Barry Hafkin

Randomized Comparison of Linezolid (PNU-100766) versus Oxacillin-Dicloxacillin for Treatment of Complicated Skin and Soft Tissue Infections

ABSTRACT This randomized, double-blind, multicenter trial compared the efficacy and safety of linezolid, an oxazolidinone, with those of oxacillin-dicloxacillin in patients with complicated skin and soft tissue infections. A total of 826 hospitalized adult patients were randomized to receive linezolid (600 mg intravenously [i.v.]) every 12 h or oxacillin (2 g i.v.) every 6 h; following sufficient clinical improvement, patients were switched to the respective oral agents (linezolid [600 mg orally] every 12 h or dicloxacillin [500 mg orally] every 6 hours). Primary efficacy variables were clinical cure rates in both the intent-to-treat (ITT) population and clinically evaluable (CE) patients and microbiological success rate in microbiologically evaluable (ME) patients. Safety and tolerability were evaluated in the ITT population. Demographics and baseline characteristics were similar across treatment groups in the 819 ITT patients. In the ITT population, the clinical cure rates were 69.8 and 64.9% in the linezolid and oxacillin-dicloxacillin groups, respectively (P = 0.141; 95% confidence interval −1.58 to 11.25). In 298 CE linezolid-treated patients, the clinical cure rate was 88.6%, compared with a cure rate of 85.8% in 302 CE patients who received oxacillin-dicloxacillin. In 143 ME linezolid-treated patients, the microbiological success rate was 88.1%, compared with a success rate of 86.1% in 151 ME patients who received oxacillin-dicloxacillin. Both agents were well tolerated; most adverse events were of mild-to-moderate intensity. No serious drug-related adverse events were reported in the linezolid group. These data support the use of linezolid for the treatment of adults with complicated skin and soft tissue infections.

Worldwide Assessment of Linezolid's Clinical Safety and Tolerability: Comparator-Controlled Phase III Studies

ABSTRACT Linezolid, an oxazolidinone antibiotic, has 100% oral bioavailability and favorable activities against gram-positive pathogens including multidrug-resistant staphylococci, enterococci, and pneumococci. Safety assessments were conducted for 2,046 linezolid-treated patients and 2,001 comparator drug-treated patients from seven controlled clinical trials comparing the activities of linezolid and comparator drugs against nosocomial and community-acquired pneumonia, skin and skin structure infections, and methicillin-resistant staphylococcal infections. Drug-related adverse events were primarily transient. The most frequent (≥2%) adverse events caused by linezolid and the comparator drugs were diarrhea (4.3 and 3.2%, respectively; P = 0.074), nausea (3.4 and 2.3%, respectively; P = 0.036), and headache (2.2 and 1.3%, respectively; P = 0.047). Treatment discontinuations due to drug-related events (2.4 and 1.9%, respectively), serious adverse events (11.4 and 10.6%, respectively), and deaths (4.8 and 4.9%, respectively) were similar. No clinically significant drug-related hematologic events were reported, and laboratory safety data were comparable. In the first 6 months of postmarketing surveillance, hematologic abnormalities were reported in 0.1% of linezolid-treated patients, but no irreversible blood dyscrasias were documented. The risk for transient, reversible hematologic effects from treatment with linezolid should be considered together with the clinical benefits associated with its use.

Mode of Action, In Vitro Activity, and In Vivo Efficacy of AFN-1252, a Selective Antistaphylococcal FabI Inhibitor

ABSTRACT The mechanism of action of AFN-1252, a selective inhibitor of Staphylococcus aureus enoyl-acyl carrier protein reductase (FabI), which is involved in fatty acid biosynthesis, was confirmed by using biochemistry, macromolecular synthesis, genetics, and cocrystallization of an AFN-1252–FabI complex. AFN-1252 demonstrated a low propensity for spontaneous resistance development and a time-dependent reduction of the viability of both methicillin-susceptible and methicillin-resistant S. aureus, achieving a ≥2-log10 reduction in S. aureus counts over 24 h, and was extremely potent against clinical isolates of S. aureus (MIC90, 0.015 μg/ml) and coagulase-negative staphylococci (MIC90, 0.12 μg/ml), regardless of their drug resistance, hospital- or community-associated origin, or other clinical subgroup. AFN-1252 was orally available in mouse pharmacokinetic studies, and a single oral dose of 1 mg/kg AFN-1252 was efficacious in a mouse model of septicemia, providing 100% protection from an otherwise lethal peritoneal infection of S. aureus Smith. A median effective dose of 0.15 mg/kg indicated that AFN-1252 was 12 to 24 times more potent than linezolid in the model. These studies, demonstrating a selective mode of action, potent in vitro activity, and in vivo efficacy, support the continued investigation of AFN-1252 as a targeted therapeutic for staphylococcal infections.

AFN-1252, a FabI Inhibitor, Demonstrates a Staphylococcus-Specific Spectrum of Activity

ABSTRACT AFN-1252, a potent inhibitor of enoyl-acyl carrier protein reductase (FabI), inhibited all clinical isolates of Staphylococcus aureus (n = 502) and Staphylococcus epidermidis (n = 51) tested, including methicillin (meticillin)-resistant isolates, at concentrations of ≤0.12 μg/ml. In contrast, AFN-1252 was inactive (MIC90, >4 μg/ml) against clinical isolates of Streptococcus pneumoniae, beta-hemolytic streptococci, Enterococcus spp., Enterobacteriaceae, nonfermentative gram-negative bacilli, and Moraxella catarrhalis. These data support the continued development of AFN-1252 for the treatment of patients with resistant staphylococcal infections.

Effects of Interferon and Adenine Arabinoside Treatment of Hepatitis B Virus Infection on Cellular Immune Responses

Fifteen patients with chronic hepatitis B were treated with adenine arabinoside (Ara-A) or human leukocyte interferon (HLI). Cellular immune response to hepatitis B virus surface antigen and antigens prepared from herpes simplex virus, varicella zoster virus, and cytomegalovirus was measured by a lymphocyte blast transformation assay and an assay for interferon production. Measurements were made before, during, and after antiviral treatment. Unlike patients convalescing from acute hepatitis B, only 2 of 15 patients with chronic hepatitis B had significant blast transformation to hepatitis B surface antigen. One such response occurred during the pretreatment period of HLI therapy, and the other was in a patient undergoing low-dose (<105 U/kg per day) HLI therapy. Mononuclear cell cultures were tested for interferon production in the presence of hepatitis B surface antigen. Cells from only 1 of 15 patients produced detectable levels of interferon. In contrast, all of these patients had normal cellular immune responses to herpesvirus antigens. Transformation responses to herpes antigens decreased three- to fivefold after patients were treated with >105 U of HLI per kg per day. Antiviral therapy with <105 U of HLI per kg per day or Ara-A did not produce a detectable depression of transformation response. Ara-A produced marked lymphocytopenia and a marked lymphocyte fragility after 5 or more days of therapy. In vitro Ara-A was toxic to lymphocytes at concentrations as low as 0.5 μg/ml. These changes in lymphocyte parameters may affect the outcome of antiviral therapy.

In vitro activity (MICs and rate of kill) of AFN-1252, a novel FabI inhibitor, in the presence of serum and in combination with other antibiotics

Abstract AFN-1252 is a novel inhibitor of FabI, an essential enzyme in fatty acid biosynthesis in Staphylococcus spp. AFN-1252 exhibits typical MIC90 values of ⩽0·015 μg/ml against diverse clinical isolates of S. aureus, oral absorption, long elimination half-live and efficacy in animal models. We now report high binding (∼95%) to serum proteins of mouse, rat, dog and humans, associated with an eight-fold increase in minimal inhibitory concentration (MIC) and which may be responsible for the long elimination half-lives on pharmacokinetic studies. Unlike daptomycin, AFN-1252 activity is not reduced in the presence of lung surfactant. AFN-1252 exhibits a short post-antibiotic effect of 1·1 hours against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) following a 4-hour exposure period. The AFN-1252 unique spectrum of activity is not compromised by interactions with major antibiotic classes, but demonstrates synergy with low concentrations of gentamicin against MSSA and MRSA. These studies support the continued investigation of AFN-1252 as a targeted therapeutic for staphylococcal infections.

AFN-1252 in vitro absorption studies and pharmacokinetics following microdosing in healthy subjects.

OBJECTIVES To investigate the absorption, distribution, metabolism and excretion of AFN-1252, a novel inhibitor of the essential FabI enzyme in Staphylococcus spp., in vitro and following microdosing in healthy adult male subjects following intravenous and oral administration. METHODS Three ADME studies, comprising a Caco-2 assay, a rat intestinal perfusion model and a microdosing study in healthy human volunteers, were conducted. RESULTS The Caco-2 assay indicated that AFN-1252 in solution is well-absorbed and undergoes insignificant efflux, and its transport across the intestinal wall is probably passive. In the rat intestinal perfusion model, AFN-1252 exhibited high permeability potential across three segments, in the rank order of jejunum=ileum>colon. Taken together with the low aqueous solubility, the data from these studies indicate that AFN-1252 is a BCS Class II molecule with solubility-limited absorption. Analysis of the [(14)C]-AFN-1252 radioactivity concentration-time data indicated similar pharmacokinetics following intravenous and oral administration in the microdosing study in healthy volunteers. These included long terminal half-lives of ∼7 h and 83% bioavailability, indicating that there was little first-pass metabolism following oral dosing. AFN-1252 exhibited good distribution to skin and skin structures where its anti-staphylococcal activity may be required. Urinary and faecal excretion are major elimination routes for [(14)C]-AFN-1252 following intravenous or oral administration. CONCLUSIONS AFN-1252 has the potential for both intravenous and oral administration, once- or twice-daily dosing and good tissue distribution in humans. Further safety, efficacy and pharmacokinetic studies in man are required to investigate therapeutically-relevant doses for this novel agent and its targeted selectivity and high potency against Staphylococcus spp.

Safety, tolerability and pharmacokinetics of AFN-1252 administered as immediate release tablets in healthy subjects

AIMS AFN-1252 is a novel inhibitor of FabI, an essential enzyme in Staphylococcus spp. This study was undertaken to assess the safety, tolerability and pharmacokinetic properties of AFN-1252, following oral administration in an ascending dose trial. MATERIALS & METHODS This was a double-blind, randomized, placebo-controlled, two-part study. In Part I, single doses (QD) of 100, 200, 300, or 400 mg AFN-1252 were administered. In Part II, subjects received 200, 400, 600, or 800 mg (total daily dose) where 100, 200 and 400-mg doses were given twice in one day. RESULTS AFN-1252 was well-absorbed with Cmax at 3-4 h when given once per day and 2.5-9 h when dosed twice in a single dosing day. T½ ranged from 8 to 11 h. Total and peak exposures of AFN-1252 increased nonlinearly. Adverse events were primarily mild and resolved promptly. CONCLUSIONS Oral doses of AFN-1252 were safe and well tolerated. AFN-1252 has the potential for once or twice-a-day dosing for treatment of staphylococcal infections.

Safety, tolerability and pharmacokinetics of multiple oral doses of AFN-1252 administered as immediate release (IR) tablets in healthy subjects

Background: AFN-1252 is a novel inhibitor of FabI, which is essential in Staphylococcus spp. This study evaluated the safety, tolerability and pharmacokinetics of multiple oral doses of AFN-1252 immediate-release tablets. Methods: Part I evaluated AFN-1252 as a single 200 mg dose in fed versus fasted subjects. Part II evaluated 200, 300 and 400 mg doses of AFN-1252 administered once-daily for 10 days. Results: Pharmacokinetics indicated good absorption with a median Tmax of 2–3 hours, and a mean t1/2 of 7–10 hours, for all doses. Cmax and AUC responses were non-linear. A high-fat meal reduced AUC0–t and Cmax values by 62% and 48%, respectively, and delayed Tmax by 2.5 hours. All adverse events, including possibly drug-related headache and nausea, were mild or moderate. Conclusions: Multiple ascending doses of AFN-1252 were safe and well tolerated. AFN-1252 has potential for once- or twice-daily dosing in the treatment of staphylococcal infections.

Single- and Multiple-Dose Study To Determine the Safety, Tolerability, Pharmacokinetics, and Food Effect of Oral MRX-I versus Linezolid in Healthy Adult Subjects

ABSTRACT A multipart phase 1 study was conducted to determine the safety, tolerability, pharmacokinetics, and food effect of the novel oral oxazolidinone, MRX-I, in healthy adults, as well as the tolerability of longer-term exposure of both oral MRX-I and linezolid. Thirty subjects in part 1 received single ascending doses of MRX-I or placebo under fasting or fed condition in a double-blind crossover design. Twelve subjects in part 2 received MRX-I at 800 mg every 12 h (q12h) for 14 days in a double-blind, placebo-controlled design. In part 3, 24 subjects were randomized to receive 28 days of MRX-I at 800 mg q12h or oral linezolid at 600 mg q12h for 28 days in a double-blind, double-dummy design. Oral MRX-I was associated with a greater bioavailability and exposure when administered with food, and minimal accumulation of MRX-I occurred after multiple-dose administration. Oral MRX-I was well tolerated at single doses of up to 1,200 and 800 mg q12h for up to 28 days; all adverse events were mild to moderate in severity, and there was no drug discontinuation due to adverse events. These data support further clinical development of oral MRX-I in the treatment of resistant Gram-positive bacterial infections.