Omeprazole is a proton pump inhibitor (PPI) that is indicated for gastroduodenal ulcer, gastroesophageal reflux and hypersecretory states. It has an excellent safety profile with a low incidence of adverse effects. We report an Omeprazole-induced urticaria in a patient and emphasize the role of allergological work-up to point out the culprit drug and in exploring cross-reactivity. A 56-year-old man with a history of Biermer anemia treated by vitamin B12. He has asthma and no other illnesses, allergic diseases or reactions, especially to drugs. He was treated with Omeprazole, for abdominal discomfort. Four hours after the first dose, the patient developed urticarial lesions with annular erythematous wheals localized on the trunk and upper limbs. There was neither angioedema nor respiratory and hemodynamic symptoms. An acute generalized urticaria to omeprazole was suspected. Four weeks later, Skin prick test than intradermal tests (IDT) to omeprazole were performed on the patient’s forearm. They revealed respectively a negative and a positive result. To assess cross-reactivity to other PPIs in our patient, we subsequently performed prick test to lansoprazole and IDT to esomeprazole, and pantoprazole that were negative at 20-min reading. Moreover, graded oral provocation test with these drugs were carried out with negative result. In conclusion we add to the medical literature a case report of omeprazole-induced urticaria without a cross reactivity and point out the usefulness and safety of skin and provocation testing in diagnosing this drug reaction and in the assessment of cross-reactivity between PPIs. KEYWORDS: omeprazole, urticaria, cross-reactivity, selective hypersensitivity

A 42-year-old female, treated with isoniazid, rifampicin, pyrazinamide and ethambutol for multifocal tuberculosis, developed, forty days later, hyperthermia, facial edema, cervical lymphadenopathy and generalized exanthema. Biological test results revealed eosinophilia, atypical lymphocytes, thrombocytopenia and liver injury. DRESS was suspected, and four antituberculosis drugs (ATD) were withdrawn. As patch tests for the four ATD showed negative results, we decided to reintroduce pyrazinamide, ethambutol and rifampicin separately with a three-day interval. Pyrazinamide and rifampicin were tolerated by the patient. However, six hours after receiving ethambutol, she developed fever and generalized rash, with no biological abnormalities, which resolved two days later. Since ethambutol was claimed to be the culprit drug, isoniazid was added, and 10 hours later, the patient developed fever, facial edema, generalized rash, eosinophilia and liver injury. This clinical and biological pattern resolved two weeks later. This report suggests a hypersensitivity relapse to ethambutol after isoniazid-induced DRESS in patients treated with first-line ATD.

Erythema nodosum (EN), the most form of panniculitis, is mainly caused by numerous infective (especially Beta-hemolytic streptococcal infections) and non-infective (especially sarcoidosis) diseases and drugs. EN associated with vaccines has been rarely reported. We describe herein, an original clinical observation of EN induced by BNT162b2, an mRNA vaccine. A 75-year-old woman presented with diffuse erythematous painful rounded nodular lesions, located symmetrically over her legs. Six days before, she had received the second dose of Covid-19 vaccine (BNT162b2 (Pfizer–BioNTech)), followed by a sudden asthenia, polyarthralgia, throbbing and edema over her lower limbs. She had been given the first dose of the same Covid-19 vaccine 29 days prior to the second without incident. General physical examination was normal. Skin examination showed multiple, erythematous tender, nodules, 10–30 mm in diameter, over the tibial area. Complete blood count, renal and hepatic tests, antistreptolysin O titer, antinuclear antibody, thyroid test and chest radiograph and PCR, were carried out, and found to be normal. Histopathology revealed infiltration of deep dermal vessels and subcutaneous fat with lymphomononuclear cells and neutrophils, consistent with erythema nodosum. Treatment with analgesics led to complete resolution of the lesion after three months. The patient has shown no relapse after follow-up for three months. In conclusion, to our knowledge, this is the first case of EN induced by the second dose of BNT162b2 (Pfizer–BioNTech) Covid-19 vaccine. It is important for clinicians to be aware of this rare, yet potential, adverse effect to this vaccine.