The U.S. Food and Drug Administration has alerted health care professionals, drug compounders and patients about the risk of allergic reactions to sulfite-containing compounded drugs.

The FDA said it had received reports of complaints of conjunctivitis or pink eye, itchy eyes, swollen eyelids and breathing difficulty with low blood oxygen, potentially related to sulfite-containing compounded drugs. They may cause severe allergic reactions and life-threatening or less severe asthmatic episodes in susceptible patients.

"Sulfites are substances that may be added to certain drug products as preservatives, to help prevent the active drug ingredient from breaking down and becoming less effective," the regulator said. Examples include sodium bisulfite, sodium metabisulfite, sodium sulfite, potassium bisulfite, potassium metabisulfite.

The FDA asked compounders to indicate the presence of sulfites on product labels or include a sulfite warning statement.

Compounded drugs are not FDA-approved, but sulfite-containing drugs approved by the regulator are required to include a warning statement on their labels. Drug compounding is the process of combining, mixing, or altering ingredients to create a medication tailored to the needs of an individual patient, the FDA said.