Sodium thiosulfate (STS) is a medication used in patients with chronic kidney disease who are undergoing long-term dialysis. It functions primarily as a chelating agent, meaning it binds to certain substances in the body. The medication is delivered intravenously during the dialysis session to facilitate its action and removal. Only trained medical personnel are authorized to prepare and administer STS.
Medical Rationale for Sodium Thiosulfate Use in Dialysis
Sodium thiosulfate is most frequently used to treat calciphylaxis, a severe, life-threatening complication of chronic kidney disease also known as calcific uremic arteriolopathy (CUA). This condition involves the progressive calcification, or hardening, of the small and medium-sized blood vessels in the skin and fat tissue. Vascular calcification leads to intense pain, tissue ischemia, and the formation of non-healing skin ulcers, which carry a high mortality risk due to infection.
The body’s inability to properly regulate calcium and phosphate due to kidney failure contributes significantly to this hardening. STS works by interacting directly with the calcium deposits in the vessel walls. It acts as a calcium chelator, binding to the insoluble calcium salts and forming the more soluble compound, calcium thiosulfate. This soluble compound can then be cleared from the body primarily through the dialysis process.
Beyond its chelating properties, sodium thiosulfate also exhibits antioxidant effects that may help improve blood vessel function.
Preparation and Dosing Requirements
The preparation of sodium thiosulfate for administration must be performed before the dialysis session is complete. Although STS is not formally approved by regulatory bodies for calciphylaxis, common practice dictates a standardized dosing regimen. The typical dose for an adult patient is 25 grams, administered three times per week during each hemodialysis session.
For smaller patients, a reduced dose of 12.5 grams may be suggested, especially for those weighing less than 60 kilograms. The medication is generally available as a concentrated solution (such as 25% or 50%) and often requires dilution before infusion. A common preparation involves diluting the 25-gram dose in 100 milliliters of 0.9% sodium chloride (normal saline).
The timing of administration is important, as the medication is typically infused toward the end of the hemodialysis session. Administering it during this time allows the dialysis machine to help remove the thiosulfate breakdown products and mitigate some potential side effects.
Step-by-Step Administration During Hemodialysis
The administration of sodium thiosulfate is performed by trained staff, typically in the last hour of the hemodialysis treatment. Before beginning, the medical professional must confirm the patient’s identity and verify the prepared dose against the physician’s order. The prepared STS solution, often diluted in 100 mL of normal saline, is connected to an infusion pump.
The medication is infused directly into the patient’s bloodstream through the venous access line of the dialysis circuit. This route allows the medication to be delivered systemically while also benefiting from the immediate clearance mechanisms of the dialysis filter. The medication must be administered as a slow, continuous intravenous infusion rather than a rapid push.
The standard infusion time is between 30 and 60 minutes, with 60 minutes being a common target to reduce the risk of adverse reactions. The infusion pump is set to deliver the total volume of the diluted STS solution over this precise time frame. During the infusion, the access site must be carefully monitored for any signs of infiltration or irritation.
Once the STS solution has completely infused, a final flush is performed using 0.9% sodium chloride to ensure the patient receives the full dose. This flush washes any residual medication from the infusion line into the venous circulation. The administration must be completed while the patient is still connected to the dialysis machine.
Monitoring and Managing Common Side Effects
Patients receiving sodium thiosulfate must be closely monitored throughout the infusion and immediately afterward for potential side effects. The most common adverse events are nausea and vomiting. These symptoms are often transient but can be managed by pre-treating the patient with anti-nausea medication, such as ondansetron, 30 minutes before the STS infusion begins.
Another frequent side effect is transient hypotension, a temporary drop in blood pressure. Blood pressure should be checked frequently—for example, every 10 to 15 minutes—during the infusion. If a significant drop in blood pressure occurs, the infusion rate may need to be slowed, or in severe cases, the infusion may need to be temporarily stopped.
Sodium thiosulfate administration can also contribute to metabolic acidosis and may increase the sodium load. Medical staff monitor for this by regularly checking blood work, including electrolytes and acid-base balance. If metabolic acidosis develops, it is typically managed by adjusting the bicarbonate concentration in the dialysis solution. Less frequent side effects include a metallic or salty taste in the mouth, headache, and a sensation of warmth throughout the body.