LINEZOLID
Clinical safety rating: caution
Animal studies have proved adverse effects but may be safe for humans
Linezolid is a synthetic antibacterial agent that inhibits bacterial protein synthesis by binding to the 23S ribosomal RNA of the 50S subunit, preventing the formation of a functional 70S initiation complex. It is a bacteriostatic agent against most susceptible organisms.
| Metabolism | Linezolid is primarily metabolized by oxidation of the morpholine ring, resulting in two inactive metabolites: aminoethoxyacetic acid (metabolite A) and hydroxyethyl glycine (metabolite B). Metabolism is not mediated by CYP450 enzymes; it is thought to be via non-enzymatic oxidation. |
| Excretion | Approximately 80% of linezolid is excreted renally as unchanged drug, with 30% as parent drug and the remainder as metabolites. About 7% is excreted in feces (biliary/fecal route). |
| Half-life | Terminal elimination half-life is approximately 4.5-5.5 hours in adults with normal renal function. Half-life is not significantly altered in hepatic impairment but may be prolonged in severe renal impairment (up to 7-8 hours). |
| Protein binding | Approximately 31% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Volume of distribution is about 0.6-0.7 L/kg, indicating extensive distribution into well-perfused tissues. It distributes widely into skin, soft tissue, lung, and cerebrospinal fluid (CSF penetration ~70% with inflamed meninges). |
| Bioavailability | Oral bioavailability is approximately 100% (nearly complete absorption), allowing intravenous-to-oral switch without dose adjustment. |
| Onset of Action | Oral: Peak concentrations achieved within 1-2 hours; bacteriostatic action begins within 2-4 hours. Intravenous: Immediate clinical effect, with therapeutic concentrations achieved by end of infusion. |
| Duration of Action | Bacteriostatic activity persists for approximately 12 hours post-dose, supporting twice-daily dosing. Duration may be prolonged in patients with renal impairment. |
600 mg IV or orally every 12 hours
| Dosage form | SOLUTION |
| Renal impairment | No dosage adjustment required for any degree of renal impairment; monitor for accumulation of metabolites in severe renal impairment (CrCl <30 mL/min) |
| Liver impairment | No dosage adjustment required for mild-to-moderate hepatic impairment (Child-Pugh A or B); not adequately studied in severe hepatic impairment (Child-Pugh C) |
| Pediatric use | Infants and children <12 years: 10 mg/kg IV or orally every 8 hours; children ≥12 years: 600 mg IV or orally every 12 hours (maximum 600 mg/dose) |
| Geriatric use | No specific dosage adjustment; monitor renal function and platelet counts as elderly patients may have age-related renal impairment and increased risk of thrombocytopenia |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Can cause serotonin syndrome with serotonergic drugs like SSRIs Can cause myelosuppression and peripheral neuropathy.
| Breastfeeding | Linezolid is excreted into human milk at low concentrations. The milk-to-plasma ratio is approximately 0.84. A nursing infant would receive about 1.3% of the maternal weight-adjusted dose, which is not expected to cause adverse effects. However, due to limited data, caution is recommended, and breastfeeding should be avoided if the infant is premature, has renal impairment, or is sensitive to MAO inhibitors. |
| Teratogenic Risk | Linezolid is classified as FDA Pregnancy Category C. Animal studies have shown embryotoxicity and fetal toxicity at doses 0.125 times the human exposure based on AUC, but there are no adequate and well-controlled studies in pregnant women. In the first trimester, there is a potential risk of fetal harm based on animal data. In the second and third trimesters, limited human data do not suggest an increased risk of major birth defects, but caution is advised. Linezolid should only be used if the potential benefit justifies the potential risk to the fetus. |
■ FDA Black Box Warning
Mortality imbalance observed in a clinical trial in patients with catheter-related bloodstream infections (CRBSI) when linezolid was compared to vancomycin/dicloxacillin/oxacillin (78.2% vs 66.1% survival). All-cause mortality was higher in linezolid-treated patients.
| Common Effects | VRE) |
| Serious Effects |
["Hypersensitivity to linezolid or any component of the formulation","Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 2 weeks of MAOI use","Uncontrolled hypertension, pheochromocytoma, thyrotoxicosis, or carcinoid syndrome unless immediate surgical intervention is required","Use of serotonergic agents (e.g., SSRIs, SNRIs, triptans, bupropion, meperidine, buspirone) due to risk of serotonin syndrome"]
| Precautions | ["Myelosuppression (including anemia, leukopenia, thrombocytopenia) – monitor complete blood counts weekly","Lactic acidosis – monitor for unexplained acidosis, nausea, or low bicarbonate levels","Serotonin syndrome when used with serotonergic drugs (e.g., SSRIs, SNRIs, MAOIs) – avoid co-administration","Peripheral and optic neuropathy – may occur, especially with prolonged use; monitor for visual changes","Hypertension – caution in patients with uncontrolled hypertension; monitor blood pressure","Convulsions – reported in patients with history of seizures or risk factors","Clostridioides difficile-associated diarrhea","Hypoglycemia – reported in patients with diabetes; monitor glucose"] |
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| Fetal Monitoring | Monitor for maternal adverse effects including myelosuppression (complete blood count weekly), peripheral and optic neuropathy (report vision changes), lactic acidosis (serum lactate if symptoms), serotonin syndrome if co-administered with serotonergic drugs. For fetal monitoring, standard prenatal care with ultrasound as indicated for growth and anatomy. |
| Fertility Effects | Animal studies have shown no significant effects on fertility in male and female rats at doses up to 6 mg/kg/day. In humans, no data are available on fertility effects. Linezolid is not expected to impair fertility based on its mechanism of action (protein synthesis inhibitor). |