Paul M. Tulkens

Aminoglycosides: Activity and Resistance

Aminoglycosides are highly potent, broad-spectrum antibiotics with many desirable properties for the treatment of life-threatening infections ([28][1]). Their history begins in 1944 with streptomycin and was thereafter marked by the successive introduction of a series of milestone compounds (

Tackling antibiotic resistance

The development and spread of antibiotic resistance in bacteria is a universal threat to both humans and animals that is generally not preventable but can nevertheless be controlled, and it must be tackled in the most effective ways possible. To explore how the problem of antibiotic resistance might best be addressed, a group of 30 scientists from academia and industry gathered at the Banbury Conference Centre in Cold Spring Harbor, New York, USA, from 16 to 18 May 2011. From these discussions there emerged a priority list of steps that need to be taken to resolve this global crisis.

Antibiotic efflux pumps.

Active efflux from procaryotic as well as eucaryotic cells strongly modulates the activity of a large number of antibiotics. Effective antibiotic transport has now been observed for many classes of drug efflux pumps. Thus, within the group of primary active transporters, predominant in eucaryotes, six families belonging to the ATP-binding cassette superfamily, and including the P-glycoprotein in the MDR (Multi Drug Resistance) group and the MRP (Multidrug Resistance Protein), have been recognized as being responsible for antibiotic efflux. Within the class of secondary active transporters (antiports, symports, and uniports), ten families of antibiotic efflux pumps have been described, distributed in five superfamilies [SMR (Small Multidrug Resistance), MET (Multidrug Endosomal Transporter), MAR (Multi Antimicrobial Resistance), RND (Resistance Nodulation Division), and MFS (Major Facilitator Superfamily)]. Nowadays antibiotic efflux pumps are believed to contribute significantly to acquired bacterial resistance because of the very broad variety of substrates they recognize, their expression in important pathogens, and their cooperation with other mechanisms of resistance. Their presence also explains high-level intrinsic resistances found in specific organisms. Stable mutations in regulatory genes can produce phenotypes of irreversible multidrug resistance. In eucaryotes, antibiotic efflux pumps modulate the accumulation of antimicrobials in phagocytic cells and play major roles in their transepithelial transport. The existence of antibiotic efflux pumps, and their impact on therapy, must now be taken fully into account for the selection of novel antimicrobials. The design of specific, potent inhibitors appears to be an important goal for the improved control of infectious diseases in the near future.

Effect of a collaborative approach on the quality of prescribing for geriatric inpatients: a randomized, controlled trial.

OBJECTIVES: To evaluate the effect of pharmaceutical care provided in addition to acute Geriatric Evaluation and Management (GEM) care on the appropriateness of prescribing.

Mechanism of aminoglycoside-induced lysosomal phospholipidosis: In vitro and in vivo studies with Gentamicin and Amikacin

Gentamicin, a widely used aminoglycoside antibiotic, is concentrated in lysosomes of proximal tubular cells of the kidney, and induces therein an accumulation of myelin-like material. We show that treatment of rats with Gentamicin (10 mg/kg, 7 days) induces a loss of activity of lysosomal sphingomyelinase and phospholipase A1, associated with an increase in the amount of total lipid phosphorus in the kidney cortex. In vitro, Gentamicin is shown by gel permeation to bind to phospholipid bilayers (liposomes) under conditions which mimic the lysosomal environment (acid pH and presence of phosphatidylinositol). The reversal of this binding by an increase in the ionic strength (less than 0.04) suggests electrostatic interaction between the hydrophilic, polycationic aminoglycoside and the negatively charged phospholipids. Binding of Gentamicin impairs the hydrolysis of phosphatidylcholine present in the bilayer, by lysosomal phospholipases A1 and A2 from the liver or kidney. We also show that lysosomal sphingomyelinase is readily and irreversibly inactivated by liposomes in the absence of detergent. The lysosomal phospholipidosis induced by Gentamicin in the kidney, as in cultured cells [Aubert-Tulkens et al., Lab. Invest. 40, 481 (1979)] appears therefore to be a direct consequence of the lysosomotropic character of this drug and its ability to inhibit therein phospholipid breakdown. Amikacin, a semi-synthetic aminoglycoside, binds more loosely to phospholipid bilayers, induces less inhibition of phospholipases in vitro and is less taken up by tubular cells in vivo. Accordingly, Amikacin does not provoke significant lysosomal phospholipidosis or loss of sphingomyelinase and phospholipase A1 activities in vivo at the doses and time investigated (0-40 mg/kg, 7 days). Inasmuch as Amikacin is reported to be less toxic to the kidney, we suggest that lysosomal alterations are an early and significant step in aminoglycoside-induced nephrotoxicity.

Intracellular distribution and activity of antibiotics.

Intracellular penetration, accumulation and disposition are important parameters governing the activity of antibiotics against intracellular bacteria. Beta-lactams diffuse into but do not accumulate in phagocytes, probably because of their acidic character. Aminoglycosides are too polar to pass across membranes and are therefore only taken up slowly by endocytosis, which results in an exclusively lysosomal localization. Lincosaminides, macrolides and fluoroquinolones all accumulate in phagocytes, the two former classes of drugs showing both a cytosolic and a lysosomal localization. Fluoroquinolones appear to be entirely soluble in cells. Analysis of their activity in a model ofStaphylococcus aureus-infected J774 macrophages has revealed low activity of clindamycin, whereas macrolides, and even more so fluoroquinolones, easily reduce the original inoculum.

Pharmacodynamic evaluation of the intracellular activities of antibiotics against Staphylococcus aureus in a model of THP-1 macrophages

ABSTRACT The pharmacodynamic properties governing the activities of antibiotics against intracellular Staphylococcus aureus are still largely undetermined. Sixteen antibiotics of seven different pharmacological classes (azithromycin and telithromycin [macrolides]; gentamicin [an aminoglycoside]; linezolid [an oxazolidinone]; penicillin V, nafcillin, ampicillin, and oxacillin [β-lactams]; teicoplanin, vancomycin, and oritavancin [glycopeptides]; rifampin [an ansamycin]; and ciprofloxacin, levofloxacin, garenoxacin, and moxifloxacin [quinolones]) have been examined for their activities against S. aureus (ATCC 25923) in human THP-1 macrophages (intracellular) versus that in culture medium (extracellular) by using a 0- to 24-h exposure time and a wide range of extracellular concentrations (including the range of the MIC to the maximum concentration in serum [Cmax; total drug] of humans). All molecules except the macrolides caused a net reduction in bacterial counts that was time and concentration/MIC ratio dependent (four molecules tested in detail [gentamicin, oxacillin, moxifloxacin, and oritavancin] showed typical sigmoidal dose-response curves at 24 h). Maximal intracellular activities remained consistently lower than extracellular activities, irrespective of the level of drug accumulation and of the pharmacological class. Relative potencies (50% effective concentration or at a fixed extracellular concentration/MIC ratio) were also decreased, but to different extents. At an extracellular concentration corresponding to their Cmaxs (total drug) in humans, only oxacillin, levofloxacin, garenoxacin, moxifloxacin, and oritavancin had truly intracellular bactericidal effects (2-log decrease or more, as defined by the Clinical and Laboratory Standards Institute guidelines). The intracellular activities of antibiotics against S. aureus (i) are critically dependent upon their extracellular concentrations and the duration of cell exposure (within the 0- to 24-h time frame) to antibiotics and (ii) are always lower than those that can be observed extracellularly. This model may help in rationalizing the choice of antibiotic for the treatment of S. aureus intracellular infections.

Glycopeptide antibiotics: from conventional molecules to new derivatives.

Vancomycin and teicoplanin are still the only glycopeptide antibiotics available for use in humans. Emergence of resistance in enterococci and staphylococci has led to restriction of their use to severe infections caused by Gram-positive bacteria for which no other alternative is acceptable (because of resistance or allergy). In parallel, considerable efforts have been made to produce semisynthetic glycopeptides with improved pharmacokinetic and pharmacodynamic properties, and with activity towards resistant strains. Several molecules have now been obtained, helping to better delineate structure-activity relationships. Two are being currently evaluated for skin and soft tissue infections and are in phases II/ III. The first, oritavancin (LY333328), is the 4′-chlorobiphenylmethyl derivative of chloroeremomycin, an analogue to vancomycin. It is characterised by: i) a spectrum covering vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA) and to some extent glycopeptide-intermediate S. aureus (GISA); ii) rapid bactericidal activity including against the intracellular forms of enterococci and staphylococci; and iii) a prolonged half-life, allowing for daily administration. The second molecule is dalbavancin (BI397), a derivative of the teicoplanin analogue A40926. Dalbavancin has a spectrum of activity similar to that of oritavancin against vancomycin-sensitive strains, but is not active against VRE. It can be administered once a week, based on its prolonged retention in the organism. Despite these remarkable properties, the use of these potent agents should be restricted to severe infections, as should the older glycopeptides, with an extension towards resistant or poorly sensitive bacteria, to limit the risk of potential selection of resistance.

Renal cell apoptosis induced by nephrotoxic drugs: cellular and molecular mechanisms and potential approaches to modulation

Apoptosis plays a central role not only in the physiological processes of kidney growth and remodeling, but also in various human renal diseases and drug-induced nephrotoxicity. We present in a synthetic fashion the main molecular and cellular pathways leading to drug-induced apoptosis in kidney and the mechanisms regulating it. We illustrate them using three main nephrotoxic drugs (cisplatin, gentamicin, and cyclosporine A). We discuss the main regulators and effectors that have emerged as key targets for the design of therapeutic strategies. Novel approaches using gene therapy, antisense strategies, recombinant proteins, or compounds obtained from both classical organic and combinatorial chemistry are examined. Finally, key issues that need to be addressed for the success of apoptosis-based therapies are underlined.

Comparative Stability Studies of Antipseudomonal β-Lactams for Potential Administration through Portable Elastomeric Pumps (Home Therapy for Cystic Fibrosis Patients) and Motor-Operated Syringes (Intensive Care Units)

ABSTRACT The stability of antipseudomonal β-lactams in concentrated solutions was examined in view of their potential administration by continuous infusion with external pumps (for intensive care patients) or with portable pumps carried under clothing (for cystic fibrosis patients). Aztreonam (100 g/liter), piperacillin (128 g/liter, with tazobactam), and azlocillin (128 g/liter) remained 90% stable for up to more than 24 h at 37°C (mezlocillin [128 g/liter] was stable at 25°C but not at 37°C). Ceftazidime (120 g/liter), cefpirome (32 g/liter), and cefepime (50 g/liter) remained 90% stable for up to 24, 23.7, and 20.5 h at 25°C but only for 8, 7.25, and 13 h at 37°C, respectively. The control of temperature therefore appears to be critical for all three cephalosporins that cannot be recommended for use in portable pumps carried under clothes for prolonged periods for reasons of stability. Cefpirome and cefepime solutions developed an important color change (from light yellow to dark red) upon exposure when stored at 30°C or higher. Degradation of ceftazidime was accompanied by the liberation of pyridine which, at 37°C, was in excess of what is allowed by the U.S. Pharmacopeia, i.e., 1.1 mg/liter, after 8 and 12 h for drug concentrations of 12 and 8.3%, respectively. Imipenem and meropenem are too unstable (10% degradation at 25°C after 3.5 and 5.15 h, respectively) to be recommended for use by continuous infusion. Faropenem, examined in comparison with imipenem and meropenem, proved as stable as aztreonam or piperacillin.