Is there an allergy to magnesium sulfate IV?

There is no IgE-mediated allergy to magnesium sulfate IV. However, magnesium sulfate-induced nonallergic anaphylaxis has been reported in the literature (only 2-3 cases).

Case presentation

A 50-year-old female reported intolerance to magnesium sulfate, on multiple occasions, as per her recollection, she had immediate symptoms with magnesium sulfate IV, with throat discomfort, symptoms resolved after the infusion was stopped and Benadryl was given. No symptoms with oral or NG magnesium replacement were reported. Magnesium replacement was needed during hospitalization because blood magnesium level was 0.9. History of sulfonamide antibiotic allergy was also reported.

Sulfonamide antibiotics do not cross react with sulfates, or even with non-antibiotic sulfonamides or pharmaceuticals with sulfur.

There is no reported IgE-mediated allergy to magnesium sulfate in the medical literature. There is no available skin or blood test for magnesium sulfate. These tests detect IgE-mediated allergy.

There are 2-3 case reports in the medical literature (referenced below) of suspected non-IgE-mediated anaphylaxis to magnesium sulfate. The reactions occurred within 60 min and 30 min, respectively (reference 1).
 
Based on the literature review (see above), if blood Mg level can be maintained at 1.0 or above, no IV replacement is recommended. Replacement PO or via NGT can be sufficient.

If Mg level is below 1.0 and there is no alternative, magnesium sulfate can be administered via a modified graded dose drug challenge with the medication in ICU with 1:1 observation following the protocol below:

The patient agreed to proceed and signed a the consent form. A sample text is below: Procedure: drug allergy test and challenge. I have informed the patient of all risks, benefits and alternatives to treatment including but not limited to the following: reactions may consist of any or all the following symptoms: itchy eyes, nose, or throat; nasal congestion; runny nose; tightness in the throat or chest; coughing; increased wheezing; lightheadedness; faintness; nausea and vomiting; hives; generalized itching; and shock, the last under extreme conditions. The anaphylactic shock reaction can lead to death. The opportunity has been provided for the patient to ask questions. Patient understands the risks and agrees to proceed.

Instructions are below. The allergist on call was available for questions.

To be available at bedside: EpiPen 0.3 mg (2 pens), Cetirizine 10 mg  (2 doses), Solu-Medrol 125 mg IV (2 doses).
 
Magnesium sulfate challenge
Time BP P RR

Magnesium sulfate Dose          
1 10% of dose          
2 90% of dose     

Procedure
1. Obtain vital signs (BP, Pulse and Respiration) before the start of the test and at the end of each dosing interval.
2. Administer the doses sequentially
3. Wait 30 minutes between doses 1 and 2.
4. Document the time of each dose.
5. Notify the doctor if the patient develops any symptoms and document above.
6. Observe patient for 120 minutes (2 hours after the last dose).
7. If there are severe symptoms or anaphylaxis, administer EpiPen 0.3 mg x 1. The dose can be repeated x 1.

The patient's magnesium level was corrected successfully with Mg oxide via NGT and PO and IV Mg was not needed.

References:

1. https://www.annallergy.org/article/S1081-1206(10)60724-7/abstract
2. https://www.aaaai.org/ask-the-expert/sulfate
3. https://www.ncbi.nlm.nih.gov/pubmed/2801834