"Allergic reactions can be quite frightening to patients and physicians, and can lead to discontinuation of the medication," said the study's lead author, Nicholas E. Walker, MD, a cardiology fellow at the University of Iowa, Iowa City. "We showed we could successfully and safely desensitize patients who had just recently had a drug-eluting stent placed. That's a critical population to manage."
Perhaps two out of every hundred patients treated with the anti-clotting medication clopidogrel develop an allergic reaction marked by rash, itching, hives, or swelling of the tongue and airway. A small number of patients even develop an anaphylactic reaction and go into shock.
Physicians generally discontinue a medication that provokes an allergic reaction and prescribe an alternative. However, in the case of clopidogrel, substitute medications are either just as likely to provoke allergy symptoms or markedly less effective. Stopping the medication may be riskier than continuing it: Patients who do not take clopidogrel after stenting--particularly after receiving a drug-eluting stent--face approximately three times the risk of a blood clot blocking the stent and causing a heart attack.
"With widespread use of drug-eluting stents, it's going to be more common to see allergic reactions to clopidogrel, and more critical that we find a way to keep patients on the medication," said Phillip A. Horwitz, MD, a professor of medicine and an interventional cardiologist at the University of Iowa Hospitals and Clinics.
Eight patients with clopidogrel hypersensitivity were treated with the desensitization protocol, which was developed by University of Iowa allergist Mary Beth Fasano, MD. While being monitored in the cardiac intensive care unit, patients were first given a dose of clopidogrel so small it had to be mixed into a drinkable solution. Every 15 minutes over the next several hours they received an additional, higher dose of the drug, until they were able to tolerate a target dose of 75 mg. Altogether, they received nine clopidogrel doses totaling 150 mg.
Patients who developed allergy symptoms during the desensitization process were treated with antihistamines and other anti-allergy medications. All patients were able to complete desensitization and safely take a daily 75-mg dose of clopidogrel at home without experiencing delayed allergic reactions.
Dr. Walker noted that patients who had the most severe form of allergic reaction to clopidogrel--anaphylactic shock--were excluded from the study; therefore, the safety and effectiveness of the desensitization protocol has not been established in such patients.