Linezolid Injection: Indications, Dosage, Precautions, Adverse Effects
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Linezolid Injection - Product Information

Manufacture: Fresenius Kabi USA, LLC
Country: Canada
Condition: Bacteremia, Bacterial Infection, Methicillin-Resistant Staphylococcus Aureus Infection, Nosocomial Pneumonia, Pneumonia, Skin and Structure Infection
Class: Oxazolidinone antibiotics
Form: Liquid solution, Intravenous (IV)
Ingredients: Linezolid

Summary Product Information

Route of Administration Dosage Form / Strength Clinically Relevant Nonmedicinal Ingredients
Intravenous Injection Intravenous Injection 2 mg/mL None

For a complete listing, see Dosage Forms, Composition and Packaging section.

Indications and Clinical Use

Linezolid injection is indicated for:

Treatment of adult patients with the following infections, when caused by susceptible strains of the designated aerobic Gram-positive micro-organisms:

Note: Linezolid injection 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 (see Warnings and Precautions).

Vancomycin-Resistant Enterococcus faecium (VREF) Infections: Linezolid injection is indicated for the treatment of the following infections when due to VREF:

  • Intra-abdominal, skin and skin-structure, and urinary tract infections (including cases associated with concurrent bacteremia) (see Clinical Trials section).

Note: This indication for VREF is based on non-comparative studies.

Nosocomial pneumonia caused by Staphylococcus aureus (methicillin-susceptible and – resistant strains), or Streptococcus pneumoniae (penicillin-susceptible strains only).

Community-acquired pneumonia caused by Streptococcus pneumoniae (penicillin-susceptible strains only) including cases with concurrent bacteremia or Staphylococcus aureus (methicillin-susceptible and – resistant strains).

Complicated skin and skin structure infections, including non-limb threatening diabetic foot infections, without concomitant osteomyelitis, caused by Staphylococcus aureus (methicillin -susceptible and – resistant strains), Streptococcus pyogenes, or Streptococcusagalactiae.

Note: Linezolid injection has not been studied in the treatment of necrotizing fasciitis or decubitus ulcers.

Uncomplicated skin and skin structure infections caused by Staphylococcus aureus (methicillin-susceptible strains only) or Streptococcus pyogenes.

Prior to instituting treatment with linezolid injection, appropriate specimens should be obtained for isolation of the causative organism(s) and for determination of susceptibility to linezolid injection. In infections where concomitant Gram-negative and/or anaerobic pathogens are suspected or are known to be present, linezolid injection must be used in combination with an appropriate antibiotic in order to provide adequate antimicrobial coverage.

If clinically indicated, treatment with linezolid injection may be started empirically before results of susceptibility testing are available. Local epidemiology and susceptibility patterns may help in the selection of empiric therapy. Once culture results become available, antimicrobial therapy can be adjusted accordingly.

To reduce the development of drug-resistant bacteria and maintain the effectiveness of linezolid injection and other antibacterial drugs, linezolid injection should be used only to treat infections that are proved or suspected to be caused by susceptible bacteria. Because the inappropriate use of antibiotics can increase organism resistance, prescribers should carefully consider alternatives before initiating treatment with linezolid injection in an outpatient setting.

Contraindications

Linezolid is 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 (see Drug Interactions, Drug-Drug Interactions).

Potential Interactions Producing Elevation of Blood Pressure

Unless patients are monitored for potential increases in blood pressure, linezolid should not be administered to patients with uncontrolled hypertension, pheochromocytoma, thyrotoxicosis and/or patients taking any of the following types of medications: directly and indirectly acting sympathomimetic agents (e.g., pseudoephedrine, phenylpropanolamine), vasopressive agents (e.g., epinephrine, norepinephrine), dopaminergic agents (e.g., dopamine, dobutamine) (see Drug Interactions, Drug-Drug Interactions).

Potential Serotonergic Interactions

Unless patients are carefully observed for signs and/or symptoms of serotonin syndrome, linezolid should not be administered to patients with carcinoid syndrome and/or patients taking any of the following medications: serotonin re-uptake inhibitors, tricyclic antidepressants, serotonin 5-HT1 receptor agonists (triptans), meperidine or buspirone (see Drug Interactions, Drug-Drug Interactions).

Warnings and Precautions

General

The use of antibiotics may promote the overgrowth of nonsusceptible organisms. Should superinfection occur during therapy, appropriate measures should be taken.

Linezolid has not been studied in patients with uncontrolled hypertension, pheochromocytoma, carcinoid syndrome, or untreated hyperthyroidism.

Large quantities of foods or beverages with high tyramine content should be avoided while taking linezolid (see Drug Interactions, Drug-Drug Interactions for foods or beverages with high tyramine content).

The safety and efficacy of linezolid given for longer than 28 days have not been evaluated in controlled clinical trials.

Lactic Acidosis

Lactic acidosis has been reported with the use of linezolid. Patients who develop recurrent nausea or vomiting, unexplained acidosis, or a low bicarbonate level while receiving linezolid should receive immediate medical attention.

Mortality Imbalance in an Investigational Study in Patients with Catheter-Related Bloodstream Infections, including those with catheter-site infections.

An imbalance in mortality was seen in patients treated with linezolid relative to vancomycin/dicloxacillin/oxacillin in an open-label study in seriously ill patients with intravascular catheter-related infections [78/363 (21.5%) vs. 58/363 (16.0%); odds ratio 1.426, 95% CI 0.970, 2.098]. While causality has not been established, this observed imbalance occurred primarily in linezolid-treated patients in whom either Gram-negative pathogens, mixed Gram-negative and Gram-positive pathogens, or no pathogen were identified at baseline, but was not seen in patients with Gram-positive infections only.

Linezolid is not approved and should not be used for the treatment of patients with catheter-related bloodstream infections or catheter-site infections.

Linezolid has no clinical activity against Gram-negative pathogens and 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; appropriate concomitant therapy is also required when anaerobic pathogens are isolated (see Indications and Clinical Use).

Serotonin Syndrome

Very rare spontaneous reports of serotonin syndrome with co-administration of linezolid and serotonergic agents have been reported. Since there is limited experience with concomitant administration of linezolid and serotonergic agent (such as serotonin re-uptake inhibitors, tricyclic antidepressants and serotonin 5-HT1 receptor agonists), physicians should be alert to the possibility of signs and symptoms of serotonin syndrome (e.g., hyperpyrexia, and cognitive dysfunction) in patients receiving such concomitant therapy (see Contraindications and Drug Interactions, Drug-Drug Interactions, Serotonergic Agents).

Carcinogenesis and Mutagenesis

See Toxicology, Carcinogenicity, and Mutagenicity.

Gastrointestinal

Clostridium difficile-associated disease

Clostridium difficile -associated disease (CDAD) has been reported with the use of many antibacterial agents, including linezolid. CDAD may range in severity from mild diarrhea to fatal colitis. It is important to consider this diagnosis in patients who present with diarrhea, or symptoms of colitis, pseudomembranous colitis, toxic megacolon, or perforation of colon subsequent to the administration of any antibacterial agent. CDAD has been reported to occur over 2 months after the administration of antibacterial agents.

Treatment with antibacterial agents may alter the normal flora of the colon and may permit overgrowth to Clostridium difficile. Clostridium difficile produces toxins A and B, which contribute to the development of CDAD. CDAD may cause significant morbidity and mortality. CDAD can be refractory to antimicrobial therapy.

If the diagnosis of CDAD is suspected or confirmed, appropriate therapeutic measures should be initiated. Mild cases of CDAD usually respond to discontinuation of antibacterial agents not directed against Clostridium difficile. In moderate to severe cases, consideration should be given to management with fluids and electrolytes, protein supplementation, and treatment with an antibacterial agent clinically effective against Clostridium difficile. Surgical evaluation should be instituted as clinically indicated, as surgical intervention may be required in certain severe cases (see Adverse Reactions sections).

Hematologic

Myelosuppression

Myelosuppression (anemia including pure red blood cell aplasia, leucopenia, pancytopenia, and thrombocytopenia) has been reported in patients receiving linezolid. In cases where the outcome is known, when linezolid was discontinued, the affected hematologic parameters have risen toward pretreatment levels. Complete blood counts should be monitored at least weekly in patients who receive linezolid, particularly in those who receive linezolid for longer than two weeks, patients who are at increased risk for bleeding, those with pre-existing myelosuppression, those receiving concomitant drugs that produce bone marrow suppression, or decreased hemoglobin levels or platelet counts or function, or those with a chronic infection who have received previous or concomitant antibiotic therapy. Discontinuation of therapy with linezolid should be considered in patients who develop or have worsening myelosuppression.

Animal Pharmacology

Dose- and time-dependent myelosuppression, as evidenced by bone marrow hypocellularity, decreased hematopoiesis, and decreased levels of circulating erythrocytes, leukocytes, and platelets, has been seen in animal studies. The hematopoietic effects occurred at oral dose of 40 and 80 mg/kg/day in dogs and rats, respectively (at exposures approximately 0.6 times in the dog and equal in the rat to the expected human exposure based on AUC). Hematopoietic effects were reversible, although in some studies reversal was incomplete within the duration of the recovery period.

Neurologic

Peripheral neuropathy has been reported primarily in patients treated for longer than the maximum recommended duration of 28 days with linezolid. When outcome was known, recovery was reported in only some cases following linezolid withdrawal.

If symptoms of peripheral neuropathy such as numbness, tingling, prickling sensations or burning pain occur, the continued use of linezolid should be weighed against the potential risk.

Convulsions have been reported to occur rarely in patients when treated with linezolid. In most of these cases, a history of seizures or risk factors for seizures was reported.

Ophthalmologic

Optic neuropathy has been reported in patients treated with linezolid, primarily those treated for longer than the maximum recommended duration of 28 days. When outcome was known, recovery was reported in some cases following linezolid withdrawal. In cases of optic neuropathy that progressed to loss of vision, patients were treated for longer than the maximum recommended duration. Visual blurring has been reported in some patients treated with linezolid for less than 28 days.

Visual function should be monitored in all patients taking linezolid for longer than the maximum recommended duration and in all patients reporting new visual symptoms regardless of length of therapy with linezolid. If patients experience symptoms of visual impairment, such as changes in visual acuity, changes in colour vision, blurred vision, or visual field defect, prompt ophthalmologic evaluation is recommended. If optic neuropathy occurs, the continued use of linezolid in these patients should be weighed against the potential risks.

Special Populations

Pregnant Women

There are no adequate and well-controlled studies in pregnant women. Linezolid should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Women

Linezolid and its metabolites are excreted in the milk of lactating rats. Concentrations in milk were similar to those in maternal plasma. It is not known whether linezolid is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when linezolid is administered to a nursing woman.

Pediatrics

There are insufficient data on the safety and efficacy of linezolid in children and adolescents (< 18 years old) to establish dosage recommendations (see Action and Clinical Pharmacology, Special Populations and Conditions, Pediatrics). Therefore, until further data are available, the use of linezolid in this age group is not recommended.

Geriatrics

Of the 2046 patients treated with linezolid in phase III comparator-controlled clinical trials, 589 (29%) were 65 years or older and 253 (12%) were 75 years or older. No overall differences in safety or effectiveness were observed between these patients and younger patients.

Monitoring and Laboratory Tests

Complete blood counts should be monitored at least weekly in patients who receive linezolid, particularly in those who receive linezolid for longer than two weeks, patients who are at increased risk for bleeding, those with pre-existing myelosuppression, those receiving concomitant drugs that produce bone marrow suppression, or decreased hemoglobin levels or platelet counts or function, or those with a chronic infection who have received previous or concomitant antibiotic therapy (see Warnings and Precautions, Hematologic, Myelosuppression).

Visual function should be monitored in all patients taking linezolid for longer than the maximum recommended duration and in all patients reporting new visual symptoms regardless of length of therapy with linezolid. If patients experience symptoms of visual impairment, such as changes in visual acuity, changes in colour vision, blurred vision, or visual field defect, prompt ophthalmologic evaluation is recommended (see Warnings and Precautions, Ophthalmologic).

Adverse Reactions

Adverse Drug Reaction Overview

The safety of linezolid was evaluated in 2046 adult patients enrolled in seven phase III comparator-controlled clinical trials, who were treated for up to 28 days. In these studies, 85% of the adverse events reported with linezolid were described as mild to moderate in intensity. The most common adverse events in patients treated with linezolid were diarrhea (incidence across studies: 2.8% to 11.0%), headache (incidence across studies: 0.5% to 11.3%), and nausea (incidence across studies: 3.4% to 9.6%).

Other adverse events reported in phase II and phase III studies included oral moniliasis, vaginal moniliasis, hypertension, dyspepsia, localized abdominal pain, pruritus, and tongue discolouration.

Clinical Trial Adverse Drug Reactions

Because clinical trials are conducted under very specific conditions, the adverse reaction rates observed in the clinical trials may not reflect the rates observed in practice and should not be compared to the rates in the clinical trials of another drug. Adverse drug reaction information from clinical trials is useful for identifying drug-related adverse events and for approximating rates.

Phase III Clinical Trials

Table 1 shows the incidence of drug-related adverse events reported in at least 1% of adult patients in these trials by dose of linezolid.

Table 1. Incidence of Drug-Related Adverse Events Occurring in > 1% of Adult Patients Treated with Linezolid in Comparator-Controlled Clinical Trials
Adverse Event Uncomplicated Skin and Skin Structure Infections All Other Indications
Linezolid 400 mg PO q12h (n = 548) Comparator (n = 537) Linezolid 600 mg q12h (n = 1498) All Other Comparators (n = 1464)
% of patients with at least 1 drug-related adverse event 25.4 19.6 20.4 14.3
% of patients discontinuing due to drug-related adverse events* 3.5 2.4 2.1 1.7
Diarrhea 5.3 4.8 4 2.7
Nausea 3.5 3.5 3.3 1.8
Headache 2.7 2.2 1.9 1
Taste alteration 1.8 2 0.9 0.2
Vaginal moniliasis 1.6 1.3 1 0.4
Fungal infection 1.5 0.2 0.1

< 0.1

Abnormal liver function tests 0.4 0 1.3 0.5
Vomiting 0.9 0.4 1.2 0.4
Tongue discolouration 1.1 0.0 0.2 0.0
Dizziness 1.1 1.5 0.4 0.3
Oral moniliasis 0.4 0 1.1 0.4

* The most commonly reported drug-related adverse events leading to discontinuation in patients treated with linezolid were nausea, headache, diarrhea, and vomiting.

In controlled clinical trials, abdominal pain/cramp/distension and abnormal hematology tests were also reported occurring at an incidence of at least 1%.

Less Common Clinical Trial Adverse Drug Reactions (< 1%)

Adverse drug reactions that were possibly or probably related to linezolid with an incidence less than 1.0% but greater than 0.1% in controlled clinical trials were:

Body System
Metabolic and Nutritional Amylase Increased, Hyperglycemia, Hyponatremia, Lipase High, Serum Creatine Phosphokinase Increased, AST Increased and ALT Increased
Special Senses Blurred Vision, Tinnitus
Musculo-skeletal None
Hemic and Lymphatic Eosinophilia, Neutropenia, Thrombocytopenia
Respiratory None
Cardiovascular Hypertension, Phlebitis
Digestive Constipation, Dry Mouth, Dyspepsia, Gastritis, Glossitis, Increased Thirst, Stomatitis and Tongue Discolouration
Nervous Dizziness, Hypoesthesia, Insomnia, Paresthesia
Body as a whole Abdominal Pain, Chills, Diaphoresis, Fatigue, Fungal Injection, Injection/Vascular Catheter Site Pain, and Injection/Vascular Catheter Site Phlebitis/Thrombophlebitis
Urogenital Polyuria, and Vaginitis/Vaginal Infection
Skin Dermatitis, Moniliasis Skin, Pruritus, Rash, and Urticaria

In controlled clinical trials, the pattern of drug- related adverse reactions by body system with an incidence less than 1.0% but greater than 0.1% were similar to comparators.

Serious adverse reactions in controlled clinical trials considered possibly or probably related to linezolid treatment with an incidence less than 0.1% were Hypertension, Kidney Failure, Liver Function Test Abnormality, Pancreatitis, Thrombocytopenia, Transient Ischemic Attacks and Vomiting.

Phase IV Clinical Trials

In a phase IV comparator-controlled study (Study 113) of adult diabetic patients which clinically documented complicated skin and skin structure infections (“diabetic foot infections”) (see Clinical Trials), most drug-related adverse events were rated as mild or moderate in intensity; 13.0% were rated as severe, and with the exception of diarrhea (0.8%), each severe drug-related event was reported in no more than one patient.

Table 2. Frequencies of Study-emergent Drug-Related Adverse Events Reported for ≥ 1% of Patients in Either Treatment Group [Study 113, linezolid in the treatment of adult diabetic patients with clinically documented complicated skin and skin structure infections (“diabetic foot infections”)]
COSTART Body System Classification Adverse Event (Medically Equivalent Term*) Treatment Group
Linezolid N = 241 n (%)† Comparator N = 120 n (%)†
Total Reported Patients reporting at least 1 drug-related AE 64 (26.6) 12 (10.0)
Digestive Diarrhea 18 (7.5) 4 (3.3)
Nausea 14 (5.8) 0
Vomiting 4 (1.7) 1 (0.8)
Dyspepsia 3 (1.2) 1 (0.8)
Appetite decreased 3 (1.2) 0
Hemic and Lymphatic Anemia 11 (4.6) 0
Thrombocytopenia 9 (3.7) 0

* The information represents the number (%) of patients who reported a given study-emergent adverse event. Any patient with multiple reports of the same event was counted only once for that event.

All percentages are based on the number of ITT patients.

Less Common Clinical Trial Adverse Drug Reactions (< 1%)

In Study 113, adverse drug reactions that were possibly or probably related to linezolid with an incidence less than 1.0% but greater than 0.1% were:

Body System
Metabolic and Nutritional Healing Abnormal, Hypoglycemia, Hypokalemia, LDH Increased
Special Senses Taste Perversion
Musculo-skeletal None
Hemic and Lymphatic Ecchymosis/Bruise, Neutropenia
Respiratory Dyspnea
Cardiovascular Congestive Heart Failure, Disorder Peripheral Vascular
Digestive Anorexia, Bilary Pain, C. Difficile Colitis, Cholestatic Jaundice, Disorder Gastrointestinal NOS, Disorder Rectal, Flatulence, Gastrointestinal Bleeding, Monilia Oral
Nervous Disorientation, Dizziness, Somnolence
Body as a whole Abdominal Cramp, Abdominal Pain Localized, Asthenia, Disorder Mucous Membrane, Fatigue, Headache, Fungal Infection NOS, Infection NEC, Laboratory Test Abnormality, Others
Urogenital None
Skin Dermatitis, Dermatitis Fungal, Erythema, Rash, Ulcer Skin

Abbreviations: NEC = not elsewhere classified; NOS = not elsewhere specified

In Study 113, serious drug-related events were reported for seven patients in the linezolid treatment group: congestive heart failure, peripheral vascular disease; biliary pain and cholestatic jaundice; Clostridium difficile colitis; gastrointestinal bleeding; anemia; and hypokalemia.

Phase III Clinical Trials

Abnormal Hematologic and Clinical Chemistry Findings

Linezolid has been associated with thrombocytopenia when used in adults in doses up to and including 600 mg every 12 hours for up to 28 days. In phase III comparator-controlled trials, the percentage of patients who developed a substantially low platelet count (defined as less than 75% of lower limit of normal and/or baseline) was 2.4% (range among studies: 0.3 to 10.0%) with linezolid and 1.5% (range among studies: 0.4 to 7.0%) with a comparator.

Thrombocytopenia associated with the use of linezolid appears to be dependent on duration of therapy (generally greater than 2 weeks of treatment). The platelet counts for most patients returned to the normal range/baseline during the follow-up period. No related clinical adverse events were identified in phase III clinical trials in patients developing thrombocytopenia. Bleeding events were identified in thrombocytopenic patients in a compassionate use program for linezolid; the role of linezolid in these events cannot be determined (see Warnings and Precautions).

Changes seen in other laboratory parameters, without regard to drug relationship, revealed no substantial differences between linezolid and the comparators. These changes were generally not clinically significant, did not lead to discontinuation of therapy, and were reversible. The incidence of patients with at least one substantially abnormal hematologic or serum chemistry value is presented in Tables 3 and 4.

Table 3. Percent of Adult Patients who Experienced at Least One Substantially Abnormal* Hematology Laboratory Value in Comparator-Controlled Clinical Trials with Linezolid
Laboratory Assay Uncomplicated Skin and Skin Structure Infections All Other Indications
Linezolid 400 mg q12h Comparator Linezolid 600 mg q12h All Other Comparators
Hemoglobin (g/L) 0.9 0.0 7.1 6.6
Platelet count (x 109/L) 0.7 0.8 3.0 1.8
WBC (x 109/L) 0.2 0.6 2.2 1.3
Neutrophils (x 106/L) 0.0 0.2 1.1 1.2

*   < 75% (< 50% for neutrophils) of Lower Limit of Normal (LLN) for values normal at baseline;
    < 75% (< 50% for neutrophils) of LLN and of baseline for values abnormal at baseline.

Table 4. Percent of Adult Patients who Experienced at Least One Substantially Abnormal* Serum Chemistry Laboratory Value in Comparator-Controlled Clinical Trials with Linezolid
Laboratory Assay Uncomplicated Skin and Skin Structure Infections All Other Indications
Linezolid 400 mg q12h Comparator Linezolid 600 mg q12h All Other Comparators
AST (U/L) 1.7 1.3 5.0 6.8
ALT (U/L) 1.7 1.7 9.6 9.3
LDH (U/L) 0.2 0.2 1.8 1.5
Alkaline phosphatase (U/L) 0.2 0.2 3.5 3.1
Lipase (U/L) 2.8 2.6 4.3 4.2
Amylase (U/L) 0.2 0.2 2.4 2.0
Total bilirubin (μmol/L) 0.2 0.0 0.9 1.1
BUN (mmol/L) 0.2 0.0 2.1 1.5
Creatinine (μmol/L) 0.2 0.0 0.2 0.6

*   > 2 x Upper Limit of Normal (ULN) for values normal at baseline;
    > 2 x ULN and > 2 x baseline for values abnormal at baseline.

Phase IV Clinical Trials

Table 5 shows the frequencies of selected abnormal hematologic test values in Study 113 at End of Treatment.

Table 5. Frequencies of Abnormal Values for Selected Hematology Assays at EOT [Study 113, linezolid in the treatment of adult diabetic patients with clinically documented complicated skin and skin structure infections (“diabetic foot infections”)]
Hematology Assay Clinically Significant Abnormal*/All abnormal values for assay
Linezolid n/N (%) Comparator n/N (%)
Hemoglobin 9/111 (8.1) 1/52 (1.9)
Hematocrit 6/112 (5.4) 1/49 (2.0)
WBC 2/26 (7.7) 1/12 (8.3)
Platelet Count 9/43 (20.9) 3/16 (18.8)

Abbreviations: EOT = end of treatment, WBC = white blood count

*    Abnormal values assessed by the investigator as clinically significant.

Table 6 summarizes abnormal chemistry values in Study 113 assessed at End of Treatment.

Table 6. Frequencies of Abnormal Values for Selected Chemistry Assays at EOT [(Study 113, linezolid in the treatment of adult diabetic patients with clinically documented complicated skin and skin structure infections (“diabetic foot infections”)]
Chemistry Assay Clinically Significant Abnormal*/All abnormal values for assay
Linezolid n/N (%) Comparator n/N (%)
ALT 3/32 (9.4) 1/15 (6.7)
AST 1/24 (4.2) 1/19 (5.3)
Bicarbonate 1/22 (4.5) 0/15
Lactic dehydrogenase 3/38 (7.9) 0/16
Amylase 3/17 (17.6) 0/18

Abbreviations: ALT = Alanine aminotransferase, AST = Aspartate Aminotransferase, EOT = End of Treatment

*    Assessed by the investigator as clinically significant.

Postmarket Adverse Drug Reactions

Myelosuppression (anemia including pure red blood cell aplasia, leukopenia, pancytopenia, and thrombocytopenia) has been reported during postmarketing use of linezolid (see Warnings and Precautions).

Peripheral neuropathy, and optic neuropathy sometimes progressing to loss of vision, have been reported in patients treated with linezolid. These reports have primarily been in patients treated for longer than the maximum recommended duration of 28 days (see Warnings and Precautions).

Lactic acidosis (see Warnings and Precautions, General), convulsions (see Warnings and Precautions, Neurologic), angioedema and anaphylaxis have been reported.

Very rare reports of bullous skin disorders such as those described as Stevens-Johnson syndrome have been received.

Very rare spontaneous reports of serotonin syndrome with co-administration of linezolid and serotonergic agents have been reported (see Warnings and Precautions and Drug Interactions).

These events have been chosen for inclusion due to either their seriousness, frequency of reporting, possible causal connection to linezolid, or a combination of these factors. Because they are reported voluntarily from a population of unknown size, estimates of frequency cannot be made and causal relationship cannot be precisely established.

Drug Interactions

Overview

Drugs Metabolized by Cytochrome P450

Linezolid is not an inducer of cytochrome P450 (CYP) in rats. It is not detectably metabolized by human cytochrome P450 and it does not inhibit the activities of clinically significant human CYP isoforms (1A2, 2C9, 2C19, 2D6, 2E1, 3A4). Therefore, no CYP450-induced drug interactions are expected with linezolid. Concurrent administration of linezolid does not substantially alter the pharmacokinetic characteristics of (S)-warfarin, which is extensively metabolized by CYP2C9. Drugs such as warfarin and phenytoin, which are CYP2C9 substrates, may be given with linezolid without changes in dosage regimen.

Drug-Drug Interactions

Monoamine Oxidase Inhibition

Linezolid is a mild reversible nonselective inhibitor of MAO-A and MAO-B. Therefore, linezolid has the potential for interaction with adrenergic and serotonergic agents. Studies in healthy volunteers have examined the effect of linezolid on the pharmacodynamic responses to tyramine, sympathomimetic amines, and dextromethorphan (see Contraindications).

Adrenergic Agents

A significant pressor response has been observed in normal adult subjects receiving linezolid and tyramine doses of more than 100 mg. Therefore, patients receiving linezolid need to avoid consuming large amount of foods or beverages with high tyramine content.

Some individuals receiving linezolid may experience a reversible enhancement of the pressor response to indirect-acting sympathomimetic agents, vasopressor or dopaminergic agents. Initial doses of adrenergic agents, such as dopamine or epinephrine, should be reduced and titrated to achieve the desired response (see Contraindications).

A reversible enhancement of the pressor response of either pseudoephedrine HCl (PSE) or phenylpropanolamine HCl (PPA) is observed when linezolid is administered to healthy normotensive subjects. A similar study has not been conducted in hypertensive patients. The interaction studies conducted in normotensive subjects evaluated the blood pressure and heart rate effects of placebo, PPA or PSE alone, linezolid alone, and the combination of steady- state linezolid (600 mg q12h for 3 days) with two doses of PPA (25 mg) or PSE (60 mg) given 4 hours apart. Heart rate was not affected by any of the treatments. Blood pressure was increased with both combination treatments. Maximum blood pressure levels were seen 2 to 3 hours after the second dose of PPA or PSE, and the returned to baseline 2 to 3 hours after peak.

Serotonergic Agents

A study to assess the potential interaction of linezolid with a serotonin-reuptake inhibitor (dextromethorphan) was conducted in healthy volunteers. No significant differences were found in the pharmacodynamic measures of temperature, digit symbol substitution, nurse-rated sedation, blood pressure, or pulse when subjects were administered dextromethorphan with or without linezolid. The effects of other serotonin-reuptake inhibitors have not been studied. Very rare spontaneous reports of serotonin syndrome with co-administration of linezolid and serotonergic agents have been reported. Since there is limited experience with concomitant administration of linezolid and serotonergic agents, physicians should be alert to the possibility of signs and symptoms of serotonin syndrome (e.g., hyperpyrexia, and cognitive dysfunction) in patients receiving such concomitant therapy (see Contraindications).

Antibiotics

Aztreonam – The pharmacokinetics of linezolid or aztreonam are not altered when administered together.

Gentamicin – The pharmacokinetics of linezolid or gentamicin are not altered when administered together.

Antacids

No studies have been conducted with antacids and chelating agents. Based on the chemical structure, concurrent administration with these agents is not expected to affect absorption of linezolid.

Drug-Food Interactions

Large quantities of foods or beverages with high tyramine content should be avoided while taking linezolid. Quantities of tyramine consumed should be less than 100 mg per meal. Foods high in tyramine content include those that may have undergone protein changes by aging, fermentation, pickling, or smoking to improve flavour, such as aged cheeses (0 to 15 mg tyramine per 28 g); fermented or air-dried meats (0.1 to 8 mg tyramine per 28 g); sauerkraut

(8 mg tyramine per 224 g); soy sauce (5 mg tyramine per 1 teaspoon); tap beer (4 mg tyramine per 360 mL); red wine (0 to 6 mg tyramine per 240 mL). The tyramine content of any protein-rich food may be increased if stored for long periods or improperly refrigerated.

Drug-Herb Interactions

Interactions with herbal products have not been established.

Drug-Laboratory Interactions

There are no reported drug-laboratory test interactions.

Dosage and Administration

Recommended Dose and Dosage Adjustment

The recommended dosage for Linezolid injection for the treatment of infections in adults is described in Table 7. Doses of Linezolid injection are administered every 12 hours (q12h).

Table 7. Dosage Guidelines for Linezolid injection
Infection* Dosage and Route of Administration Recommended Duration of Treatment (consecutive days)
Vancomycin-resistant Enterococcus faecium infections, including concurrent bacteremia 600 mg i.v. q12h 14 to 28
Nosocomial pneumonia 600 mg i.v. q12h 10 to 14
Complicated skin and skin structure infections:
  1. Except diabetic foot infections
  2. Non-limb threatening diabetic foot infections, without concomitant osteomyelitis
 
600 mg i.v. q12h

600 mg i.v. q12h
 
10 to 14

14 to 28
Community-acquired pneumonia, including concurrent bacteremia 600 mg i.v. q12h 10 to 14

* Due to the designated pathogens (see Indications and Clinical Use)

Patients with infection due to MRSA should be treated with linezolid injection 600 mg q12h.

In controlled clinical trials, the protocol-defined duration of treatment for all infections ranged from 7 to 28 days. Total treatment duration was determined by the treating physician based on site and severity of the infection, and on the patient’s clinical response.

Administration

Linezolid 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 linezolid 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 linezolid injection with an infusion solution compatible with linezolid injection and with any other drug(s) administered via this common line (see Compatible Intravenous Solutions under Dosage and Administration).

Linezolid injection is supplied as a ready-to-use sterile isotonic solution for intravenous infusion. As with all parenteral drug products, intravenous solutions should be inspected visually for clarity, particulate matter, precipitate and leakage prior to administration, whenever solution and container permit. Solutions showing haziness, particulate matter, precipitate or leakage should not be used.

Linezolid injection may exhibit a yellow colour that can intensify over time without adversely affecting potency. Discard unused portions.

Compatible Intravenous Solutions

5% Dextrose Injection, USP

0.9% Sodium Chloride Injection, USP

Lactated Ringer’s Injection, USP

Compatibility

Physical incompatibilities resulted when linezolid injection was combined with the following drugs during simulated Y-site administration: amphotericin B, chlorpromazine HCl, diazepam, pentamidine isethionate, erythromycin lactobionate, phenytoin sodium, and trimethoprim-sulfamethoxazole. Additionally, chemical incompatibility resulted when linezolid injection was combined with ceftriaxone sodium.

Overdosage

For management of a suspected drug overdose, contact your regional poison centre.

In the event of overdosage, supportive care is advised, with maintenance of glomerular filtration. Hemodialysis may facilitate more rapid elimination of linezolid. In a phase I clinical trial, approximately 30% of a dose of linezolid was removed during a 3-hour hemodialysis session beginning 3 hours after the dose of linezolid was administered. Data are not available for removal of linezolid with peritoneal dialysis or hemoperfusion. Clinical signs of acute toxicity in animals were decreased activity and ataxia in rats and vomiting and tremors in dogs treated with 3000 mg/kg/day and 2000 mg/kg/day, respectively.

Action and Clinical Pharmacology

Mechanism of Action

Linezolid is a synthetic antibacterial agent of a new class of antibiotics, the oxazolidinones, with in vitro activity against aerobic gram-positive bacteria, certain gram-negative bacteria, and anaerobic microorganisms. Linezolid inhibits bacterial protein synthesis through a unique mechanism of action. Linezolid binds to sites 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 mechanism of action of linezolid (oxazolidinones) differs from that of other antibiotic classes (e.g., aminoglycosides, beta-lactams, folic acid antagonists, glycopeptides, lincosamides, quinolones, rifamycins, streptogramins, tetracyclines, chloramphenicol). Therefore, cross-resistance between linezolid and the mentioned classes of antibiotics is unlikely. Linezolid is active against selected gram-positive bacteria that are susceptible or resistant to these antibiotics. In vitro tests have shown that resistance to linezolid develops slowly via multiple-step mutations in the 23S ribosomal RNA and occurs at a frequency of 1 x 10-9 to 1 x 10-11.

Pharmacokinetics

The mean pharmacokinetic parameters of linezolid in adults after single and multiple oral and intravenous doses are summarized in Table 8. Plasma concentrations of linezolid at steady-state following oral dosing of 600 mg every 12 hours (q12h) are shown in Figure 1.

Table 8. Mean (standard deviation) Pharmacokinetic Parameters of Linezolid in Adults
Dose of Linezolid Cmax (μg/mL) Cmin (μg/mL) Tmax (hrs) AUC* (µg • h/mL) t½ (hrs) CL (mL/min)
400 mg tablet            
Single dose† 8.10 (1.83) --- 1.52 (1.01) 55.10 (25.00) 5.2 (1.50) 146 (67)
Bid dose 11.00 (4.37) 3.08 (2.25) 1.12 (0.47) 73.40 (33.50) 4.69 (1.70) 110 (49)
600 mg tablet            
Single dose 12.70 (3.96) --- 1.28 (0.66) 91.40 (39.30) 4.26 (1.65) 127 (48)
Bid dose 21.20 (5.78) 6.15 (2.94) 1.03 (0.62) 138.00 (42.10) 5.40 (2.06) 80 (29)
600 mg IV injection ‡            
Single dose 12.90 (1.60) --- 0.50 (0.10) 80.20 (33.30) 4.40 (2.40) 138 (39)
Bid dose 15.10 (2.52) 3.68 (2.36) 0.51 (0.03) 89.70 (31.00) 4.80 (1.70) 123 (40)
600 mg oral suspension            
Single dose 11.00 (2.76) --- 0.97 (0.88) 80.80 (35.10) 4.60 (1.71) 141 (45)

*    AUC for single dose = AUC0-∞; for multiple-dose = AUC0-τ

†    Data dose-normalized from 375 mg

‡    Data dose-normalized from 625 mg

Cmax = Maximum plasma concentration;

Cmin = Minimum plasma concentration;

Tmax = Time to Cmax;

AUC = Area under concentration-time curve;

t½ = Elimination half-life;

CL = Systemic clearance

The average minimum plasma concentrations (Cmin) at steady state for oral administration of 400 or 600 mg linezolid every 12 hours were 3.08 and 6.15 μg/mL, respectively, and the corresponding average maximum concentrations (Cmax) were 11.0 and 21.2 μg/mL, respectively. These results indicate that for these dose regimens, the Cmin values are near or above the highest MIC90 (4 μg/mL) for target microorganisms.

Figure 1 – Steady-state Linezolid Plasma Concentrations in Healthy Adults Following Oral Dosing of 600 mg (Tablets) Every 12 Hours (Mean ± Standard Deviation, n = 16)

Absorption

Linezolid is rapidly and extensively absorbed after oral dosing. As shown in Figure 1, maximum plasma concentrations are reached approximately 1 to 2 hours after dosing, and the absolute bioavailability is approximately 100%. Therefore, Linezolid may be given orally or intravenously without dose adjustment.

Linezolid may be administered without regard to the timing of meals. The time to reach the maximum concentration is delayed from 1.5 hours to 2.2 hours and Cmax is decreased by about 17% when high fat food is given with linezolid. However, the total exposure measured as AUC0-∞ values is similar under both conditions.

Distribution

Animal and human pharmacokinetic studies have demonstrated that linezolid readily distributes to well-perfused tissues. The plasma protein binding of linezolid is approximately 31% and is concentration-independent. The volume of distribution of linezolid at steady-state averaged 40 to 50 liters in healthy adult volunteers.

Linezolid concentrations have been determined in various fluids from a limited number of subjects in Phase I volunteer studies following multiple dosing of linezolid. The ratio of linezolid in saliva relative to plasma was 1.2 to 1 and for sweat relative to plasma was 0.55 to 1. The ratio for epithelial lining fluid was 4.5 to 1, and for alveolar cells of the lung was 0.15 to 1, when measured at steady-state Cmax. In a small study of subjects with ventricular-peritoneal shunts and essentially non-inflamed meninges, the ratio of linezolid in cerebrospinal fluid to plasma at Cmax was 0.7 to 1 after multiple dosing of linezolid.

Metabolism

Linezolid is primarily metabolized by oxidation of the morpholine ring, which results in two inactive ring-opened carboxylix acid metabolites: the aminoethoxyacetic acid metabolite (A), and the hydroxyethyl glycine metabolite (B). Formation of metabolite B is mediated by a non-enzymatic chemical oxidation mechanism in vitro. Linezolid is not an inducer of cytochrome P450 (CYP) in rats, and it has been demonstrated from in vitro studies that linezolid is not detectably metabolized by human cytochrome P450 and it does not inhibit the activities of clinically significant human CYP isoforms (1A2, 2C9, 2C19, 2D6, 2E1, 3A4).

The lack of effect of linezolid to induce CYP2C9 was shown in a healthy volunteer study using warfarin as a metabolism probe.

Excretion

Nonrenal clearance accounts for approximately 65% of the total clearance of linezolid. Under steady-state conditions, approximately 30% of the dose appears in the urine as linezolid, 40% as metabolite B, and 10% as metabolite A. The renal clearance of linezolid is low (average 40 mL/min) and suggests net tubular re-absorption. Virtually no linezolid appears in the feces, while approximately 6% of the dose appears in the feces as metabolite B, and 3% as metabolite A.

A small degree of nonlinearity in clearance was observed with increasing doses of linezolid, which appears to be due to lower renal and non-renal clearance of linezolid at high concentrations. However, the difference in clearance was small and was not reflected in the apparent elimination half-life.

Special Populations and Conditions

Pediatrics

Currently, there are limited data on the pharmacokinetics of linezolid during multiple dosing in pediatric patients of all ages. There are insufficient data on the safety and efficacy of linezolid in children and adolescents (< 18 years old). Further studies are needed to establish safe and effective dosage recommendations.

Pharmacokinetic studies indicate that after single and multiple doses in children (1 week to < 12 years), linezolid clearance (based on kg body weight) was greater in pediatric patients than in adults, but decreased with increasing age.

In children 1 week to < 12 years old, administration of 10 mg/kg every 8 hours daily gave exposure approximating to that achieved with 600 mg twice daily in adults.

In neonates up to 1 week of age, the systemic clearance of linezolid (based on kg body weight) increases rapidly in the first week of life. Therefore, neonates given 10 mg/kg every 8 hours daily will have the greatest systemic exposure on the first day after delivery. However, excessive accumulation is not expected with this dosage regimen during the first week of life as clearance increases rapidly over that period.

In adolescents (≥ 12 to < 18 years old), linezolid pharmacokinetics were similar to that in adults following a 600 mg dose. Therefore, adolescents administered 600 mg every 12 hours daily will have similar exposure to that observed in adults receiving the same dosage.

Geriatrics

The pharmacokinetics of linezolid are not significantly altered in elderly patients (65 years or older). Therefore, dose adjustment for geriatric patients is not necessary.

Gender

Females have a slightly lower volume of distribution of linezolid than males. Plasma concentrations are higher in females than in males, which is partly due to body weight differences. After a 600 mg dose, mean oral clearance is approximately 38% lower in females than in males. However, there are no significant gender differences in mean apparent elimination-rate constant or half-life. Thus, drug exposure in females is not expected to substantially increase beyond levels known to be well tolerated. Therefore, dose adjustment by gender is not necessary.

Race

The total clearance of linezolid is not influenced by race. Therefore, dose adjustment is not necessary for different races.

Hepatic Insufficiency

The pharmacokinetics of linezolid are not altered in patients (n = 7) with mild-to-moderate hepatic insufficiency (Child-Pugh class A or B). On the basis of the available information, no dose adjustment is recommended for patients with mild-to-moderate hepatic insufficiency. The pharmacokinetics of linezolid in patients with severe hepatic insufficiency have not been evaluated.

Renal Insufficiency

The pharmacokinetics of the parent drug linezolid is not altered in patients with any degree of renal insufficiency. Because similar plasma concentrations of linezolid are achieved regardless of renal function, no dose adjustment is recommended for patients with renal insufficiency. However, given the absence of information on the clinical significance of accumulation of the primary metabolites, the use of linezolid in patients with renal insufficiency should be weighed against the potential risks of accumulation of these metabolites. Both linezolid and the two metabolites are eliminated by dialysis. No information is available on the effect of peritoneal dialysis on the pharmacokinetics of linezolid. Approximately 30% of a dose was eliminated in a 3-hour dialysis session beginning 3 hours after the dose of linezolid was administered; therefore, linezolid should be given after hemodialysis.

Storage and Stability

Store Linezolid Injection infusion bags in controlled room temperature between 15 °C ‒ 25 °C. Protect from light. Protect from freezing. Keep the infusion bags in the overwrap until ready to use. Linezolid Injection may exhibit a yellow colour that can intensify over time without adversely affecting potency.

Dosage Forms, Composition and Packaging

Linezolid Injection is available in single-use, ready-to-use flexible plastic infusion bags in a foil laminate overwrap. The infusion bags and ports are PVC-free and latex-free. The infusion bags are available in the following package size:

600 mg linezolid in 300 mL of solution per bag

Linezolid Injection is supplied as a ready-to-use sterile isotonic solution for intravenous infusion. Each mL contains:

Linezolid 2.0 mg
Dextrose, USP 50.24 mg
Sodium Citrate, USP 1.64 mg
Citric Acid, USP 0.85 mg
Hydrochloric Acid, NF pH adjusted
Sodium Hydroxide, NF pH adjusted
Water for Injection, USP q.s. to 1 mL