Glycopeptide antibiotic

Glycopeptide antibiotics are a class of antibiotic drugs. The class is composed of a glycosylated cyclic or polycyclic nonribosomal peptides. Significant glycopeptide antibiotics include vancomycin, teicoplanin, telavancin, bleomycin, ramoplanin, and decaplanin.

Mechanism

This class of drugs inhibit the synthesis of cell walls in susceptible microbes by inhibiting peptidoglycan synthesis. They bind to the amino acids within the cell wall preventing the addition of new units to the peptidoglycan. In particular they bind to acyl-D-alanyl-D-alanine in peptidoglycan. The D stands for the dextro stereoisomer of the amino acid, which is signigficant as amino acids are normal L or levo stereoisomers.

Use

Due to their toxicity, their use is restricted to those patients who are critically ill or who have a demonstrated hypersensitivity to the β-lactams. Principally effective against gram positive cocci, they exhibit a narrow spectrum of action and while they are bacteriostatic against most species, they are only bacteriocidal against the enterococci. Some tissues are not penetrated very well by glycopeptides, and they don't penetrate into the CSF.

History

Historically, glycopeptides were the last effective line of defense for cases of Methicillin-resistant "Staphylococcus aureus", however several newer classes of antibiotics, including linezolid of the oxazolidinone class and daptomycin of the lipopeptide class have proven to have activity against MRSA. [Loffler CA, Macdougall C, Update on prevalence and treatment of methicillin-resistant Staphylococcus aureus infections, Expert Rev Anti Infect Ther. 2007 Dec;5(6):961-81; http://www.future-drugs.com/doi/abs/10.1586/14787210.5.6.961] Vancomycin-resistant staphylococcus aureus has been seen in some countries.

While not approved for use in the U.S., teicoplanin was discovered in the early 1990s and is marketed in Europe. It is more lipophillic than vancomycin, as it has more fatty acid chains. It is considered to be 50 to 100 times more lipophillic than vancomycin. Teicoplanin has an increased half life compared to vancomycin, as well as having better tissue penetration. It can be two to four times more active than vancomycin, but it does depend upon the organism. Teicoplanin is more acidic, forming water soluble salts, so it can be given intramuscularly. Teicoplanin is much better at penetrating into leucocytes and phagocytes than vancomycin.

Research

Several derivatives of vancomycin are currently being developed, including oritavancin and dalbavancin. Possessing longer half-lives than vancomycin [ Van Bambeke F. Glycopeptides and glycodepsipeptides in clinical development: a comparative review of their antibacterial spectrum, pharmacokinetics and clinical efficacy, Curr Opin Investig Drugs. 2006 Aug;7(8):740-9;] , these newer candidates may demonstrate improvements over vancomycin due to less frequent dosing and activity against vancomycin-resistant bacteria.

Administration

Vancomycin is usually given intravenously, as an infusion, and can cause tissue necrosis and phlebitis at the injection site if given too rapidly. Indeed pain at site of injection is a common adverse event. One of the side effects is 'Red man syndrome', an idiosyncratic reaction to bolus, caused by histamine release. Some other side effects of vancomycin are nephrotoxicity including renal failure and interstitial nephritis, blood disorders including neutropenia and deafness, which is reversible once therapy has stopped. Oral preparations are available, however they aren't absorbed from the lumen of the gut, so are of no use in treating systemic infections. The oral preparations are formulated for the treatment of infections within the Gastro-Intestinal tract, "Clostridium difficile" for example. Over 90% of the dose is excreted in the urine, therefore there is a risk of accumulation in patients with renal impairment, so therapeutic drug monitoring (TDM) is recommended.

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