Dalbavancin is an intravenous lipoglycopeptide with activity against Gram-positive pathogens and an MIC 90 for Staphylococcus aureus of 0.06 g/ml. With a terminal half-life of >14 days, dosing regimens with infrequent parenteral administration become available to treat infectious diseases such as osteomyelitis and endocarditis that otherwise require daily dosing for many weeks. In order to support a rationale for these novel regimens, the pharmacokinetics over an extended dosing interval and the distribution of dalbavancin into bone and articular tissue were studied in two phase I trials and pharmacokinetic modeling was performed. Intravenous administration of 1,000 mg of dalbavancin on day 1 followed by 500 mg weekly for seven additional weeks was well tolerated and did not demonstrate evidence of drug accumulation. In a separate study, dalbavancin concentrations in cortical bone 12 h after infusion of a single 1,000-mg intravenous infusion were 6.3 g/g and 2 weeks later were 4.1 g/g. A twodose, once-weekly regimen that would provide tissue exposure over the dalbavancin MIC for Staphylococcus aureus for 8 weeks, maximizing the initial exposure to treatment while minimizing the frequency of intravenous therapy, is proposed. Osteomyelitis is an infection of the bone associated with either hematogenous dissemination or direct inoculation as a consequence of trauma or infection from contiguous tissues. Its presentation may be either acute or chronic. The most common pathogen responsible for acute infection in adults is Staphylococcus aureus, with Pseudomonas aeruginosa, Serratia marcescens, and Escherichia coli also involved in traumatic infections and chronic presentations. Infection in children occurs less frequently and is predominantly a result of bacteremia with S. aureus and infection in the growth plate (1). Treatment regimens extend for 4 to 6 weeks, with durations as long as 8 weeks recommended for treatment of infection due to methicillin-resistant S. aureus (MRSA) (2). Commonly used therapies include cefazolin, oxacillin, or vancomycin for coverage of Gram-positive pathogens and cephalosporins, carbapenems, and the -lactamase inhibitor agents for treatment of Gram-negative pathogens (2,3). No other therapies in recent times have received FDA approval.Because the incidence of MRSA in the community in the United States is as high as 40% (4), empirical treatment of osteomyelitis now requires consideration of antimicrobial coverage of this organism, typically with vancomycin. Vancomycin has been demonstrated to be active in animal models of osteomyelitis (5). Concentrations in bone from 2.7 to 9.3 g/ml have been documented (6, 7), exceeding the vancomycin MIC 90 for S. aureus of 1 g/ml (8). Because of the wide variety of underlying etiologies and comorbidities associated with osteomyelitis, it is difficult to generalize the rates of clinical success from clinical trials, but one study documented a clinical response in 10/15 patients after continuous intravenous (i.v.) infusion of vancomycin (9). Long-term d...
iThe percentage of time that free drug concentrations remain above the MIC (fT >MIC ) that is necessary to prevent mortality among cefepime-treated patients with Gram-negative bloodstream infections (GNBSI) is poorly defined. We conducted a retrospective study of adult patients with GNBSI. Eligible cases were frequency matched to ensure categorical representation from all MICs. Organism, MIC, infection source, gender, age, serum creatinine, weight, antibiotic history, and modified APACHE II score were collected from hospital records. Two population pharmacokinetic models (models 1 and 2) were used to impute exposures over the first 24 h in each patient from mean model parameters, covariates, and dosing history. From the imputed exposures, survival thresholds for fT >MIC were identified using classification and regression tree (CART) analysis and analyzed as nominal variables for univariate and multivariate regressions. A ntimicrobial resistance among contemporary Gram-negative (GN) isolates has eroded the efficacy of many first-line antibiotics. Increasing beta-lactam MICs have been correlated with increasing antimicrobial failures in the treatment of serious bacterial infections (1-4). Elevated beta-lactam MICs can be expected to reduce the probability of achieving pharmacokinetic-pharmacodynamic (PK/PD) targets for beta-lactams. As the percentage of time in 24 hours that free drug concentrations are above the MIC (fT ϾMIC ) is the PK/PD target predictive of microbiologic efficacy for beta-lactams (5), decreasing fT ϾMIC is expected to result in worse patient outcomes (6).Cefepime, a broad-spectrum fourth-generation cephalosporin, is widely prescribed as the primary therapy for serious Gramnegative infections, including bloodstream infections (termed GNBSIs) (7). Several clinical studies have associated elevated cefepime MICs with an increased risk of treatment failure and mortality for cefepime-treated patients (1,3,8,9), while other investigations have shown improved clinical outcomes among patients receiving aggressive cefepime dosing for bloodstream infections (BSIs) (10, 11). These previous studies lacked PK/PD data, which could be highly useful in interpreting observed outcomes. Very few studies have analyzed patient outcomes according to fT ϾMIC in cefepime-treated patients (12-14). As such, the necessary fT ϾMIC to prevent mortality for cefepime-treated patients with GNBSI is not well defined.We sought to analyze the cefepime fT ϾMIC to see if a threshold existed for improved survival among patients treated with cefepime for GNBSIs. Secondarily, we sought to examine if candidate clinical threshold values for cefepime fT ϾMIC were predictive of other outcomes, such as hospital and intensive care unit (ICU) lengths of stay (LOS) and 30-day readmission rates. MATERIALS AND METHODSThis retrospective cohort study was conducted at Northwestern Memorial Hospital (NMH) in Chicago, Illinois. Study methods were reviewed and approved by the Institutional Review Boards at Northwestern University and Midwestern Univ...
Garenoxacin (T-3811ME, BMS-284756) is a novel, broad-spectrum des-F(6) quinolone currently under study for the treatment of community-acquired respiratory tract infections. This analysis assessed garenoxacin population pharmacokinetics and exposure-response relationships for safety (adverse effects [AE]) and antimicrobial activity (clinical cure and bacteriologic eradication of Streptococcus pneumoniae and the grouping of Haemophilus influenzae, Haemophilus parainfluenzae, and Moraxella catarrhalis). Data were obtained from three phase II clinical trials of garenoxacin administered orally as 400 mg once daily for 5 to 10 days for the treatment of community-acquired pneumonia, acute exacerbation of chronic bronchitis, and sinusitis. Samples were taken from each patient before drug administration, 2 h following administration of the first dose, and on the day 3 to 5 visit. Individual Bayesian estimates of the fu (fraction unbound), the C max , and the fu for the area under the concentration-time curve from 0 to 24 h (fu AUC 0-24 ) were calculated as measurements of drug exposure by using an ex vivo assessment of average protein binding. Regression analysis was performed to examine the following relationships: treatment-emergent AE incidence and AUC 0-24 , C max , or patient factors; clinical response or bacterial eradication and drug exposure (fu C max /MIC, fu AUC 0-24 /MIC, and other exposure covariates); or disease and patient factors. Garenoxacin pharmacokinetics were described by a one-compartment model with first-order absorption and elimination. Clearance was dependent on creatinine clearance, ideal body weight, age, obesity, and concomitant use of pseudoephedrine. The volume of distribution was dependent on weight and gender. Patients with mild or moderate renal dysfunction had, on average, approximately a 16 or 26% decrease in clearance, respectively, compared to patients of the same gender and obesity classification with normal renal function. AE occurrence was not related to garenoxacin exposure. Overall, clinical cure and bacterial eradication rates were 91 and 90%, respectively, for S. pneumoniae and 93 and 92%, respectively, for the grouping of H. influenzae, H. parainfluenzae, and M. catarrhalis. The fu AUC 0-24 /MIC ratios were high (>90% were >200), and none of the pharmacokinetic-pharmacodynamic exposure measurements indexed to the MIC or other factors were significant predictors of clinical or bacteriologic response. Garenoxacin clearance was primarily related to creatinine clearance and ideal body weight. Although garenoxacin exposure was approximately 25% higher for patients with moderate renal dysfunction, this increase does not appear to be clinically significant as exposures in this patient population were not significant predictors of AE occurrence. Garenoxacin exposures were at the upper end of the exposure-response curves for measurements of antimicrobial activity, suggesting that 400 mg of garenoxacin once daily is a safe and adequate dose for the treatment of the specified community-ac...
Intravenous (IV) minocycline is increasingly used to treat infections caused by multi-drug resistant (MDR)-Acinetobacter baumannii. Despite being approved nearly 50 years ago, published information on its pharmacokinetic (PK) prolife is limited. This multi-center study examined the PK and probability of pharmacokinetic-pharmacodynamic (PK-PD) target attainment profile of IV minocycline in critically ill patients, with suspected or documented infection with Gram-negative bacteria. The PK study population included 55 patients who received a single 200 mg IV dose of minocycline. Plasma PK samples were collected pre-dose and 1, 4, 12, 24, 36, and 48 hours after initiation of minocycline. Total and unbound minocycline concentrations were determined at each timepoint. Probabilities of achieving the PK-PD targets associated with stasis and 1-log killing (fAUC:MIC of 12 and 18, respectively) were evaluated. A two-compartment population PK model with zero-order IV input and first-order elimination, which estimated a constant fraction unbound (fub) for minocycline, best characterized the total and unbound plasma minocycline concentration-time data. The only two covariates retained in the final PK model were body surface area [associated with central volume of distribution] and albumin (associated with fub). In the PK-PD target attainment analyses, minocycline 200 mg IV Q12H was predicted to result in a suboptimal PK-PD profile for patients with A. baumannii infections with MIC values ≥ 1 mg/L. These findings cast uncertainty on the appropriateness of the current minocycline FDA susceptibility breakpoints and suggest that clinicians should strongly consider only combination antibiotic therapy with IV minocycline for all patients with serious Acinetobacter sp. infections.
The relationship between drug exposure and the time course of antimicrobial effect at the primary infection site for acute maxillary sinusitis has not previously been explored. This single-center, open-label study quantified the time course of sinus sterilization, described gatifloxacin exposure at the infection site, and posed the hypothesis that the use of continuous and quantitative time-related end points may allow for better characterization of drug effect with fewer patients than traditional clinical trial approaches. Of the 12 enrolled patients, 10 were clinically evaluable, from whom 7 pathogens were isolated: 4 Streptococcus pneumoniae, 2 staphylococci, and 1 Enterobacter aerogenes. The median predicted 24-h area under the curve (AUC) in sinus aspirates and plasma samples was 54.7 mg x h/L and 30.1 mg x h/L, respectively. The median 24-h AUC ratio for sinus aspirates and plasma samples was 1.51 (range, 0.88-2.23). For patients infected with pneumococci, the median time to sinus sterilization was 50 h. The use of quantitative time-related end points may be useful in evaluating the efficacy of antimicrobial agents with fewer patients.
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