Investigation of the early killing of Staphylococcus aureus by daptomycin by using an in vitro pharmacodynamic model

Development and validation of sensitive and selective quantification of total and free daptomycin in human plasma using ultra-performance liquid chromatography coupled to tandem mass spectrometry

Recently, several studies on pharmacokinetics parameters of daptomycin reported that plasma trough concentration was linked to efficacy and adverse effects, suggesting the usefulness of therapeutic drug monitoring. Although some methods for determining total daptomycin concentration using liquid chromatography coupled to tandem mass spectrometry were established previously, no sensitive quantification method for free drug concentration was established. In this study, we aimed to develop a quantitative method of measuring both total and free daptomycin concentrations using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS), by which both trough and maximum concentrations can be measured. Plasma samples were prepared by solid phase extraction. Free fractions were obtained by ultrafiltration. The assay fulfilled the requirements of US Food and Drug Administration and the European Medicines Agency for assay validation. The methods for total and free drug showed good fit over wide ranges of 0.5-200 and 0.04-40 μg/mL, with lower limits of quantitation of 0.5 and 0.04 μg/mL, respectively. Recovery rate of free daptomycin from ultrafiltration was approximately 100%. Extraction recovery rates of total and free drug measurements ranged from 57.1 to 67.4% and 54.6 to 62.3%, while matrix effect varied between 111.9 and 118.7% and 104.0 and 127.1%, respectively. The maximum and trough concentrations of total and free daptomycin in plasma from two patients in intensive care unit were successfully determined, demonstrating the feasibility of clinical application of the novel methods for determining plasma total and free daptomycin concentrations. In conclusion, we succeeded to develop a sensitive and selective method using UPLC-MS/MS for quantitative measurement of total and free daptomycin concentrations in plasma.

Therapeutic drug monitoring of anti-infective agents in critically ill patients

Initial adequate anti-infective therapy is associated with significantly improved clinical outcomes for patients with severe infections. However, in critically ill patients, several pathophysiological and/or iatrogenic factors may affect the pharmacokinetics of anti-infective agents leading to suboptimal drug exposure, in particular during the early phase of therapy. Therapeutic drug monitoring (TDM) may assist to overcome this problem. We discuss the available evidence on the use of TDM in critically ill patient populations for a number of anti-infective agents, including aminoglycosides, β-lactams, glycopeptides, antifungals and antivirals. Also, we present the available evidence on the practices of anti-infective TDM and describe the potential utility of TDM to improve treatment outcome in critically ill patients with severe infections. For aminoglycosides, glycopeptides and voriconazole, beneficial effects of TDM have been established on both drug effectiveness and potential side effects. However, for other drugs, therapeutic ranges need to be further defined to optimize treatment prescription in this setting.

Pharmacokinetics of antibacterial agents in the CSF of children and adolescents

The adequate management of central nervous system (CNS) infections requires that antimicrobial agents penetrate the blood-brain barrier (BBB) and achieve concentrations in the CNS adequate for eradication of the infecting pathogen. This review details the currently available literature on the pharmacokinetics (PK) of antibacterials in the CNS of children. Clinical trials affirm that the physicochemical properties of a drug remain one of the most important factors dictating penetration of antimicrobial agents into the CNS, irrespective of the population being treated (i.e. small, lipophilic drugs with low protein binding exhibit the best translocation across the BBB). These same physicochemical characteristics determine the primary disposition pathways of the drug, and by extension the magnitude and duration of circulating drug concentrations in the plasma, a second major driving force behind achievable CNS drug concentrations. Notably, these disposition pathways can be expected to change during the normal process of growth and development. Finally, CNS drug penetration is influenced by the nature and extent of the infection (i.e. the presence of meningeal inflammation). Aminoglycosides have poor CNS penetration when administered intravenously. Intrathecal gentamicin has been studied in children with more promising results, often exceeding the minimum inhibitory concentration. There are very limited data with intrathecal tobramycin in children. However, in the few patients that have been studied, the CSF concentrations were highly variable. Penicillins generally have good CNS penetration. Aqueous penicillin G reaches greater concentrations than procaine or benzathine penicillin. Concentrations remain detectable for ≥ 12 h. Of the aminopenicillins, both ampicillin and parenteral amoxicillin reach adequate CNS concentrations; however, orally administered amoxicillin resulted in much lower concentrations. Nafcillin and piperacillin are the final two penicillins with pediatric data: their penetration is erratic at best. Cephalosporins vary greatly in regard to their CSF penetration. Few first- and second-generation cephalosporins are able to reach higher CSF concentrations. Cefuroxime is the only exception and is usually avoided due to its adverse effects and slower sterilization of the CSF than third-generation agents. Ceftriaxone, cefotaxime, ceftazidime, cefixime and cefepime have been studied in children and are all able to adequately penetrate the CSF. As with penicillins, concentrations are greatest in the presence of meningeal inflammation. Meropenem and imipenem are the only carbapenems with pediatric data. Imipenem reaches higher CSF concentrations; however, meropenem is preferred due to its lower incidence of seizures. Aztreonam has also demonstrated favorable penetration but only one study has been completed in children. Both chloramphenicol and sulfamethoxazole/trimethoprim (cotrimoxazole) penetrate into the CNS well; however, significant toxicities limit their use. The small size and minimal protein binding of fosfomycin contribute to its favorable CNS PK. Although rarely used, it achieves higher concentrations in the presence of inflammation and accumulation is possible. Linezolid reaches high CSF concentrations; however, more frequent dosing might be required in infants due to their increased elimination. Metronidazole also has very limited information but it demonstrated favorable results similar to adult data; CSF concentrations even exceeded plasma concentrations at certain time points. Rifampin (rifampicin) demonstrated good CNS penetration after oral administration. Vancomycin demonstrates poor CNS penetration after intravenous administration. When combined with intraventricular therapy, CNS concentrations are much greater. Of the antituberculosis agents, isoniazid, pyrazinamide and streptomycin have been studied in children. Isoniazid and pyrazinamide have favorable CSF penetration. Streptomycin appears to produce unpredictable CSF levels. No pediatric-specific data are available for clindamycin, daptomycin, macrolides, tetracyclines, and fluoroquinolones. Daptomycin, fluoroquinolones, and tetracyclines have demonstrated favorable CNS penetration in adults; however, data are limited due to their potential pediatric-specific toxicities and newness within the marketplace. Macrolides and clindamycin have demonstrated poor CNS penetration in adults and thus have not been studied in pediatrics.

Multiple-dose pharmacokinetics of daptomycin during continuous venovenous haemodiafiltration

OBJECTIVES

Daptomycin is bactericidal against Gram-positive bacteria, with peak-dependent effect but trough-dependent toxicity. This study was performed to develop dosing recommendations in continuous venovenous haemodiafiltration (CVVHDF).

PATIENTS AND METHODS

Nine critically ill patients in intensive care units of the Medical University Hospital of Vienna, requiring CVVHDF due to acute renal failure and antimicrobial treatment, were included. Blood and effluent samples were collected over 72 h to determine daptomycin concentrations by HPLC. Pharmacokinetic parameters were based on 10 sampling timepoints during the first 24 h, and peak and trough samples thereafter. An open two-compartment model was fitted to each subject's plasma concentration-time data. Simulations of serum concentration-time profiles after different doses and intervals were performed using ADAPT 5.

RESULTS

Peak plasma concentrations with 6 mg/kg daptomycin were 62.2 ± 16.2, 66.1 ± 17.3 and 78.5 ± 22.1 mg/L on days 1, 2 and 3, respectively. The total clearance was 6.1 ± 4.9 mL/min, and the elimination half-life was 17.8 ± 9.7 h. Daptomycin was filtrated and could therefore be measured in the effluent. Protein binding was lower than that seen in healthy volunteers. The unbound fraction was 16 ± 4.5%. All subjects maintained trough serum concentrations above 4 mg/L, at which relevant pathogens are considered daptomycin-susceptible. Accumulation resulted when daptomycin was given every 24 h. Simulation of 8 mg/kg daptomycin given every 48 h resulted in adequate levels without accumulation.

CONCLUSIONS

We recommend 8 mg/kg daptomycin every 48 h in patients on CVVHDF and therapeutic drug monitoring, if possible.

Daptomycin pharmacokinetics in critically ill patients receiving continuous venovenous hemodialysis

OBJECTIVE

To investigate daptomycin pharmacokinetics in critically ill patients receiving continuous venovenous hemodialysis to develop dosing recommendations.

DESIGN

Prospective, open-label pharmacokinetic study.

SETTING

: Intensive care units located within a teaching medical center.

PATIENTS

Eight adults with known/suspected Gram-positive infections receiving continuous venovenous hemodialysis and daptomycin.

INTERVENTIONS

Daptomycin at 8 mg/kg intravenously over 30 mins. Serial blood and effluent samples were collected over the next 48 hrs. Daptomycin protein binding was determined by equilibrium dialysis. Daptomycin continuous venovenous hemodialysis transmembrane clearance was determined by dividing daptomycin effluent by serum concentrations and multiplying by mean effluent production rate for each subject. Equations describing a two-compartment, open-pharmacokinetic model were fitted to each subject's daptomycin concentration-time data and pharmacokinetic parameters were determined by standard methods. Serum concentration-time profiles were simulated for two daptomycin regimens (8 mg/kg every 48 hrs and 4 mg/kg every 24 hrs).

MEASUREMENTS AND MAIN RESULTS

A total of 7.7 ± 0.6 mg/kg (mean ± sd) of daptomycin was administered, resulting in an observed peak concentration of 81.2 ± 19.0 μg/mL. Daptomycin steady-state volume of distribution (0.23 ± 0.14 L/kg) and free fraction (17.5% ± 5.0%) were increased in critically ill subjects receiving continuous venovenous hemodialysis compared with previous values reported in healthy volunteers. Daptomycin transmembrane clearance (6.3 ± 2.9 mL/min) accounted for more than half of total clearance (11.3 ± 4.7 mL/min). Simulations demonstrated 8 mg/kg daptomycin every 48 hrs would result in higher peak (88.8 ± 20.0 μg/mL vs. 53.0 ± 12.3 μg/mL) and lower trough concentrations (7.2 ± 5.2 μg/mL vs. 12.3 ± 5.1 μg/mL) than 4 mg/kg every 24 hrs.

CONCLUSIONS

Daptomycin at 8 mg/kg every 48 hrs in critically ill patients receiving continuous venovenous hemodialysis resulted in good drug exposure, achieved high peak concentrations to maximize daptomycin's concentration-dependent activity, and resulted in trough concentration that would minimize the risk of myopathy. CLINICALTRIALS.GOV IDENTIFIER: NCT00663403.

In vitro pharmacodynamic models to determine the effect of antibacterial drugs

In vitro pharmacodynamic (PD) models are used to obtain useful quantitative information on the effect of either single drugs or drug combinations against bacteria. This review provides an overview of in vitro PD models and their experimental implementation. Models are categorized on the basis of whether the drug concentration remains constant or changes and whether there is a loss of bacteria from the system. Further subdifferentiation is based on whether bacterial loss involves dilution of the medium or is associated with dialysis or diffusion. For comprehension of the underlying principles, experimental settings are simplified and schematically illustrated, including the simulations of various in vivo routes of administration. The different model types are categorized and their (dis)advantages discussed. The application of in vitro models to special organs, infections and pathogens is comprehensively presented. Finally, the relevance and perspectives of in vitro investigations in drug discovery and clinical research are elucidated and discussed.

Daptomycin pharmacokinetics in adult oncology patients with neutropenic fever

Daptomycin is the first antibacterial agent of the cyclic lipopeptides with in vitro bactericidal activity against gram-positive organisms, including vancomycin-resistant enterococci, methicillin-resistant staphylococci, and glycopeptide-resistant Staphylococcus aureus. The pharmacokinetics of daptomycin were determined in 29 adult oncology patients with neutropenic fever. Serial blood samples were drawn at 0, 0.5, 1, 2, 4, 8, 12, and 24 h after the initial intravenous infusion of 6 mg/kg of body weight daptomycin. Daptomycin total and free plasma concentrations were determined by high-pressure liquid chromatography. Concentration-time data were analyzed by noncompartmental methods. The results (presented as means +/- standard deviations and ranges, unless indicated otherwise) were as follows: the maximum concentration of drug in plasma (C(max)) was 49.04 +/- 12.42 microg/ml (range, 21.54 to 75.20 microg/ml), the 24-h plasma concentration was 6.48 +/- 5.31 microg/ml (range, 1.48 to 29.26 microg/ml), the area under the concentration-time curve (AUC) from time zero to infinity was 521.37 +/- 523.53 microg.h/ml (range, 164.64 to 3155.11 microg.h/ml), the volume of distribution at steady state was 0.18 +/- 0.05 liters/kg (range, 0.13 to 0.36 liters/kg), the clearance was 15.04 +/- 6.09 ml/h/kg (range, 1.90 to 34.76 ml/h/kg), the half-life was 11.34 +/- 14.15 h (range, 5.17 to 83.92 h), the mean residence time was 15.67 +/- 20.66 h (range, 7.00 to 121.73 h), and the median time to C(max) was 0.6 h (range, 0.5 to 2.5 h). The fraction unbound in the plasma was 0.06 +/- 0.02. All patients achieved C(max)/MIC and AUC from time zero to 24 h (AUC(0-24))/MIC ratios for a bacteriostatic effect against Streptococcus pneumoniae. Twenty-seven patients (93%) achieved a C(max)/MIC ratio for a bacteriostatic effect against S. aureus, and 28 patients (97%) achieved an AUC(0-24)/MIC ratio for a bacteriostatic effect against S. aureus. Free plasma daptomycin concentrations were above the MIC for 50 to 100% of the dosing interval in 100% of patients for S. pneumoniae and 90% of patients for S. aureus. The median time to defervescence was 3 days from the start of daptomycin therapy. In summary, a 6-mg/kg intravenous infusion of daptomycin every 24 h was effective and well tolerated in neutropenic cancer patients.

Update on daptomycin: the first approved lipopeptide antibiotic

Daptomycin, the first approved member of the lipopeptide antibiotic class, exhibits potent bactericidal in vitro activity against most Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus species and penicillin-resistant Streptococcus species. Since its approval in 2003 for the treatment of complicated skin and skin structure infections, several review articles have summarised daptomycin's mechanism of action, pharmacokinetics, pharmacodynamics, clinical trials and safety profiles. The objective of this paper is to summarise past information with a focus on the latest susceptibility data of isolates collected worldwide, new pharmacodynamic studies, clinical data regarding bacteraemia/endocarditis and postmarketing surveillance in the treatment of skin and skin-structure infections.

Modulation of the cellular accumulation and intracellular activity of daptomycin towards phagocytized Staphylococcus aureus by the P-glycoprotein (MDR1) efflux transporter in human THP-1 macrophages and madin-darby canine kidney cells

P-glycoprotein (P-gp; MDR1), a major efflux transporter, recognizes various antibiotics and is present in macrophages. We have examined its effect on the modulation of the intracellular accumulation and activity of daptomycin towards phagocytized Staphylococcus aureus (ATCC 25923) in human THP-1 macrophages, in comparison with MDCK epithelial cells (wild type and MDCK-MDR1 overexpressing P-gp; the bulk of the protein was immunodetected at the surface of all three cell types). Daptomycin displayed concentration-dependent intracellular activity (Hill equation pattern) in THP-1 and MDCK cells with (i) 50% effective drug extracellular concentration (EC(50); relative potency) and static concentrations at 9 to 10 times the MIC and (ii) maximal efficacy (E(max); CFU decrease at infinite extracellular drug concentration) at 1.6 to 2 log compared to that of the postphagocytosis inoculum. Verapamil (100 microM) and elacridar (GF 120918; 0.5 microM), two known inhibitors of P-gp, decreased daptomycin EC(50) (about threefold) in THP-1 and MDCK cells without affecting E(max). Daptomycin EC(50) was about three- to fourfold higher and accumulation in MDCK-MDR1 commensurately lower than in wild-type cells. In THP-1 macrophages, (i) verapamil and ATP depletion increased, and ouabain (an inducer of mdr1 [the gene encoding P-gp] expression) decreased the accumulation of daptomycin in parallel with that of DiOC(2) (a known substrate of P-gp); (ii) silencing mdr1 with duplex human mdr1 siRNAs reduced the cell content in immunoreactive P-gp to 15 to 30% of controls and caused an eight- to 13-fold increase in daptomycin accumulation. We conclude that daptomycin is subject to efflux from THP-1 macrophages and MDCK cells by P-gp, which reduces its intracellular activity against phagocytized S. aureus.

Daptomycin: a rapidly bactericidal lipopeptide for the treatment of Gram-positive infections

Antimicrobial resistance among Gram-positive organisms continues to increase and has reached epidemic proportions in a number of countries and within medical centers worldwide. Daptomycin is a new lipopeptide antibiotic with rapid bactericidal activity against Staphylococcus aureus. It is also active against coagulase-negative staphylococci, enterococci and streptococci. It exerts its effect through cell membrane disruption that results in dissipation of the membrane potential. Daptomycin exhibits a prolonged postantibiotic effect and is well tolerated. In Phase III clinical trials, daptomycin was found to be similar in efficacy to standard therapy in complicated skin and skin structure infections. More recently, it was approved for the treatment of S. aureus bacteremia and right-sided endocarditis. Daptomycin is not indicated for pulmonary infections. Preliminary data suggest that daptomycin may be effective in urinary tract, bone and joint infections. However, randomized clinical trials are needed to confirm these findings. Daptomycin is an effective antimicrobial agent for the treatment of various serious Gram-positive infections, especially those caused by methicillin-resistant S. aureus.

The protein-binding and drug release properties of macromolecular conjugates containing daptomycin and dextran

Prototype daptomycin-dextran macromolecular conjugates were prepared in an attempt to modify the biodistribution and protein-binding properties of daptomycin. Synthesis of daptomycin macromolecular conjugates involved dextran activation, daptomycin-dextran coupling, and purification. The reaction mixtures were separated on a Sephadex G-100 column using 10% acetronitrile in water as a mobile phase. UV and fluorescence characteristics of high molecular weight fractions demonstrated imine product formation while the lower molecular weight fractions contained free daptomycin, imine, and anilide products. Daptomycin macromolecular conjugates were characterized by drug loading, drug release, and binding affinity for fibrinogen using HPLC analysis and surface plasmon resonance. Drug loading was calculated to be 160mg of daptomycin per gram of macromolecule. Approximately 9% of the conjugated daptomycin was released from the macromolecular conjugates in aqueous media in the pH range of 1-7.4. The conjugates possessed higher affinity for fibrinogen than that of daptomycin.

Evaluation of daptomycin activity against Staphylococcus aureus in an in vitro pharmacodynamic model under normal and simulated impaired renal function

OBJECTIVES

Daptomycin is a lipopeptide antimicrobial that is primarily excreted by the kidney. We examined daptomycin bactericidal activity in an in vitro pharmacodynamic model (IVPM) under normal and simulated impaired renal function against methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA).

METHODS

Two clinical strains MSSA-1199 and MRSA-494 were used in an IVPM. MICs and MBCs were determined according to CLSI. Daptomycin free concentrations were simulated that corresponded to dose regimens of 4, 6 and 8 mg/kg every 24 h at 8 h t(1/2) (Scheme I) and every 48 h at 30 h t(1/2) (Scheme II). In addition, we simulated daptomycin free concentrations corresponding to fractional dose regimens of 2, 3 and 4 mg/kg every 24 h at 30 h t(1/2) (Scheme III). The targeted C(max free)/MIC for 2, 3, 4, 6 and 8 mg/kg against MSSA-1199 ranged from 5.2 to 21.2. The targeted C(max free)/MIC for 2, 3, 4, 6 and 8 mg/kg against MRSA-494 ranged from 10.4 to 42.2. The targeted AUC(free)/MIC for Schemes I, II and III against MSSA-1199 ranged from 94 to 392. The targeted AUC(free)/MIC for Schemes I, II and III against MRSA-494 ranged from 188 to 581. Bactericidal activity and the potential for resistance were determined over 96 h. All models were completed in triplicate.

RESULTS

Daptomycin MICs (MBCs) for MSSA-1199 and MRSA-494 were 0.5 (1.0) mg/L and 0.25 (0.25) mg/L, respectively. Daptomycin 6 and 8 mg/kg at both 8 and 30 h t(1/2) achieved 99.9% kill as early as 1 h. Daptomycin 4 mg/kg achieved 99.9% kill as early as 1 h when given at 8 and 30 h t(1/2) but was not maintained to an endpoint of 96 h (P > 0.05).

CONCLUSIONS

Overall, there was no difference in kill noted for daptomycin regimens at 4, 6 and 8 mg/kg every 24 h at 8 h t(1/2) versus every 48 h at 30 h t(1/2). Fractional doses of daptomycin at 30 h t(1/2) were inferior to daptomycin regimens of 4, 6 and 8 mg/kg administered every 48 h (P = 0.03).

Daptomycin: a novel cyclic lipopeptide antimicrobial

PURPOSE

The development, activity, pharmacokinetics, pharmacodynamics, clinical efficacy, adverse effects, and dosage and administration of daptomycin are reviewed.

SUMMARY

Daptomycin, a novel cyclic lipopeptide antimicrobial, is bactericidal against a range of gram-positive bacteria, including many multiple-drug-resistant isolates. It has only minimal activity against anaerobic bacteria and no activity against gram-negative bacteria. Daptomycin exhibits linear pharmacokinetics, and the plasma concentration-versus-time relationship is best described by a two-compartment model with first-order elimination. The initial bactericidal activity is rapid, extensive, and concentration related. In clinical trials, daptomycin has shown efficacy in treating complicated skin and skin-structure infections (CSSSIs); the drug carries FDA-approved labeling for same. The adverse effects of daptomycin appear comparable to those of vancomycin and semisynthetic penicillins. The dosage for CSSSIs is 4 mg/kg by i.v. infusion every 24 hours.

CONCLUSION

Daptomycin is bactericidal against gram-positive organisms and offers an option in the treatment of CSSSIs.

Daptomycin: a cyclic lipopeptide antimicrobial agent

Objectives:

The aims of this article were: to summarize the pharmacology, pharmacokinetics, and efficacy ofdaptomycin; to explore its safety profile; and to discuss its current and potential roles as an antimicrobial therapy.

Methods:

A literature search was conducted using the MEDLINE (1966–August 2004) and InternationalPharmaceutical Abstracts (1970–August 2004) databases with the search terms daptomycin, LY146032, and lipopeptide antibiotics. Abstracts of the Interscience Conference on Antimicrobial Agents and Chemotherapy and documents submitted to the US Food and Drug Administration were also reviewed.

Results:

Phase III study results suggest no difference in efficacy or tolerability between daptomycin 4 mg/kgIV QD and vancomycin or semisynthetic penicillins for complicated skin and skin-structure infections. Animal studies suggest daptomycin may be useful for the treatment of endocarditis. Daptomycin is not indicated for pneumonia, with poorer outcomes than conventional treatment It is available as an IV medication and exhibits 92% plasma protein binding in vitro. In healthy adult humans, daptomycin has a volume of distribution of 0.1 Ukg and a plasma elimination half-life of ∼9 hours, and is eliminated primarily by renal excretion (∼54%). In patients with reduced renal function, including those receiving hemodialysis and peritoneal dialysis, the dose interval should be 48 hours. No dosage adjustment appears to be necessary for mild to moderate hepatic impairment. The use of daptomycin in patients with severe hepatic impairment has not been assessed. The most commonly reported adverse events include constipation, nausea, injection-site reactions, headache, and diarrhea. Patients should also be monitored regularly for skeletal muscle toxicity.

Conclusions:

Daptomycin may be useful for complicated skin and skin-structure infections and gram-positive pathogens resistant to conventional antimicrobials. However, limited data are currently available for duration of treatment beyond 14 days and at doses >4 mg/kg QD.

Daptomycin: a novel agent for Gram-positive infections

The alarming increase in the incidence of Gram-positive infections, including those caused by resistant bacteria, has sparked renewed interest in novel antibiotics. One such agent is daptomycin, a novel lipopeptide antibiotic with proven bactericidal activity in vitro against all clinically relevant Gram-positive bacteria. These include resistant pathogens, such as vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), glycopeptide intermediately susceptible Staphylococcus aureus (GISA), coagulase-negative staphylococci (CNS) and penicillin-resistant Streptococcus pneumoniae (PRSP), for which there are very few therapeutic alternatives. Daptomycin provides rapid, concentration-dependent killing and a relatively prolonged concentration-dependent post-antibiotic effect in vitro. Spontaneous acquisition of resistance to daptomycin occurs rarely. Daptomycin exhibits linear pharmacokinetics, minimal accumulation with once-daily dosing, and low plasma clearance and volume of distribution. Phase II clinical trials indicate that daptomycin at doses of 2 mg/kg q24 h and 3 mg/kg q12 h is efficacious against skin and soft tissue infections and bacteremia, respectively. In addition, results in endocarditis suggested potential efficacy with higher doses. On the basis of clinical trials to date, it appears that daptomycin has an excellent safety profile, with the incidence and nature of serious adverse events comparable to those observed with conventional therapy. Adverse events associated with other classes of antimicrobials (nephrotoxicity, local irritation, ototoxicity, hypersensitivity, and gastrointestinal effects) were uncommon with daptomycin. Minimal skeletal muscle toxicity was seen at only the highest dose tested (4 mg/kg q12 h), predicted by elevations in serum creatinine phosphokinase, and readily reversible upon discontinuation of treatment. There were no signs of toxicity in cardiac or smooth muscle. Phase II and III clinical trials are underway to evaluate daptomycin for the treatment of Gram-positive bacteremia and complicated skin and soft tissue infections, respectively. Daptomycin holds promise as a rapidly acting and highly effective antibiotic for Gram-positive infections.

Daptomycin

Daptomycin is a lipopeptide antibacterial with rapid in vitro activity against Gram-positive cocci. It is approved for use in patients with complicated skin and skin structure infections (cSSSIs) caused by specified Gram-positive cocci. In vitro, daptomycin was active against Staphylococcus aureus (including meticillin-resistant strains), Streptococcus pyogenes, S. agalactiae, group C and G beta-haemolytic streptococci and vancomycin-susceptible Enterococcus faecalis. Bactericidal activity in vitro was rapid and concentration dependent. In two randomised, investigator-blinded, multicentre trials in patients with cSSSIs, intravenous daptomycin 4 mg/kg once daily was as effective as standard therapy (intravenous semi-synthetic penicillin 4-12 g/day or vancomycin 1 g 12-hourly). Clinical success rates assessed 6-20 days after treatment end were 82.1% in daptomycin recipients and 82.9% in recipients of standard therapy (pooled data). In patients with cSSSIs, the adverse event profiles of daptomycin and vancomycin were similar. Creatine phosphokinase (CPK) levels increased in 2.8% of daptomycin recipients and 1.8% of patients who received standard therapy; only one daptomycin recipient (0.2%) experienced increased CPK levels and muscle symptoms that were not associated with any comorbid factors.

Daptomycin pharmacokinetics and safety following administration of escalating doses once daily to healthy subjects

The purpose of this paper is to establish the pharmacokinetics and safety of escalating, once-daily doses of daptomycin, a novel lipopeptide antibiotic active against gram-positive pathogens, including those resistant to methicillin and vancomycin. This phase 1, multiple-dose, double-blind study involved 24 healthy subjects in three dose cohorts (4, 6, and 8 mg/kg of body weight) who were randomized to receive daptomycin or the control at a 3:1 ratio and administered the study medication by a 30-min intravenous infusion every 24 h for 7 to 14 days. Daptomycin pharmacokinetics was assessed by blood and urine sampling. Safety and tolerability were evaluated by monitoring adverse events (AEs) and laboratory parameters. Daptomycin pharmacokinetics was linear through 6 mg/kg, with a slight ( approximately 20%) nonlinearity in the area under the curve and trough concentration at the highest dose studied (8 mg/kg). The pharmacokinetic parameters measured on the median day of the study period, (day 7) were half-life ( approximately 9 h), volume of distribution ( approximately 0.1 liters/kg), systemic clearance ( approximately 8.2 ml/h/kg), and percentage of the drug excreted intact in urine from 0 to 24 h ( approximately 54%). Daptomycin protein binding (mean amount bound, 91.7%) was independent of the drug concentration. No gender effect was observed. All subjects who received daptomycin completed the study. The frequencies and distributions of treatment-emergent AEs were similar for the subjects who received daptomycin and the control subjects. There were no serious AEs and no pattern of dose-related events. The pharmacokinetics of once-daily administration of daptomycin was linear through 6 mg/kg. For all three doses, plasma daptomycin concentrations were consistent and predictable throughout the dosing interval. Daptomycin was well tolerated when it was administered once daily at a dose as high as 8 mg/kg for 14 days.