Linezolid Kalceks
Oxazolidinone antibiotic for serious gram-positive infections including MRSA and VRE
Quick Facts about Linezolid Kalceks
Key Takeaways
- Linezolid Kalceks is a hospital-administered IV antibiotic effective against serious MRSA, VRE, and other resistant gram-positive infections.
- It works by a unique mechanism (inhibiting bacterial protein synthesis at the 50S ribosomal subunit) with no cross-resistance to other antibiotic classes.
- Weekly blood count monitoring is essential due to the risk of myelosuppression, especially thrombocytopenia.
- Linezolid is a reversible MAO inhibitor — avoid concurrent serotonergic drugs and excessive tyramine-rich food intake to prevent serotonin syndrome and hypertensive episodes.
- Treatment duration should generally not exceed 28 days; prolonged use increases the risk of peripheral neuropathy, optic neuropathy, and lactic acidosis.
What Is Linezolid Kalceks and What Is It Used For?
Linezolid Kalceks contains the active substance linezolid, which belongs to the oxazolidinone class of antibacterial agents. This class represents one of the few genuinely novel antibiotic mechanisms developed in recent decades, making linezolid a critically important weapon against multidrug-resistant bacteria. Linezolid was originally developed by Pharmacia (now Pfizer) and first approved by the FDA in 2000. Linezolid Kalceks is a generic formulation manufactured by AS Kalceks, supplied as a ready-to-use solution for intravenous infusion at a concentration of 2 mg/ml.
Linezolid works by inhibiting bacterial protein synthesis through a unique mechanism. It binds to the 23S ribosomal RNA component of the bacterial 50S ribosomal subunit, preventing the formation of the functional 70S initiation complex that is essential for the earliest step of protein translation. Because this binding site and mechanism differ fundamentally from those of all other antibiotics, there is no inherent cross-resistance between linezolid and other antibacterial classes such as beta-lactams, aminoglycosides, macrolides, fluoroquinolones, glycopeptides, or tetracyclines.
Linezolid demonstrates potent activity against a broad range of aerobic gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis (MRSE), vancomycin-resistant Enterococcus faecium (VRE), penicillin-resistant Streptococcus pneumoniae, and other streptococcal species. It is bacteriostatic against staphylococci and enterococci, and bactericidal against the majority of streptococcal strains.
Approved Indications
Linezolid Kalceks is indicated for the treatment of the following infections when caused by susceptible gram-positive organisms, and specifically when other antibiotics are not suitable:
- Nosocomial (hospital-acquired) pneumonia — particularly pneumonia caused by MRSA, where linezolid has demonstrated particular clinical benefit due to its excellent penetration into lung epithelial lining fluid.
- Community-acquired pneumonia — caused by susceptible gram-positive pathogens including Streptococcus pneumoniae and Staphylococcus aureus.
- Complicated skin and soft tissue infections (cSSTIs) — including diabetic foot infections, post-surgical wound infections, and deep soft tissue abscesses caused by gram-positive organisms including MRSA.
In clinical practice, linezolid is also used off-label for other serious gram-positive infections, including bone and joint infections (osteomyelitis), central nervous system infections, endocarditis, and tuberculosis (as part of multi-drug regimens for multidrug-resistant TB). The Infectious Diseases Society of America (IDSA) guidelines include linezolid as a recommended agent for MRSA infections in multiple clinical settings. Linezolid is included on the WHO Model List of Essential Medicines, underscoring its global importance as a reserve antibiotic for resistant infections.
Linezolid Kalceks should only be initiated under the supervision of a physician experienced in the treatment of serious infections. It should be reserved for situations where susceptibility testing has confirmed (or is strongly suspected of) resistant gram-positive organisms, in order to preserve its efficacy and limit the development of resistance.
What Should You Know Before Receiving Linezolid Kalceks?
Contraindications
Linezolid Kalceks must not be used in the following situations:
- Hypersensitivity to linezolid or any of the excipients in the formulation (sodium citrate dihydrate, citric acid monohydrate, glucose anhydrous, hydrochloric acid, sodium hydroxide, water for injections).
- Concurrent use of monoamine oxidase (MAO) inhibitors or within two weeks of taking such agents (e.g. phenelzine, isocarboxazid, selegiline, rasagiline, moclobemide).
- Uncontrolled hypertension, pheochromocytoma, carcinoid tumour, thyrotoxicosis, bipolar depression, schizoaffective disorder, or acute confusional states — unless patients are under close observation and blood pressure monitoring.
Warnings and Precautions
Before and during treatment with linezolid, several important precautions must be observed by the treating healthcare team:
Myelosuppression: Linezolid can suppress bone marrow function, leading to anaemia, leucopenia, pancytopenia, and most commonly thrombocytopenia (low platelet count). The risk increases significantly when treatment extends beyond 14 days. Complete blood counts (including haemoglobin, platelets, and white blood cell count with differential) should be performed at baseline and monitored at least weekly during treatment. Treatment should be discontinued if significant myelosuppression develops. Most haematological changes are reversible upon cessation of therapy.
Serotonin syndrome: Linezolid is a reversible, non-selective inhibitor of monoamine oxidase (MAO). This means it can potentiate the effects of serotonergic drugs, leading to serotonin syndrome — a potentially life-threatening condition characterised by agitation, confusion, restlessness, tachycardia, hyperthermia, diaphoresis, tremor, muscle rigidity, myoclonus, hyperreflexia, and in severe cases, rhabdomyolysis, renal failure, and death. Concomitant use with SSRIs, SNRIs, tricyclic antidepressants, triptans, buspirone, pethidine, tramadol, or other serotonergic agents should be avoided unless the benefit clearly outweighs the risk and close monitoring is possible.
Peripheral and optic neuropathy: Cases of peripheral neuropathy (including numbness, tingling, or pain in the extremities) and optic neuropathy (which may progress to optic neuritis and vision loss) have been reported, primarily with prolonged treatment exceeding 28 days. Patients should be advised to report any visual disturbances or symptoms of neuropathy promptly. Regular ophthalmological assessments are recommended for patients requiring treatment beyond 28 days.
Lactic acidosis: Cases of symptomatic lactic acidosis have been reported during linezolid therapy, thought to be related to mitochondrial toxicity from inhibition of mitochondrial protein synthesis. Patients who develop signs of lactic acidosis (recurrent nausea, vomiting, unexplained acidosis, or low bicarbonate levels) should be evaluated immediately and linezolid discontinued if confirmed.
Tyramine interaction: Because of its MAO-inhibitory activity, patients receiving linezolid should avoid consuming excessive amounts of tyramine-rich foods and beverages (such as mature cheese, yeast extracts, fermented soya products, tap beer, and red wine). Tyramine intake should be limited to less than 100 mg per meal to avoid the risk of hypertensive episodes.
Clostridioides difficile-associated diarrhoea (CDAD): As with all antibiotics, linezolid therapy may be associated with the development of CDAD, ranging from mild diarrhoea to fatal colitis. Patients who develop diarrhoea during or after treatment should be evaluated for this possibility.
If linezolid must be used in a patient already taking a serotonergic agent, the serotonergic drug should be stopped and the patient closely monitored for signs of serotonin syndrome for the duration of linezolid treatment and for two weeks (or five half-lives of the serotonergic drug, whichever is longer) after discontinuation. Seek immediate medical attention if symptoms develop.
Pregnancy and Breastfeeding
There are no adequate and well-controlled studies of linezolid in pregnant women. Animal reproductive studies have shown some evidence of embryotoxicity at high doses, but no teratogenic effects. Linezolid should only be used during pregnancy if the potential benefit justifies the potential risk to the foetus, and only when no safer alternative antibiotic is available.
Linezolid and its metabolites are excreted in breast milk in animal studies. The effects on a breastfed infant are unknown. Due to the potential for adverse effects in nursing infants, including disruption of intestinal flora and possible myelosuppression, a decision should be made whether to discontinue breastfeeding or discontinue the drug, taking into account the importance of the antibiotic to the mother.
Paediatric Use
The safety and efficacy of linezolid have been established in paediatric patients from birth to 17 years. However, it should be noted that linezolid clearance is higher in younger children compared to adults, which may necessitate different dosing regimens. The intravenous formulation (Linezolid Kalceks) is appropriate for paediatric use when IV administration is required.
How Does Linezolid Kalceks Interact with Other Drugs?
Understanding drug interactions with linezolid is essential for safe prescribing. As a reversible, non-selective monoamine oxidase (MAO) inhibitor, linezolid can potentiate the effects of adrenergic and serotonergic substances. However, linezolid is not metabolised by the cytochrome P450 enzyme system and does not inhibit or induce clinically significant CYP isoenzymes, meaning it has a relatively low potential for pharmacokinetic drug interactions.
Major Interactions (Contraindicated or Avoid)
| Interacting Drug / Class | Mechanism | Clinical Effect | Recommendation |
|---|---|---|---|
| SSRIs (e.g. fluoxetine, sertraline, citalopram, paroxetine) | Additive serotonergic activity via MAO inhibition | Serotonin syndrome | Avoid; discontinue SSRI before starting linezolid if possible |
| SNRIs (e.g. venlafaxine, duloxetine) | Additive serotonergic activity | Serotonin syndrome | Avoid; discontinue SNRI before starting linezolid if possible |
| MAO inhibitors (e.g. phenelzine, selegiline, rasagiline) | Additive MAO inhibition | Hypertensive crisis, serotonin syndrome | Contraindicated; allow 2-week washout |
| Pethidine (meperidine) | Serotonergic and possible opioid-MAO interaction | Serotonin syndrome, seizures, cardiovascular instability | Contraindicated |
| Tricyclic antidepressants (e.g. amitriptyline, clomipramine) | Serotonergic and noradrenergic potentiation | Serotonin syndrome | Avoid if possible; close monitoring if essential |
| Triptans (e.g. sumatriptan, zolmitriptan) | Serotonin 5-HT1 receptor agonism plus MAO inhibition | Serotonin syndrome | Avoid concurrent use |
Moderate Interactions (Use with Caution)
| Interacting Drug / Class | Mechanism | Clinical Effect | Recommendation |
|---|---|---|---|
| Sympathomimetics (e.g. pseudoephedrine, phenylephrine, dopamine) | Potentiation of adrenergic effects via MAO inhibition | Hypertension, tachycardia | Use reduced initial doses; monitor blood pressure |
| Tramadol | Serotonin reuptake inhibition plus MAO inhibition | Serotonin syndrome, seizures | Avoid if possible; use alternative analgesic |
| Buspirone | Serotonergic potentiation | Serotonin syndrome | Avoid if possible; monitor closely |
| Tyramine-rich foods (mature cheese, fermented products, yeast extract) | Impaired tyramine metabolism via MAO inhibition | Hypertensive episodes | Limit tyramine intake to <100 mg per meal |
| Warfarin | No direct pharmacokinetic interaction but linezolid-induced thrombocytopenia may increase bleeding risk | Increased bleeding risk | Monitor INR and platelet counts closely |
Importantly, linezolid does not interact with drugs primarily metabolised through the cytochrome P450 system (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4). This means it can generally be co-administered safely with drugs such as paracetamol, statins, benzodiazepines, and calcium channel blockers without dose adjustment. However, always consult with a pharmacist or prescribing physician before combining any medications.
What Is the Correct Dosage of Linezolid Kalceks?
Linezolid Kalceks is supplied as a ready-to-use 2 mg/ml solution for infusion. Each 300 ml infusion bag contains 600 mg of linezolid. The solution does not require further dilution before administration. It should be infused intravenously over a period of 30 to 120 minutes. The infusion bag should be inspected visually before use and discarded if particulate matter or discolouration is present.
Adults
Standard Adult Dosing
The recommended dose for all approved indications in adults is 600 mg every 12 hours, administered as an intravenous infusion. No dose adjustment is required based on age, gender, or hepatic impairment in adults.
| Indication | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| Nosocomial pneumonia | 600 mg | IV infusion | Every 12 hours | 10–14 days |
| Community-acquired pneumonia | 600 mg | IV infusion | Every 12 hours | 10–14 days |
| Complicated skin and soft tissue infections | 600 mg | IV infusion | Every 12 hours | 10–14 days |
| VRE infections (including bacteraemia) | 600 mg | IV infusion | Every 12 hours | 14–28 days |
No dose adjustment is required in patients with renal impairment, as linezolid is not significantly removed by haemodialysis. However, the two primary metabolites of linezolid (aminoethoxyacetic acid and hydroxyethyl glycine) accumulate in patients with severe renal impairment. The clinical significance of this accumulation is not fully established, and these patients should be monitored carefully. Linezolid is removed partially by haemodialysis; approximately 30% of a dose is cleared during a 3-hour session. Therefore, linezolid should be given after haemodialysis sessions.
Children
Paediatric Dosing
The recommended dose for children depends on age. Neonates and infants under 12 years of age typically receive 10 mg/kg every 8 hours. Children aged 12 years and above receive the adult dose of 600 mg every 12 hours. Neonates in the first week of life may have lower clearance; specialist guidance should be followed for this population.
| Age Group | Dose | Frequency | Notes |
|---|---|---|---|
| Preterm neonates (<7 days old) | 10 mg/kg | Every 12 hours | Lower clearance in first week; specialist supervision |
| Term neonates to <12 years | 10 mg/kg | Every 8 hours | Maximum 600 mg per dose |
| 12–17 years | 600 mg | Every 12 hours | Same as adult dosing |
Elderly
No dose adjustment is necessary for elderly patients. However, elderly patients may be more susceptible to myelosuppression and should have their blood counts monitored particularly closely. Renal function and nutritional status should also be assessed, as these factors can affect drug clearance and the risk of adverse effects.
Missed Dose
As Linezolid Kalceks is administered by healthcare professionals in a clinical setting, missed doses are unlikely. However, if a dose is inadvertently missed, it should be given as soon as possible. The dosing interval should then be adjusted to maintain the standard 12-hourly schedule. Two doses should never be given simultaneously to compensate for a missed dose.
Overdose
There is limited clinical experience with linezolid overdose. In reported cases and in healthy volunteer studies at supratherapeutic doses (up to 2400 mg/day), the following adverse effects have been observed: nausea, vomiting, headache, diarrhoea, and tremor. Management of overdose is supportive, with treatment directed at symptoms. Linezolid is approximately 30% removed by haemodialysis, which may assist in removal in cases of severe overdose.
Linezolid has nearly 100% oral bioavailability. When a patient's clinical condition allows, the treating physician may consider switching from IV to oral linezolid (tablets or oral suspension) at the same dose without any loss of efficacy. This approach is commonly used in clinical practice to facilitate earlier hospital discharge.
What Are the Side Effects of Linezolid Kalceks?
Like all medicines, Linezolid Kalceks can cause side effects, although not everybody gets them. The side effect profile of linezolid has been well characterised through extensive clinical trials involving over 2,000 patients and more than two decades of post-marketing surveillance. The majority of adverse effects are mild to moderate in severity and resolve after treatment is completed.
The frequency categories below follow the international convention used by the EMA and WHO: very common (≥1/10), common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), rare (≥1/10,000 to <1/1,000), and very rare (<1/10,000).
Common
Affects 1 to 10 in every 100 patients
- Diarrhoea
- Nausea
- Vomiting
- Headache
- Dysgeusia (altered or metallic taste)
- Thrombocytopenia (low platelet count)
- Anaemia
- Dizziness
- Insomnia
- Fungal infections (candidiasis) due to disruption of normal flora
- Elevated liver enzymes (AST, ALT)
- Elevated blood urea nitrogen (BUN)
Uncommon
Affects 1 to 10 in every 1,000 patients
- Leucopenia (low white blood cell count)
- Neutropenia
- Pancytopenia
- Abdominal pain
- Constipation
- Dry mouth
- Glossitis (tongue inflammation)
- Stomatitis (mouth ulcers)
- Pruritus (itching)
- Rash
- Hypertension
- Transient ischaemic attacks
- Polyuria (increased urination)
- Elevated creatinine, sodium, bilirubin, or amylase
Rare
Affects 1 to 10 in every 10,000 patients
- Serotonin syndrome (with concurrent serotonergic drugs)
- Peripheral neuropathy (numbness, tingling in hands/feet)
- Optic neuropathy / optic neuritis (visual disturbances, potential vision loss)
- Lactic acidosis (nausea, vomiting, rapid breathing, metabolic acidosis)
- Seizures
- Sideroblastic anaemia (ring sideroblasts on bone marrow examination)
- Pancreatitis
- Superficial tooth discolouration (reversible with dental cleaning)
- Tongue discolouration
Very Rare / Post-Marketing Reports
Affects fewer than 1 in 10,000 patients
- Anaphylaxis (severe allergic reaction)
- Angioedema (facial/throat swelling)
- Stevens-Johnson syndrome / toxic epidermal necrolysis
- Bullous skin reactions
- Clostridioides difficile-associated diarrhoea / pseudomembranous colitis
- Hyponatraemia (low sodium)
Thrombocytopenia is the most clinically significant haematological adverse effect and appears to be dose- and duration-dependent. In clinical trials, the incidence of thrombocytopenia (platelet count <75% of lower limit of normal) was approximately 2.4% in patients treated for up to 28 days. The mechanism is thought to involve immune-mediated platelet destruction and direct suppression of megakaryocyte production. Platelet counts typically recover within 1–2 weeks of discontinuing linezolid.
Peripheral neuropathy and optic neuropathy are the most concerning long-term complications, generally associated with treatment durations exceeding 28 days. While peripheral neuropathy may be only partially reversible, early detection and discontinuation of linezolid generally leads to improvement. All patients should be counselled about the importance of reporting visual symptoms, numbness, or tingling.
Contact your treating physician or emergency services immediately if you experience: signs of a severe allergic reaction (difficulty breathing, swelling of face/throat, severe rash); unusual bleeding or bruising; persistent nausea and vomiting with rapid breathing (possible lactic acidosis); sudden visual changes or vision loss; signs of serotonin syndrome (agitation, confusion, rapid heartbeat, high temperature, muscle rigidity).
How Should You Store Linezolid Kalceks?
Proper storage of Linezolid Kalceks is essential to maintain the stability and efficacy of the medication. The following storage conditions should be observed:
- Temperature: Store below 25°C (77°F). Do not refrigerate or freeze the infusion solution, as low temperatures may cause precipitation.
- Light protection: Keep the infusion bags in the outer overwrap to protect from light until ready for use. Linezolid solution is sensitive to light and may undergo degradation if exposed to prolonged direct or artificial light.
- Shelf life: The shelf life of the unopened product is stated on the packaging. Do not use after the expiry date printed on the bag and carton.
- After opening: Linezolid Kalceks is a single-use product. Chemical and physical in-use stability has been demonstrated for 24 hours at 25°C when removed from the overwrap. From a microbiological point of view, the product should be used immediately. Any unused solution remaining in the infusion bag must be discarded.
- Keep out of reach: Keep all medicines out of the sight and reach of children.
- Disposal: Do not dispose of medicines via wastewater or household waste. Return unused or expired medicines to your pharmacy or hospital for safe disposal in accordance with local requirements.
Before administration, the infusion solution should be visually inspected. It is a clear, colourless to yellow solution. Do not use if the solution is cloudy, contains visible particles, or if the container appears damaged. The solution is compatible with 5% glucose (dextrose), 0.9% sodium chloride, and Ringer's lactate solutions. It should not be mixed with other medicinal products in the same infusion line unless compatibility has been verified.
What Does Linezolid Kalceks Contain?
Linezolid Kalceks solution for infusion is a sterile, ready-to-use formulation designed for direct intravenous administration. Understanding its composition is important for healthcare professionals assessing compatibility and for patients with specific hypersensitivities.
Active Ingredient
The active substance is linezolid. Each millilitre of solution contains 2 mg of linezolid, and each 300 ml infusion bag delivers a total dose of 600 mg. Linezolid (chemical name: (S)-N-[[3-[3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl]acetamide) has a molecular weight of 337.35 g/mol and is slightly soluble in water.
Excipients (Inactive Ingredients)
- Sodium citrate dihydrate — used as a buffering agent to maintain the pH of the solution within the optimal range (pH 3.8–5.5).
- Citric acid monohydrate — co-buffer to maintain solution stability and pH.
- Glucose anhydrous — provides an isotonic vehicle for the infusion. Each 300 ml bag contains approximately 13.7 g of glucose, which should be considered in patients with diabetes mellitus or those on carbohydrate-restricted diets.
- Hydrochloric acid and/or sodium hydroxide — for pH adjustment during manufacturing.
- Water for injections — solvent.
The sodium content of each 300 ml infusion bag is approximately 114 mg (approximately 5 mmol), which should be taken into account for patients on sodium-restricted diets or those with conditions requiring careful fluid and electrolyte management, such as heart failure or renal impairment.
Linezolid Kalceks does not contain latex, preservatives, or antimicrobial agents in the formulation. The infusion solution is presented in single-use, flexible, non-PVC infusion bags with an aluminium overwrap for light protection.
Frequently Asked Questions about Linezolid Kalceks
References
All medical information in this article is based on peer-reviewed research, international clinical guidelines, and authoritative pharmaceutical references. The following sources were used:
- World Health Organization (WHO). Model List of Essential Medicines – 23rd list (2023). Geneva: WHO; 2023.
- European Medicines Agency (EMA). Linezolid – Summary of Product Characteristics. EMA; 2024.
- U.S. Food and Drug Administration (FDA). Zyvox (Linezolid) – Prescribing Information. FDA; 2023.
- British National Formulary (BNF). Linezolid. NICE/BNF; 2025.
- Liu C, Bayer A, Cosgrove SE, et al. Clinical practice guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children. Clin Infect Dis. 2011;52(3):e18-e55. doi:10.1093/cid/ciq146
- Wunderink RG, Niederman MS, Kollef MH, et al. Linezolid in methicillin-resistant Staphylococcus aureus nosocomial pneumonia: a randomized, controlled study. Clin Infect Dis. 2012;54(5):621-629. doi:10.1093/cid/cir895
- Bressler AM, Zimmer SM, Gilmore JL, Somani J. Peripheral neuropathy associated with prolonged use of linezolid. Lancet Infect Dis. 2004;4(8):528-531. doi:10.1016/S1473-3099(04)01109-0
- Narita M, Tsuji BT, Yu VL. Linezolid-associated peripheral and optic neuropathy, lactic acidosis, and serotonin syndrome. Pharmacotherapy. 2007;27(8):1189-1197. doi:10.1592/phco.27.8.1189
- Moellering RC Jr. Linezolid: the first oxazolidinone antimicrobial. Ann Intern Med. 2003;138(2):135-142. doi:10.7326/0003-4819-138-2-200301210-00015
- Kalceks AS. Linezolid Kalceks – Summary of Product Characteristics. Updated 2024.
Editorial Team
This article was written and medically reviewed by the iMedic Medical Editorial Team, comprising licensed physicians specialising in infectious disease, clinical pharmacology, and clinical microbiology.
iMedic Medical Editorial Team
Specialists in Infectious Disease & Clinical Pharmacology
iMedic Medical Review Board
Independent medical expert panel
Level 1A Evidence
GRADE Framework Applied
WHO, EMA, FDA, BNF, IDSA
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