[Mechanisms of azithromycin accumulation and efflux in human polymorphonuclear leukocytes]. / Mekhanizmy nakopleniia i vybrosa azitromitsina v polimorfnoiadernykh leikotsitakh cheloveka.

Azithromycin achieves prolonged, high tissue concentrations in spite of low serum levels and obviously must be effective at tissue sites of infection. 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.

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.

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.

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.

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.

Pentoxifylline modulation of plasma membrane functions in human polymorphonuclear leukocytes.

Pentoxifylline is known to have major effects on cell membrane function in mammalian cells, including human leukocytes. The protective effects of this agent in animal models of infection and inflammation may be due to alterations in phagocyte (neutrophil and macrophage) function. However, the exact mechanism of action of pentoxifylline is unknown. In this study, we evaluated the effect of the drug on several membrane-associated activities in human polymorphonuclear neutrophils and investigated possible mechanisms for the observed changes in neutrophil function. Pentoxifylline inhibited ingestion of microbial particles (Staphylococcus aureus and zymosan); decreased superoxide generation activated by zymosan, formyl-methionyl-leucyl-phenylalanine, and concanavalin A (but not phorbol myristate acetate); and decreased uptake (transport) of adenosine stimulated by formyl-methionyl-leucyl-phenylalanine and zymosan. In contrast, pentoxifylline actually increased clindamycin uptake in zymosan-stimulated polymorphonuclear neutrophils. However, pentoxifylline had no effect on uptake of adenosine or clindamycin in unstimulated neutrophils. In comparison with known inhibitors of nucleoside transport (nitrobenzylthioinosine and dipyridamole), the results suggested that pentoxifylline does not bind to membrane nucleoside transport receptors. At concentrations which inhibit neutrophil function, pentoxifylline activity is not mediated through external membrane nucleoside regulatory sites. Thus, pentoxifylline affects the activation signal chain at a point beyond the membrane receptors. Whatever its precise mechanism of action, pentoxifylline has a striking modulatory effect on cell membrane-associated responses in stimulated leukocytes and may prove useful for control of injurious inflammatory states.

PharmaTrend as a management tool: experience with the program.

A hospital's experiences with two pharmacy workload measurement systems, PharmaTrend and the pharmacy productivity unit (PPU) system it replaced at the institution, are compared. In 1976 a 352-bed general acute-care hospital implemented the locally developed PPU system. Typical drug distribution-related activities were defined and were assigned standard times per work unit; miscellaneous activities were assigned constant times per month. The PPU system served the institution well but had three important limitation: (1) new pharmaceutical services were not adequately represented, (2) the data collected had to be manually manipulated in order to calculate indicators, and (3) it was not possible to compare the data with those of similar institutions. In January 1988 the hospital implemented PharmaTrend. PharmaTrend was found to be a useful management tool because of the relative ease of data collection and the system's report-generation capabilities. By combining pharmacy workload data (including non-drug-distribution-related components) with data on finance, personnel hours, and patient admissions, PharmaTrend calculated indicators that were used for determining staffing and other needs and for financial reporting. The limitations of the PPU system were eliminated, except that it was still not possible to make valid comparisons with other hospitals because of the small number of participating hospitals that consistently report data to the PharmaTrend database. PharmaTrend offers advantages over previous pharmacy workload-monitoring systems by allowing for the expanded analysis and application of data.

Implementation of a modified decentralized drug distribution system with the use of master medication carts.

A decentralized drug distribution system with the use of master medication carts was implemented. This system was designed so that roving pharmacists could dispense new medication orders quickly and develop a more personal means of nurse-pharmacist interaction for the benefit of better patient care. The key to the system using roving pharmacists is a master medication cart, a pharmacy dispensing unit on wheels, which travels to each nursing unit. The pharmacy medication profiles are kept with the cart, and at each nursing unit patient medication profiles are reviewed, new drug orders are filled, missing medications and discrepancies are resolved, and nurse-pharmacist consultations can take place. There are two roving pharmacists who make simultaneous rounds of all nursing units in the hospital with two similarly stocked master medication carts from 9 A.M. to 9 P.M., seven days a week. All unit dose drawers are filled in the central pharmacy and are exchanged once daily at 2 A.M. by the night pharmacy technician. Each master medication cart carries about 300 different medications, which comprise nearly 95% of the drug needs of the 340 patients served by the two medication carts. The pharmacy department has added 1.4 Full-Time Equivalent (FTE) registered pharmacists and eliminated 2.8 FTE pharmacy messengers in implementing the decentralized drug distribution system. Currently, three registered pharmacists per day are assigned to the inpatient unit dose drug distribution system (two roving pharmacists and one unit dose filling pharmacist). Our roving pharmacists play a vital role in improving patient care. The overwhelming support by the nursing and medical staff represents an attempt by the hospital to continue to provide an optimal health care delivery system.