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Dr. David Derry Answers Reader Questions
Brought to you by Mary Shomon, Your Thyroid Guide
Index of Q&As with Dr. David Derry

Topic: Sulfur Allergies & Levoxyl

A Reader Writes:

I am allergic to all sulfur derivatives (i.e., sulfates, sulfites) and had a bad reaction to Levoxyl. It contains "Croscarmellose" which has a "sulfated ash" component. I have noticed Croscarmellose is being put in an increasing number of products ... without any warning that it could be harmful. About 10% or so of the population are sensitive or allergic to sulfur and its derivatives. Can you talk a bit more about this?

David Derry Responds:

Dear Patient

Allergies are related to an abnormal immune system. You possibly react to croscarmellose in Levoxyl but that is hard to prove it is related to sulfur products. Levothyroxine has problems which are well documented over the last 50 years. The highly fat soluble thyroxine (T4) molecule has to go into a pill which will release into the watery environment of your gut. (1) No one has solved the problem of variable absorption of T4 with any of the thyroxine products. I am sure that the pharmaceutical industry is continuing to try new methods of making thyroxine more absorbable. Also there is a portion of the levothyroxine when swallowed which becomes insoluble when it gets into the gut. Nothing seems to alter the fact that a good 40 percent of the eltroxine exits at the other end having not been absorbed. These difficulties with T4 absorption can be overcome by raising the dose.

To add to the problems of interpretation of your sulfur allergy, we know sulfur is everywhere in your body all the time. One important essential amino acid (methionine) has sulfur as part of its structure and thus is found in many body proteins.(2) In addition many body proteins have sulfur linkages (connections in their structures) between their different subparts of which insulin, used for diabetes, is the most famous. In the case of iodine allergies, the allergy is not to the iodine but to the compound iodine is bound to. So if the iodine is in a lobster and you show an allergic reaction, the reaction is not to the iodine but to the combined iodine-compound which is usually a protein within the lobster.(3-4)

Iodine like sulfur is a normal part of every cell and is found in the blood of every person. So a pure iodine or sulfur allergy is really not possible. I am not saying this information helps your problem only it is nice to be aware of the true nature of the allergy problem. There are many drugs, such as antibiotics, anti-inflammatory agents, oral anti-diabetic agents and diuretics to name a few, used today with sulfur in them and you must continue to be careful to inform people ahead of time of your allergy.

1. Haynes RCJr. Thyroid and Antithyroid Drugs. In: Gilman AG, Rall TW, Nies AS, Taylor P, editors. Goodman and Gilman's The Pharmacological Basis of Therapeutics. Toronto: Pergamon Press, 1990: 1361-1383.

2. Stryer L. Biochemistry. Third ed. New York: W.H. Freeman and Company, 1988.

3. Wayne EJ, Koutras DA, Alexander WD. Clinical aspects of iodine metabolism. Philadelphia: F.A. Davis Company, 1964.

4. Kelly FC. Iodine in medicine and pharmacy since its discovery--1811-1961. Proc R Soc Med 54, 831-836. 1961.

About Dr. Derry:

Dr. Derry is no longer practicing medicine.

These answers are personal opinions. Please discuss any ideas you get with your physician.

Born in 1937, I am at the cutting edge of the war baby boom. With one exception the baby boomers tend to do what I do in large numbers about ten years later. The exception was that after finishing my internship at the Toronto General Hospital in 1963, as I had planned, I started a PhD in biochemistry at the Montreal Neurological Institute at McGill University in Montreal. After completing my PhD, I was hired by the Department of Pharmacology at the University of Toronto to teach and do research. Within a short time I became a Medical Research Council Scholar, which meant the Medical Research Council of Canada paid my salary to do research. Domestic rearrangements suddenly placed five children between the ages of 5 and 9 under my care. I abandoned my research career and took all five children, a new wife and dog out west to Victoria British Columbia.

My aim in 30 years of General Practice (an honor and a privilege) was to learn carefully and persistently how to listen to the patient. This is the one area of medical research that has gone almost totally un-examined. Sir William Osler, who I feel was the greatest physician of all time, said: if you listen to the patient they will usually give you the diagnosis and if you listen even more carefully they will likely indicate the best treatment for them. Gradually with the help of multiple self-development courses over the years I learned to listen by just getting my ego out of the way. From my patients I learned everything. Because of the arrival of effective treatments with potential side-effects, in 1945 the out-dated Hippocratic oath of “do no harm” was replaced with a new principle of ethical patient care namely “Consider first the well-being of the patient.” Combining extensive medical-literature reading with what I learned daily from patients clarified which approaches and treatments assured the “well-being of the patient.”

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