Membrane transport of clindamycin in alveolar macrophages

Host cell environments and antibiotic efficacy in tuberculosis

The aetiologic agent of tuberculosis (TB), Mycobacterium tuberculosis (Mtb), can survive, persist, and proliferate in a variety of heterogeneous subcellular compartments. Therefore, TB chemotherapy requires antibiotics crossing multiple biological membranes to reach distinct subcellular compartments and target these bacterial populations. These compartments are also dynamic, and our understanding of intracellular pharmacokinetics (PK) often represents a challenge for antitubercular drug development. In recent years, the development of high-resolution imaging approaches in the context of host-pathogen interactions has revealed the intracellular distribution of antibiotics at a new level, yielding discoveries with important clinical implications. In this review, we describe the current knowledge regarding cellular PK of antibiotics and the complexity of drug distribution within the context of TB. We also discuss the recent advances in quantitative imaging and highlight their applications for drug development in the context of how intracellular environments and microbial localisation affect TB treatment efficacy.

Lung penetration and pneumococcal target binding of antibiotics in lower respiratory tract infection

OBJECTIVES

To achieve the therapeutic effects, antibiotics must penetrate rapidly into infection sites and bind to targets. This study reviewed updated knowledge on the ability of antibiotics to penetrate into the lung, their physicochemical properties influencing the pulmonary penetration and their ability to bind to targets on pneumococci.

METHODS

A search strategy was developed using PubMED, Web of Science, and ChEMBL. Data on serum protein binding, drug concentration, target binding ability, drug transporters, lung penetration, physicochemical properties of antibiotics in low respiratory tract infection (LRTI) were collected.

RESULTS

It was seen that infection site-to-serum concentration ratios of most antibiotics are >1 at different time points except for ceftriaxone, clindamycin and vancomycin. Most agents have proper physicochemical properties that facilitate antibiotic penetration. In antimicrobial-resistant Streptococcus pneumoniae, the binding affinity of antibiotics to targets mostly decreases compared to that in susceptible strains. The data on binding affinity of linezolid, clindamycin and vancomycin were insufficient. The higher drug concentration at the infection sites compared to that in the blood can be associated with inflammation conditions. Little evidence showed the effect of drug transporters on the clinical efficacy of antibiotics against LRTI.

CONCLUSIONS

Data on antibiotic penetration into the lung in LRTI patients and binding affinity of antibiotics for pneumococcal targets are still limited. Further studies are required to clarify the associations of the lung penetration and target binding ability of antibitotics with therapeutic efficacy to help propose the right antibiotics for LRTI.

Ways to Improve Insights into Clindamycin Pharmacology and Pharmacokinetics Tailored to Practice

Given the increase in bacterial resistance and the decrease in the development of new antibiotics, the appropriate use of old antimicrobials has become even more compulsory. Clindamycin is a lincosamide antibiotic approved for adults and children as a drug of choice for systemic treatment of staphylococcal, streptococcal, and gram-positive anaerobic bacterial infections. Because of its profile and high bioavailability, it is commonly used as part of an oral multimodal alternative for prolonged parenteral antibiotic regimens, e.g., to treat bone and joint or prosthesis-related infections. Clindamycin is also frequently used for (surgical) prophylaxis in the event of beta-lactam allergy. Special populations (pediatrics, pregnant women) have altered cytochrome P450 (CYP)3A4 activity. As clindamycin is metabolized by the CYP3A4/5 enzymes to bioactive N-demethyl and sulfoxide metabolites, knowledge of the potential relevance of the drug’s metabolites and disposition in special populations is of interest. Furthermore, drug–drug interactions derived from CYP3A4 inducers and inhibitors, and the data on the impact of the disease state on the CYP system, are still limited. This narrative review provides a detailed survey of the currently available literature on pharmacology and pharmacokinetics and identifies knowledge gaps (special patient population, drug–drug, and drug–disease interactions) to describe a research strategy for precision medicine.

Efficacy of Intraperitoneal Clindamycin in Refractory Peritonitis Report of Two Cases

Two patients on CAPD developed peritonitis refractory to antibiotics appropriate to the cultured organisms. In one case, cultures remained positive for the offending bacteria (Staphylococcus aureus) and, in the other, cultures of Enterobacter agglomerans rapidly became negative but signs and symptoms of peritonitis persisted. Empiric clindamycin therapy was associated with rapid resolution of peritonitis in both instances without necessitating catheter removal. We suggest that, in selected cases of refractory peritonitis, the addition of clindamycin may lead to clearing of the infection with preservation of the peritoneal catheter.

Delayed parasite elimination in human infections treated with clindamycin parallels ‘delayed death’ of Plasmodium falciparum in vitro

Clindamycin is safe and effective for the treatment of Plasmodium falciparum malaria, but its use as monotherapy is limited by unacceptably slow initial clinical response rates. To investigate whether the protracted action is due to an accumulative, time of exposure-dependent or a delayed effect on parasite growth, we studied the in vivo and in vitro pharmacodynamic profiles of clindamycin against P. falciparum. In vivo, elimination of young, circulating asexual parasite stages during treatment with clindamycin displayed an unusual biphasic kinetic: a plateau phase was followed by a precipitated decline of asexual parasite densities to nearly undetectable levels after 72 and 60 h in adult patients and asymptomatic children, respectively, suggesting an uninhibited capacity to establish a second, but not third, infectious cycle. In vitro, continuous exposure of a laboratory-adapted P. falciparum strain to clindamycin with concentrations of up to 100 microM for two replication cycles (96 h) did not produce inhibitory effects of >50% compared with drug-free controls as measured by the production of P. falciparum histidine-rich protein II (PfHRP2). PfHRP2 production was completely arrested after the second cycle (96-144h) (>10,000-fold decrease of mean half-inhibitory concentrations measured at 96-144h compared to 48-96h). Furthermore, incubation with clindamycin during only the first (0-48h) versus three (0-144h) parasite replication cycles led to comparable inhibition of PfHRP2 production in the third infectious cycle (96-144h) (mean IC(99) of 27 and 22nM, respectively; P=0.2). When parasite cultures were exposed to different concentrations of clindamycin ranging from 50 to 1,000nM for 72h and followed up in an experiment designed to simulate a typical 3-day treatment regimen, parasitaemia was initially suppressed below the microscopic detection threshold. Nonetheless, parasites reappeared in a dose-dependent manner after removal of drug at 72h but not in continuously drug-exposed controls. The delayed, but potent, antimalarial effect of clindamycin appears to be of greatest potential benefit in new combinations of clindamycin with rapidly acting antimalarial combination partners.

Influence on mitochondria and cytotoxicity of different antibiotics administered in high concentrations on primary human osteoblasts and cell lines

Osteomyelitis, osteitis, spondylodiscitis, septic arthritis, and prosthetic joint infections still represent the worst complications of orthopedic surgery and traumatology. Successful treatment requires, besides surgical débridement, long-term systemic and high-concentration local antibiotic therapy, with possible local antibiotic concentrations of 100 microg/ml and more. In this study, we investigated the effect of 20 different antibiotics on primary human osteoblasts (PHO), the osteosarcoma cell line MG63, and the epithelial cell line HeLa. High concentrations of fluoroquinolones, macrolides, clindamycin, chloramphenicol, rifampin, tetracycline, and linezolid during 48 h of incubation inhibited proliferation and metabolic activity, whereas aminoglycosides and inhibitors of bacterial cell wall synthesis did not. Twenty percent inhibitory concentrations for proliferation of PHO were determined as 20 to 40 microg/ml for macrolides, clindamycin, and rifampin, 60 to 80 microg/ml for chloramphenicol, tetracylin, and fluoroquinolones, and 240 microg/ml for linezolid. The proliferation of the cell lines was always less inhibited. We established the measurement of extracellular lactate concentration as an indicator of glycolysis using inhibitors of the respiratory chain (antimycin A, rotenone, and sodium azide) and glycolysis (iodoacetic acid) as reference compounds, whereas inhibition of the respiratory chain increased and inhibition of glycolysis decreased lactate production. The measurement of extracellular lactate concentration revealed that fluoroquinolones, macrolides, clindamycin, rifampin, tetracycline, and especially chloramphenicol and linezolid impaired mitochondrial energetics in high concentrations. This explains partly the observed inhibition of metabolic activity and proliferation in our experiments. Because of differences in the energy metabolism, PHO provided a more sensitive model for orthopedic antibiotic usage than stable cell lines.

Effects of furazolidone pretreatment of Salmonella enteritidis PT4 at sub- and suprainhibitory concentrations on phagocytosis and intracellular survival in chicken macrophages

The antimicrobial effect of the nitrofuran derivative furazolidone at sub- and suprainhibitory concentrations on Salmonella enteritidis PT4 and the influence with regard to interaction with avian macrophages was investigated in this study. Phagocytosis of furazolidone-sensitive (FzS) S. enteritidis with chicken macrophages in the presence of furazolidone at concentrations of 1/8, 1/4, 1/2 and 8x MIC resulted in an increase in the rate of phagocytic killing of approximately 3-, 6-, 6.5- and 9-fold, respectively, with 1/2 and 8x MIC concentrations producing statistically significant (P<0.05) increases in phagocytosis. Treatment of the FzS Salmonella with furazolidone at concentrations of 4x and 10x MIC, for 15 min prior to phagocytosis, also significantly (P<0.005) increased phagocytic uptake when compared with untreated bacteria. The rate of phagocytosis monitored over 90 min was highest between 30 and 60 min with the furazolidone pretreated salmonella, compared with the delayed rate of the control between 60 and 90 min. Exposure of FzS and FzR strains with suprainhibitory concentrations of furazolidone at 4x, 8x and 10x MIC for 30 min prior to phagocytosis demonstrated an increase in bacterial killing. Exposure of strains to sub-inhibitory concentrations of furazolidone led to an increase in chemiluminescence during phagocytosis with macrophages, suggesting an increase in oxidative metabolism in the macrophages as a result of an increase in activation and phagocytosis. Pretreatment of the strains with suprainhibitory concentrations of furazolidone for 30 min prior to phagocytosis demonstrated a similar increase in oxidative metabolism in the macrophages. Measurement of the amount of 14C-furazolidone associated with chicken macrophages was determined over 20 h incubation. The level of radioactivity of 14C-furazolidone alone was used to estimate the amount of cell-associated nitrofuran when incubated with the macrophages by means of regression analysis. Incubation with concentrations of 16, 32 and 64 microg/ml for 20 h resulted in the cell association of >or=1 microg/ml of furazolidone, which is the concentration required for the agent to exhibit bactericidal activity on furazolidone-sensitive Salmonella strains. Furazolidone was able to reduce intracellular salmonella viability at all concentrations, but total killing was achieved only with concentrations of >or=8 microg/ml, which supports the results for furazolidone association with the macrophages. This substantiates that the bioactivity of the nitrofuran was not inhibited or diminished in the intracellular environment of the macrophage and that exposure of salmonella to nitrofurans enhances phagocytosis.

Intracellular pharmacodynamics of antibiotics

This article establishes the pharmacokinetic-pharmacodynamic parameters that are important when considering the intracellular activity of antibiotics. Generally speaking, the main classes of antibiotics seem to share globally the same properties against extracellular and intracellular organisms. The specific cellular pharmacokinetic properties may modulate those parameters so as to let other ones to become critical. Simple rules, such as equating accumulation and activity, are certainly incorrect, and other determinants need to be added to the equation. Finally, this article emphasizes the fact that much remains to be done in this area before rational therapeutic choices can be made.

Characteristics and mechanisms of azithromycin accumulation and efflux in human polymorphonuclear leukocytes

Azithromycin achieves prolonged, high tissue concentrations in spite of low serum levels and obviously must be active at tissue sites of infection to be effective. These unique features prompted us to evaluate the interactions of azithromycin and human polymorphonuclear leukocytes (PMN). Uptake of radiolabeled antibiotic by PMN was determined by a velocity-gradient centrifugation technique and expressed as the ratio of cellular to extracellular drug concentration (C/E). Azithromycin was massively accumulated by human PMN (C/E=387.2 at 2 h). Uptake was not influenced by inhibitors of cellular metabolism, but phagocytosis slightly inhibited the entry of azithromycin into PMN. After removal of extracellular drug, the release (efflux) of azithromycin from PMN was extremely slow. Agents which neutralize lysosomal pH, preventing protonation and trapping of azithromycin, markedly increased antibiotic efflux. Active concentration and prolonged retention of azithromycin by phagocytic cells should allow delivery and subsequent release of accumulated drug at sites of infection.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Penetration of clindamycin and its metabolite N-demethylclindamycin into cerebrospinal fluid following intravenous infusion of clindamycin phosphate in patients with AIDS

Clindamycin, which is usually used in combination with pyrimethamine, has been proven effective in the treatment of cerebral toxoplasmosis in human immunodeficiency virus-infected patients. However, it is not known if clindamycin achieves inhibitory concentrations at the site of infection. Also, it has been hypothesized that the activity of clindamycin against Toxoplasma gondii may be due, at least in part, to a metabolite. We evaluated the penetration of clindamycin and its major metabolite, N-demethylclindamycin (NDC), into cerebrospinal fluid (CSF) of AIDS patients undergoing lumbar puncture for diagnostic purposes. A single, 1,200-mg dose of clindamycin was administered as a 45-min intravenous infusion beginning at 1.5 or 2.5 h before CSF sampling. The concentrations of clindamycin in CSF ranged from 0.091 to 0.429 mg/liter at 1.5 h and from 0.120 to 0.283 mg/liter at 2.5 h following the beginning of the infusion. The concentrations of clindamycin in CSF were well above the 50% inhibitory concentration of 0.001 mg/liter and the parasiticidal concentration of 0.006 mg/liter. NDC was undetectable both in plasma and in CSF. Our study provides a pharmacokinetic rationale for the clinical efficacy of clindamycin in the treatment of cerebral toxoplasmosis.

Optimum treatment of intracellular infection

The intracellular location of some micro-organisms has been early recognised as a critical point to explain failure of antibiotic therapy to eradicate such pathogens from infected hosts. Most often parasites invade 'professional' phagocytic cells, including neutrophils, monocytes and macrophages, by resisting the intracellular bactericidal phagolysosomal pathway. Alternatively, they may invade 'non-professional' phagocytic cells (cells with fewer phagocytic and bactericidal abilities) such as endothelial cells, or even cells without lysosomes such as erythrocytes. The intracellular activity of an antibiotic depends on several factors including its ability to reach the eukaryotic cell membrane, its subcellular localisation as compared to that of the parasite, the possibility that the intracellular milieu may partially inactivate its activity, and the susceptibility of the intracellular form of the parasite. In vitro and animal models have been developed to investigate antibiotic activity against intracellular pathogens. However, it should be emphasised that only data obtained from patients give reliable information to define the optimum antibiotic regimen.

Pharmacokinetics of antimicrobial agents in the respiratory tract

The ability of antibiotics to penetrate into the respiratory tract has been investigated at several sites, namely, sputum and bronchial secretions, tissue homogenates, pleural fluid and, more recently, epithelial lining fluid and alveolar macrophages. The major reason for such investigations is that these data may be helpful to a more thorough understanding of drug distribution in the lung tissue and fluids and to a more accurate prediction of clinical outcome. However, the study of drug concentration at each of these sites presents problems in terms of methodology and data interpretation. The advantages and disadvantages of each of these methods are considered, and the data on penetration of betalactams, aminoglycosides, macrolides, fluoroquinolones and other antimicrobial agents (including antifungal and antiprotozoan drugs) are reviewed.

Paradoxical effect of clindamycin in experimental, acute toxoplasmosis in cats

Cats were experimentally inoculated parenterally with the ME49 strain of Toxoplasma gondii to characterize the efficacies of two different dosages of orally administered clindamycin hydrochloride in the treatment of ocular toxoplasmosis. Concentrations of clindamycin hydrochloride at levels previously suggested to be inhibitory to T. gondii replication in vitro were achieved in the serum and aqueous humor but not in the cerebrospinal fluid. Antibiotic therapy, initiated 7 days after inoculation, resulted in no significant difference in the morphometric severity of ocular posterior segment lesions compared with that in the control groups. Treatment appeared to blunt T. gondii-specific immunoglobulin M production but had no significant effect on immunoglobulin G titers. Paradoxically, clindamycin administration was associated with increased morbidity and mortality from hepatitis and interstitial pneumonia, which are characteristic of generalized toxoplasmosis. Serum tumor necrosis factor alpha activity was detected at moderate levels in all groups of cats and correlated with the severity of clinical disease. The results of the study suggest that clindamycin, when administered at this specific time interval following inoculation, does not ameliorate ocular lesions and has a detrimental effect on the clinical course of acute, experimental toxoplasmosis in cats. The factors responsible for and the relevance of this detrimental effect to naturally occurring toxoplasmosis in humans and pet cats were not clear from the study but may relate to an antibiotic-associated decrease in the antitoxoplasmic activity of phagocytic cells responsible for the control of T. gondii.

Uptake and intracellular activity of NM394, a new quinolone, in human polymorphonuclear leukocytes

The uptake of NM394, a new quinolone, by and its subsequent elution from human polymorphonuclear leukocytes were studied and compared with those of ofloxacin and ciprofloxacin. The kinetics of the uptake of NM394 was similar to that of ciprofloxacin. The maximum intracellular-to-extracellular concentration ratio was 12.3, compared with 8.6 for ciprofloxacin and 4.9 for ofloxacin at the extracellular concentration of 20 micrograms/ml. The elution of NM394 from human polymorphonuclear leukocytes occurs relatively slowly; 5 min after the removal of extracellular NM394, nearly 100% still remained in polymorphonuclear leukocytes, compared with ofloxacin, which was so rapidly eluted that only 12% remained. The uptake of NM394 was significantly decreased at 4 degrees C and by the presence of NaCN but was not affected by the presence of L-glycine, L-leucine, L-serine, adenosine, or NaF. NM394 showed intracellular activity at a concentration of 0.1 microgram/ml that significantly reduced the number of phagocytosed Pseudomonas aeruginosa cells with 2 h of incubation. These results suggest that uptake of NM394 by human polymorphonuclear leukocytes occurs via an active transport system differing from that of ofloxacin, whose uptake is affected by the presence of L-glycine and L-leucine, and that once accumulated, NM394 remains intracellularly active and participates in protection against bacterial infection.

Uptake of azithromycin by various cells and its intracellular activity under in vivo conditions

The concentrations of azithromycin in polymorphonuclear leukocytes (PMNLs), monocytes, erythrocytes, and plasma were measured in six healthy volunteers after the last treatment of a 3-day regimen of 500 mg once daily. Marked enrichment of azithromycin was found in PMNLs and monocytes. The drug concentrations after the last dose amounted to 114 +/- 43 (mean +/- standard deviation) mg/liter at 12 h in PMNLs and 34 +/- 17 mg/liter at 6 h in monocytes. Fourteen days thereafter, azithromycin was still detectable in the PMNLs at 53 +/- 34 mg/liter and in the monocytes at 1 +/- 2 mg/liter, although the drug was no longer detectable in plasma (< 0.02 mg/liter). Maximum drug concentrations for azithromycin in plasma (0.40 +/- 0.30 mg/liter) and erythrocytes (0.15 +/- 0.05 mg/liter) at 3 h after the last administration were much lower and occurred earlier than those observed in the phagocytic cells. The mean enrichment factors (cellular/extracellular ratios) of azithromycin in phagocytes relative to plasma came to 231 +/- 150 and 3,924 +/- 584 at 3 and 120 h, respectively, for PMNLs and 83 +/- 55 and 523 +/- 285 at 3 and 120 h for monocytes, respectively, after the last dose. The phagocytosis tests with PMNLs separated from the blood of volunteers at various times after the last treatment confirmed the enhanced intracellular activity of these cells against staphylococci.

Influence of pentoxifylline and its derivatives on antibiotic uptake and superoxide generation by human phagocytic cells

Pentoxifylline modulates multiple activities of stimulated polymorphonuclear neutrophils (PMNs), including the respiratory burst response and membrane transport of certain substances (e.g., nucleosides). We found that several weakly basic antibiotics are highly concentrated by human PMNs and that these drugs also inhibit the respiratory burst response (by a mechanism different from that of pentoxifylline). Since both pentoxifylline and antibiotics will be administered to some patients with serious infections, we have evaluated several types of interactions between these drugs and human PMNs and have attempted to identify the mechanisms that produce alterations in cellular function. Roxithromycin, dirithromycin, and clindamycin were avidly concentrated by PMNs. Pentoxifylline and two derivatives (HWA-448 [torbafylline] and HWA-138 [albifylline]) increased the uptake of these antibiotics by PMNs, both in the resting state and during phagocytosis. Pentoxifylline, HWA-448, HWA-138, and the highly concentrated antibiotics each exerted an inhibitory effect on the stimulated respiratory burst response in PMNs. The combination of both pentoxifylline and a modulatory antibiotic (roxithromycin or clindamycin) inhibited superoxide production to a greater extent than either agent alone. This additive effect might be expected, since pentoxifylline and the modulatory antibiotics influence the respiratory burst activation pathway at different sites. The ability of pentoxifylline to augment the entry of antibiotics into neutrophils has important therapeutic implications. The consequences of this phenomenon might include improved intracellular bactericidal activity as well as efficient antibiotic delivery and release at sites of infection.

Antibiotics for pneumonia therapy

When treating any infectious disease, a physician selects an antimicrobial based on the following considerations: the in vitro activity of the drug, its pharmacokinetic properties, the efficacy data based on properly designed and conducted clinical trials, and finally the adverse effects. In this article, all of these factors, with the exception of adverse effects, were discussed. It was neither my intent nor my purpose to deal with side effects or adverse drug reactions because these are well covered in standard texts or physician references such as the Physicians' Desk Reference and the American Hospital Formulary Service (United States) and the Compendium of Pharmaceuticals and Specialties (Canada).

Intracellular concentrations of antibacterial agents and related clinical implications

Intracellular penetration, accumulation and disposition of antibacterial agents is crucial for effective treatment of infections caused by intracellular bacteria. Intracellular concentrations and locations of both antibacterials and bacteria remain poorly understood and further research is needed to establish the importance of these concepts. For example, concepts that have been shown to be important outcome predictors when applied to concentrations of antibacterial agents in the serum include: (i) the effect of the peak antibacterial serum concentration to minimum concentration inhibitory to 90% of organisms (MIC90) for bacteria; (ii) the effect of length of time the serum antibacterial concentration remains above the MIC90 curve; or (iii) the area under the MIC90 curve, but above the serum antibacterial concentration curve. Further research should determine whether or not these concepts have important applications in an intracellular environment. Intracellular pathogens have been increasingly contributing to respiratory infections in the community. Therefore, on the basis of intracellular activity against bacteria causing respiratory infections, macrolides are favoured as the most broad spectrum class of oral antibacterial agents available for the treatment of patients with community-acquired respiratory infections.

Interactions of dirithromycin with human polymorphonuclear leukocytes

Dirithromycin, a new macrolide antibiotic, achieves prolonged, high levels in tissue. We previously demonstrated that certain macrolides are highly concentrated within phagocytic cells. This background information prompted us to evaluate the interactions of dirithromycin and human polymorphonuclear leukocytes (PMNs). After incubation with radiolabeled dirithromycin, antibiotic uptake by PMNs was determined by a velocity-gradient centrifugation technique and was expressed as the ratio of the cellular to the extracellular drug concentration (C/E). Dirithromycin was avidly accumulated by PMNs (C/E, 5 at 15 min, 10 at 30 min, 19 at 1 h, and 35 at 2 h). Uptake was dependent on cell viability, physiologic environmental temperature, and pH (optimum 8.6), but was not influenced by potential competitive inhibitors of membrane transport. Incubation with sodium cyanide caused an increase in dirithromycin accumulation by PMNs. Ingestion of microbial particles (mimicking in vivo infection) modestly inhibited the entry of dirithromycin into PMNs. After removal of extracellular drug, the efflux (release) of dirithromycin from PMNs was slow; only 10% was released within the first 30 min. This prolonged retention of dirithromycin within phagocytic cells might allow delivery and release of accumulated drug at sites of infection. The impact of intraphagocytic dirithromycin on cellular function was also evaluated. In a manner similar to that of other highly concentrated, weakly basic antibiotics, dirithromycin inhibited the respiratory burst response (superoxide production) in stimulated PMNs. The presence of dirithromycin slightly increased the intraphagocytic killing of Staphylococcus aureus in human PMNs. These interactions of dirithromycin with phagocytic cells may promote the extraphagocytic, and possibly the intraphagocytic, killing of infecting organisms.

Comparative bronchoalveolar concentrations of ciprofloxacin and lomefloxacin following oral administration

In a comparative study, the concentrations of two fluoroquinolone antimicrobials, ciprofloxacin and lomefloxacin, were measured in serum, bronchial mucosal biopsies, epithelial lining fluid (ELF) and alveolar macrophages (AM). Thirty-four subjects received either ciprofloxacin 250 mg b.d. (17 subjects) or lomefloxacin 400 mg o.d. for 4 days prior to sampling by bronchoscopic bronchial biopsy and bronchoalveolar lavage. Both ciprofloxacin and lomefloxacin showed favourable accumulation in the sites of infection with bronchial biopsy concentrations of 1.6 and 1.7 times those of serum respectively; ELF concentrations of 2.1 and 1.9 times serum; and AM concentrations of 11.8 and 20.1 times serum respectively. The MIC90 for most of the common chest pathogens was reliably exceeded by both agents except for that of Streptococcus pneumoniae.

Uptake of itraconazole by alveolar macrophages

Itraconazole is a broad-spectrum potent triazole antifungal agent. Its efficacy in treatment cannot always be explained by body fluid drug levels. In this study, itraconazole was shown to accumulate into host cells. Its intracellular accumulation in cells is greater than that of the antibacterial agent clindamycin, which is known for intracellular localization, and the uptake process does not appear to be active. This ability to reach high concentrations intracellularly may be an important property for the in vivo efficacy of itraconazole.

Cellular uptake and activity of rufloxacin in different cell types and professional phagocytic cells

The penetration of the new quinolene rufloxacin into human professional phagocytic cells and different cell types was determined. The intracellular distribution was demonstrated in all cells studied. At 4 degrees C the transport of rufloxacin was reduced. An intracellular dose-dependent activity was demonstrated for rufloxacin in monocytes and granulocytes infected with E. coli and S. aureus. In all the experiments rufloxacin was able to eliminate all intracellular bacteria.

Pulmonary disposition of antimicrobial agents: methodological considerations

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Uptake and intracellular activity of sparfloxacin in human polymorphonuclear leukocytes and tissue culture cells

The penetration of sparfloxacin into human neutrophils (PMN) and different tissue culture cells (HEp-2 and McCoy) was evaluated. The cellular to extracellular concentration ratios (C/E) of sparfloxacin were always higher than 4 at extracellular concentrations ranging from 0.5 to 25 mg/liter. The uptake of sparfloxacin by PMN was rapid, nonsaturable, reversible, not energy dependent, and significantly reduced at pH 8. The penetration of this agent into PMN was similar when viable and Formalin-killed cells were used and was not affected by environmental temperature. Ingestion of opsonized zymosan significantly increased the amount of PMN-associated sparfloxacin. Sparfloxacin at a concentration of 0.5 mg induced a significant reduction in the survival of intracellular Staphylococcus aureus. It is concluded that sparfloxacin reaches intracellular concentrations within leukocytic cells much higher than extracellular concentrations, while remaining active intracellularly.

Activity of antibiotics against Staphylococcus aureus within polymorphonuclear neutrophils

The intracellular location of certain strains of Staphylococcus aureus serves as a reservoir of bacteria which is thought to be important in therapy of recurrent infections in humans and in chronic staphylococcal mastitis in dairy cows. This overview summarizes data pertaining to the intracellular survival of Staphylococcus aureus within polymorphonuclear neutrophils (PMNs) both in vitro and in vivo in the face of antibiotic treatment. While compounds such as rifampin, clindamycin, erythromycin, and ciprofloxacin have been shown to be rapidly taken up by PMNs, the ability of antibiotics to concentrate within PMNs did not strictly correlate with their ability to kill intracellular Staphylococcus aureus. Rifampin and ciprofloxacin have been shown to be the most effective intraphagocytic killing agents, while clindamycin and erythromycin were inactive in these in vitro assays. In vivo, in therapy of Staphylococcus aureus arthritis and peritonitis in humans and in certain mouse models rifampin has generally been shown to be more effective than comparator antibiotics. In a staphylococcal subcutaneous abscess model, however, clindamycin was very effective in curing the Staphylococcus aureus abscesses in this system where PMNs were the primary inflammatory cells involved. The intracellular bacterial counts decreased as rapidly as the extracellular bacteria. Rifampin was also effective in the abscess model but ciprofloxacin was ineffective at the highest doses tested. The relevance of in vitro and in vivo models and the importance of PMNs as a reservoir of infection in staphylococcal diseases in humans and the dairy cow are discussed.

Concentrations of temafloxacin in serum and bronchial mucosa

The bronchial mucosal concentrations of temafloxacin hydrochloride were determined in specimens obtained at fibreoptic bronchoscopy and compared with simultaneous serum concentrations. The 18 patients studied were given an oral dose of 400 mg b.i.d for three days to achieve steady state levels. The mean serum concentration was 6.9 mg/l (SD 2.5 mg/l) and the mean bronchial mucosal concentration 12.2 mg/kg (SD 4 mg/kg). The mucosal levels exceeded those required to inhibit most of the common respiratory pathogens, including Streptococcus pneumoniae and Pseudomonas aeruginosa. These data support the use of temafloxacin for therapy of bronchial infections.

Uptake of antibiotics by human polymorphonuclear leukocyte cytoplasts

Enucleated human polymorphonuclear leukocytes (PMN cytoplasts), which have no nuclei and only a few granules, retain many of the functions of intact neutrophils. To better define the mechanisms and intracellular sites of antimicrobial agent accumulation in human neutrophils, we studied the antibiotic uptake process in PMN cytoplasts. Entry of eight radiolabeled antibiotics into PMN cytoplasts was determined by means of a velocity gradient centrifugation technique. Uptakes of these antibiotics by cytoplasts were compared with our findings in intact PMN. Penicillin entered both intact PMN and cytoplasts poorly. Metronidazole achieved a concentration in cytoplasts (and PMN) equal to or somewhat less than the extracellular concentration. Chloramphenicol, a lipid-soluble drug, and trimethoprim were concentrated three- to fourfold by cytoplasts. An unusual finding was that trimethroprim, unlike other tested antibiotics, was accumulated by cytoplasts more readily at 25 degrees C than at 37 degrees C. After an initial rapid association with cytoplasts, cell-associated imipenem declined progressively with time. Clindamycin and two macrolide antibiotics (roxithromycin, erythromycin) were concentrated 7- to 14-fold by cytoplasts. This indicates that cytoplasmic granules are not essential for accumulation of these drugs. Adenosine inhibited cytoplast uptake of clindamycin, which enters intact phagocytic cells by the membrane nucleoside transport system. Roxithromycin uptake by cytoplasts was inhibited by phagocytosis, which may reduce the number of cell membrane sites available for the transport of macrolides. These studies have added to our understanding of uptake mechanisms for antibiotics which are highly concentrated in phagocytes.

Concentrations of oral lomefloxacin in serum and bronchial mucosa

The bronchial mucosal concentrations of lomefloxacin were determined for specimens obtained by fiber-optic bronchoscopy and compared with simultaneous concentrations in serum. The 23 patients studied were given an oral dose of 400 mg once daily for 4 days to achieve steady-state levels. The median concentration in serum was 2.5 micrograms/ml (range, 1.0 to 5 micrograms/ml), and the median bronchial mucosal concentration was 5.0 micrograms/g (range, 0.7 to 18.6 micrograms/g). The median percent penetration was 177% (range, 69 to 541%). The concentrations in serum and mucosa exceeded the MIC for 90% of strains of organisms causing bronchial infections but not sufficiently to recommend lomefloxacin for the routine treatment of pneumococcal infections.

Antibiotic inhibition of the respiratory burst response in human polymorphonuclear leukocytes

Recently we found that certain antibiotics which are markedly concentrated by human polymorphonuclear leukocytes (PMN) failed to kill susceptible, intraphagocytic Staphylococcus aureus, even though cellular drug levels were quite high. The possibility that specific antibiotics might adversely affect phagocyte antibacterial function was considered. Thus, we studied the effects of multiple antibiotics and adenosine, a known modulator of the PMN respiratory burst response, on neutrophil antibacterial function. At nontoxic concentrations, these drugs had no effect on degranulation in stimulated PMN. Adenosine was a potent inhibitor of formyl-methionyl-leucyl-phenylalanine (FMPL)-stimulated superoxide and hydrogen peroxide generation in PMN but produced less inhibition of microbial particle-induced respiratory burst activity. Three of the tested antibiotics, all of which reach high concentrations in phagocytic cells, had a marked modulatory effect on the PMN respiratory burst. Clindamycin, which enters phagocytes by the cell membrane adenosine (nucleoside) transport system, had only a modest effect on FMLP-mediated superoxide production but inhibited the microbial particle-induced response by approximately 50%. Roxithromycin and trimethoprim were efficient inhibitors of PMN superoxide generation stimulated by FMLP and concanavalin A (also inhibited by erythromycin) but had less effect on zymosan-mediated respiratory burst activity. Antibiotics which entered phagocytes less readily had no effect on the respiratory burst response in PMN. These results, as well as those of experiments with inhibitors of cell membrane nucleoside receptors, indicated that the antibiotic effect is mediated through intraphagocytic pathways. The possibility that antibiotic-associated inhibition of the PMN respiratory burst response might alter leukocyte antimicrobial and inflammatory function deserves further evaluation.

Fluorometric measurement of ofloxacin uptake by human polymorphonuclear leukocytes

A fluorometric assay, based on the natural fluorescence of the quinolone nucleus, was used to determine the uptake of ofloxacin by human polymorphonuclear leukocytes. The ratio of cellular concentration to extracellular concentration (C/E) at 20 min and 37 degrees C was 7.2, using an extracellular concentration of 5 micrograms/ml. Uptake was rapid and was not affected by pH (5 to 9), but required elevated environmental temperature and cell viability. The metabolic inhibitors sodium fluoride and sodium cyanide significantly decreased the uptake of ofloxacin. The penetration of ofloxacin was not affected by the presence of glucose or adenosine, but was decreased by L-amino acids (lysine, leucine, and glycine). These results suggest that ofloxacin could be transported via an amino acid transport system and that the fluorometric assay is a useful method for determining the intracellular penetration of fluoroquinolones, avoiding the use of radiolabeled antimicrobial agents.

Clindamycin for colonization and infection by methicillin-resistant Staphylococcus aureus

Effective antimicrobial therapy for infection or colonization by methicillin-resistant Staphylococcus aureus (MRSA) is very limited. In some institutions, the majority of strains remain susceptible to clindamycin in vitro. We report five patients with colonization or infection of varying severity caused by MRSA who had the organism successfully eradicated by clindamycin. In one patient who had an MRSA infection that persisted during vancomycin therapy clindamycin therapy was able to finally eradicate the organism. Clindamycin should be seriously considered as alternative therapy for colonization or infection by MRSA.

High-performance liquid chromatography measurement of antimicrobial concentrations in polymorphonuclear leukocytes

High-performance liquid chromatography was used to determine the penetration of 19 antimicrobial agents into human polymorphonuclear leukocytes. The ratios of the intracellular concentration to the extracellular concentration of ampicillin, piperacillin, cefazolin, ceftizoxime, cefpimizole, and ceftazidime were all less than 0.6. Lincomycin showed a high intracellular-to-extracellular ratio (3.0), while clindamycin achieved a ratio of 15.5, which was the highest ratio of all of the 19 tested antibiotics. Ratios for rifampin, isoniazid, chloramphenicol, and trimethoprim were 8.2, 1.1, 9.6, and 6.1, respectively. Six quinolone-class antimicrobial agents had ratios from 2.2 to 8.2. Flucytosine showed a penetration ratio of 4.6. Clindamycin uptake was temperature dependent and occurred best with live polymorphonuclear leukocytes; sodium fluoride, adenosine, and puromycin were inhibitory. The results obtained in this study correlate well with the results of other studies involving radioisotopic methods. This indicates that high-performance liquid chromatography is a useful method for determining the intracellular penetration of antimicrobial agents.

Entry of roxithromycin (RU 965), imipenem, cefotaxime, trimethoprim, and metronidazole into human polymorphonuclear leukocytes

Entry of antibiotics into phagocytes is necessary for activity against intracellular organisms. Therefore, we examined the uptake of five of the newer antibiotics--roxithromycin (RU 965), imipenem, cefotaxime, trimethoprim, and metronidazole--by human polymorphonuclear leukocytes (PMN). Antibiotic uptake by PMN was determined by a velocity gradient centrifugation technique and expressed as the ratio of the cellular concentration of antibiotic to the extracellular concentration (C/E). Cefotaxime, like other beta-lactam antibiotics, was taken up poorly by phagocytes (C/E less than or equal to 0.3). The metronidazole concentration within PMN was similar to the extracellular level. Imipenem bound rapidly to phagocytes (C/E = 3), but cell-associated drug progressively declined during the incubation period. Trimethoprim was well concentrated by PMN (C/E = 9 to 13), and uptake was unexpectedly greater at 25 degrees C than at 37 degrees C. The most striking finding was that roxithromycin was more avidly concentrated by PMN (C/E = 34) than any other antibiotic we studied. Entry of roxithromycin into phagocytes was an active process and displayed saturation kinetics characteristic of a carrier-mediated membrane transport system. Ingestion of microbial particles by PMN slightly decreased the ability of these cells to accumulate roxithromycin (C/E = 24 to 31). These studies identified two antibiotics, trimethoprim and especially roxithromycin, which are markedly concentrated within human PMN and may prove useful in treatment of infections caused by susceptible intracellular organisms.

Pulmonary disposition of roxithromycin (RU 28965), a new macrolide antibiotic

The penetration of roxithromycin (RU 28965), an ether oxime derivative of erythromycin, into the cells and fluid lining the epithelial surface of the lower respiratory tract was studied by performing fiber-optic bronchoscopy with bronchoalveolar lavage on eight patients who had received roxithromycin at 300 mg perorally every 12 h for 5 days. The apparent volume of epithelial lining fluid recovered by bronchoalveolar lavage was determined by using urea as an endogenous marker. There was a significant relationship (r = 0.75; P less than 0.02) between roxithromycin levels in plasma and epithelial lining fluid, with a correlation whose slope suggested that the level of drug penetration into the lining fluid was 0.2. Concentrations of the antibiotic in cells recovered by bronchoalveolar lavage (21 +/- 10 micrograms/ml) were 2 and 10 times higher than in plasma (11.4 +/- 5.7 micrograms/ml) and epithelial lining fluid (2.0 +/- 1.7 micrograms/ml), respectively. Thus, when administered perorally in humans, roxithromycin is markedly accumulated by resident alveolar macrophages in concentrations largely exceeding the MBCs of the drug for most facultative intracellular pathogens including Legionella pneumophila, despite low concentrations in the epithelial lining fluid.

Effect of phagocyte membrane stimulation on antibiotic uptake and intracellular bactericidal activity

Phagocytosis stimulated a substantial increase in clindamycin uptake and a smaller increase in rifampin accumulation by polymorphonuclear leukocytes. The effect of this increased antibiotic uptake on intraphagocytic bactericidal activity was evaluated. Although zymosan stimulated antibiotic uptake by polymorphonuclear leukocytes, neither zymosan nor formyl-methionyl-leucyl-phenylalanine enhanced the ability of clindamycin or rifampin to kill ingested staphylococci. Properties other than antibiotic uptake are important in determining intraphagocytic bactericidal activity.

Contrasts between phagocyte antibiotic uptake and subsequent intracellular bactericidal activity

An ideal antibiotic for therapy of infections due to facultative intracellular organisms would enter phagocytes readily and kill intracellular bacteria. We have examined the consequences of antibiotic uptake by human polymorphonuclear lymphocytes (PMN) on intraphagocytic bactericidal activity, using antibiotics which differ markedly in their ability to enter PMN. After ingestion of Staphylococcus aureus, PMN were evaluated in regard to uptake of antibiotics and survival of intraphagocytic bacteria in the presence or absence of these drugs. Except for erythromycin, the uptake of which was slightly decreased, the entry of tested antibiotics into PMN was increased or unchanged after ingestion of S. aureus. Clindamycin and erythromycin, which achieved high cellular levels in PMN, failed to produce a significant reduction in viable intraphagocytic S. aureus during 3 h of antibiotic exposure. In contrast, rifampin, which was concentrated severalfold by phagocytes, was able to kill intracellular staphylococci. Gentamicin and penicillin G penetrated PMN rather poorly. However, while gentamicin demonstrated efficient intraphagocytic killing of bacteria, penicillin had no intracellular effect during the 3-h incubation period. These observations document that the ability to enter phagocytes is only one of the factors which determine the intracellular antibacterial activity of an antibiotic.

Antibiotic uptake by alveolar macrophages of smokers

Cigarette smoking, particularly when associated with chronic pulmonary disease, increases the risk of respiratory tract infection. Thus, we elevated the uptake of antibiotics by alveolar macrophages (AM) obtained by bronchoalveolar lavage from persons who smoke and have associated pulmonary abnormalities, circumstances which adversely affect certain macrophage functions. The entry of radiolabeled drugs into AM was determined by a velocity-gradient centrifugation technique, and uptake was expressed as the ratio of cellular to extracellular antibiotic concentration (C/E). Cefamandole and penicillin G were taken up poorly by the AM obtained from smokers (C/E less than or equal to 1). Cellular levels of isoniazid, gentamicin, and tetracycline were similar to their extracellular concentrations. The lipid-soluble drugs lincomycin, chloramphenicol, and rifampin were concentrated severalfold by the AM from smokers (C/E = 3 to 11). Ethambutol also entered macrophages readily (C/E = 11). Erythromycin and clindamycin were massively concentrated by the AM from smokers (C/E = 23 to 56). The AM of smokers accumulated a lipid-soluble antibiotic (rifampin) and actively transported agents (erythromycin propionate, clindamycin) more avidly than did the AM of nonsmokers. Augmented uptake of these antibiotics by the AM of smokers may be related to structural and functional alterations induced by smoking.

New micromethod to study the effect of antimicrobial agents on Toxoplasma gondii: comparison of sulfadoxine and sulfadiazine individually and in combination with pyrimethamine and study of clindamycin, metronidazole, and cyclosporin A

An in vitro method by which reagents, cells, and Toxoplasma gondii trophozoites are conserved (micromethod) was developed to quantitate the effect of antimicrobial agents on T. gondii. Sulfadoxine alone had no effect on T. gondii in vitro when evaluated with a macromethod, the new micromethod, or visual inspection of Giemsa-stained preparations. Sulfadoxine combined with pyrimethamine inhibited T. gondii more than did pyrimethamine alone, but the combination of sulfadoxine plus pyrimethamine was slightly less active than was the combination of sulfadiazine plus pyrimethamine. Neither clindamycin nor metronidazole, alone or in combination with sulfadiazine or pyrimethamine and sulfadiazine, had any effect on intracellular T. gondii. Brief exposure (10 min before and during challenge) to clindamycin had no effect on extracellular T. gondii when clindamycin was studied alone or with sulfadiazine or pyrimethamine plus sulfadiazine. Cyclosporin A inhibited T. gondii replication at concentrations of ca. greater than or equal to 2 micrograms/ml.

Influence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin on Staphylococcus aureus growth in human phagocytic cells

After an initial 2-h incubation with phagocytic cells, the growth of surviving intracellular Staphylococcus aureus was examined in the presence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin. One-tenth of the minimal inhibitory concentrations of these antibiotics markedly reduced bacterial growth in normal polymorphonuclear leukocytes. In contrast, when human alveolar macrophages were studied, no inhibition of growth was seen. Subinhibitory concentrations of these antibiotics and polymorphonuclear leukocytes acted synergistically to reduce intracellular survival of S. aureus. This synergy did not appear to be dependent upon the microbicidal potential of the leukocyte respiratory burst, since no differences were found when polymorphonuclear leukocytes obtained from patients with chronic granulomatous disease were compared with those from normal donors.