Vancomycin

 Vancomycin is produced by Streptomyces orientalis. It is poorly absorbed from the intestine.

Vancomycin is markedly bactericidal for staphylococci, some clostridia, and some bacilli. The drug inhibits early stages in cell wall peptidoglycan synthesis. Drug-resistant strains do not emerge rapidly. Vancomycin is given intra venously for serious systemic staphylococcal infections, including endocarditis, especially if resistant to nafcillin. For enterococcal sepsis or endocarditis, vancomycin can be effective if combined with an aminoglycoside. Oral vancomycin is indicated in antibiotic-associated pseudomembranous colitis.

The development of vancomycin resistance in enterococci has had a major impact on the treatment of severe multidrug-resistant enterococcal infections. See the section Clinical Implications of Drug Resistance earlier in this chapter and Chapter 14.

S. aureus of intermediate susceptibility to vancomycin in vitro has been isolated from patients in several countries, including the United States. These patients have tended to have complex illnesses that included long-term therapy with vancomycin. In some cases, the infections appeared to have failed vancomycin therapy.

High-level vancomycin resistance in S. aureus is of major international concern. The mechanism is the same as or similar to the transposon-mediated vancomycin resistance in enterococci (acquisition of vanA genes ). Such isolates have been cultured from several patients and may occur in more patients in the future.

Undesirable side effects are thrombophlebitis, skin rashes, nerve deafness, leukopenia, and perhaps kidney dam age when used in combination with an aminoglycoside.

Teicoplanin

Teicoplanin has a structure similar to that of vancomycin. It is active against staphylococci (including methicillin resistant strains), streptococci, enterococci, and many other Gram-positive bacteria. Enterococci with VanA resistance to vancomycin are also resistant to teicoplanin, but enterococci with VanB vancomycin resistance are susceptible to teicoplanin. The drug has a long half-life and is administered once a day. Adverse effects include localized irritation at injection sites, hypersensitivity, and the potential for ototoxicity and nephrotoxicity. Teicoplanin is available in Europe and Asia, but not in the United States.

Daptomycin

 Daptomycin is a naturally occurring cyclic lipopeptide produced by Streptomyces roseosporus. Structurally, it has a 10-member amino acid ring, a 10-carbon decanoic acid attached to a terminal l-tryptophan. It is bactericidal by causing depolarization of the bacterial membrane in a calcium-dependent manner. It is available in a parenteral form administered once daily. It is highly protein bound and excreted in the kidneys as parent drug. Dosage adjustment is required in patients with creatinine clearance below 30 mL/min.

A major adverse effect of daptomycin is reversible myopathy. This side effect appears to occur more often with the higher dose (6 mg/kg/day) used to treat S. aureus bacteremia. Weekly monitoring of creatine phosphokinase (CPK) is recommended, and the drug should be discontinued when levels reach five times normal. Currently, daptomycin is approved for use in the United States for treatment of skin and soft tissue infections caused by susceptible and resistant Gram-positive cocci and for S. aureus bacteremia. In vitro synergy is seen when daptomycin is combined with gentamicin and combination therapy with other agents such as rifampin and β-lactam antibiotics is being explored.

Telavancin, Dalbavancin, and Oritavancin

 Some newer lipoglycopeptides with hydrophobic substituents have dual mechanisms of action. The lipophilic side chain among this group of agents prolongs the half-life. They inhibit the transglycosylation of cell wall peptidoglycan synthesis by forming a complex with the d-alanyl-d-alanine residues, and they also depolarize the bacterial cell membrane. Telavancin, the first agent of this group to get approval in the United States for acute bacterial skin and skin structure infections as well as for the treatment of refractory S. aureus nosocomial pneumonia, has a prolonged half-life of 7–9 hours and has good penetration into tissues. It is excreted mainly by the kidneys.

Dalbavancin was recently FDA approved and its half-life of 8.5 days allows for once weekly administration. Its indication is similar to that of telavancin. Oritavancin was approved in the summer of 2014.

These lipoglycopeptides are more active against a broad range of Gram-positive pathogens, including MRSA, vancomycin-intermediate S. aureus (VISA), and vancomycin resistant S. aureus (VRSA) strains than vancomycin. They have activity against some Gram-positive organisms that may be resistant to linezolid and daptomycin. Common adverse reactions include taste disturbance, nausea, vomiting, and reversible renal dysfunction.

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