Polymyxin antibiotics for gram-negative infections

Clinical characteristics and risk factors of colistin-induced nephrotoxicity

Since multidrug-resistant gram-negative organisms have been increasing, polymyxin E (colistin) has been reintroduced despite its nephrotoxicity. A case-control study was performed to investigate the incidence, clinical characteristics and risk factors of colistin-induced nephrotoxicity. From August 2006 to June 2008, 47 cases receiving at least one defined daily dose (DDD) of intravenous colistin were included; 15 (31.9%) of the 47 cases developed nephrotoxicity with preserved urine output, 3 (20%) of whom underwent renal replacement therapy. The mean dosage of colistimethate sodium was 2.25 g (22.5 DDD; range 0.6-8.7 g) at the time of nephrotoxicity. Of 10 patients who were re-assessed for renal function after 1 month, 9 (90%) recovered their renal function. In the univariate analysis, site of infection, hypoalbuminaemia and cumulative dosage of the second-generation fluoroquinolones, aminoglycosides and non-steroidal anti-inflammatory drugs (NSAIDs) co-administered during colistin treatment as well as concomitant use of NSAIDs were risk factors for nephrotoxicity. However, in the logistic regression hypoalbuminaemia and the use of NSAIDs were significant risk factors for increased nephrotoxicity during colistin administration, suggesting that free colistin might cause renal toxicity. In conclusion, colistin-induced nephrotoxicity occurred at a high rate, and hypoalbuminaemia and concomitant use of NSAIDs were significant risk factors.

Lipopeptides as anti-infectives: a practical perspective

Lipopeptide antibiotics represent an old class of antibiotics that were discovered over 50 years ago, which includes the old polymyxins but also new entries, such as the recently approved daptomycin. They generally consist of a hydrophilic cyclic peptide portion attached to a fatty acid chain which facilitates insertion into the lipid bilayer of bacterial membranes. This review presents an overview of this class of antibiotics, focusing on their therapeutic applications and putting particular emphasis on chemical modifications introduced to improve their activity.

Polymyxin B identified as an inhibitor of alternative NADH dehydrogenase and malate: quinone oxidoreductase from the Gram-positive bacterium Mycobacterium smegmatis

Tuberculosis is the leading cause of death due to a single infectious agent in the world and the emergence of multidrug-resistant strains prompted us to develop new drugs with novel targets and mechanism. Here, we screened a natural antibiotics library with Mycobacterium smegmatis membrane-bound dehydrogenases and identified polymyxin B (cationic decapeptide) and nanaomycin A (naphtoquinone derivative) as inhibitors of alternative NADH dehydrogenase [50% inhibitory concentration (IC(50)) values of 1.6 and 31 microg/ml, respectively] and malate: quinone oxidoreductase (IC(50) values of 4.2 and 49 microg/ml, respectively). Kinetic analysis on inhibition by polymyxin B showed that the primary site of action was the quinone-binding site. Because of the similarity in K(m) value for ubiquinone-1 and inhibitor sensitivity, we examined amino acid sequences of actinobacterial enzymes and found possible binding sites for L-malate and quinones. Proposed mechanisms of polymyxin B and nanaomycin A for the bacteriocidal activity were the destruction of bacterial membranes and production of reactive oxygen species, respectively, while this study revealed their inhibitory activity on bacterial membrane-bound dehydrogenases. Screening of the library with bacterial respiratory enzymes resulted in unprecedented findings, so we are hoping that continuing efforts could identify lead compounds for new drugs targeting to mycobacterial respiratory enzymes.

Neurotoxicity in patients treated with intravenous polymyxin B: Two case reports

PURPOSE

Two cases of reversible neurotoxicity associated with the administration of intravenous polymyxin B are described.

SUMMARY

In the first case, a 60-year-old, obese, white woman with a medical history of recurring urinary tract infections, nephrolithiasis, and chronic renal insufficiency was admitted for parenteral antibiotics for dysuria and hematuria despite outpatient management with oral antibiotics. Her urinalysis revealed pyuria and large blood content. The corresponding urine culture contained >or=100,000 colony-forming units/mL of multidrug-resistant (MDR) Klebsiella pneumoniae. The patient was treated with polymyxin B at 20,000 units/kg i.v. as a loading dose and then 10,000 units/kg i.v. daily based on her renal function. The patient experienced oral paresthesia that resolved upon discontinuation of the infusion with no further complications. In the second case, a 57-year-old white man with hypertension and ascending cholangitis was admitted. He required percutaneous drainage of an infected pancreatic cyst and received polymyxin B at 25,000 units/kg i.v. as a loading dose and then 15,000 units/kg i.v. daily in addition to imipenem-cilastatin based on the sensitivities of two organisms (Escherichia coli and MDR K. pneumoniae) isolated from the abdominal drainage. For his pancreatic abscess, the patient received a prolonged course of polymyxin B, which was well tolerated for the first four weeks. On day 30 of the polymyxin B, the patient reported oral and lower extremity paresthesias. The symptoms resolved upon discontinuation of the polymyxin B.

CONCLUSION

Two patients developed symptoms of neurotoxicity after receiving intravenous polymyxin B for the treatment of MDR gram-negative infections.

Amplification of vacuole-targeting fungicidal activity of antibacterial antibiotic polymyxin B by allicin, an allyl sulfur compound from garlic

A cationic antibacterial peptide, polymyxin B (PMB), was evaluated as an antifungal antibiotic against various yeasts and filamentous fungi when used in combination with allicin, an allyl sulfur compound from garlic. Allicin was not lethal but could markedly amplify the fungicidal activity of PMB, which was weakly detected with the increase in the plasma membrane permeability in Saccharomyces cerevisiae. Their combined actions caused a dynamic structural damage to the yeast vacuole as judged by the disappearance of its swollen spherical architecture. The vacuole-targeting activity of PMB was similarly amplified in medium with t-butyl hydroperoxide as a substitute for the action of allicin. These findings suggest that the allicin-mediated lipoperoxide production in fungal plasma membrane is the cause of the enhancement in the cellular uptake of PMB as well as its action against the vacuole.