Mechanism of Action
Linezolid is a synthetic antibacterial agent of a new class of antibiotics, the oxazolidinones, which has clinical utility in the treatment of infections caused by aerobic Gram-positive bacteria. The in vitro spectrum of activity of linezolid also includes certain Gram-negative bacteria and anaerobic bacteria. Linezolid inhibits bacterial protein synthesis through a mechanism of action different from that of other antibacterial agents; therefore, cross-resistance between linezolid and other classes of antibiotics is unlikely. Linezolid binds to a site on the bacterial 23S ribosomal RNA of the 50S subunit and prevents the formation of a functional 70S initiation complex, which is an essential component of the bacterial translation process. The results of time-kill studies have shown linezolid to be bacteriostatic against enterococci and staphylococci. For streptococci, linezolid was found to be bactericidal for the majority of isolates.
Mechanisms of Resistance
In clinical trials, resistance to linezolid developed in 6 patients infected with Enterococcus faecium (4 patients received 200 mg every 12 hours, lower than the recommended dose, and 2 patients received 600 mg every 12 hours). In a compassionate use program, resistance to linezolid developed in 8 patients with E. faecium and in 1 patient with Enterococcus faecalis. All patients had either unremoved prosthetic devices or undrained abscesses. Resistance to linezolid occurs in vitro at a frequency of 1 × 10 –9 to 1 × 10 –11. In vitro studies have shown that point mutations in the 23S rRNA are associated with linezolid resistance. Reports of vancomycin-resistant E. faecium becoming resistant to linezolid during its clinical use have been published. There are reports of Staphylococcus aureus (methicillin-resistant) developing resistance to linezolid during clinical use. The linezolid resistance in these organisms is associated with a point mutation in the 23S rRNA (substitution of thymine for guanine at position 2576) of the organism. Also linezolid resistance in staphylococci mediated by the enzyme methyltransferase has been reported. This resistance is mediated by the cfr (chloramphenicol-florfenicol) gene located on a plasmid which is transferable between staphylococci.
Resistance to linezolid has not been reported in Streptococcus spp., including Streptococcus pneumoniae.
Interaction with Other Antimicrobials
In vitro studies have demonstrated additivity or indifference between linezolid and vancomycin, gentamicin, rifampin, imipenem-cilastatin, aztreonam, ampicillin, or streptomycin.
Linezolid has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section (1).
Enterococcus faecium (vancomycin-resistant isolates only)
Staphylococcus aureus (including methicillin-resistant isolates)
The following in vitro data are available, but their clinical significance is unknown. At least 90% of the following microorganisms exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint for linezolid. However, the safety and effectiveness of linezolid in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials.
Enterococcus faecalis (including vancomycin-resistant isolates)
Enterococcus faecium (vancomycin-susceptible isolates)
Staphylococcus epidermidis (including methicillin-resistant isolates)
Viridans group streptococci
INDICATIONS AND USAGE:
ZYVOX is indicated for the treatment of infections caused by susceptible strains of the designated microorganisms in the specific conditions listed below. ZYVOX is not indicated for the treatment of Gram-negative infections. It is critical that specific Gram-negative therapy be initiated immediately if a concomitant Gram-negative pathogen is documented or suspected.
Nosocomial pneumonia caused by Staphylococcus aureus (methicillin-susceptible and -resistant isolates) or Streptococcus pneumoniae.
Community-acquired pneumonia caused by Streptococcus pneumoniae, including cases with concurrent bacteremia, or Staphylococcus aureus (methicillin-susceptible isolates only) [see Clinical Studies (14)].
Skin and Skin Structure Infections
Complicated skin and skin structure infections, including diabetic foot infections, without concomitant osteomyelitis, caused by Staphylococcus aureus (methicillin-susceptible and -resistant isolates), Streptococcus pyogenes, or Streptococcus agalactiae. ZYVOX has not been studied in the treatment of decubitus ulcers.
Uncomplicated skin and skin structure infections caused by Staphylococcus aureus (methicillin-susceptible isolates only) or Streptococcus pyogenes.
Vancomycin-resistant Enterococcus faecium Infections
Vancomycin-resistant Enterococcus faecium infections, including cases with concurrent bacteremia.
To reduce the development of drug-resistant bacteria and maintain the effectiveness of ZYVOX and other antibacterial drugs, ZYVOX should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.
The safety and efficacy of ZYVOX formulations given for longer than 28 days have not been evaluated in controlled clinical trials.
ZYVOX formulations are contraindicated for use in patients who have known hypersensitivity to linezolid or any of the other product components.
Monoamine Oxidase Inhibitors
Linezolid should not be used in patients taking any medicinal product which inhibits monoamine oxidases A or B (e.g., phenelzine, isocarboxazid) or within two weeks of taking any such medicinal product.
WARNING AND PRECAUTIONS:
- Myelosuppression: Monitor complete blood counts weekly. Consider discontinuation in patients who develop or have worsening myelosuppression.
- Peripheral and optic neuropathy: Reported primarily in patients treated for longer than 28 days. If patients experience symptoms of visual impairment, prompt ophthalmic evaluation is recommended.
- Serotonin syndrome: Patients taking serotonergic antidepressants should receive ZYVOX only if no other therapies are available. Discontinue serotonergic antidepressants and monitor patients for signs and symptoms of both serotonin syndrome and antidepressant discontinuation.
- A mortality imbalance was seen in an investigational study in linezolid-treated patients with catheter-related bloodstream infections.
- Clostridium difficile associated diarrhea: Evaluate if diarrhea occurs.
- Potential interactions producing elevation of blood pressure: monitor blood pressure.
- Hypoglycemia: Postmarketing cases of symptomatic hypoglycemia have been reported in patients with diabetes mellitus receiving insulin or oral hypoglycemic agents.
DOSAGE AND ADMINISTRATION:
General Dosage and Administration
The recommended dosage for ZYVOX formulations for the treatment of infections is described in Table 1.
Table 1. Dosage Guidelines for ZYVOX:
|Dosage and Route of Administration
||Recommended Duration of Treatment (consecutive days)
|Pediatric Patients† (Birth through 11 Years of Age)
||Adults and Adolescents
(12 Years and Older)
||10 mg/kg intravenously or oral‡ every 8 hours
||600 mg intravenously or oral‡ every 12 hours
||10 to 14
|Community-acquired pneumonia, including concurrent bacteremia
|Complicated skin and skin structure infections
|Vancomycin-resistant Enterococcus faecium infections, including concurrent bacteremia
||10 mg/kg intravenously or oral‡ every 8 hours
||600 mg intravenously or oral‡ every 12 hours
||14 to 28
|Uncomplicated skin and skin structure infections
||<5 yrs: 10 mg/kg oral‡ every 8 hours
5–11 yrs: 10 mg/kg oral‡ every
|Adults: 400 mg oral‡ every
Adolescents: 600 mg oral‡ every 12 hours
10 to 14
*Due to the designated pathogens [see Indications and Usage (1)]
† Neonates <7 days: Most pre-term neonates <7 days of age (gestational age <34 weeks) have lower systemic linezolid clearance values and larger AUC values than many full-term neonates and older infants. These neonates should be initiated with a dosing regimen of 10 mg/kg every 12 hours. Consideration may be given to the use of 10 mg/kg every 8 hours regimen in neonates with a sub-optimal clinical response. All neonatal patients should receive 10 mg/kg every 8 hours by 7 days of life.
‡ Oral dosing using either ZYVOX Tablets or ZYVOX for Oral Suspension.
No dose adjustment is necessary when switching from intravenous to oral administration.
ZYVOX I.V. Injection is supplied in single-use, ready-to-use infusion bags. Parenteral drug products should be inspected visually for particulate matter prior to administration. Check for minute leaks by firmly squeezing the bag. If leaks are detected, discard the solution, as sterility may be impaired. Keep the infusion bags in the overwrap until ready to use. Store at room temperature. Protect from freezing. ZYVOX I.V. Injection may exhibit a yellow color that can intensify over time without adversely affecting potency.
ZYVOX I.V. Injection should be administered by intravenous infusion over a period of 30 to 120 minutes. Do not use this intravenous infusion bag in series connections. Additives should not be introduced into this solution. If ZYVOX I.V. Injection is to be given concomitantly with another drug, each drug should be given separately in accordance with the recommended dosage and route of administration for each product.
If the same intravenous line is used for sequential infusion of several drugs, the line should be flushed before and after infusion of ZYVOX I.V. Injection with an infusion solution compatible with ZYVOX I.V. Injection and with any other drug(s) administered via this common line.
Compatible intravenous solutions include 0.9% Sodium Chloride Injection, USP, 5% Dextrose Injection, USP, and Lactated Ringer's Injection, USP.
Constitution of Oral Suspension
ZYVOX for Oral Suspension is supplied as a powder/granule for constitution. Gently tap bottle to loosen powder. Add a total of 123 mL distilled water in two portions. After adding the first half, shake vigorously to wet all of the powder. Then add the second half of the water and shake vigorously to obtain a uniform suspension. After constitution, each 5 mL of the suspension contains 100 mg of linezolid. Before using, gently mix by inverting the bottle 3 to 5 times. Do not shake. Store constituted suspension at room temperature. Use within 21 days after constitution.
ZYVOX I.V. Injection: 100-mL (200 mg linezolid), 200-mL (400 mg linezolid) and 300-mL (600 mg linezolid) single-use, ready-to-use flexible plastic infusion bags in a foil laminate overwrap. The infusion bags and ports are latex-free.
ZYVOX 600 mg Tablet: white, capsule-shaped, film-coated tablet printed with "ZYVOX 600 mg"
ZYVOX for Oral Suspension: dry, white to off-white, orange-flavored granule/powder. When constituted as directed, each bottle will contain 150 mL of a suspension providing the equivalent of 100 mg of linezolid per each 5 mL.
SOURCE: Package insert data: