Sodium colistimethate. I. Dissociations of aminomethanesulfonates in aqueous solution

Colistin: the phoenix arises

The polymyxins were discovered in the 1940s and represent a group of closely related polypeptide antibiotics obtained fromBacillus polymyxa, which was originally isolated from soil (1,2). Although they have been used extensively worldwide in topical otic and ophthalmic solutions for decades, the intravenous formulations were gradually abandoned in most parts of the world in the early 1980s because of the reported high incidence of nephrotoxicity (3-5). As a result, the use of polymyxin preparations has been mainly restricted to the treatment of lung infections due to multidrug-resistant (MDR) gram-negative bacteria in patients with cystic fibrosis (6,7). The emergence of bacteria resistant to most classes of commercially available antibiotics and the shortage of novel antimicrobial agents with activity against gram-negative microorganisms have led to the reemergence of polymyxins as a valuable addition to the therapeutic armamentarium. It was thus considered timely to review colistin and its emerging role in managing infections due to MDR gram-negative bacteria.

Applying antimicrobial pharmacodynamics to resistant gram-negative pathogens

PURPOSE

Guided antibiotic adjustment for the treatment of multidrug-resistant, gram-negative pathogens is explored.

SUMMARY

Multidrug-resistant pathogens are being isolated with increasing frequency, while the production of novel agents to circumvent resistance has slowed to a near halt. Hence, antimicrobial adjustment based on drug pharmacokinetic and pharmacodynamic properties has moved to the forefront of treatment. Pharmacodynamic principles for major classes of antimicrobials are reviewed, and the use of susceptibility reports to optimize pharmacodynamics to treat gram-negative infections is described. The need for the application of antimicrobial pharmacodynamics continues to grow as resistance to the agents becomes more common. Susceptibility reports, including antibiograms, and their limitations are briefly discussed. The resistance profiles of the beta-lactams (including carbapenems), aminoglycosides, fluoroquinolones, tetracyclines and glycylcyclines, and the polymyxins are reviewed, and the pharmacodynamic optimization of these profiles is explored.

CONCLUSION

Various mechanisms account for resistance of bacteria to antibiotics. The appropriate use of pharmacokinetics and pharmacodynamics can guide antibiotic therapy and enhance the likelihood of success.

Colistin: the revival of polymyxins for the management of multidrug-resistant gram-negative bacterial infections

The emergence of multidrug-resistant gram-negative bacteria and the lack of new antibiotics to combat them have led to the revival of polymyxins, an old class of cationic, cyclic polypeptide antibiotics. Polymyxin B and polymyxin E (colistin) are the 2 polymyxins used in clinical practice. Most of the reintroduction of polymyxins during the last few years is related to colistin. The polymyxins are active against selected gram-negative bacteria, including Acinetobacter species, Pseudomonas aeruginosa, Klebsiella species, and Enterobacter species. These drugs have been used extensively worldwide for decades for local use. However, parenteral use of these drugs was abandoned approximately 20 years ago in most countries, except for treatment of patients with cystic fibrosis, because of reports of common and serious nephrotoxicity and neurotoxicity. Recent studies of patients who received intravenous polymyxins for the treatment of serious P. aeruginosa and Acinetobacter baumannii infections of various types, including pneumonia, bacteremia, and urinary tract infections, have led to the conclusion that these antibiotics have acceptable effectiveness and considerably less toxicity than was reported in old studies.

Evaluation of colistin as an agent against multi-resistant Gram-negative bacteria

Infections caused by multi-resistant Gram-negative bacteria, particularly Pseudomonas aeruginosa, are increasing worldwide. In patients with cystic fibrosis (CF), resistance in P. aeruginosa to numerous anti-pseudomonal agents is becoming common. The absence since 1995, of new substances active against resistant Gram-negative bacteria, has caused increasing concern. Colistin, an old antibiotic also known as polymyxin E, has attracted more interest recently because of its significant activity against multi-resistant P. aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae, and the low resistance rates to it. Because its use as an anti-pseudomonal agent was displaced by the potentially less toxic aminoglycosides in 1970s, our knowledge of this drug is limited. However, there has been a significant recent increase in the data gathered on colistin, focussing on its chemistry, antibacterial activity, mechanism of action and resistance, pharmacokinetics, pharmacodynamics and new clinical application. It is likely that colistin will be an important antimicrobial option against multi-resistant Gram-negative bacteria, for some years to come.

Reaction of sodium hydroxymethanesulfonate with substituted anilines

The reactions of substituted anilines with sodium hydroxymethanesulfonate to form the anilinomethanesulfonates were studied in 50% ethanol--water at 0--50 degrees. The Arrhenius rate constants were 5.4 X 10(10) exp(--16,400/RT) M-1 min-1 for aniline, 4.8 X 10(11) exp(--17,100RT) M-1 min-1 for p-anisidine, 7.1 X 10(9) exp(--14,500/RT) M-1 min-1 for p-toluidine, 1.5 X 10(13) exp(--21,100/RT) M-1 min-1 for p-chloroaniline, and 1.1 X 10(12) exp(--19,800/RT) M-l min-1 for p-bromoaniline. Some equilibrium constants and hydrolysis rate constants of the products also were calculated. Hydrolysis rate constants were temperature independent. These reactions had a p value of --3.40 in the Hammett equation. The solvent concentrations used proved to be very convenient for obtaining high yields of the aminomethanesulfonates.