Daptomycin: A Review 4 Years after First Approval

Abstract

Daptomycin is the first approved member of a new class of antibiotics, namely the cyclic lipopeptides. Daptomycin has rapid bactericidal activity against Gram-positive pathogens. It acts by penetrating into the bacterial cell wall with consecutive formation of pores, loss of electrical membrane potential and inhibition of peptidoglycan synthesis. As the mode of action of daptomycin is ‘concentration-dependent’, the pharmacokinetic/pharmacodynamic indices that correlate best with its activity are the ratios of the peak concentration (C_max) to minimum inhibitory concentration (MIC) or the area under the curve (24-hour AUC) to MIC. Daptomycin should be administered intravenously once daily, because adverse effects on skeletal muscle associated with an increase in plasma levels of creatine phosphokinase and myopathy were observed more frequently at shorter dosing intervals. Overall, the rate of adverse events during daptomycin therapy is comparable to that of other standard regimens. Daptomycin was shown to be not inferior to antimicrobial standard therapy and therefore was approved for complicated skin and skin structure infections at a dose of 4 mg/kg, for Staphylococcus aureus bacteremia and right-sided endocarditis at a dose of 6 mg/kg. Dosage regimens remain a matter of discussion, and an increase in the currently approved doses from 4–6 to 6–8 mg/kg per day for severe infections seems promising. Though not approved up to now, daptomycin appears to be a treatment alternative for Gram-positive bone and joint infections based on clinical observations. Large international studies showed high susceptibility of relevant Gram-positive pathogens to daptomycin, even in multidrug-resistant strains. Thus, treatment of infections caused by Gram-positive cocci resistant to other antimicrobial drugs is a potential indication of daptomycin. Since glycopeptides and daptomycin have the same target site, there appears to be a risk of reduced susceptibility to both drugs after consecutive use. Therefore, daptomycin should be used with caution for treatment of vancomycin-resistant isolates or after prior vancomycin (glycopeptide) therapy. This review describes the history, mechanism of action, susceptibility, recent discoveries and clinical experience regarding daptomycin, discussing its current role in the field of infectious diseases.

The action mechanism of daptomycin

“…Daptomycin and all other members of the A21978C group of lipopeptides are synthesized by the same modular non-ribosomal synthetase system 22 (see Figure 2) and contain the same peptide moiety; the only part of the structure that differs between them is the N-terminally attached fatty acyl residue. The common peptide moiety contains 13 amino acids, six of which are non-proteinogenic: D-Asn (2) , ornithine (Orn (6) ), D-Ala (8) , D-Ser (11) , (2S,3R)-methylglutamate (MeGlu (12) ), and kynurenine (Kyn (13) ). The C-terminal ten amino acids form a macrocyclic core, which contains a ring-closing depsi (ester) bond between the side chain of Thr (4) and the α-COOH of the C-terminal Kyn (13) .…”

“…Between pH 2.5 and 4, apo-daptomycin exists primarily as a neutral or monoanionic species. As the pH increases to 7, deprotonation of Asp (3) and mGlu (12) will cause the dianionic and trianionic forms to dominate.…”

“…The decanoyl residue was flexible with a large degree of conformational freedom. They suggested that the four acidic residues, Asp (3) , Asp (7) , Asp (9) and mGlu (12) are not close enough to each other to render an effective Ca 2+ binding site.…”

“…NMR experiments as well as analogue studies suggest that Kyn (13) and mGlu (12) may also be involved in binding to Ca 2+ (see section 8.3).…”

“…Readers interested in learning more about these topics are referred to several previous reviews. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] …”