Oxazolidinone antibiotic; bacterial protein synthesis

Linezolid inhibits initiation complex formation with either the 30S or the 70S ribosomal subunits from Escherichia coli. Linezolid inhibits complex formation with Staphylococcus aureus 70S tight-couple ribosomes. Linezolid is a potent inhibitor of cell-free transcription-translation in E. coli, exhibiting 50% inhibitory concentrations (IC50s) of 1.8 mM. Linezolid is an oxazolidinone, a new class of antibacterial agents with enhanced activity against pathogens. Linezolid MICs vary slightly with the test method, laboratory, and significance attributed to thin hazes of bacterial survival, but all workers find that the susceptibility distributions are narrow and unimodal, with MIC values between 0.5 and 4 mg/L for streptococci, enterococci and staphylococci. Linezolid entails mutation of the 23S rRNA that forms the binding site. Linezolid is an oxazolidinone whose mechanism of action involves inhibition of protein synthesis at a very early stage. Linezolid is added to 7H10 agar medium (Difco) supplemented with OADC (oleic acid, albumin, dextrose, and catalase) at 50°C to 56°C by doubling the dilutions to yield a final concentration of 0.125 μg/mL to 4 μg/mL. Linezolid shows excellent in vitro activity against all the strains tested (MICs ≤ 1 μg/ml), including those resistant to SIRE.

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Initiation of translation requires the formation of a ternary complex between tRNAfMet, the 30S or the 70S subunit, and mRNA. This initiation complex can be assayed by measuring the binding of radiolabeled tRNAfMet to either the 30S or the 70S subunit. Figure 1A shows that in the presence of the initiation factors IF1, IF2, and IF3, Linezolid had 50% inhibitory concentrations (IC50s) of 110 μM (37 μg/ml) and 130 μM (44 μg/ml) for E. coli 30S and 70S initiation complex formation, respectively. The integrity of the assay was confirmed by demonstrating that kasugamycin was inhibitory to 70S initiation complex formation, with an IC50 of 154 μM (Fig. 1B). Oxazolidinone inhibition of initiation complex formation was studied further with S. aureus 70S ribosomes (Fig. 2). With a truncated mRNA, an IC50 value of 116 μM was obtained for linezolid. These reactions were performed in the absence of initiation factors and with salt-washed 70S ribosomes. Initiation factors IF1, IF2, and IF3 play important roles in the initiation of translation in bacteria. The tRNAfMet is bound by IF2 and is delivered to the 30S subunit joining IF1, IF3, and the mRNA as part of the initiation complex. Linezolid did not inhibit formation of the IF2-tRNAfMet complex when either 5 or 0.5 pmol of E. coli IF2 was used (Table 1). The role of initiation factors in the mechanism of action of linezolid was further investigated by forming E. coli 70S ribosome initiation complexes in the absence of any of the three factors. Figure 4 demonstrates that an IC50 of 152 μM was obtained for linezolid under these conditions. [1]

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The oxazolidinones are a new class of synthetic antibiotics with good activity against gram-positive pathogenic bacteria. Experiments with a susceptible Escherichia coli strain, UC6782, demonstrated that in vivo protein synthesis was inhibited by both eperezolid (formerly U-100592) and Linezolid (formerly U-100766). Both Linezolid and eperezolid were potent inhibitors of cell-free transcription-translation in E. coli, exhibiting 50% inhibitory concentrations (IC50s) of 1.8 and 2.5 microM, respectively. The ability to demonstrate inhibition of in vitro translation directed by phage MS2 RNA was greatly dependent upon the amount of RNA added to the assay. For eperezolid, 128 microg of RNA per ml produced an IC50 of 50 microM whereas a concentration of 32 microg/ml yielded an IC50 of 20 microM. Investigating lower RNA template concentrations in linezolid inhibition experiments revealed that 32 and 8 microg of MS2 phage RNA per ml produced IC50s of 24 and 15 microM, respectively. This phenomenon was shared by the translation initiation inhibitor kasugamycin but not by streptomycin. Neither oxazolidinone inhibited the formation of N-formylmethionyl-tRNA, elongation, or termination reactions of bacterial translation. The oxazolidinones appear to inhibit bacterial translation at the initiation phase of protein synthesis [2].

Linezolid is fully bioavailable following oral administration, with maximum plasma linezolid concentrations achieved between 1 and 2 hours after oral administration. The elimination half-life of linezolid is 5–7 hours, and twice-daily administration of 400–600mg provides steady-state concentrations in the therapeutic range.

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Finally, we compared the activities of Linezolid and vancomycin in pneumonia induced by IRDL-7971 in HLA-DR3 transgenic mice using a previously used dosing regimen (20). As shown in Fig. 5, Linezolid conferred significant protection over vancomycin (P = 0.0002; n = 10 to 14 mice/group) and untreated mice (P = 0.0004; n = 8 to 10 mice/group). Surprisingly, vancomycin failed to confer significant protection from lethal pneumonia (P = 0.50; n = 8 to 14 mice/group). Serum cytokine analyses revealed that compared to untreated and vancomycin-treated mice infected with IDRL-7971, linezolid-treated HLA-DR3 transgenic mice infected with IDRL-7971, had significantly lower levels of IL-2, IL-6, and the chemokine KC (Fig. 6). These results suggest that linezolid played a protective role by attenuating the production of SAg in vivo [4].

Synthesis of [32P]mRNA for ribosome binding studies. [1]
The one-step PCR procedure described by Sandhu et al. (24) was used to synthesize a 200-bp mRNA with a defined sequence. Four adjacent oligonucleotide primers with short overlaps were annealed to each other and were subjected to PCR. The primer sequences were as follows (primer sequences are 5′ to 3′): primer 1, GGGAATTCGCAGGTTTAAAAATGAAAGGTAAAGGTAAAGGTAAA; primer 2, GGTGGTGGCCTGGGCAAAGGTAAAGGT; primer 3, AAAGGT AAAAAAGGTAAAGGTAAAGGTAAAAAAGGTAAAAAAGGTAAAGG TGGTGGTTAATAAAAAAAATAAAAAG; and primer 4, CTAGAGGATCCTTTTTATTTTTTTATTAACCACCAC. Primers 1 and 2 were annealed to the sequence 5′-ACCTTTTTTACCTTTACCTTTACCTTTTTTACCTTTTTTACCTTTACCTTTACCTTATCCTTTACCTTTGCCCAGGCCAC-3′. Primer 3 was annealed to the sequence 5′-ACCTTTGCCCAGGCCACCACCTTTACCTTTTTTACCTTTTTTACCTTTACCTTCACC-3′, and primer 4 was annealed to primer 3. Extension by PCR resulted in the asymmetric synthesis of intermediates which annealed to each other, thereby priming the synthesis of a double-stranded DNA template. This template was subsequently used to produce an mRNA with the sequence 5′-GGGAAUUCGGAGGUUUAAAAAUG-(GGUAAA)33UAAUAA-3′ (the Shine-Dalgarno sequence and the AUG start codon are underlined). The coding sequence contained Gly (GGU) and Lys (AAA) codons followed by tandem stop codons. [32P]mRNA was transcribed with a Ribomax kit and either [32P]CTP or [32P]GTP. RNA was isolated by phenol extraction and chromatography through a Quick Spin G-25 column.

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Binding of labeled synthetic mRNA to ribosomes. [1]
Binding of 32P-labeled synthetic mRNA was carried out for 15 min at 24°C in duplicate 50-μl reaction mixtures containing 200 to 400 μg of 70S ribosomes, 20 mM MgCl2, 10 mM Tris-HCl (pH 7.4), 1 mM DTT, 80 mM NH4Cl, and 1 μl (16,000 dpm) of 32P-labeled mRNA. Duplicate reactions were terminated by the addition of 1 ml of ice-cold buffer containing 20 mM Tris (pH 7.4), 20 mM MgCl2, and 100 mM NH4Cl. The mRNA-ribosome complex was then trapped on Millipore HA filters, and the radioactivity was counted after the addition of scintillation fluid.

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E. coli initiation complex assay with AUG. [1]
E. coli 70S ribosomes (10 pmol) were incubated with [35S]tRNAfMet (45,000 dpm) in 20-μl reaction mixtures containing 20 mM HEPES (pH 7.6), 3 mM MgCl2, 150 mM NH4Cl, 4 mM DTT, 0.05 mM spermine, 2 mM spermidine, and 0.25 μg of the AUG trinucleotide. Duplicate reaction mixtures were incubated at 37°C for 10 min, and the reactions were stopped by the addition of 2 ml of cold buffer A. Complexes were filtered through Millipore filters (pore size, 0.45 μm) and washed with 50 ml of buffer A, and the radioactivity was counted after the addition of scintillation fluid.

Linezolid was a potent inhibitor of cell-free transcription-translation in E. coli. IC50 was 1.8 mM. linezolid MICs vary slightly owing to the different test method and laboratory. The MIC values were between 0.5 and 4 mg/L for streptococci, enterococci and staphylococci.

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Preparation of E. coli 70S ribosomes.[1]
Ribosomes were prepared by the method of Rheinberger et al. Fifty grams (wet weight) of frozen MRE600 cells was mixed with an equal weight of alumina, and the cells were lysed at 0°C by grinding with a mortar and pestle. Fifty milliliters of buffer A containing 1 μg of DNase per ml was added and the suspension was stirred for 20 min. The alumina, unbroken cells, and cellular debris were removed by two centrifugations at 10,000 × g for 10 min. The supernatant was centrifuged again for 30 min at 30,000 × g, and the upper two-thirds of the resulting supernatant was centrifuged again at 30,000 × g for 16 h (S30 extract). The ribosome pellet was suspended in buffer B and centrifuged at 10,000 × g for 10 min, and the clear supernatant was centrifuged at 105,000 × g for 4 h. The pelleted ribosomes were washed twice more in buffer C while maintaining the ribosomes at 5 to 10 mg/ml (14.4 A260 units = 1 mg/ml), suspended in buffer A at 80 to 100 mg of ribosomes per ml, and stored at −80°C.

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Preparation of E. coli ribosomal subunits.[1]
Ribosomal subunits were prepared as described by Staehelin and Maglott, with the following modifications. The S30 extract was prepared as described above by using MRE600 mid-logarithmic-phase cells, and the 30S subunits were stored in liquid nitrogen.

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Preparation of S. aureus ribosomes.[1]
S. aureus cells (50 g [wet weight]) were resuspended in 100 ml of lysis buffer (50 mM Tris-HCl [pH 8.0], 100 mM NaCl, 2 mg of lysostaphin per ml, 10,000 U of DNase I) and incubated for 1 h in a 37°C water bath. β-Mercaptoethanol was added to a final concentration of 5 mM, and the lysed cells were centrifuged at 10,000 × g for 10 min to remove unbroken cells and cell fragments. The supernatant was centrifuged at 30,000 × g, and the resulting supernatant was centrifuged at 100,000 × g for 16 h to pellet the ribosomes. The ribosome pellet was resuspended in buffer B and was again centrifuged at 100,000 × g for 16 h. The pellet was resuspended in buffer A, applied to linear 5 to 40% (wt/vol) sucrose gradients prepared in buffer A, and centrifuged for 16 h in a Beckman SW28 rotor. Gradients were fractionated; and the 70S ribosomes were pooled, pelleted at 300,000 × g for 5 h, and resuspended in buffer A before they were stored at −80°C.

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Initiation factor assays.[1]
Initiation factors were assayed as described by Hershey et al. Complexes between IF2 and tRNAfMet were formed in the reaction mixtures (final volume, 65 μl) containing 190 mM Tris-HCl (pH 7.4), 19 mM MgCl2, 3.8 mM DTT, 1.9 mM GTP, 540 mM NH4Cl, 5 pmol of IF2, and 2 μl of [35S]tRNAfMet (10,000 dpm). Duplicate reaction mixtures were incubated for 10 min at 37°C, and the reactions were stopped by the addition of 1 ml ice-cold buffer A containing 1% glutaraldehyde. Complexes were trapped on Millipore HA filters (pore size, 0.45 μm), washed with 50 ml of buffer A containing 1% glutaraldehyde, and counted after the addition of liquid scintillation fluid.

Absorption, Distribution and Excretion
Linezolid is widely absorbed after oral administration, with an absolute bioavailability of approximately 100%. Peak plasma concentrations (Tmax) are reached approximately 1 to 2 hours after administration, with a range of 8.1–12.9 mcg/mL after a single dose and 11.0–21.2 mcg/mL after multiple doses. Oral absorption of linezolid is not significantly affected by food intake; therefore, the timing of administration is not limited by mealtimes. Linezolid and its metabolites are primarily excreted in the urine. Under steady-state conditions, approximately 84% of the radioactive material is recovered in the urine after administration of radiolabeled linezolid, of which approximately 30% is the parent drug, 40% is a hydroxyethylglycine metabolite, and 10% is an aminoethoxyacetic acid metabolite. Fecal excretion is relatively small; the original drug was not detected in feces, with only 6% and 3% of the administered dose present in feces as metabolites of hydroxyethylglycine and aminoethoxyacetic acid, respectively. At steady state, the volume of distribution (VolD) of linezolid in a healthy adult is approximately 40–50 L. The total clearance of linezolid is estimated at 100–200 mL/min, most of which appears not to be cleared by the kidneys. The mean renal clearance is approximately 40 mL/min, suggesting net renal tubular reabsorption; non-renal clearance is estimated to account for approximately 65% of the total clearance, averaging 70–150 mL/min. The clearance of linezolid is highly variable, especially non-renal clearance. Linezolid is distributed in well-perfused tissues; the VolD is slightly lower in women than in men. The steady-state VolD is 40–50 L. Compared to adults, pediatric patients had lower AUC values, and linezolid AUC variability was higher in all age groups of children than in adults. Most preterm infants (less than 7 days gestation, less than 34 weeks gestation) had higher AUC values than many full-term newborns and older infants. Following oral administration, linezolid is rapidly absorbed, with oral bioavailability >95% in rats and dogs, and >70% in mice. A 28-day intravenous/oral toxicokinetic study in rats (20–200 mg kg⁻¹ day⁻¹) and dogs (10–80 mg kg⁻¹ day⁻¹) showed no significant increase in clearance or accumulation of linezolid after multiple doses. Linezolid has limited protein binding (<35%) and is well distributed, reaching most extravascular sites, with a steady-state volume of distribution (V_ss) approximately equal to total body fluid. Linezolid circulates primarily as the parent drug and is excreted mainly as the parent drug and two inactive carboxylic acids, PNU-142586 and PNU-142300. A small number of secondary metabolites were also identified. In all species, clearance was determined by metabolism. Radioactive recovery was largely completed within 24–48 hours. The parent drug and its metabolites are primarily excreted via the kidneys. Reabsorption of the parent drug via the renal tubules significantly slows its excretion, making this slow metabolic process the rate-limiting step for overall clearance. In conclusion, the ADME data are relatively consistent across species, supporting rats and dogs as the primary species for nonclinical safety studies. In two randomized, double-blind, placebo-controlled, dose-escalation trials, subjects received linezolid orally (375, 500, or 625 mg) orally or intravenously (500 or 625 mg) twice daily, orally or intravenously. Blood and urine samples were collected continuously for up to 18 days after the first dose and subsequent doses. Non-compartmental pharmacokinetic analysis was used to describe the in vivo distribution of linezolid. Plasma linezolid concentrations and the area under the concentration-time curve (AUC) increased proportionally with dose, regardless of the route of administration. Plasma linezolid concentrations were above the MIC90 (4.0 mg/L) for most of the 12-hour dosing interval. Mean clearance, half-life, and volume of distribution were similar regardless of oral or intravenous administration, independent of dose. Linezolid was well tolerated, with similar incidence of drug-related adverse events in the linezolid and placebo groups. Both oral and intravenous linezolid exhibited linear pharmacokinetic characteristics, with concentrations above the target MIC90 (minimum inhibitory concentration) for most of the dosing interval. These results support the twice-daily dosing regimen of linezolid and demonstrate the feasibility of switching from intravenous to oral administration without dose adjustment.
For more complete data on absorption, distribution, and excretion of linezolid (16 items in total), please visit the HSDB record page.

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Metabolism/Metabolites
Linezolid is primarily metabolized into two inactive metabolites: aminoethoxyacetic acid metabolite (PNU-142300) and hydroxyethylglycine metabolite (PNU-142586), both products of morpholine ring oxidation. The hydroxyethylglycine metabolite is the most abundant of the two metabolites and is likely generated via a non-enzymatic process, but the specific mechanism remains unclear. Although the specific enzymes responsible for linezolid biotransformation are not identified, it does not appear to be metabolized by the CYP450 enzyme system, nor does it significantly inhibit or induce these enzymes. However, linezolid is a reversible, non-selective inhibitor of monoamine oxidases. In vitro studies have shown that linezolid is not metabolized by human cytochrome P450 enzymes. Linezolid does not inhibit cytochrome P450 enzymes. Linezolid is primarily metabolized via the oxidation of the morpholine ring, generating two inactive metabolites: aminoethoxyacetic acid metabolite and hydroxyethylglycine metabolite. The hydroxyethylglycine metabolite is generated in vitro via a non-enzymatic chemical oxidation mechanism. This drug is primarily metabolized oxidatively to two inactive metabolites: aminoethoxyacetic acid metabolite and hydroxyethylglycine metabolite. Linezolid is hardly metabolized by the cytochrome P450 (CYP) enzyme system. Linezolid does not inhibit CYP isoenzymes 1A2, 2C9, 2C19, 2D6, 2E1, or 3A4, nor is it an enzyme inducer, suggesting that this drug is unlikely to alter the pharmacokinetics of drugs metabolized by these enzymes. In vitro studies aimed to identify the hepatic enzymes responsible for the oxidative metabolism of linezolid. In human liver microsomes, linezolid is oxidized to a single metabolite, hydroxylinezolid (M1). The generation of M1 depends on microsomal proteins and NADPH. The rate of M1 generation follows first-order (unsaturated) kinetics across a concentration range of 2 to 700 μM. Based on the following experiments, the molecular origin of M1 could not be determined using conventional in vitro techniques: a) Inhibitors/substrates of various cytochrome P-450 (CYP) enzymes failed to inhibit M1 formation; b) In 14 human liver samples, M1 formation was not correlated with any measured catalytic activity (r(2) < 0.23); c) M1 formation was not detected when incubated with microsomes prepared from baculovirus insect cell lines expressing CYP 1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, 3A5, and 4A11. Furthermore, in vitro P-450 inhibition screening showed that linezolid had no inhibitory activity against the following CYP enzymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4). Further in vitro studies ruled out the possibility of flavin-containing monooxygenases and monoamine oxidases as metabolites generating potential enzymes. However, metabolite formation was most ideal under alkaline conditions (pH 9.0), suggesting the possible involvement of an unknown P-450 enzyme or another microsomal-mediated oxidation pathway. Linezolid is primarily metabolized via the oxidation of the morpholine ring, producing two inactive open-ring carboxylic acid metabolites: aminoethoxyacetic acid metabolite (A) and hydroxyethylglycine metabolite (B). The formation of metabolite B in vitro is mediated by a non-enzymatic chemical oxidation mechanism. Linezolid is not an inducer of rat cytochrome P450 (CYP), and in vitro studies have confirmed that linezolid is not significantly metabolized by human cytochrome P450, nor does it inhibit the activity of clinically significant human CYP isoenzymes (1A2, 2C9, 2C19, 2D6, 2E1, 3A4). Linezolid is rapidly and extensively absorbed after oral administration. Peak plasma concentrations are reached approximately 1 to 2 hours after administration, with an absolute bioavailability of approximately 100%. Linezolid is primarily metabolized via the oxidative degradation of the morpholine ring, yielding two inactive open-ring carboxylic acid metabolites: aminoethoxyacetic acid metabolite (A) and hydroxyethylglycine metabolite (A308). Half-life: 4.5–5.5 hours. Elimination half-life is estimated to be between 5 and 7 hours. A significant but weak correlation was observed between age and total clearance. The mean (± standard deviation) elimination half-life, total clearance, and apparent volume of distribution were 3.0 ± 1.1 hours, 0.34 ± 0.15 L/h/kg, and 0.73 ± 0.18 L/kg, respectively. ...
The following are the elimination half-lives for adults taking linezolid at different doses: 400 mg tablets (single dose) - 5.2 hours; 400 mg tablets every 12 hours - 4.69 hours; 600 mg tablets (single dose) - 4.26 hours; 600 mg tablets every 12 hours - 5.4 hours; 600 mg oral suspension (single dose) - 4.6 hours; 600 mg intravenous injection (single dose) - 4.4 hours; 600 mg intravenous injection every 12 hours - 4.8 hours. The half-life is shorter in children aged 7 days to 11 years than in adults.

Toxicity Summary
Linezolid targets the 39S large subunit of the mitochondrial ribosome, thereby inhibiting mitochondrial protein synthesis. Therefore, linezolid is cytotoxic to the most metabolically active cells or tissues, including the heart, liver, thymus, and bone marrow (A7823). A possible target of linezolid is the 16S rRNA molecule in the mitochondrial ribosome, which is similar to the 23S rRNA in bacterial ribosomes. Hepatotoxicity
Linezolid treatment is associated with mild, transient increases in serum transaminase and alkaline phosphatase levels in 1% to 10% of patients. Although similar elevation rates have been observed in infected patients treated with similar drugs, no enzyme elevations were found in healthy volunteers taking linezolid for short periods. On the other hand, ALT elevations during linezolid treatment worsened with increasing dose, but all ALT elevations were asymptomatic and returned to normal upon discontinuation of the drug. Despite its limited availability and restricted use, several cases of linezolid treatment with clinically significant liver disease and jaundice have been reported. One case was reported involving a hypersensitivity reaction with rash, eosinophilia, renal insufficiency (drug reaction accompanied by eosinophilia and systemic symptoms), and mild elevation of serum enzymes. More commonly, linezolid is associated with lactic acidosis, typically occurring 1 to 8 weeks after treatment, sometimes with evidence of liver damage and jaundice. Lactic acidosis is usually caused by mitochondrial damage and dysfunction, leading to microvesicular steatosis and liver dysfunction (not necessarily accompanied by jaundice, and even elevated ALT or alkaline phosphatase). Mitochondrial damage caused by linezolid treatment can also lead to other serious side effects, including peripheral neuropathy and optic neuropathy, pancreatitis, serotonin syndrome, and kidney damage. Risk factors for linezolid-induced lactic acidosis include higher doses, longer treatment duration, and the presence of underlying chronic liver or kidney disease. Mitochondrial damage is thought to be caused by inhibition of mitochondrial ribosome function, consistent with the known effects of linezolid on bacterial ribosome function. Lactic acidosis typically develops 1 to 8 weeks after treatment and can be severe, but usually resolves rapidly upon discontinuation of the drug. In contrast, linezolid-induced optic neuropathy and peripheral neuropathy resolve more slowly and may cause permanent damage. Lactic acidosis can be fatal; liver dysfunction and jaundice have been reported in cases of severe linezolid-induced lactic acidosis.
Probability Score: A (Established clinically significant cause of liver damage, usually associated with lactic acidosis).
Pregnancy and Lactation Effects
◉ Overview of Use During Lactation
Linezolid is excreted into breast milk, and its concentration may be effective against Staphylococcus strains commonly found in mastitis. Limited data suggest that the maximum dose ingested by infants through breast milk is only 6% to 9% of the standard infant dose, and the drug concentration in infant serum is extremely low. If the mother needs to take linezolid, breastfeeding should not be discontinued. Monitor the infant for possible gastrointestinal reactions, such as diarrhea and vomiting.
◉ Effects on breastfed infants
No relevant published information found as of the revision date.
◉ Effects on lactation and breast milk
No relevant published information found as of the revision date.

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Protein binding
Linezolid has a plasma protein binding rate of approximately 31%, primarily binding to serum albumin, and this binding is concentration-dependent.

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Interactions
Concomitant use with linezolid resulted in a slight but statistically significant increase in plasma concentrations of pseudoephedrine and phenylpropanolamine; and a slight but statistically significant decrease in plasma concentrations of dextromethorphan (the major metabolite of dextromethorphan). Increased blood pressure was observed when linezolid was used in combination with pseudoephedrine or phenylpropanolamine; no significant effect was observed when used in combination with dextromethorphan. None of these concomitant drugs had a significant effect on the pharmacokinetics of linezolid. Adverse event reports are extremely rare. The enhancement of sympathomimetic activity by linezolid is considered clinically insignificant, but caution should be exercised in patients sensitive to elevated blood pressure due to predisposing factors. There are no restrictions on the combined use of dextromethorphan and linezolid. Two cases of serotonin poisoning (ST) associated with the combined use of linezolid and serotonergic drugs are reported, along with a review of previously published case reports. Case 1: A 38-year-old white woman with cystic fibrosis was treated with venlafaxine 300 mg/day for one year. She was prescribed linezolid 600 mg intravenously every 12 hours for a methicillin-resistant Staphylococcus aureus (MRSA) lung infection. Eight days into treatment, the patient developed ST symptoms. After the venlafaxine dose was reduced to 150 mg/day, the symptoms gradually subsided within 36 hours. Case 2: A 37-year-old male with multiple myeloma was taking citalopram 40 mg/day and trazodone 150 mg/day for anxiety-related disorders. Due to MRSA cellulitis, he started taking linezolid 600 mg orally twice daily. The following day, the patient developed anxiety, panic attacks, tremors, tachycardia, and hypertension, which persisted until the end of linezolid treatment. The symptoms eventually subsided 5 days after discontinuing linezolid.
Potential drug interaction (serotonin syndrome). Although serotonin syndrome has not been reported in clinical trials of linezolid, there are a few post-marketing case reports of patients developing the syndrome shortly after concomitant use of linezolid or discontinuation of certain selective serotonin reuptake inhibitors (SSRIs) (e.g., citalopram, paroxetine, sertraline). Clinicians should consider this possibility if patients receiving such combination therapy develop signs and symptoms of serotonin syndrome (e.g., high fever, cognitive impairment). Some clinicians advise caution when using linezolid in patients taking selective serotonin reuptake inhibitors (SSRIs); others recommend discontinuing SSRIs before starting linezolid and not restarting them within two weeks of finishing linezolid treatment. Toxicity caused by excessive intrasynaptic serotonin, historically known as serotonin syndrome, is now considered a phenomenon related to intrasynaptic serotonin concentration. Recent studies have more clearly defined serotonin toxicity as an independent toxic syndrome characterized by clonic seizures, hyperreflexia, high fever, and agitation. Serotonergic drugs can produce serotonergic side effects; overdose of serotonin reuptake inhibitors (SRIs) often leads to significant serotonergic side effects. Moderate serotonergic toxicity occurs in 15% of cases, but is not severe and does not lead to high fever or death. Only the combined use of serotonergic drugs with different mechanisms of action can raise intrasynaptic serotonin levels to life-threatening levels. The most common combination therapy is a monoamine oxidase inhibitor (MAOI) with any SRI. Some lesser-known drugs are also MAOIs, such as linezolid and moclobemide; some opioid analgesics also have serotonergic activity. When these drugs are used in combination, they can cause life-threatening serotonergic toxicity. Some preventable deaths still occur. Therefore, understanding the properties of these drugs will help ensure that problems are avoided in most clinical situations and that appropriate treatment is given when problems do occur (5-HT(2A) antagonists can be used in severe cases). For more complete data on interactions of linezolids (12 in total), please visit the HSDB records page.

[1]. Antimicrob Agents Chemother.1998 Dec;42(12):3251-5.

[2]. Antimicrob Agents Chemother.1997 Oct;41(10):2132-6.

[3]. Drugs. 2000 Apr;59(4):815-27; discussion 828.

[4]. Antimicrob Agents Chemother . 2012 Oct;56(10):5401-5.

Therapeutic Uses

Antimicrobial Agents

Linezolid, administered intravenously and orally, is indicated for the treatment of hospital-acquired pneumonia caused by methicillin-sensitive and methicillin-resistant Staphylococcus aureus or penicillin-sensitive Streptococcus pneumoniae. /Included on US Product Label/
Linezolid, administered intravenously and orally, is indicated for the treatment of vancomycin-resistant Enterococcus faecalis infections. /Included on US Product Label/
Oral linezolid is indicated for the treatment of uncomplicated skin and soft tissue infections caused by methicillin-sensitive Staphylococcus aureus or Streptococcus pyogenes. /Included on US Product Label/
For more complete data on the therapeutic uses of linezolids (16 in total), please visit the HSDB record page.

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Drug Warnings
Myelosuppression (including anemia, leukopenia, pancytopenia, and thrombocytopenia) has been reported in patients treated with linezolid. In cases with known outcomes, affected hematological parameters returned to pre-treatment levels upon discontinuation of linezolid. Patients receiving linezolid treatment should have their complete blood count monitored weekly, especially those receiving linezolid treatment for more than two weeks, those with a history of bone marrow suppression, those taking medications that can cause bone marrow suppression, and those with chronic infections who have previously received or are currently receiving antibiotic treatment. Discontinuation of linezolid treatment should be considered for patients who develop or experience worsening bone marrow suppression. Lactic acidosis has been reported with Zyvox. In reported cases, patients experienced recurrent nausea and vomiting. Patients experiencing recurrent nausea or vomiting, unexplained acidosis, or low bicarbonate levels during Zyvox treatment should seek immediate medical attention. Serotonin syndrome has been reported when Zyvox is used in combination with serotonergic drugs, including antidepressants such as selective serotonin reuptake inhibitors (SSRIs). If clinical considerations suggest that Zyvox is appropriate for use in combination with serotonergic drugs, patients should be closely monitored for signs and symptoms of serotonin syndrome, such as cognitive impairment, high fever, hyperreflexia, and incoordination. If related signs or symptoms appear, the physician should consider discontinuing one or both medications. Peripheral neuropathy and optic neuropathy have been reported in patients treated with Zyvox, primarily in those treated for longer than the recommended maximum duration of 28 days. In cases where optic neuropathy progressed to vision loss, the treatment duration exceeded the recommended maximum duration. Blurred vision has also been reported in some patients treated with Zyvox for less than 28 days. If a patient develops symptoms of visual impairment, such as decreased vision, altered color vision, blurred vision, or visual field defects, an immediate ophthalmological examination is recommended. Visual function should be monitored in all patients taking Zyvox long-term (≥3 months) and in all patients developing new visual symptoms, regardless of the duration of Zyvox treatment. If peripheral neuropathy or optic neuropathy occurs, the potential risks of continuing Zyvox use in these patients should be weighed. For more complete data on linezolid (18 in total), please visit the HSDB records page.

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Pharmacodynamics
Linezolid is an oxazolidinone antibacterial drug effective against most aerobic Gram-positive bacteria and mycobacteria. It has bacteriostatic activity against Staphylococcus and Enterococcus, and bactericidal activity against most Streptococcus isolates. Linezolid shows some activity against Gram-negative bacteria and anaerobes in vitro, but is ineffective against these microorganisms. Linezolid is a reversible, non-selective monoamine oxidase (MAO) inhibitor; therefore, co-administration with serotonergic drugs such as selective serotonin reuptake inhibitors (SSRIs) or tricyclic antidepressants (TCAs) may lead to serotonin syndrome. Linezolid should not be used to treat catheter-related bloodstream infections or catheter site infections, as the risks appear to outweigh the benefits in these cases.

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Linezolid is an oxazolidinone antibacterial drug whose mechanism of action is by inhibiting the initiation of bacterial protein synthesis. No cross-resistance has been found between linezolid and other protein synthesis inhibitors. Linezolid exhibits broad-spectrum antibacterial activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae (PRS), and vancomycin-resistant Enterococcus faecalis and Enterococcus faecium. Anaerobic bacteria such as Clostridium spp., Peptostreptococcus spp., and Prevotella spp. are also sensitive to linezolid. Linezolid has bacteriostatic activity against most susceptible bacteria, but exhibits bactericidal activity against certain strains of Streptococcus pneumoniae, Bacteroides fragilis, and Clostridium perfringens. In clinical trials for hospitalized patients with skin/soft tissue infections (primarily Staphylococcus aureus infections), intravenous/oral linezolid (up to 1250 mg daily) showed a clinical efficacy exceeding 83%. In patients with community-acquired pneumonia, the efficacy exceeded 94%. Preliminary clinical data also indicate that twice-daily intravenous/oral administration of 600 mg linezolid is comparable to intravenous administration of 1 g vancomycin in the treatment of hospital-acquired pneumonia and methicillin-resistant Staphylococcus aureus infections. In addition, linezolid 600 mg twice daily achieved a clinical/microbiological cure rate of over 85% for vancomycin-resistant enterococcal infections. Linezolid is generally well tolerated, with the most common adverse reaction being gastrointestinal disturbances. There have been no clinical reports of adverse reactions due to monoamine oxidase inhibition. [3]

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Superantigens (SAg) are potent activators of the immune system and are important determinants of the virulence and pathogenicity of Staphylococcus aureus. In human leukocyte antigen (HLA)-DR3 transgenic mice, hyperresponsiveness to SAg made them more susceptible to pneumonia caused by SAg-producing Staphylococcus aureus strains than C57BL/6 mice. Linezolid is a bacterial protein synthesis inhibitor that is superior to vancomycin in inhibiting SAg production in Staphylococcus aureus in vitro and provides better protection against pneumonia caused by SAg-producing Staphylococcus. [4]

C16H20FN3O4

337.35

337.143

C, 56.97; H, 5.98; F, 5.63; N, 12.46; O, 18.97

165800-03-3

Linezolid-d3;1127120-38-0

441401

White to off-white solid powder

1.3±0.1 g/cm3

585.5±50.0 °C at 760 mmHg

176-1780C

307.9±30.1 °C

0.0±1.6 mmHg at 25°C

1.554

0.3

1

6

4

24

472

1

FC1C([H])=C(C([H])=C([H])C=1N1C([H])([H])C([H])([H])OC([H])([H])C1([H])[H])N1C(=O)O[C@@]([H])(C([H])([H])N([H])C(C([H])([H])[H])=O)C1([H])[H]

TYZROVQLWOKYKF-ZDUSSCGKSA-N

InChI=1S/C16H20FN3O4/c1-11(21)18-9-13-10-20(16(22)24-13)12-2-3-15(14(17)8-12)19-4-6-23-7-5-19/h2-3,8,13H,4-7,9-10H2,1H3,(H,18,21)/t13-/m0/s1

N-[[(5S)-3-(3-fluoro-4-morpholin-4-ylphenyl)-2-oxo-1,3-oxazolidin-5-yl]methyl]acetamide

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: This product requires protection from light (avoid light exposure) during transportation and storage.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : 68~100 mg/mL ( 201.57~296.43 mM )
Ethanol : ~10 mg/mL

Solubility in Formulation 1: ≥ 2.5 mg/mL (7.41 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (7.41 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (7.41 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 30% PEG400 + 0.5% Tween 80+ 5% propylene glycol: 30mg/ml (88.93mM)

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 (Please use freshly prepared in vivo formulations for optimal results.)