Inhibitory effect of heparin on gentamicin concentrations in blood

Retrospective evaluation of in vitro effect of gentamicin B1 against Fusarium species

The in vitro susceptibility of gentamicin fractions against Fusarium growth was the subject of this retrospective study. Fusariosis was earlier an exceptionally rare human disease and an unrealistic idea to treat soil saprophytes and plant pathogens with expensive antibiotics such as gentamicins or their minor components. Disseminated fusariosis is now the second most frequent lethal fungal infection after aspergillosis especially in neutropenic patients with hematologic malignancy. Results of this study obtained between May and November 1973 were interesting but not practicable and remained unpublished. Seven Fusarium and 28 other fungal strains were tested for their susceptibility to gentamicin B1. The anti-Fusarium activity of gentamicin B1 was between 0.2 and 3.1 μg/ml minimum inhibitory concentration (MIC) values. The MIC values of clotrimazol and amphotericin B against Fusarium species were significantly higher, 3.1-12.5 μg/ml and 3.1-50 μg/ml, respectively. Gentamicin B1 and its structurally related congeners including hygromycin B, paromomycin, tobramycin (nebramycin factor 5'), nebramycin (nebramycin factor 4), and sisomicin exerted strong in vitro inhibition against Fusarium species between 0.2 and 12.5 μg/ml concentrations. The antibacterial MIC concentration of gentamicin B1 tested on 20 bacterial strains ranged between 0.1 and 50 μg/ml. Gentamicin B1, a minor fraction of the gentamicin complex, inhibited effectively the growth of Gram-positive (Staphylococcus, Streptococcus, Bacillus subtilis) bacteria and Gram-negative (Escherichia coli, Salmonella, Proteus, Pseudomonas) pathogens. Gentamicins and related aminoglycoside antibiotics are used in medical practice. It is proposed that due to the increasing incidence of fusariosis and drug resistance, gentamicin components, particularly minor fraction B1 and related aminoglycoside antibiotics, could be tested for their in vivo activity against fusariosis and aspergillosis either alone or in combination with other antifungal agents.

Benefits and harms of citrate locking solutions for hemodialysis catheters: a systematic review and meta-analysis

BACKGROUND

Citrate has theoretical advantages over heparin for locking hemodialysis central venous catheters (CVCs), but the comparative effectiveness of these agents is not clear.

OBJECTIVES

1) To compare the benefits and harms of citrate versus heparin locking solutions among patients undergoing hemodialysis through CVCs; 2) to appraise methodological quality of the supporting evidence.

DATA SOURCES

CENTRAL, MEDLINE, EMBASE, CINAHL, ISI Web of Science, and nephrology conference abstracts.

STUDY ELIGIBILITY PARTICIPANTS AND INTERVENTIONS

We included randomized, parallel arm clinical trials that enrolled adult patients (>18 years) receiving chronic hemodialysis through CVCs using a citrate locking solution. We excluded studies in which citrate was combined with other agents, such as antibiotics.

APPRAISAL AND SYNTHESIS METHODS

We used the GRADE approach to systematic reviews and quality appraisal. Two reviewers performed data extraction independently and in duplicate. We pooled count data using generic inverse variance with random-effects models, and used fixed-effect models when only two studies were available for pooling. Subgroups included low (≤5%) vs. higher (≥30%) citrate.

RESULTS

We screened 600 citations. Forty-one proceeded to full-text screen; 5 met inclusion criteria. Studies included between 19 and 291 participants (Median N = 61) followed for a total of 174.6 catheter-years; 2 were multi-centred trials. Three studies assessed all-cause mortality; the pooled relative risk for death was 0.71 (95% CI = 0.42-1.24; p = 0.21; I(2) = 0%). The rate ratio for bacteremic episodes was 0.54 (95% CI = 0.23-1.29; p = 0.16; I(2) = 65%) while the rate ratio for bleeding was 0.48 (95% CI = 0.3-0.75; p = 0.001;I I(2) = 5%). Rates of catheter exchange/replacement, all-cause hospitalization and in-situ thrombolysis were not significantly different between groups in any of the pooled analyses. Risk of bias within pooled studies was low.

LIMITATIONS

Outcome definitions varied across studies. Imprecision due to small sample sizes and low event rates reduce our overall confidence in the pooled effect estimates.

IMPLICATIONS

Benefits and harms of citrate vs. heparin locking solutions remain unclear; larger studies and standardization of outcome measurement and reporting are warranted.

TRIAL REGISTRATION

Protocol Registration Number: CRD42013004781.

Effect of antimicrobial locks for tunneled hemodialysis catheters on bloodstream infection and bacterial resistance: a quality improvement report

BACKGROUND

Catheter-restricted antimicrobial lock (AML) use reduces catheter-associated bloodstream infection (CA-BSI) in clinical trial settings, but may not be as effective in clinical settings and may increase bacterial resistance.

DESIGN

Quality improvement report analyzed using a cross-sectional time series (unbalanced panel) design.

SETTING & PARTICIPANTS

The study cohort comprised all prevalent adults treated with hemodialysis through a tunneled catheter for any, but not necessarily all, of the time from January 1, 2003, to June 30, 2006, in Manukau City, New Zealand (135,346 catheter-days, 404 tunneled catheters, 320 patients).

QUALITY IMPROVEMENT PLAN

Catheter-restricted AMLs (heparin plus gentamicin) for all tunneled catheters from July 1, 2004.

MEASURES

Repeated observations of CA-BSI, hospitalization, tunneled catheter removal, and death from CA-BSI analyzed by using generalized estimating equations with a single level of clustering for each tunneled catheter and patterns of bacterial resistance analyzed by using simple descriptive statistics.

RESULTS

AML use was associated with reductions in rates of CA-BSI and hospitalization for CA-BSI by 52% and 69% for patients with tunneled catheters locked continuously with AMLs since their insertion compared with those with tunneled catheters that were not, respectively. AML exposure also was associated with a trend to increased gentamicin resistance amongst coagulase-negative staphylococci isolates, a pattern similar to that observed for BSIs in our general hemodialysis population in which tunneled catheters were not the source of BSI, but different from that in the general non-end-stage renal disease population in the region.

LIMITATIONS

This is an uncontrolled observational study and cannot prove causality. The follow-up period of 18 months is longer than for other studies, but still too short to definitely answer whether AML use drives bacterial resistance.

CONCLUSIONS

A change to use of AMLs may improve clinical outcomes; however, additional study of associated bacterial resistance is needed before AML use becomes standard care.

Antimicrobial locks: putting the lock on catheter infections

Infectious complications resulting from catheter use in the hemodialysis population remain as the significant cause of morbidity and mortality in this patient population. Because conservation of vascular access sites remains a therapeutic mainstay for chronic hemodialysis patients, clinical investigators have evaluated the safety and efficacy of catheter preservation with antimicrobial lock solutions instilled into the lumens of catheters to treat and prevent infectious complications. The recommended treatment of catheter-related bacteremia includes administration of systemic antibiotics with catheter removal. To date, 4 studies in the hemodialysis population have evaluated the use of systemic antibiotics with an antimicrobial lock solution for treatment of catheter-related bacteremias to amplify the success of catheter salvage. The use of antimicrobial lock solutions for the treatment of catheter-related bacteremia has resulted in successful catheter salvage in approximately 69% of patients, with the remainder requiring catheter removal following a lack of clinical improvement after 48 hours. The antimicrobial lock has also been studied as a prophylactic measure to prevent catheter-related bacteremia. Six studies in the hemodialysis population have evaluated the use of an antimicrobial lock for the prevention of catheter-related bacteremia with an overall 64%-100% reduction in the frequency of catheter-related bacteremia. Although the use of antimicrobial lock for prophylaxis has demonstrated efficacy in clinical trials, its long-term consequences, including potential impact on antimicrobial resistance, are unknown. The objectives of this review are to evaluate the current body of evidence espousing the utilization of an antimicrobial lock solution in tunneled cuffed and uncuffed catheters that are utilized during chronic intermittent hemodialysis.

Prolonged Stability of Stored Vancomycin, Gentamicin, and Heparin for Use in the Antibiotic-Lock Technique

The antibiotic-lock technique has been effective in salvaging tunneled catheters in hemodialysis patients with bacteremia. However, a practical concern exists with respect to the stability of the antibiotics and heparin in normal saline, when stored for a prolonged period. Vancomycin, gentamicin, and heparin were diluted in normal saline to a final concentration of 100 microg/ml of each antibiotic and 5000 units/ml heparin. Fresh samples, and samples refrigerated at 4 degrees C for 48 hours, 1 week, 2 weeks, 3 weeks, and 4 weeks, were assayed (in triplicate) for gentamicin and vancomycin concentration and bactericidal activity (Schlichter test) using methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. An anti-Xa activity assay was used for monitoring heparin anticoagulant activity of the fresh samples and samples refrigerated for 2 and 4 weeks. Mean (+/- SD) anti-Xa activity for heparin/vancomycin solution was 7900 +/- 173 u/ml, and for heparin/gentamicin solution was 7467 +/- 751u/ml; both were stable over a 4-week storage period. Mean bactericidal titer for vancomycin was 1:121 +/- 11, and for gentamicin was 1:242 +/- 22; both were stable over a 4-week storage period. Mean vancomycin concentration was 97 +/- 4 microg/ml, and gentamicin concentration was 86 +/- 3 microg/ml; both were stable over a 4-week storage period. Vancomycin and gentamicin in a heparin/saline solution can be stored at 4 degrees C for up to 4 weeks without adversely affecting antibiotic concentration, bactericidal activity, or heparin anticoagulant activity.

Design, Synthesis, and Evaluation of a Liposaccharide Drug Delivery Agent: Application to the Gastrointestinal Absorption of Gentamicin

The design, synthesis, and evaluation of a liposaccharide (11) for use as an agent to enhance the gastrointestinal absorption of charged, hydrophilic drugs with poor membrane permeability is reported. 11 was designed to possess both surfactant and ion-pairing properties and was conveniently synthesized from d-glucuronic acid (2) and N-Boc-lipoamino acid (5) precursors in eight steps in good yield. Isothermal titration microcalorimetry was used to determine the critical micelle concentration of 11 (in PBS) to be 2.09 +/- 0.01 mM with an enthalpy of demicellization of 4.91 +/- 0.11 kJ/mol. The ability of 11 to enhance the gastrointestinal absorption of the aminoglycoside antibiotic gentamicin (1), a hydrophilic polycation with negligible oral bioavailability, was assessed in vivo using rats. Rats dosed orally with a mixture of 11 (100 mg/kg) and 1 (60 mg/kg) had a statistically significant (P < or = 0.034) increase in Cmax, AUC120, and percent absolute bioavailability (F) compared to control 1 (60 mg/kg) alone. The highest bioavailability (F = 9.1 +/- 2.0%) was achieved by dosing with the mixture 11 (100 mg/kg) and 1 (15 mg/kg). This represents a 6-fold increase in bioavailability compared to the control (F = 1.4 +/- 0.3%). These results suggest that the molar ratio of 1:11 may be critical in optimizing the delivery system, a finding ascribed in part to the ion-pairing properties of 11. The effect of 11 on the gastrointestinal mucosa was assessed using light microscopy to examine tissue samples from rats used in the pharmacokinetic study. No morphological changes were found in either the esophagi or duodena of the rats examined. One rat dosed with 11 (100 mg/kg) and 1 (60 mg/kg) exhibited slight gastric erosion, which could be attributed to 11.

Management of hemodialysis catheter-related bacteremia with an adjunctive antibiotic lock solution

BACKGROUND

Tunneled dialysis catheters are complicated by frequent systemic infections. Standard therapy of catheter-associated bacteremia involves both systemic antibiotics and catheter replacement. Recent data suggest that biofilms in the catheter lumen are responsible for the bacteremia, and that instillation of an antibiotic lock (highly concentrated antibiotic solution) into the catheter lumen after dialysis sessions can eradicate the biofilm.

METHODS

We analyzed prospectively the efficacy of an antibiotic lock protocol, in conjunction with systemic antibiotics, for treatment of patients with dialysis catheter-associated bacteremia without catheter removal. Protocol success was defined as resolution of fever and negative surveillance cultures one week following completion of the protocol. Protocol failure was defined as persistence of fever or surveillance cultures positive for any pathogen. In addition, infection-free catheter survival was compared to that observed in institutional historical control patients treated with catheter replacement.

RESULTS

Blood cultures were positive in 98 of 129 of episodes (76%) in which patients dialyzing with a catheter had fever or chills. Protocol success occurred in 40 of 79 infected patients (51%) treated with the antibiotic lock. Protocol failure occurred in 39 cases (49%): 7 had persistent fever, 15 had positive surveillance cultures (9 for Candida and 6 for bacteria), and 17 required catheter removal due to malfunction. Each of the pathogens in the surveillance cultures was different from the original pathogen in that patient. Eight of the 9 secondary Candida infections and all 6 secondary bacterial infections resolved after catheter exchange and specific antimicrobial treatment. Overall catheter survival with the antibiotic lock protocol was similar to that observed among patients managed with catheter replacement (median survival, 64 vs. 54 days, P = 0.24).

CONCLUSIONS

Use of an antibiotic lock, in conjunction with systemic antibiotic therapy, can eradicate catheter-associated bacteremia while salvaging the catheter in about one half of cases. Moreover, this management approach offers clinical advantages over routine catheter exchange.

Persistent staphylococcal bacteremia in an intravenous drug abuser

A patient with methicillin-resistant Staphylococcus aureus bacteremia received vancomycin (MIC = 0.8 microgram/ml, MBC = 15 micrograms/ml) and heparin simultaneously through the same intravenous line to treat a septic deep venous thrombosis. Bacteremia persisted for 7 days. Bacteremia terminated when the simultaneous infusion of heparin and vancomycin through the same line was stopped. This suggested that an interaction between vancomycin and heparin may have occurred, which resulted in a reduction in vancomycin activity. To test for such an interaction, mixtures of heparin and vancomycin in various concentrations were made and tested for antimicrobial activity against the organisms in the patient. A precipitate formed at the concentrations achieved in the intravenous lines, and when the vancomycin concentrations were measured by bioassay, a 50 to 60% reduction in activity was noted. In contrast, when these solutions were prepared and mixed at microgram concentrations, a precipitate was no longer observed, and antimicrobial activity was not reduced. Heparin appeared to interact unfavorably with vancomycin at the concentrations in the intravenous lines when these drugs were administered simultaneously to patients. This may be the cause of poor therapeutic responses to vancomycin in some patients, especially those infected with tolerant organisms.

Analytical accuracy of determinations of aminoglycoside concentrations by enzyme multiplied immunoassay, fluorescence polarization immunoassay, and radioimmunoassay in the presence of heparin

The accuracy of gentamicin, netilmicin, and tobramycin concentration determinations by enzyme multiplied immunoassay technique (EMIT; Syva Corp., Palo Alto, Calif.), fluorescence polarization immunoassay (TDx; Abbott Diagnostics, Irving, Tex.), and radioimmunoassay were compared in the presence of 0 to 3,000 USP units of porcine heparin per ml. Gentamicin, netilmicin, and tobramycin concentrations determined by EMIT decreased by 10 and 50% in the presence of 75 and 1,000 USP units/ml, 2 and 5 USP units/ml, and 2 and 7.5 USP units/ml, respectively. Accuracy of the TDx and radioimmunoassay determinations, however, were not affected by the presence of heparin. Blood samples for the determination of gentamicin, netilmicin, and tobramycin by EMIT should not be collected in evacuated heparinized tubes.

Heparin interferes with tobramycin serum concentration determinations by Emit

Enzyme multiplied immunoassay (Emit) commonly is used to determine aminoglycoside concentrations. Its accuracy generally is comparable to that of radioimmunoassay (RIA). Poor reproducibility and questionable quantitation by the Emit assay have been reported when heparinized, severely lipemic, or icteric samples have been used. However, the significance of these interferences is documented poorly. We observed a ESRD patient in whom the underestimation by Emit of the tobramycin concentration in a plasma sample (heparin concentration of 41 U/ml) could have resulted in excessive drug administration and potential toxicity. Tobramycin therapy was initiated with a loading dose of 1.6 mg/kg and three tobramycin concentrations were obtained (2, 12, and 36 hours post-infusion) to define the patient's pharmacokinetic parameters. The first and third samples were collected in serum specimen tubes while the second sample was collected in a plasma tube. The tobramycin concentration in the plasma sample measured by Emit was 82 percent lower than the RIA value. Analyses of other samples by both procedures revealed no clinically significant differences. This case demonstrates that the presence of heparin may interfere with the Emit tobramycin assay in the clinical setting. The degree of reduction in tobramycin concentrations may be dramatic and potentially can alter a patients apparent tobramycin dosing requirements. Further investigation is warranted.

Drug interferences with plasma assays in therapeutic drug monitoring

In this article, many of the reports which describe the various assay procedures for 8 of the most commonly monitored drugs in plasma (digoxin, gentamicin, phenobarbitone, phenytoin, procainamide, quinidine, salicylates and theophylline) are reviewed, together with studies dealing with interferences of other drugs with these assays. Factors which are evaluated include whether the interference was studied when the drug was taken by a patient or a volunteer or by adding it to serum in vitro, the concentration or dose of the interfering drug (when reported), and the clinical implications of the interference. Suggestions as to how to eliminate some of these potential sources of interference are made.

Renal clearance of gentamicin in cystic fibrosis

This study was designed to corroborate previous observations of low serum concentrations of aminoglycosides after usual doses in patients with cystic fibrosis and to investigate possible mechanisms for this change. We studied gentamicin clearance after single and multiple intravenously administered doses in 10 non-acutely ill patients with mild to moderate CF. The data could best be described by a two-compartment model for drug elimination. The mean 1-hour serum concentration, mean volume of distribution, and mean total plasma clearance of gentamicin were not different from those reported for patients without CF. The similarity of the plasma and the renal gentamicin clearances, supported by the observations that greater than 80% of administered drug was excreted in the urine by 4 hours and that negligible amounts were detected in sweat, saliva, or sputum, implies that the kidney is the major route of elimination in patients with mild CF. The correlation of increased plasma gentamicin clearance as NIH score decreases supports the hypothesis that aminoglycoside pharmacokinetics are changed as the severity of disease increases. For patients with mild CF, standard doses of gentamicin (60 mg/m2) will give safe and therapeutic concentrations.

Antibiotic activity in peritoneal dialysate

There are few studies investigating whether antibiotics added to 30% glucose concentrate preserve their activity in the delivered dialysate. Using a Drake-Willock proportioning system, samples were obtained from the "to" patient path at ten minutes after starting and at four hours. Samples were tested for minimal inhibitory dilution (MID) against Escherichia coli and Staphylococcus aureus. Antibiotics evaluated included amikacin, tobramycin, gentamicin, cephalothin, cefamandole, moxalactam, ampicillin, penicillin, carbenicillin, and vancomycin. In all antibiotics studied, similar MIDs were obtained at the ten-minute and four-hour samples. Compared to saline, dialysate significantly impaired the antibiotic activity (a difference of two or more tube dilutions) of all antimicrobial agents except amikacin and vancomycin.

Inhibition of aminoglycoside activity in heparin

Measurements of aminoglycosides by an agar disk diffusion assay are inhibited by heparin in a dose-dependent way. When assayed by a homogeneous immunoassay, this was only evident for tobramycin. This indicates that specimens for aminoglycoside measurement should not be obtained in heparinized tubes. When heparin is used clinically as an anticoagulant, the amount in blood does not reach levels that affect the aminoglycoside activity.

Factors affecting gentamicin assay

Measurements of gentamicin concentrations in serum by the luciferase method are affected by sodium phosphate, glucose, and heparin. The effects of the first two factors can be eliminated by omitting phosphate and increasing the level of glucose in the culture medium. The effects of heparin cannot be easily circumvented, thus precluding use of this agent as an anticoagulant. Bilirubin, which purportedly inhibits measurement of gentamicin in serum by the disk diffusion assay, does not affect the accuracy of the luciferase method.

Gentamicin in ophthalmology

Gentamicin, widely used in the treatment of ocular infections, is discussed in terms of its chemical structure, effectiveness against various organisms, and pharmacology. Dosages and methods of administration are detailed and toxic effects, reversible and irreversible, are noted.