Tadim (Colistimethate Sodium)

What Is Tadim and What Is It Used For?

Tadim (colistimethate sodium) is a polymyxin antibiotic administered intravenously to treat severe infections caused by certain aerobic gram-negative bacteria. It is used as a last-resort treatment when other antibiotics are not appropriate, particularly for multidrug-resistant (MDR) infections including those caused by Pseudomonas aeruginosa, Acinetobacter baumannii, and carbapenem-resistant Enterobacterales.

Colistimethate sodium, the active ingredient in Tadim, belongs to the polymyxin class of antibiotics, specifically polymyxin E. This class of antibiotics was first discovered in the late 1940s but fell out of clinical favor in the 1970s and 1980s due to concerns about nephrotoxicity (kidney damage) and neurotoxicity (nerve damage). However, the global rise of multidrug-resistant gram-negative bacteria has led to a resurgence in the clinical use of colistimethate sodium as one of the few remaining treatment options for these life-threatening infections.

Colistimethate sodium is a prodrug, meaning it is inactive in its administered form and must be converted by the body into its active form, colistin, to exert its antibacterial effects. This conversion occurs through hydrolysis in the bloodstream and tissues. Colistin works by disrupting the outer cell membrane of gram-negative bacteria. It binds to lipopolysaccharide (LPS) molecules on the bacterial surface, displacing the calcium and magnesium ions that normally stabilize the membrane structure. This leads to increased cell permeability, leakage of cellular contents, and ultimately bacterial cell death.

The spectrum of activity of colistin includes most aerobic gram-negative bacilli, making it particularly valuable against organisms that have developed resistance to virtually all other antibiotic classes. Common target organisms include Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae (including carbapenem-resistant strains), and Escherichia coli. However, certain gram-negative bacteria are inherently resistant, including Proteus, Providencia, Morganella, and Serratia species, as well as Burkholderia cepacia.

Internationally, colistimethate sodium is marketed under several brand names, including Tadim (in Austria, the Netherlands, and Sweden) and Promixin (in Germany, Denmark, and Norway). It is approved by regulatory authorities across the European Economic Area. The drug is manufactured by Xellia Pharmaceuticals and marketed by Zambon S.p.A.

What Should You Know Before Receiving Tadim?

Before receiving Tadim, your doctor must evaluate your kidney function, medical history, and current medications. Tadim is contraindicated in patients allergic to colistimethate sodium, colistin, or other polymyxins. Special caution is needed for patients with kidney disease, myasthenia gravis, or porphyria.

Contraindications

You must not receive Tadim if you are allergic (hypersensitive) to colistimethate sodium, colistin, or other polymyxin antibiotics. Polymyxin allergy, while relatively uncommon, can manifest as anaphylaxis or severe hypersensitivity reactions. If you have a known allergy to any polymyxin antibiotic, inform your healthcare provider immediately before treatment begins.

Cross-reactivity between polymyxin B and colistin (polymyxin E) is well-documented, so patients with a known allergy to either should avoid both. Your doctor will ask about your complete allergy history before prescribing Tadim. If you experience any allergic symptoms during treatment, such as skin rash, raised red skin lesions (urticaria), swollen eyelids, face, lips, mouth or tongue, itching, or difficulty breathing or swallowing, treatment must be stopped immediately and emergency medical care sought.

Warnings and Precautions

Several medical conditions require special caution when using Tadim. Inform your doctor if any of the following apply to you:

• Kidney disease or impaired renal function: Nephrotoxicity is the most clinically significant adverse effect of colistimethate sodium. Patients with pre-existing kidney disease are at substantially higher risk of worsening renal function during treatment. Your doctor will adjust the dose based on your kidney function and monitor it closely with regular blood tests throughout treatment.
• Myasthenia gravis: This rare neuromuscular disorder causes extreme muscle weakness and fatigue. Colistimethate sodium can exacerbate myasthenia gravis symptoms by interfering with neuromuscular transmission. Patients with this condition require very careful monitoring and may experience worsening weakness, including potentially life-threatening respiratory muscle weakness.
• Porphyria: This rare inherited metabolic disorder affects the production of heme, a component of hemoglobin. Colistimethate sodium should be used with extreme caution in patients with porphyria, as it may trigger acute porphyric attacks.

Special caution is required in premature and newborn infants, as their kidneys are not yet fully developed and are more susceptible to nephrotoxic effects. Pediatric dosing is carefully calculated based on body weight, and kidney function is monitored even more frequently in this population.

Pregnancy and Breastfeeding

Tadim should only be used during pregnancy if the potential benefit to the mother outweighs the possible risks to the unborn child. There are limited clinical data on the use of colistimethate sodium in pregnant women, and it is not known whether the drug can cause fetal harm. Animal studies have shown some evidence of teratogenicity at high doses, but the relevance of these findings to human use is uncertain. If you are pregnant, planning to become pregnant, or suspect you may be pregnant, discuss this with your doctor before receiving treatment.

Breastfeeding is not recommended during treatment with Tadim. Colistimethate sodium has been shown to pass into breast milk, and the potential effects on the nursing infant are not well characterized. A clinical decision must be made between discontinuing breastfeeding or discontinuing treatment, taking into account the benefit of breastfeeding for the child and the necessity of treatment for the mother. If breastfeeding is interrupted for treatment, mothers may wish to express and discard breast milk to maintain milk supply.

Driving and Operating Machinery

Tadim may cause dizziness, confusion, or visual disturbances such as blurred vision. If you experience any of these effects, do not drive, use tools, or operate machinery. You are responsible for assessing your own fitness to perform these activities. Since Tadim is typically administered in a hospital setting, this consideration is most relevant during the recovery period and after discharge.

How Does Tadim Interact with Other Drugs?

Tadim can interact with nephrotoxic drugs (increasing kidney damage risk), neurotoxic drugs (increasing nerve damage risk), and neuromuscular blocking agents (enhancing muscle paralysis). Patients with myasthenia gravis face additional risks when combining Tadim with macrolide or fluoroquinolone antibiotics.

Drug interactions are a significant clinical concern with colistimethate sodium therapy. Because Tadim is typically used in critically ill patients who are often receiving multiple medications simultaneously, the potential for harmful interactions must be carefully evaluated before and during treatment. Your healthcare team will review all medications you are taking, including prescription drugs, over-the-counter medicines, and herbal supplements.

Major Interactions

The most clinically significant interactions involve other nephrotoxic drugs. When colistimethate sodium is administered concurrently with aminoglycoside antibiotics (such as gentamicin, tobramycin, or amikacin), the risk of acute kidney injury is substantially increased due to their shared nephrotoxic mechanisms. Both drug classes cause tubular cell damage in the kidneys, and their combined effect can be more than additive. Similarly, concurrent use with vancomycin, amphotericin B, or cyclosporine amplifies kidney damage risk and should be avoided when clinically feasible.

Neuromuscular blocking agents, commonly used during general anesthesia, represent another major interaction concern. Colistimethate sodium can potentiate the effects of non-depolarizing neuromuscular blockers (such as tubocurarine) and depolarizing agents (such as succinylcholine), leading to prolonged neuromuscular blockade and respiratory depression. If you are scheduled for surgery requiring general anesthesia, it is critical to inform your anesthesiologist that you are receiving Tadim.

Minor Interactions

Drugs that affect the nervous system may have enhanced neurotoxic effects when used alongside colistimethate sodium. While the clinical significance of these interactions is often less pronounced than the nephrotoxic interactions, monitoring for neurological symptoms (dizziness, confusion, visual disturbances) is recommended. Additionally, when inhaled colistimethate sodium is used concurrently with intravenous Tadim (a scenario sometimes encountered in cystic fibrosis patients with respiratory infections), the total systemic exposure to colistin may be increased, raising the risk of both nephrotoxicity and neurotoxicity.

What Is the Correct Dosage of Tadim?

The standard adult dose of Tadim is 9 million International Units (IU) per day, divided into 2 or 3 doses, administered as an intravenous infusion over 30-60 minutes. A loading dose of 9 million IU may be given initially in critically ill patients. Dose adjustments are required for patients with impaired kidney function.

Tadim is always administered by a healthcare professional in a hospital or clinical setting. The powder must first be reconstituted into a solution suitable for intravenous infusion. The dosing regimen is determined by your physician based on the severity and type of infection, your body weight, kidney function, and the susceptibility of the infecting organism.

Adults

The concept of a loading dose is particularly important in critically ill patients. Because colistimethate sodium is a prodrug that requires in vivo conversion to active colistin, there can be a significant delay in achieving therapeutic colistin concentrations in the blood. A loading dose helps to overcome this delay and achieve effective drug levels more quickly, which is crucial in life-threatening infections where every hour of inadequate antibiotic coverage can worsen patient outcomes.

Children

Elderly

Elderly patients often have age-related decline in kidney function that may not be reflected in standard blood tests (serum creatinine). Dosing in elderly patients should be based on estimated or measured creatinine clearance rather than serum creatinine alone. Lower doses are typically required, and kidney function should be monitored more frequently. Elderly patients are also at increased risk of neurotoxic effects, including confusion and dizziness.

Patients with Kidney Impairment

Missed Dose

Since Tadim is administered by healthcare professionals in a clinical setting, it is unlikely that a dose will be missed. However, if you believe a dose has been missed:

• If it has been less than 3 hours since the scheduled dose time, contact your healthcare team so the dose can be given
• If it has been more than 3 hours since the missed dose, your healthcare team will wait until the next scheduled dose
• Do not double the dose to compensate for a missed one

Overdose

Overdose with colistimethate sodium can cause serious symptoms due to neurotoxic and nephrotoxic effects. Since the drug is administered by healthcare professionals, overdose is unlikely but can occur through dosing errors. Symptoms of overdose may include:

• Dizziness and vertigo (sensation of spinning)
• Slurred speech
• Visual disturbances
• Confusion and mental disturbance
• Facial flushing
• Kidney problems (reduced urine output, elevated creatinine)
• Muscle weakness
• Respiratory insufficiency (difficulty breathing)

There is no specific antidote for colistimethate sodium overdose. Treatment is supportive and may include hemodialysis, although the effectiveness of dialysis in removing colistin from the bloodstream is limited. If overdose is suspected, treatment is stopped and the patient is monitored closely in an intensive care setting with supportive measures including maintenance of airway, breathing, and circulation.

What Are the Side Effects of Tadim?

The most clinically significant side effects of Tadim are nephrotoxicity (kidney damage) and neurotoxicity. Very common side effects include changes in kidney function, headache, perioral and facial paresthesia (tingling/numbness), itching, and muscle weakness. Kidney failure is a rare but serious complication.

Like all medications, Tadim can cause side effects, although not everyone who receives it will experience them. The risk and severity of side effects depend on factors including the dose, duration of treatment, kidney function, and concurrent medications. Your healthcare team will monitor you closely during treatment to detect any side effects early.

Nephrotoxicity (Kidney Damage)

Nephrotoxicity is the most clinically important adverse effect of colistimethate sodium and deserves detailed discussion. Changes in kidney function, detected through routine blood tests, are very common and occur in more than 10% of patients receiving the drug. The mechanism of kidney damage involves direct toxic effects on tubular epithelial cells in the kidneys, leading to acute tubular necrosis.

Risk factors for colistimethate-induced nephrotoxicity include higher doses, longer treatment duration, concurrent use of other nephrotoxic drugs, pre-existing kidney disease, advanced age, critical illness with hemodynamic instability, and dehydration. Your doctor will minimize risk by using the lowest effective dose, ensuring adequate hydration, avoiding concomitant nephrotoxic medications when possible, and monitoring renal function regularly (typically every 2-3 days).

In most cases, kidney function changes are reversible upon discontinuation of the drug or dose reduction. However, in rare cases, acute kidney injury can progress to kidney failure requiring temporary dialysis. Early detection through regular monitoring is key to preventing serious renal complications.

Neurotoxicity

Neurotoxic effects of colistimethate sodium are primarily dose-dependent and usually reversible. Perioral and facial paresthesia (tingling or numbness around the mouth and face) is one of the most frequently reported neurological side effects and typically occurs within the first few days of treatment. Other neurotoxic manifestations include dizziness, visual disturbances, confusion, and speech difficulties.

In rare cases, more severe neurotoxicity can occur, including neuromuscular blockade leading to muscle weakness and, in extreme cases, respiratory paralysis. Patients with myasthenia gravis or other neuromuscular disorders are at particularly high risk of neurotoxic complications and require very careful monitoring.

Pseudo-Bartter Syndrome

After intravenous administration, some patients may develop Pseudo-Bartter syndrome, a rare metabolic disturbance characterized by hypokalemia (low potassium), hypochloremia (low chloride), metabolic alkalosis, and increased urine output. Symptoms include muscle cramps, fatigue, and increased urination. This condition is more common with prolonged treatment and can be managed with electrolyte supplementation and dose adjustment. Prompt reporting of these symptoms to your healthcare team is important.

How Should Tadim Be Stored?

Unopened Tadim vials do not require special storage conditions. After reconstitution, the solution must be used immediately as it contains no preservatives. All storage and preparation are handled by healthcare professionals in a clinical setting.

Keep Tadim out of the sight and reach of children. Do not use Tadim after the expiry date stated on the vial or carton. The expiry date refers to the last day of the stated month.

Unopened vials of Tadim do not require any special storage conditions and can be kept at room temperature. This makes the drug relatively easy to stock and manage in hospital pharmacies and clinical settings.

Importantly, Tadim does not contain any preservatives. Therefore, once the powder has been reconstituted into a solution for infusion, it must be used immediately. Any unused reconstituted solution must be discarded. Healthcare professionals are responsible for the proper preparation, storage, and disposal of the medicine, including environmentally safe disposal of any unused product.

What Does Tadim Contain?

Each vial of Tadim contains 1 million International Units (IU) of colistimethate sodium, weighing approximately 80 mg. There are no other ingredients (excipients). The product is supplied as a white to off-white powder in glass vials, packaged in cartons of 10.

Tadim has a remarkably simple formulation. Each glass vial contains only the active substance, colistimethate sodium, at a strength of 1 million IU (approximately 80 mg). There are no excipients, fillers, preservatives, or other inactive ingredients. This simplicity reduces the risk of excipient-related allergic reactions or incompatibilities.

The product is supplied as a powder that must be reconstituted before use. The powder appears as a white to slightly off-white cake or powder within a sealed glass vial. Each carton contains 10 vials. Before administration, healthcare professionals dissolve the powder in a suitable diluent (typically sterile water for injection or sodium chloride 0.9% solution) to create the infusion solution.

It is worth noting the distinction between units of measurement used for colistimethate sodium. In Europe, dosing is expressed in International Units (IU), while in some other countries (notably the United States), dosing is expressed in milligrams of colistin base activity (CBA). These are not interchangeable, and conversion errors have historically been a source of dosing mistakes. One million IU of colistimethate sodium is approximately equivalent to 80 mg of colistimethate sodium or approximately 33.3 mg of colistin base activity.

Frequently Asked Questions About Tadim