Abstract
The triple combination trimethoprim, EDTA, and ethanol (B-Lock), is an antimicrobial lock solution for use in indwelling intravascular catheters to prevent and treat catheter-associated infections. B-Lock demonstrated MICs of ≤0.05% (percentage of solution) against Candida spp. (n = 125) and 0.003% to 25% against bacterial strains (n = 175). B-Lock was also fungicidal against the majority of the Candida strains at 6% to 25%. B-Lock demonstrates potential value for the prevention and treatment of catheter-associated infections.
TEXT
Central venous access is an important tool for the appropriate treatment and support of patients in the intensive care unit (ICU), hospitals, and outpatient settings for many life-threatening diseases, such as cancer and end-stage renal disease. However, central line-associated bloodstream infections contribute to patient morbidity and mortality, extended length of hospital stay, and increased cost of care (4–6, 8, 9, 11). Therefore, prompt intervention to prevent and salvage the functionality of the indwelling catheter is essential.
The Infectious Diseases Society of America (IDSA) guidelines for intravascular catheter-related infection recommend that antibiotic lock therapy should be used for catheter salvage (7). B-Lock catheter lock solution (B-Lock), a sterile, clear liquid solution consisting of (by wt/vol) 0.5% trimethoprim (5 mg/ml), 19% ethanol (25% by volume), and 3% calcium disodium EDTA (Ca EDTA) in phosphate-buffered saline (PBS) buffer, is an antimicrobial lock solution developed for prevention of microbial infections in indwelling intravascular devices (catheters) (1, 2).
The MIC of B-Lock was determined against 25 clinical strains each of the Candida spp. C. albicans, C. glabrata, C. krusei, C. parapsilosis, and C. tropicalis (including fluconazole-susceptible and fluconazole-resistant isolates) and 25 clinical strains each of Acinetobacter baumanii, methicillin-resistant and -susceptible coagulase-negative Staphylococcus, methicillin-resistant and -susceptible Staphylococcus aureus, Enterobacter sp., Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa according to Clinical and Laboratory Standards Institute (CLSI) methodology (1, 2).
As can be seen in Table 1, B-Lock solution inhibited all isolates, both bacterial and fungal, at concentrations of 25% or lower, with 100% of Candida isolates (n = 125) inhibited at ≤0.05% and 90% of bacterial stains (n = 200) inhibited at 12.5%. Importantly, B-Lock had the lowest MIC50, defined as the lowest concentration to inhibit 50% of the strains tested, against C. albicans (MIC50 of 0.0015%), one of the most prevalent species infecting immunocompromised patients, and against C. glabrata (MIC50 of 0.0015%), which is increasingly reported from systemic infections. In addition, B-Lock inhibited half of the C. krusei strains tested, which are innately resistant to multiple antifungals, at a concentration of 0.003%.
Table 1.
MIC and MBC or MFC values of B-Lock against microorganisms associated with catheter infections
| Isolatea | B-Lock MIC (% solution) |
B-Lock MBC or MFC (% solution)b |
||
|---|---|---|---|---|
| Range | 50%/90%c | Range | 50%/90%c | |
| Bacterial | ||||
| Acinetobacter baumanii | 0.8–12.5 | 6.25/12.5 | 12.5–>25 | >25/>25 |
| Coagulase-negative staphylococcus, methicillin resistant | 0.003125–25 | 1.6/25 | 0.25–>25 | >25/>25 |
| Coagulase-negative staphylococcus, methicillin susceptible | 0.00625–25 | 0.2/6.25 | 0.025–>25 | >25/>25 |
| Enterobacter sp. | 0.0125–25 | 0.4/25 | 0.1–>25 | >25/>25 |
| Enterococcus faecalis | 0.003125–25 | 0.0125/12.5 | 0.05–>25 | 0.8/>25 |
| Escherichia coli | 0.00625–25 | 0.4/25 | 0.0125–>25 | 12.5/>25 |
| Klebsiella pneumoniae | 0.0125–25 | 3.125/25 | 0.05–>25 | >25/>25 |
| Pseudomonas aeruginosa | 0.1–25 | 6.25 | 1.6–>25 | >25/>25 |
| Serratia marcescens | 0.1–12.5 | 0.2 | 1.6–>25 | >25/>25 |
| Staphylococcus aureus, methicillin resistant | 0.025–25 | 0.05 | 0.1–>25 | 0.4/>25 |
| Staphylococcus aureus, methicillin susceptible | 0.0125–12.5 | 0.025 | 0.05–>25 | 0.8/>25 |
| Fungal | ||||
| Candida albicans | 0.0002–0.003 | 0.0015/0.003 | 12.5–>50 | 50/50 |
| Candida glabrata | 0.0004–0.006 | 0.0015/0.003 | 25–>50 | 50/50 |
| Candida krusei | 0.0008–0.006 | 0.003/0.006 | 25–>50 | >50/>50 |
| Candida parapsilosis | 0.0012–0.025 | 0.006/0.012 | 50–>50 | 50/>50 |
| Candida tropicalis | 0.0004–0.05 | 0.006/0.025 | 25–>50 | 50/50 |
Throughout, n = 25, except for S. marcescens (n = 18).
Minimal bactericidal concentrations (MBC) are shown for bacterial isolates, and minimal fungicidal concentrations (MFC) are shown for fungal isolates.
50%/90%, MIC50/MIC90, MBC50/MBC90, or MFC50/MFC90.
Activity against bacteria was strain specific, with the greatest inhibitory activity against E. faecalis, commonly found in bloodstream infections (MIC50 of 0.0125%). Importantly, B-Lock was also able to inhibit the growth of methicillin-resistant S. aureus (MRSA), methicillin-resistant coagulase-negative Staphylococcus, and P. aeruginosa, with MIC50s of 0.05%, 1.6%, and 6.25%, respectively.
B-Lock was fungicidal against the majority of Candida strains tested, as defined by a ≥99.9% reduction in colony count from the initial inoculum. Similarly, B-Lock was cidal against 50% of the MRSA isolates at a concentration of 0.4%, and against 50% of the E. faecalis and methicillin-susceptible S. aureus strains at a concentration of 0.8%. Overall, B-Lock demonstrated greater cidal activity against Gram-positive bacteria than against Gram-negative organisms.
The fact that B-Lock demonstrates antimicrobial activity against such a broad range of systemic microbial pathogens suggests a distinct advantage in that this lock solution targets both bacteria and fungi and alleviates the need to use specific antifungal/antibacterial solutions. The underlying reason for the broad-spectrum activity for B-Lock could be explained on the basis of its active ingredients (ethanol and trimethoprim). Exposure to ethanol has long been suspected to have deleterious effects on bacterial cell membranes. Fried and Novick (3) postulated that ethanol may directly disrupt the interactions between phospholipid hydrocarbon chains or alter the aqueous-phospholipid interface. Since the majority of the enzymes for the synthesis of phospholipids, cell wall, and outer membrane components are associated with the cytoplasmic membrane, ethanol disruption of the membrane structure could lead to a defect in the cell division process itself. The membrane damage from ethanol may facilitate the entry of trimethoprim into the cell, thereby facilitating the inhibition of the target enzyme dihydrofolate reductase, which plays a central role in the synthesis of nucleic acid precursors (10).
In conclusion, our study shows that B-Lock possesses a broad-spectrum antimicrobial activity against microorganisms known to cause central line-associated bloodstream infections. Evaluation of this solution for its efficacy to prevent such infections is warranted.
Acknowledgments
This work was supported by an SBIR from the National Institutes of Health awarded to Great Lakes Pharmaceuticals.
M.A.G. is a cofounder of Great Lakes Pharmaceuticals. The other authors have no financial disclosures.
Footnotes
Published ahead of print on 5 July 2011.
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