Cyanokit Side Effects: What to Expect and When to Call Your Doctor

Cyanokit (hydroxocobalamin for injection) is administered in emergency situations — primarily for cyanide poisoning following smoke inhalation or toxic exposure. While it is a life-saving treatment, hydroxocobalamin does produce distinctive and sometimes alarming-looking side effects that patients and families should be aware of. Most are temporary and resolve on their own, but some require ongoing monitoring.

This guide covers all known side effects of Cyanokit — common, serious, and unusual — so patients recovering from cyanide poisoning treatment can understand what to expect.

The Most Common Side Effect: Red Discoloration

The most immediately noticeable side effect of Cyanokit is a striking reddish-pink discoloration of the skin, mucous membranes, and urine. This happens because hydroxocobalamin itself is a dark red compound, and when administered in a 5-gram dose, its color temporarily tints body fluids and tissues.

• Skin redness (erythema): The skin may appear red or pink immediately after infusion. This discoloration typically lasts up to 2 weeks. While it is not known definitively whether the redness causes photosensitivity, patients are advised to avoid prolonged direct sun exposure while the discoloration persists.
• Red or pink urine (chromaturia): Urine may appear bright red, pink, or reddish-brown after Cyanokit treatment. This is expected and harmless — it reflects the renal excretion of cyanocobalamin. Urine discoloration can last up to 5 weeks after a single dose.

Both types of discoloration are cosmetic — they are not signs of bleeding or injury. However, they can interfere with medical assessments and should be communicated clearly to anyone providing follow-up care.

Full List of Common Side Effects (Occurring in More Than 5% of Patients)

The following side effects were reported in more than 5% of patients treated with Cyanokit in clinical studies:

• Chromaturia (red/pink urine) — very common; lasts up to 5 weeks
• Erythema (skin redness) — very common; lasts up to 2 weeks
• Oxalate crystals in urine — common; monitored with renal function tests
• Increased blood pressure — common; typically transient
• Nausea — common
• Headache — common
• Infusion site reactions (redness, swelling, pain at IV insertion site) — common
• Acneiform rash — may appear anywhere from 7 to 28 days after treatment; typically resolves without treatment within a few weeks

Serious Side Effects — When to Seek Immediate Medical Attention

While most Cyanokit side effects are manageable, some require prompt medical evaluation. Seek emergency care if you experience any of the following:

• Severe allergic reaction (anaphylaxis): Symptoms include chest tightness, throat swelling (angioedema), difficulty breathing, hives (urticaria), or sudden severe drop in blood pressure. Anaphylaxis to hydroxocobalamin is rare but can occur, particularly in patients with known allergy to cyanocobalamin (standard vitamin B12).
• Acute kidney injury: Acute renal failure with acute tubular necrosis has been reported following Cyanokit treatment. Symptoms include significantly reduced urine output, swelling in legs and feet, or unusual fatigue. Renal function must be monitored for 7 days after Cyanokit therapy.
• Severe hypertension: Substantial increases in blood pressure can occur following Cyanokit administration. Blood pressure is monitored continuously during infusion; post-discharge, alert your care team if you experience severe headache, vision changes, or other hypertensive crisis symptoms.

Special Considerations: Lab Tests After Cyanokit

Hydroxocobalamin's deep red color significantly interferes with colorimetric laboratory tests performed after administration. Lab values that may be unreliable following Cyanokit include:

• Bilirubin, creatinine, creatinine kinase, glucose, magnesium, and iron levels
• Co-oximetry readings (carboxyhemoglobin may appear falsely elevated)

Inform any lab, imaging center, or medical provider of recent Cyanokit treatment so they can interpret results accordingly. The deep red color can also cause hemodialysis machines to trigger a false blood-leak alarm.

Photosensitivity and Sun Exposure

Hydroxocobalamin absorbs visible light in the UV spectrum, giving it potential to cause photosensitivity. While it is not confirmed whether skin redness from Cyanokit predisposes patients to photosensitivity reactions, the FDA label advises patients to avoid direct sunlight while skin discoloration persists — typically up to 2 weeks after treatment.

What to Do After Receiving Cyanokit

After receiving Cyanokit in an emergency setting, your medical team will monitor your renal function for up to 7 days. Follow up with your primary care provider regarding any persistent symptoms. For more information about Cyanokit — including drug interactions and how it works — explore the full resource library at medfinder.com.