Prometrium and Soy Allergy
Direct Answer
Prometrium (micronized progesterone) capsules contain peanut oil as an excipient and should be avoided in patients with peanut allergy, but they do NOT contain soy and are generally safe for patients with soy allergy. However, patients with soy allergy should still be counseled about potential cross-reactivity risks with other legumes, and alternative progesterone formulations should be considered if there are concerns about multiple food allergies.
Key Clinical Considerations
Composition and Allergen Content
Prometrium capsules contain peanut oil (not soy oil) as the vehicle for micronized progesterone, making them contraindicated in peanut-allergic patients but not specifically problematic for soy allergy alone.
Soy and peanut are both legumes, and while they are botanically related, clinical cross-reactivity between soy and peanut allergies is relatively uncommon in IgE-mediated food allergy 1.
Soy protein allergy demonstrates substantially lower allergenic reactivity compared to other major food allergens, with a threshold concentration approximately 100 times higher than other allergens 1.
Risk Assessment for Soy-Allergic Patients
In patients with documented soy allergy (particularly those with food protein-induced enterocolitis syndrome or FPIES), there is a potential for cross-reactivity with other legumes, though this occurs in less than 80% of cases 2.
The majority of allergic reactions to soy are IgE-mediated and would require actual soy protein exposure, not just exposure to other legumes 2, 1.
Since Prometrium does not contain soy protein or soy-derived ingredients, the primary concern would only arise if the patient has a broader legume allergy pattern or multiple food allergies 2.
Clinical Decision Algorithm
For patients with isolated soy allergy:
- Prometrium can be safely prescribed as it contains no soy components 1.
- Verify the patient's allergy history specifically excludes peanut allergy.
- Confirm whether the soy allergy is IgE-mediated (immediate) or non-IgE-mediated (delayed) 2.
For patients with multiple legume allergies or FPIES:
- Consider alternative progesterone formulations such as progesterone-in-oil injections, vaginal progesterone gel, or synthetic progestins that do not contain legume-derived excipients 2.
- If Prometrium must be used, supervised administration with the first dose in a medical setting may be warranted for patients with severe or multiple food allergies 2.
For patients with documented peanut allergy:
- Prometrium is absolutely contraindicated due to peanut oil content.
- Alternative progesterone formulations must be used.
Important Caveats
Hidden allergens in pharmaceutical preparations can provoke severe reactions, and patients should always be counseled to review medication ingredients 3.
Even hydrolyzed or processed soy preparations may contain immunoreactive proteins, though this is not relevant to Prometrium specifically 4.
The rate of proven anaphylaxis to medications in food-allergic patients is extremely low (0.06/10,000 in one large pediatric study), and many listed food allergies are not confirmed by testing 5.
Patients with atopic conditions and multiple allergies may have heightened reactivity to various medications, independent of specific food allergen cross-reactivity 5.
Monitoring Recommendations
For any patient with food allergies starting new medications, counsel on recognition of allergic symptoms including urticaria, angioedema, wheezing, and gastrointestinal responses 2.
Emergency treatment for anaphylaxis should be readily available when introducing any new medication to patients with severe food allergies 2.
If uncertain about the severity or confirmation of the soy allergy, referral to an allergist-immunologist for diagnostic testing (skin prick tests, serum-specific IgE) can clarify true allergy status 2.