabolism in PMN. Thus, the two antibiotics that achieve the highest cellular concentrations in phagocytes were shown to be modulators of oxidative metabolism in these cells. The precise mechanism of this effect is still under investigation. A number of other tested antibiotics had little effect on the oxidative respiratory burst in PMN. The modulator effect of clindamycin and roxithromycin on the oxidative respiratory burst in phagocytes is of great interest. This type of interaction between antibiotics and host phagocytic cells has not previously been evaluated in a systematic fashion. It is obvious that these phagocyte-antibiotic interactions may have major clinical implications. For example, antibiotic-mediated modulation of oxidative metabolism might interfere with the ability of phagocytes to kill ingested organisms. On the other hand, there may be beneficial aspects to the inhibitory effects of clindamycin and roxithromycin on the oxidative respiratory burst. It is possible that derivatives of these drugs might prove useful in controlling the inflammatory response in certain disease states. In conclusion, it is obvious that the interactions between antibiotics, phagocytes, and organisms are not only interesting and important but also complex. There is a great deal to learn before we understand these relationships clearly. ACKNOWLEDGEMENTS This study was supported in part by the Medical Research Service of the Veterans Administration. I thank Brenda Bagwell for preparation of the manuscript.

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REFERENCES

1. Horwitz MA: Phagocytosis of microorganisms. Rev Infect Dis 4:104-123, 1982. 2. Report of a WHO Scientific Group: Cell-mediated immunity and resistance to infection. Int Arch Allergy Appl Immunol 44:589-648, 1973. 3. Johnson JD, Hand WL, Francis JB, et al: Antibiotic uptake by alveolar macrophages. J Lab Clin Med 95:429-439, 1980. 4. Prokesch RC, Hand WL: Antibiotic entry into human polymorphonuclear leukocytes. Antimicrob Agents Chemother 21:373-380, 1982. 5. Hand WL, Corwin RW, Steinberg TH, Grossman GD: Uptake of antibiotics by human alveolar macrophages. Am Rev Resp Dis 129:933-937, 1984. 6. Hand WL, Boozer RM, KingThompson NL: Antibiotic uptake by alveolar macrophages of smokers. Antimicrob Agents Chemother 27:42-45, 1985. 7. Hand WL, King-Thompson NL, Holman JW: Entry of roxithromycin (RU 965), imipenem, cefotaxime, trimethoprim, and metronidazole into human polymorphonuclear leukocytes. Antimicrob Agents Chemother 31:1553-1557, 1987. 8. Hand WL, King-Thompson NL: Antibiotic entry into human monocytes. Submitted for publication. 9. Hand WL, King-Thompson NL: Membrane transport of clindamycin in alveolar macrophages. Antimicrob Agents Chemother 21:241247, 1982.

COMMENT ON A N T I F U N G A L AGENTS OF THE 1980's C O R S T I A A N BRASS Buffalo General Hospital, State University of New York at Buffalo, Buffalo, New York

The review of antifungals by Dr. Graybill1 details the pertinent observations of advantages and limitations of the presently available antifungal antibiotics. The study of antifungal antibiotics is at present limited by the nature of observa-

THE ANTIMICROBIC NEWSLETTER, VOLUME 5, NUMBER 8, AUGUST 1988

10. Steinberg TH, Hand WL: Effects of phagocytosis on antibiotic and nucleoside uptake by human polymorphonuclear leukocytes. J Infect Dis 149:397-403, 1984. 11. Klempner MS, Styrt B: Clindamycin uptake by human neutrophils. J Infect Dis 144:472-479, 1981. 12. Klempner MS, Styrt B: Alkalinization of the intralysosomal pH by clindamycin and its effects on neutrophil function. J Antimicrob Chemother 12(Suppl C):39-50, 1983. 13. Carlier M-S, Zenebergh A, Tulkens PM: Cellular uptake and subcellular distribution of roxithromycin and erythromycin in phagocytic cells. J Antimicrob Chemother 20(Suppl B):47-56, 1987. 14. Hand WL, King-Thompson NL: Contrasts between phagocyte antibiotic uptake and subsequent intracellular bactericidal activity. Antimicrob Agents Chemother 29:135-140, 1986. 15. Steinberg TH, Hand WL: Effect of phagocyte membrane stimulation on antibiotic uptake and intracellular bactericidal activity. Antimicrob Agents Chemother 31:660-662, 1987. 16. Hand WL, Hand DL, KingThompson NL: Inhibition of oxidative metabolism in human polymorphonuclear leukocytes by cllndamycin and nucleosides. Submitted for publication. 17. Cronstein BN, Kramer SB, Weissman G, Hirschhorn R: Adenosine: a physiological modulator of superoxide anion generation by

tions, comparisons (or absence thereof) with other agents, and lack of identification of determinants of response in selected patient populations. The development of new azoles and the use of new technologies for the administration of amphotericin B are encouraging, but certain considerations should be borne in mind as data on these agents emerge. The development of liposomal transport of drugs and the development of surface determinants to enhance targeting of liposomal carders make this a very promising modality for therapeutic agents that are limited by dose because of un-

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human neutrophils. J Exp Med 158:1160-1177, 1983. 18. Cronstein BN, Rosenstein ED, Kramer SB, et al: Adenosine: a physiologic modulator of superoxide anion generation by human neutrophils. Adenosine acts via an A2 receptor on human neutrophils. J Immunol 135:1366-1371, 1985. 19. Holmes B, Quie PG, Windhorst DB, et al: Protection of phagocytized bacteria from the killing action of antibiotics. Nature 210:11311132, 1966. 20. Mandell GLM, Vest TK: Killing of intraleukocytic Staphylococcus aureus by rifampin: in-vitro and in-vivo studies. J Infect Dis 125:486-490, 1973. 21. Solberg CO: Protection of phagocytized bacteria against antibiotics. Acta Med Scand 191:383-387, 1972. 22. Vandaux P, Waldvogel FA: Gentamicin antibacterial activity in the presence of human polymorphonuclear leukocytes. Antimicrob Agents Chemother 16:743-749, 1979. 23. Jacobs RF, Wilson CB, Laxton JG, et al: Cellular uptake and intracellular activity of antibiotics against Haemophilus influenzae type B. J Infect Dis 145:152-159, 1982. 24. Easmon CSF, Crane JP: Cellular uptake of clindamycin and lincomycin. Br J Exp Path 65:725-730, 1984.

acceptable toxicity.2 Such may be the case for liposomal amphotericin B, however, the present studies and method of creation of liposomal amphotericin B may not represent the optimum use of this therapeutic modality. The dimension of the liposome that is used in these studies is one micron. This size of liposome has been demonstrated to be exclusively localized in the Kupper cells and other phagocytic cells abutting the sinusoidal tracts of the reticuloendothelial system. Uptake in the pulmonary circulation and tissues may also be limited by size of the liposome. Furthermore, while demonstrating 0738-1751/88/$0.00 + 2.20