NEW YORK (Reuters Health) – Most patients with allergic reactions to clopidogrel do not need to stop the drug or switch to another antiplatelet drug but rather can be successfully managed with a short course of concurrent oral prednisone therapy, research suggests.

With a short course of oral steroids, the allergic reaction typically resolves within few days as a result of immunologic tolerance, Dr. Asim Cheema, from the Terrence Donnelly Heart Center, St. Michael’s Hospital, Toronto, Ontario, Canada, told Reuters Health.

In the September 27 issue of the Journal of the American College of Cardiology, Dr. Cheema and colleagues report on 62 patients diagnosed with probable or definite clopidogrel hypersensitivity between July 2006 and March 2010 at St. Michael’s Hospital. This represents 1.6% (62 of 3,877) of the patient population undergoing percutaneous coronary intervention during the study period.

In most patients, clopidogrel hypersensitivity was characterized by a generalized exanthematous rash affecting the trunk and proximal extremities presenting a median of 5 days after clopidogrel initiation. In most cases, biopsy of affected areas demonstrated a lymphocyte-mediated delayed hypersensitivity reaction, the clinicians say.

Complete resolution of hypersensitivity reaction was observed in 61 patients (98%) with a 3-week tapering course of oral prednisone without discontinuing clopidogrel. Prednisone was started at 30 milligrams twice daily for 5 days followed by a decrease of 5 mg/day every 3 days for 15 days.

“All patients were able to continue clopidogrel for the recommended duration without recurrence of allergic reactions,” the authors say.

The prednisone dose used “is similar to the short course commonly prescribed for asthma exacerbation,” Dr. Cheema commented. “Only rarely, a patient may need a second course of the same duration. In case of a local reaction such as on hands or feet, a longer course of topical steroids have been used with success without adverse events,” he said.

In the current series, patients who also had pruritus were prescribed diphenhydramine 25 to 50 milligrams every 6 to 8 hours in addition to prednisone.

The authors acknowledge in their paper that the mechanism of action for successful treatment of clopidogrel hypersensitivity by oral steroids is “unclear but is likely related to suppression of the immune response followed by development of immunologic tolerance in sensitive individuals.”

Dr. Cheema told Reuters Health the current findings have “important implications for management of patients undergoing stenting, particularly drug-eluting stent (DES) placement due to the need for prolonged dual antiplatelet therapy.”

He noted that clopidogrel will be available as a generic in the near future “and therefore offers a cost advantage.” Moreover, “many patients may not be suitable for newer antiplatelet medications due to side effects or being at high risk of bleeding.”

In the current series, allergenic cross-reactivity was observed for ticlopidine in 10 patients (24%), prasugrel in 7 (17%), and both drugs in 3 patients (7%).

J Am Coll Cardiol 2011.