Paracetamol (acetaminophen) hypersensitivity

Background: Acetaminophen (paracetamol) is an analgesic antipyretic drug wi th no antiinflammatory effects and is widely used worldwide. Earlier clinic al studies reported IgE-mediated adverse reactions to acetaminophen, but in vivo and in vitro tests have been inconclusive. Objective: We propose to demonstrate an IgE-mediated mechanism in four pati ents with adverse reactions to acetaminophen (paracetamol). Tolerance to as pirin and other nonsteroidal antiinflammatory drugs are present in all pati ents. Methods: We studied four patients with anaphylactic reactions to acetaminop hen who tolerated aspirin and other nonsteroidal antiinflammatory drugs. Sk in tests, oral challenges and immunoassay for allergen-specific IgE antibod ies with acetaminophen were performed in all patients. Results: All patients tolerated the aspirin oral challenge without adverse effects. In contrast, the oral challenge with acetaminophen produced advers e effects in all patients. Skin tests with acetaminophen were positive in t wo patients (3-mm wheal and flare) and IgE antibodies acetaminophen were de tected in serum from two patients. Conclusion: We describe four patients with adverse reactions to acetaminoph en but with tolerance to aspirin and other nonsteroidal antiinflammatory dr ugs. Skin tests, oral challenges, and serum IgE results with acetaminophen suggest that an IgE-mediated mechanism is responsible for these reactions.